Crank Hub Question

[M 4 FUN]

More info about why a crankhub slips. Not BMW this time but a good explanation i rtalked about earlier here:
🚨 New Product alert 🚨
Introducing the ARP 2000 crank hub bolt upgrade for McLaren (3.8L & 4.0L) 😮*💨
As we began pushing the envelope of what is possible on the McLaren M838 and M840 engines, we quickly ran into newly discovered weak points.
We started building more cars above the 1,100WHP / 900FTLB mark with upgraded clutches, in environments outside of the UK with more available traction and it was becoming apparent that the crank hub on this car was a major weak point and we lost two engines due to the crank hub slipping during our development phase at 1,100WHP+.
The factory crankshaft is a split two piece design, the crankshaft itself and crank hub. The crank hub mates to the crankshaft using nothing but a diamond coated friction washer and single 12.9 grade stretch bolt. The only thing that is stopping the crank hub from slipping is the clamping force created by that bolt on the diamond coated friction washer.
The crank hub is responsible for spinning the engine oil pump, coolant pump, all 4 camshafts/cam phasers, whilst keeping the engine timed via a chain drive. All of these components are relying on that clamping force to stop the crank hub from spinning.
What can make a crank hub spin? Rolling launch control, gearbox kickdown and simply having a setup of over 1,100WHP / 900FTLB in a high traction environment. The McLaren gearboxes also feature inertia push technology and when coupled with upgraded clutches in a high traction environment put a lot of shock on the crank hub during shifts in Track mode. It is not a gradual power increase that makes the crank hub spin, but the immediate and instant torque created by the engine itself and successfully transferred to the tarmac.
What happens when the crank hub spins? If you're lucky and the hub has spun by less than 45*, the engine safeties kick in, the engine cuts out and simply requires retimed in order to be able to start back up. When this happens you will see a crank/cam correlation fault logged on the ECU. This is rarely the case however, with this being an interference engine, the valves on the cylinder head touch the pistons damaging the pistons, valves, valve seats, head and possibly even extending to the bearings and rods. It can cause catastrophic engine failure.
The problem now lies with that factory 12.9 grade bolt. Although a 12.9 grade bolt is one of the stronger fasteners out there on the market, it is still a stretch bolt which is never to be reused. According to McLaren, that bolt is not to be removed under any circumstance. They do not have a torque spec for that bolt. The bolt also cannot be purchased from McLaren. It is not uncommon to remove the bolt to make life easier during engine assembly/disassembly.
Once that bolt has been removed, not only can it not be reused, it cannot be replaced, and even if you decide to reuse or find a replacement, you are left guessing how much nm and torque angle you should carry out on this bolt.
The solution? We contacted the best fastener supplier on the planet to make us an upgraded crank bolt for this application.
Manufactured to precise specifications, this bolt requires no adjustments to the crankshaft or crank hub. Through collaboration with ARP, we've constructed these bolts from ARP 2000, ensuring a remarkable clamping force exceeding 1,000psi. The best part? You get a real torque spec on a re usable bolt which we guarantee will give you an adequate clamping force on that friction washer. Our confidence in this bolt extends to its exclusive use in our elite Stage 2 crate engines, fitting both McLaren M838T and M840T models.
It should be noted the first engine we lost during development was an untouched factory crank bolt which had never been loosened during disassembly/reassembly, the power level this car was running was 1,163whp with nitrous. The hub spun in 4th gear once the nitrous was activated. The second engine we lost was at 1,300whp+ on a factory crank bolt re torqued down to the spec we calculated using a test to find the yield point. This engine failed during an inertia push upshift.
We also tried other solutions including pinning the crank and increasing the coefficient friction of the friction washer itself which was unsuccessful. The pin will break and increasing the coefficient friction of the washer itself must be coupled with greater clamping force.
This bolt can be installed without removing the engine from the car. It will be supplied with our suggested torque spec. We recommend this bolt to anyone looking to run over 1,100whp as a mandatory upgrade.

[wheela]

Originally Posted by M 4 FUN

Yes, cylinder pressure increases on two valves at a time but as the engine spins at such a high speed and the camshaft is rotating at a linear speed or accelerates relatively slow under engine load i can't see that this would chock the crankhub. The engine revs are still very constant or increasing very slow compared to a money shift or dropping the clutch at high rpm's. What i mean is that the crankhub doesn't know if the cylinder pressure is high.
The force is not double as it's only one cylinder at a time that is in the compression stroke and five more that rotates and still push all the other valve springs. Only two of 24 valves have a bit more resistance.

First, thanks for engaging in an objective technical discussion!

Just to clarify my position - I agree with the things you identified that load up the crankhub, rapid rpm changes, money shifts, burnouts coming to abrupt stops, etc.. But I also think there are some affects due to higher torque that add loading to the crankhub, I just don't know how significant they are compared to the things you described.

Attached is a quick & dirty drawing I made to illustrate the forces I see acting on an exhaust valve when opening. Please feel free to comment if you see something missing. Valve forces are pertinent because the crankhub provides the torque that turns the valvetrain (among other things) which pushes open the valves. So if the valves get harder to push open, this extra force ultimately gets transmitted through the crank hub.

Summary of forces I see related to moving the exhaust valve;

Force to Open Exhaust valve:
-supplied by cam via torque transmitted through crank hub, and rotational inertia of all components turned by the crank hub.
-This force must be greater than the summation of other forces acting on the valve to open it.

Spring Force:
-Resists valve opening. Lowest when valve is closed, highest when valve is open.
-I found reference to a valve seat force of 72-75 lbf for s55. Not sure what the force is when fully open.
-Spring force should not vary based on rpm or engine torque (neglecting inertial effects from the spring mass for simplicity).

Valve Inertia:
-Zero at rest, resists movement in either direction.
-When opening, the inertial force resists valve opening and increases with engine rpm based on the valve's mass and linear acceleration (F=MA): higher rpm = more inertial force to overcome when opening the valve.
-When the cam is closing, the valve's inertia tries to hold it open. If the negative inertial force during closing exceeds the positive force from the valve spring, you get valve float.
-Valve inertia should not vary based on engine torque.

Pre-Turbine Back Pressure:
-Pushes on back face of valve, trying to push it open.
-Increases with load/exhaust flow (so proportional to engine torque).
-Effective surface area = crossection of back face of valve minus crossection of valve stem.
-Pre-turbine back pressure on tuned s55 will vary based on boost level, load, turbine size, exhaust, etc. but 20 - 40 psi is probably a reasonable estimate for a tuned s55.

CYLINDER PRESSURE:
-Pushes on front face of valve, holding it shut against valve seat.
-Increases with load (so proportional to engine torque).
-Effective surface area = area of front face of valve (bigger surface area than pre-turbine back pressure acts against).
-When exhaust valve tries to open, cylinder pressure tries to hold it closed, and is initially GREATER than pre-turbine back pressure (which tries to push it open).
-As the exhaust cycle completes, cylinder pressure drops down to, or just above pre-turbine back pressure.
-As engine load (and therefore engine torque) increases, cylinder pressure increases at a faster rate than pre-turbine back pressure.
-Diameter of s55 exhaust valves is 28mm (1.102"). This works out to a surface area of 0.954 in2. Force on valve due to cylinder pressure = cylinder pressure X surface area of valve.
-I don't know s55 values particularily, but a quick Google search of peak cylinder pressures on internal combustion engines yielded the following;
-Light loads: 300 psi
-Full Power: 1000 psi
-Race engines: 1500 psi
-The cylinder pressure may not be at peak when the exhaust valve opens, but for frame of reference, multiplying those values by the surface area of an s55 exhaust valve yields the following forces holding the valve shut:
-Light loads: 286 lbf
-Full load: 954 lbf
-Race engines: 1,431 lbf

This isn't a full analysis, but just rough exercise to get an estimate of the ball park ranges of forces we may be dealing with.

These forces are vector quantities, meaning they all need to be summed up to calculate the total force resisting the exhaust valve from opening. So at any given time of valve movement, the total forces acting on the valve would be:

Net force on valve = Spring Force + inertial force - force due to back pressure + force due to cylinder pressure.

If the assumptions above are correct, the force holding the valve shut due to cylinder pressure can easily exceed the force from the valve spring alone. Plus this force would be directly additive with the spring force and the inertial force needed to start moving the valve. The back pressure reduces this net force, but the back pressure force is likely > order of magnitude smaller than the cylinder force due to the smaller effective surface area on the back side of the valve, and the much lower back pressure compared to cylinder pressure.

It's clear that the force needed to open the exhaust valves will increase as cylinder pressure/torque increases. Seems like it can be considerably higher depending on level of tune. The force needed to open the valve comes from the cam, which is turned by torque transmitted through the crank hub joint. So it's clear the torque transmitted by the crankhub must also increase as torque/cylinder pressure increases.

What's not clear to me is HOW MUCH the torque transmitted through the crank hub needs to increase to cope with the higher valve force. I'm guessing friction in the valve train is significant, so if the force to open the valves doubled, it may not necessarily double the torque needed to turn the valve train.

[wheela]

Originally Posted by M 4 FUN

I understand how you think. The question is if the increased torque twist is in the small area at the crank hub bolt or if it is at the whole length of the crank where the the load from the rods are . I can't see how the crank can twist at the short end of the crank as there is no extra force there. Everything is still rotating at the same speed and nothing gives more resistance in the cam drive system, just like when stock, nothing is changed.

But there is one thing that creates more resistance on the crankhub on the S55 engines than on the N54/55 engines but noone ever mention that. Guess what it is .

For simplicity, I'm only going to talk about 1 cylinder at a time, even though obviously there are 6, with 3 power strokes per rotation.

Let's look at the torques involved in a power stroke (I'll ignore friction for simplicity, but in reality the friction here is significant). I drew another quick & dirty diagram for illustration. Here are the torques I see:

Driving Torque:
-This is the torque resulting from the piston pushing the rod against the crank.
-This torque turns the drivetrain through the back end (by piston 6), and turns the valvetrain, oil pumps and accerssories via torque transmitted through the crank hub at the front end (by piston 1).

Reaction Torque at the Flywheel:
-This is a torque that transmits through the transmission/drivetrain and transmits to the ground via the wheels.
-It's in opposition to the driving torque, due to rotational inertia of the drivetrain components, and F=MA forces to accelerate the mass of the car (which will change based on gear ratio).

Reaction Torque at Crank Hub:
-This is a torque that transmits through the crankhub to turn the valve train, oil pumps, harmonic balancer, and accessories belt.
-It's in opposition to the driving torque, due to:
-Rotational inertia of the rotating assemblies its turning
-Torque needed to rotate the cams against the valve opening forces
-Rotational F=MA forces needed to increase rotational speed of the rotating assemblies as the engine changes rpm.

As you pointed out, quick acceleration or deceleration of the engine places extra load on the crank hub joint, due to the rotational F=MA forces needed to accelerate or decelerate the parts being rotated by the crank hub. The more abrupt the change in rpm, the greater the rotational torque applied through the crank hub to rotationally accelerate or decelerate those rotating assemblies.

But my concern with crank twist, is even though AVERAGE engine torque and AVERAGE crank speed may not be changing quickly, the INSTANTANEOUS torque and INSTANANEOUS crank speed are not constant throughout an engine revolution. They both pulse up during a cylinder's power stroke, and back down again when that cylinder's exhaust valve opens up (releasing cylinder pressure, and therefore releasing driving torque). On a 4-stroke 6 cylinder engine, this happens 3 times for each engine revolution.

We generally can't feel the pulsing because of the rotational inertia of all the rotating components tied to the crankshaft, and really good engine mounts. But if you lug your engine, or get solid engine mounts, etc. the pulsing will really shake your car, especially at low rpm's where there is more time for torque to release between power strokes.

Let's say we have a stock car making max torque. That torque will force some amount of twist into the crankshaft between the flywheel and whichever piston is in power stroke. The twist will be greatest when piston 1 is in power stroke because that torque is loaded across the full length of crank shaft. When piston 6 is in power stroke, the crank twist is at its least, because it's the shortest length of crankshaft torquing against the Flywheel. When the power stroke piston's exhaust valves open, cylinder pressure will drop down to pre-turbine back pressure, releasing Driving Torque from the crank. When this happens, whatever twist was in the crankshaft due to the power stroke torque will release. The release of the twist will drive a brief rotational acceleration in the crankshaft. Since the crankhub is tied to the front of the crank, the crank un-winding will try to rotationally accelerate the crank hub and all rotating components being turned by the crank hub. Since all those rotating components have inertia, a torque will be created that the crankhub has to withstand when it tries to accelerate those parts as the crank twist releases. It would only be for a short duration of time since it happens 3 times per engine revolution. But crankshaft are extremely stout pieces of metal, so I imagine that the un-twist, though short in duration, could be quite violent if the torque on it was high enough.

I don't know how much crank twist exists at stock s55 power levels. But cranks aren't infinitely rigid, so they will twist proportionately to the torque applied to them. If you double the torque, you'll double the twist, and therefore double whatever torque effects you get at the crankhub when as the crank untwists between power strokes.

Like I said, I don't know the magnitude of this affect, it could be negligible for all I know. But I can't see how this effect can't exist at least to some extent, and the effect would increase as torque increases. This is why I think it's plausible that it could potentially be a factor in contributing to greater likelihood of spun crank hub as torque increases.

As far as what creates more resistance on s55 vs. n54 & n55? I'm not an s55 expert, but my understanding is that in addition to everything the crankhub turns on n54 & n55, the s55 crankhub also has to turn a mechanical water pump (n54 & n55 are electric), two oil pumps (vs. 1 pump for n54 & n55), and I believe the s55 harmonic balancer is also bigger than n54 & n55. I do believe this extra rotational mass on the crank hub accounts for (or at least is one reason) more prevelence of spun hub on s55 vs. n54 & n55. Does that align with your understanding?

[wheela]

Originally Posted by M 4 FUN

More info about why a crankhub slips. Not BMW this time but a good explanation i rtalked about earlier here:
🚨 New Product alert 🚨
Introducing the ARP 2000 crank hub bolt upgrade for McLaren (3.8L & 4.0L) 😮*💨
As we began pushing the envelope of what is possible on the McLaren M838 and M840 engines, we quickly ran into newly discovered weak points.
We started building more cars above the 1,100WHP / 900FTLB mark with upgraded clutches, in environments outside of the UK with more available traction and it was becoming apparent that the crank hub on this car was a major weak point and we lost two engines due to the crank hub slipping during our development phase at 1,100WHP+.
The factory crankshaft is a split two piece design, the crankshaft itself and crank hub. The crank hub mates to the crankshaft using nothing but a diamond coated friction washer and single 12.9 grade stretch bolt. The only thing that is stopping the crank hub from slipping is the clamping force created by that bolt on the diamond coated friction washer.
The crank hub is responsible for spinning the engine oil pump, coolant pump, all 4 camshafts/cam phasers, whilst keeping the engine timed via a chain drive. All of these components are relying on that clamping force to stop the crank hub from spinning.
What can make a crank hub spin? Rolling launch control, gearbox kickdown and simply having a setup of over 1,100WHP / 900FTLB in a high traction environment. The McLaren gearboxes also feature inertia push technology and when coupled with upgraded clutches in a high traction environment put a lot of shock on the crank hub during shifts in Track mode. It is not a gradual power increase that makes the crank hub spin, but the immediate and instant torque created by the engine itself and successfully transferred to the tarmac.
What happens when the crank hub spins? If you're lucky and the hub has spun by less than 45*, the engine safeties kick in, the engine cuts out and simply requires retimed in order to be able to start back up. When this happens you will see a crank/cam correlation fault logged on the ECU. This is rarely the case however, with this being an interference engine, the valves on the cylinder head touch the pistons damaging the pistons, valves, valve seats, head and possibly even extending to the bearings and rods. It can cause catastrophic engine failure.
The problem now lies with that factory 12.9 grade bolt. Although a 12.9 grade bolt is one of the stronger fasteners out there on the market, it is still a stretch bolt which is never to be reused. According to McLaren, that bolt is not to be removed under any circumstance. They do not have a torque spec for that bolt. The bolt also cannot be purchased from McLaren. It is not uncommon to remove the bolt to make life easier during engine assembly/disassembly.
Once that bolt has been removed, not only can it not be reused, it cannot be replaced, and even if you decide to reuse or find a replacement, you are left guessing how much nm and torque angle you should carry out on this bolt.
The solution? We contacted the best fastener supplier on the planet to make us an upgraded crank bolt for this application.
Manufactured to precise specifications, this bolt requires no adjustments to the crankshaft or crank hub. Through collaboration with ARP, we've constructed these bolts from ARP 2000, ensuring a remarkable clamping force exceeding 1,000psi. The best part? You get a real torque spec on a re usable bolt which we guarantee will give you an adequate clamping force on that friction washer. Our confidence in this bolt extends to its exclusive use in our elite Stage 2 crate engines, fitting both McLaren M838T and M840T models.
It should be noted the first engine we lost during development was an untouched factory crank bolt which had never been loosened during disassembly/reassembly, the power level this car was running was 1,163whp with nitrous. The hub spun in 4th gear once the nitrous was activated. The second engine we lost was at 1,300whp+ on a factory crank bolt re torqued down to the spec we calculated using a test to find the yield point. This engine failed during an inertia push upshift.
We also tried other solutions including pinning the crank and increasing the coefficient friction of the friction washer itself which was unsuccessful. The pin will break and increasing the coefficient friction of the washer itself must be coupled with greater clamping force.
This bolt can be installed without removing the engine from the car. It will be supplied with our suggested torque spec. We recommend this bolt to anyone looking to run over 1,100whp as a mandatory upgrade.

Thanks for sharing this post from McClaren. Very interesting they're also using friction disk and crank bolt. Very cool they collaborated with ARP on that stronger bolt. Hopefully they have enough surface area on their friction disks to stop them from being torn apart.

Edit: Also intersting they correlate this to higher power. They list all the abusing things they (and the transmission) can do to the hub, but they frame it like those abusive things didn't become problematic until over 1000hp? Seems to imply that the higher power level is a factor that pushes those other abusive factors past the capability of the hub to hold together.

"What can make a crank hub spin? Rolling launch control, gearbox kickdown and simply having a setup of over 1,100WHP / 900FTLB in a high traction environment. The McLaren gearboxes also feature inertia push technology and when coupled with upgraded clutches in a high traction environment put a lot of shock on the crank hub during shifts in Track mode. It is not a gradual power increase that makes the crank hub spin, but the immediate and instant torque created by the engine itself and successfully transferred to the tarmac."

[M 4 FUN]

Originally Posted by wheela

Thanks for sharing this post from McClaren. Very interesting they're also using friction disk and crank bolt. Very cool they collaborated with ARP on that stronger bolt. Hopefully they have enough surface area on their friction disks to stop them from being torn apart.

Edit: Also intersting they correlate this to higher power. They list all the abusing things they (and the transmission) can do to the hub, but they frame it like those abusive things didn't become problematic until over 1000hp? Seems to imply that the higher power level is a factor that pushes those other abusive factors past the capability of the hub to hold together.

"What can make a crank hub spin? Rolling launch control, gearbox kickdown and simply having a setup of over 1,100WHP / 900FTLB in a high traction environment. The McLaren gearboxes also feature inertia push technology and when coupled with upgraded clutches in a high traction environment put a lot of shock on the crank hub during shifts in Track mode. It is not a gradual power increase that makes the crank hub spin, but the immediate and instant torque created by the engine itself and successfully transferred to the tarmac."

Hi again . Great discussion here with a lot of good thoughts and theories .
i am from Sweden so sorry if i don't explain in the right way always but i think i make myself understood:

I understand and agree about the twisting forces of the crank as they always are there, more or less. They are worse on a 4 cylinder engine than on a 6 cylinder straight six as the straight six outbalance itself when it comes to rotational mass, BUT, there is of course load during the ignition phase, that's the power .
I think the "snapping" of the crank is a minor factor though, compared to the much higher forces when extremely fast rev changes occur. I see it like this: if the crank would have a lot of these deccelerating forces during every compression stroke it would not be able to produce such high power as it would work against itself. But yes, there is forces of course.

About resistance in the valvetrain:
I can't see that cylinder pressure is a big factor as creating more resistance in the cam drive system. The reason for this is that the high cylinder pressure is occuring when the valves are closed and AFTER that the valves are opening up and the force goes through the crank out in the drivetrain. That means that the pressure is greatly reduced when the valves open up. If we tried to open the valves at the highest cylinder pressure all power would be lost.
Another reason that i don't think this is a factor is that when we tune these turbo engines and increase boost, sometimes we need valve springs with higher seating pressure. Why? Because the stock springs have problems to close the valves on high boost as the valves opens up from the boost pressure. The only increased resistance in this case with stiffer valve springs is when we run off boost but then we have no significant load on the crankhub anyway. This tells us the the cylinder pressure is actually lower than spring pressure if they can blow open up by the boost pressure.
So what does this say? This means that higher the boost pressure is the more we LOAD OFF the cam drive system as the seating pressure of the valves decrease, "helping" the springs to open the valves .

I still am convinced that the biggest factor of the slippage of the hub is the accelerating forces. Even if there is crank twist, vibrations and more i don't think they are near as much the factor as hard, fast rev changes and of course a lot of grip together with aggressive clutch setups. These occur so hard and during such a short time that i don't think anything else isn't really comparable even if the forces are there.

Let me here what you think, i really enjoy the conversation!

Johnny.

[Track/S]

Originally Posted by M 4 FUN

More info about why a crankhub slips. Not BMW this time but a good explanation i rtalked about earlier here:
🚨 New Product alert 🚨
Introducing the ARP 2000 crank hub bolt upgrade for McLaren (3.8L & 4.0L) 😮*💨
As we began pushing the envelope of what is possible on the McLaren M838 and M840 engines, we quickly ran into newly discovered weak points.

Interesting, we should try a stronger bolt on S55.

[FrankMstein]

Originally Posted by M 4 FUN

More info about why a crankhub slips. Not BMW this time but a good explanation i rtalked about earlier here:

One thing these BMW shops say is that the friction washer more often than not splits and that releases the CH. Great info. A reusable bolt doesn't solve BMW's problem.

[FrankMstein]

Originally Posted by wheela

First, thanks for engaging in an objective technical discussion!

Do you have a TLDR ver? Good explanation, but do you?

[FrankMstein]

Originally Posted by wheela

For simplicity, I'm only going to talk about 1 cylinder at a time, even though obviously there are 6, with 3 power strokes per rotation.

Let's ...

...not over think this.
Warm the engine to operating temps - always before beating
Don't money shift/use kickdown - ever
Don't get the rear tires off the ground over 3000rpm - ever
Don't use the flappy paddles like a game controller - WTF drives like this??
Don't let off the gas at 5k (tuned) w/o upshifting first -

Problem solved, QED.

[M 4 FUN]

Originally Posted by FrankMstein

One thing these BMW shops say is that the friction washer more often than not splits and that releases the CH. Great info. A reusable bolt doesn't solve BMW's problem.

Yes, cracked washers can be a factor for sure. Maybe a thicker, stronger washer and upgraded bolt that can increase the friction on the washers would be a thing to look into.

[Info@mad-us.com]

Originally Posted by FrankMstein

...not over think this.
Warm the engine to operating temps - always before beating
Don't money shift/use kickdown - ever
Don't get the rear tires off the ground over 3000rpm - ever
Don't use the flappy paddles like a game controller - WTF drives like this??
Don't let off the gas at 5k (tuned) w/o upshifting first -

Problem solved, QED.

So get a crank hub or have no fun at all

[5ABIVT]

Originally Posted by saint80

Ok, so I've done a few modifications to my f80 and have learned about this OEM crank hub issue. I don't understand it all, but what I do understand is that when we add more HP to the OEM crank hub, it becomes more likely to fail.

My question is this - With a Stage 1 tune, Stone full exhaust, and running E85 - Do I need to worry about replacing the crank hub, or do I only need to worry about this if I add even more power to the car.

You guys are the genius's, so I figured best to ask here. Thanks ahead of time for the help!!!

If you dont understand how an engine valvetrain work check out an animated video on youtube there are tons. watch any V8 and see how the camshaft is tied to the crankshaft by a chain and how the sprockets are keyed to the hub and cam. Now imagine those sprockets held in place by glue. Just make enough power and the glue breaks and the timing is sent off and the damage potential is catastrophic. In the case of the f8x it uses a friction washer that has diamond dust on it.

anyhow.. in theory the vargas solution is a good one. but they have failed and the question arose if the material was not cutting into the crank as designed/intended . The 2 pin was the original design by many brands but they switched to a 4 pin. I believe insane does now offer a 4 pin. the pins themselves are not very strong and can shear quite easily.. and its happened. but seems like if installed accurately they are an option. Personally i prefer hubs like gintani and precision dynamics which are a key style design.

CBC just helps prevent losing the engine in the worst way possible which is the bolt loosening and the friction washer losing grip . that just sucks

[FrankMstein]

Originally Posted by Info@mad-us.com

So get a crank hub or have no fun at all

I'm on team normal rather than parking lot hotboi!

[Track/S]

Originally Posted by FrankMstein

One thing these BMW shops say is that the friction washer more often than not splits and that releases the CH. Great info. A reusable bolt doesn't solve BMW's problem.

I would like those BMW shops to explain to me how a washer under pressure can break and come out of its housing, could it be that they break when the CH spun?

I think a stronger bolt can solve the problem just like on McLaren.

Originally Posted by 5ABIVT

anyhow.. in theory the vargas solution is a good one. but they have failed and the question arose if the material was not cutting into the crank as designed/intended . The 2 pin was the original design by many brands but they switched to a 4 pin. I believe insane does now offer a 4 pin. the pins themselves are not very strong and can shear quite easily.. and its happened. but seems like if installed accurately they are an option. Personally i prefer hubs like gintani and precision dynamics which are a key style design.

2 pins are enough, the key is knowing how to make them so they are durable

[FrankMstein]

Originally Posted by Track/S

I would like those BMW shops to explain to me how a washer under pressure can break and come out of its housing, could it be that they break when the CH spun?

I think a stronger bolt can solve the problem just like on McLaren.

Have you ever seen the press channel on YouTube? Pressure will do a lot of things. The washer is between the two piece hub and is not contained in a housing. There are many many instances of it. A stronger (or reusable) bolt is not the fix to this problem. McLaren could use a paragraph devoted to the history of the BMW CH in their redesign. There are other factors such as variation in the bolt material, torque application/installation (human), plating variation, quantity (any) of lubrication on the threads, yadda yadda. Variation in the washer thickness, OD/ID, material, diamond content, yadda yadda. Assembly contaminants. A LOT of shit we will never know.

[wheela]

Originally Posted by M 4 FUN

Hi again . Great discussion here with a lot of good thoughts and theories .
i am from Sweden so sorry if i don't explain in the right way always but i think i make myself understood:

I understand and agree about the twisting forces of the crank as they always are there, more or less. They are worse on a 4 cylinder engine than on a 6 cylinder straight six as the straight six outbalance itself when it comes to rotational mass, BUT, there is of course load during the ignition phase, that's the power .
I think the "snapping" of the crank is a minor factor though, compared to the much higher forces when extremely fast rev changes occur. I see it like this: if the crank would have a lot of these deccelerating forces during every compression stroke it would not be able to produce such high power as it would work against itself. But yes, there is forces of course.

About resistance in the valvetrain:
I can't see that cylinder pressure is a big factor as creating more resistance in the cam drive system. The reason for this is that the high cylinder pressure is occuring when the valves are closed and AFTER that the valves are opening up and the force goes through the crank out in the drivetrain. That means that the pressure is greatly reduced when the valves open up. If we tried to open the valves at the highest cylinder pressure all power would be lost.
Another reason that i don't think this is a factor is that when we tune these turbo engines and increase boost, sometimes we need valve springs with higher seating pressure. Why? Because the stock springs have problems to close the valves on high boost as the valves opens up from the boost pressure. The only increased resistance in this case with stiffer valve springs is when we run off boost but then we have no significant load on the crankhub anyway. This tells us the the cylinder pressure is actually lower than spring pressure if they can blow open up by the boost pressure.
So what does this say? This means that higher the boost pressure is the more we LOAD OFF the cam drive system as the seating pressure of the valves decrease, "helping" the springs to open the valves .

I still am convinced that the biggest factor of the slippage of the hub is the accelerating forces. Even if there is crank twist, vibrations and more i don't think they are near as much the factor as hard, fast rev changes and of course a lot of grip together with aggressive clutch setups. These occur so hard and during such a short time that i don't think anything else isn't really comparable even if the forces are there.

Let me here what you think, i really enjoy the conversation!

Johnny.

Thanks for sharing your thoughts, Johnny!

That's a good point about cylinder pressures being lower than peak when the exhaust valves open. Attached is some more info I found about cylinder pressures when valves open. Definately much lower than peak, but can still be in the hundreds of psi when the valve opens. Hundereds of psi could still work out to bigger force than valve spring force. And all things being equal, higher load (boost) would still result in higher cylinder pressure for the exhaust valve to open against = more loading to crank hub.

Something struck me when looking at this pressure trace. The amount of cylinder pressure present when trying to open the exhaust valve would be significantly influenced by exhaust valve timing. If the tuner advanced exhaust valve timing for some reason, this would cause the exhaust valve to open against higher cylinder pressure (and therefore higher loading of the crank hub) - even if the load was unchanged. Not sure if it's common for tuners to advance exhaust vanos or not, I haven't dug much into vanos tuning yet.

Edit - another thing that struck me was the narrowness of the pressure peak. With a slower burning fuel, like ethanol, the width of that pressure peak would be widened. Even with advanced ignition timing for ethonol, the longer duration of the pressure peak could potentially extend such that cylinder pressure is higher when the exhaust valve opens. - end edit.

Edit to my edit: I was mistaken about ethanol burning slower than gasoline - it's the other way around. End re-edit.

As far as my crank twist theory, if there is anything to it, it's probably more to do with the power stroke pulses themselves, than a quick reduction of torque when the exhaust valve opens.

Here's a very intersting and informative thread I recently found about valve float in forced induction. Quick summary, turbo charged engines likely never see intake valve float from boost pressure, but could potentially have exhaust valve float. For super charged, it's the opposite - no exhaust valve float, but potentially some intake valve float.

Back to our duscussion, the link below also has some talk of exhaust valves opening against cylinder pressure in turbo charged engines, and how it can really destroy a valvetrain depending how bad it is:

https://www.eng-tips.com/viewthread.cfm?qid=379250

[FrankMstein]

Originally Posted by 5ABIVT

in theory the vargas solution is a good one. but they have failed and the question arose if the material was not cutting into the crank as designed/intended . The 2 pin was the original design by many brands but they switched to a 4 pin. I believe insane does now offer a 4 pin. the pins themselves are not very strong and can shear quite easily.. and its happened. but seems like if installed accurately they are an option. Personally i prefer hubs like gintani and precision dynamics which are a key style design.

CBC just helps prevent losing the engine in the worst way possible which is the bolt loosening and the friction washer losing grip . that just sucks

Keyed one piece FTW.

[Track/S]

Originally Posted by FrankMstein

Have you ever seen the press channel on YouTube? Pressure will do a lot of things. The washer is between the two piece hub and is not contained in a housing. There are many many instances of it. A stronger (or reusable) bolt is not the fix to this problem. McLaren could use a paragraph devoted to the history of the BMW CH in their redesign. There are other factors such as variation in the bolt material, torque application/installation (human), plating variation, quantity (any) of lubrication on the threads, yadda yadda. Variation in the washer thickness, OD/ID, material, diamond content, yadda yadda. Assembly contaminants. A LOT of shit we will never know.

I know where the washers are, if the sprockets don't move with each other, it will never come off or break.

[wheela]

Originally Posted by FrankMstein

One thing these BMW shops say is that the friction washer more often than not splits and that releases the CH. Great info. A reusable bolt doesn't solve BMW's problem.

Personally, I believe this is the case. Diamond impregnated washers are great for friction. But diamonds have way higher elastic modulus than any metal matrix they put them in. And they have sharp edges. So when you place the washer under extreme compressive loading, the metal matrix will compress, but not the diamonds. In this scenario, those diamond tips will be extreme stress concentrations pressing into the metal matrix of the washer.

I haven't calculated the average stress these friction disks are under when the crank bolt is fully tightened, but I wouldn't be suprised at all if locally, it's enough pressure to hit yield strength of the metal matrix at the diamond tip stress concentration areas. If this happens, the metal matrix would fall into a subset of conditions where fatigue cracks can actually grow despite the material being under compressive loading. If that happens, the friction disc could actually start to collapse from fatigue, releasing tension from the crank bolt (without the bolt rotating). If enough tension is lost, the hub will eventually spin - even on stock power levels. (Potentially leaving a visibly damaged friction disk upon disassembly of the hub)

[wheela]

Originally Posted by FrankMstein

Do you have a TLDR ver? Good explanation, but do you?

Haha, that was a little in the weeds there! OP asking if adding a tune (more power) could increase chances of his hub spinning. I guess TLDR would be that I believe it's plausible, because I think there are some mechanisms where higher torque puts greater loading on the crank hub:

1. Higher torque via a tune = higher cylinder pressure = exhaust valve opening against higher cylinder pressure = higher force needed to open exhaust valve = more torque needed to turn cams against higher valve force = more torque must be transmitted to valve train via the crankhub.

2. Torque isn't constant during a crank revolution; torque and crank speed pulse up and down during crank rotation due to each individual cylinder's torque contribution. With each pulse up and down, the crank hub will try to accelerate/decelerate all of the rotating assemblies its turning (valve train, oil pumps, water pump, harmonic balancer, alternator, pulleys, etc.). This loads the crankhub because of all the rotational inertia of those parts. So if torque increases (via a tune), I propose the amplitude of the individual torque/speed peaks from each power stroke will also increase. If the individual torque/speed peaks increase, then the crankhub will try to accelerate/decelerate all those rotating components I mentioned faster for each individual pulse, which requires more torque to be transmitted through the crank hub.

I don't know how significant those affects are (maybe not at all), but they seem plausible to me.

[FrankMstein]

Originally Posted by wheela

Haha, that was a little in the weeds there! OP asking if adding a tune (more power) could increase chances of his hub spinning. I guess TLDR would be that I believe it's plausible, because I think there are some mechanisms where higher torque puts greater loading on the crank hub:

1. Higher torque via a tune = higher cylinder pressure = exhaust valve opening against higher cylinder pressure = higher force needed to open exhaust valve = more torque needed to turn cams against higher valve force = more torque must be transmitted to valve train via the crankhub.

2. Torque isn't constant during a crank revolution; torque and crank speed pulse up and down during crank rotation due to each individual cylinder's torque contribution. With each pulse up and down, the crank hub will try to accelerate/decelerate all of the rotating assemblies its turning (valve train, oil pumps, water pump, harmonic balancer, alternator, pulleys, etc.). This loads the crankhub because of all the rotational inertia of those parts. So if torque increases (via a tune), I propose the amplitude of the individual torque/speed peaks from each power stroke will also increase. If the individual torque/speed peaks increase, then the crankhub will try to accelerate/decelerate all those rotating components I mentioned faster for each individual pulse, which requires more torque to be transmitted through the crank hub.

I don't know how significant those affects are (maybe not at all), but they seem plausible to me.

I agree with you. Due to the quantity of tuned cars with no affect to the CH it should not be considered high on the list as or a major contributing factor or it would be more pronounced given the data I crunched on the other thread in which you should post your findings there or link it.