Potential drive train issue

[rsr racer]

My "friend" has an M4 6 speed manual. This friend may have had a bit of an over zealous down shift with poor shoes on and unable to gain a proper rpm blip (in M mode)during the down shift.

Said friend's downshift from 3 to 2nd was not allowed to go into the 2nd gear position (x2) near was never engaged.
"Friend" drove a little further in the highway and then the computer screen display had a message indicating that the is a drive train malfunction.

Car would not start. Car was towed to dealer.

Data thus far by techs reveals a timing issue that was created while this friend attempted the down shift.

I am betting that 3 valves may be bent as the compression in 3 Cylinders are 100+ , and the other three are fine.

"He" is hoping that maybe someone had something similargold..

How much dothik

[Boss330]

I assume you have talked this over thoroughly with your "friend" so that you know all the details and can answer a few questions...

If I understand your post correctly 2nd gear was never engaged during this downshift? Your "friend" tried 2 times to get the gear engaged. Was the clutch decoupled at all times or did your friend release the clutch pedal at any time during these two attempts?

If 2nd gear never was engaged, how could the situation you described cause damage to the engine? If 2nd gear wasn't engaged there also was no way to over rev the engine and cause valvetrain damage... And you can't over rev the engine by the gas pedal either.

Did the engine see excessive rpm at any time during this failed gearshift situation? And it must have been pretty high rpm to cause a timing issue on the valvetrain, like well over 8000rpm IMO. And if the engine did reach rpm levels well beyond redline then 2nd gear must have been engaged to be able to accelerate the rpm that way, if only for a brief moment...

If your "friends" engine indeed has lost compression on 3 cylinders due to over revving in the way described, then the car basically needs a new engine. If the valves are bent there might also be damage to the pistons and BMW will most likely not risk repairing the engine by just replacing the bent valves.

BTW, BMW can download all data and also max rpm etc so they should be able to find the root cause if the engine has been over revved. Your local garage can't get this data AFAIK but BMW NA or via BMW in Germany.

Best of luck to your "friend"

[Vectors2final]

Too many holes in this story.

[mkoesel]

Originally Posted by Boss330

If 2nd gear never was engaged, how could the situation you described cause damage to the engine?

It can't. And I know you were asking that rhetorically, but I just wanted to make it clear for others reading who may not understand.

The OP's reference to messing up the throttle application on the attempted rev match is also immaterial to whether there was over rev. The engine is going to over rev if the wheels force it to whether you've tried to rev match or not.

If 2nd gear wasn't engaged there also was no way to over rev the engine and cause valvetrain damage...

I suspect what happened is that he (or she) began to let the clutch out, realized he was going too fast for second gear, and pushed it back in before it was fully engaged, hence the claim "2nd gear was never engaged". But it doesn't matter if the clutch pedal was never fully released. As long as the clutch plates made enough contact to get the engine spinning up to the speed of the transmission, it's game over.

Sorry to hear about your friend OP, but this is not likely to be covered by BMW. If they do cover it, consider yourself lucky.

[Boss330]

Originally Posted by mkoesel

It can't. And I know you were asking that rhetorically, but I just wanted to make it clear for others reading who may not understand.

The OP's reference to messing up the throttle application on the attempted rev match is also immaterial to whether there was over rev. The engine is going to over rev if the wheels force it to whether you've tried to rev match or not.

I suspect what happened is that he (or she) began to let the clutch out, realized he was going too fast for second gear, and pushed it back in before it was fully engaged, hence the claim "2nd gear was never engaged". But it doesn't matter if the clutch pedal was never fully released. As long as the clutch plates made enough contact to get the engine spinning up to the speed of the transmission, it's game over.

Sorry to hear about your friend OP, but this is not likely to be covered by BMW. If they do cover it, consider yourself lucky.

[Wei718]

They call that the "Money Shift" right?

[ASAP]

I saw this on an n54 numerous times... it ended with oil being spilled all over the place. I am sorry to hear about this.

[rsr racer]

Originally Posted by mkoesel

It can't. And I know you were asking that rhetorically, but I just wanted to make it clear for others reading who may not understand.

The OP's reference to messing up the throttle application on the attempted rev match is also immaterial to whether there was over rev. The engine is going to over rev if the wheels force it to whether you've tried to rev match or not.



I suspect what happened is that he (or she) began to let the clutch out, realized he was going too fast for second gear, and pushed it back in before it was fully engaged, hence the claim "2nd gear was never engaged". But it doesn't matter if the clutch pedal was never fully released. As long as the clutch plates made enough contact to get the engine spinning up to the speed of the transmission, it's game over.

Sorry to hear about your friend OP, but this is not likely to be covered by BMW. If they do cover it, consider yourself lucky.

that ^ kind of sums it up; as per my friend. you see, he had just gotten out of driving his gt3rs. the light flywheel in that car spins up so fast that very high rpm downshifts are very smooth and uninterrupted

when he went to do the same thing in the M4; the spin up of the rpm's was not nearly as fast as the gt3rs but the shifter was pulled anyway and it would appear that 2nd was resisted by the engine.

money shift. clearly it will come down to that. I will let him know. he suspected that all along.

a lighert flywheel in the M4 would be nice

at least the rs is still waiting to have fun

[gmd2003]

Originally Posted by rsr racer

that ^ kind of sums it up; as per my friend. you see, he had just gotten out of driving his gt3rs. the light flywheel in that car spins up so fast that very high rpm downshifts are very smooth and uninterrupted

when he went to do the same thing in the M4; the spin up of the rpm's was not nearly as fast as the gt3rs but the shifter was pulled anyway and it would appear that 2nd was resisted by the engine.

money shift. clearly it will come down to that. I will let him know. he suspected that all along.

a lighert flywheel in the M4 would be nice

at least the rs is still waiting to have fun

A lightweight flywheel doesn't help you out when you select the wrong gear lol .Id resist too if someone tried to kill me .

[BMWJ]

unfortunately for your friend - it sounds like definite drivetrain issue. ouch!

[rsr racer]

Originally Posted by gmd2003

A lightweight flywheel doesn't help you out when you select the wrong gear lol .Id resist too if someone tried to kill me .

wasn't the wrong gear...3rd to 2nd...just poor technique is all it boils down to

[Jaymax85]

Dct > Mt ??? Jkkk

[RingMeister01]

Warranty will not cover this as the dealer will see the RPM's went through the roof. Good luck Norm.

[8600RPM]

Helpful post norm.

[Boss330]

Originally Posted by rsr racer

that ^ kind of sums it up; as per my friend. you see, he had just gotten out of driving his gt3rs. the light flywheel in that car spins up so fast that very high rpm downshifts are very smooth and uninterrupted

when he went to do the same thing in the M4; the spin up of the rpm's was not nearly as fast as the gt3rs but the shifter was pulled anyway and it would appear that 2nd was resisted by the engine.

money shift. clearly it will come down to that. I will let him know. he suspected that all along.

a lighert flywheel in the M4 would be nice

at least the rs is still waiting to have fun

So now your "friend" has become just friend... Your first post looked like it in reality was you that drove your own car...

Anyway, the weight of the flywheel doesn't matter here. If you engage 2nd gear while the car is travelling too fast, it's the clutch speed that is your enemy. If the clutch speed is higher than redline of your engine, you end up having issues... Clutch speed is completely independent of flywheel weight. When you shift down to 2nd the rpm of the input shaft is accelerated and when you engage the clutch, this rpm is transferred to the flywheel and crank. If anything a heavy flywheel will have a larger inertia and therefore more resistant to increase the rpm transferred from the gearbox. Of course this is just a few milliseconds difference in the real world and the drivetrain rpm (or more precisely the rpm of the input shaft of the gearbox) WILL be transferred to the crank and thereby over rev the engine...

[rsr racer]

Originally Posted by RingMeister01

Warranty will not cover this as the dealer will see the RPM's went through the roof. Good luck Norm.

so much for being on DL.....

[rsr racer]

Originally Posted by Boss330

So now your "friend" has become just friend... Your first post looked like it in reality was you that drove your own car...

Anyway, the weight of the flywheel doesn't matter here. If you engage 2nd gear while the car is travelling too fast, it's the clutch speed that is your enemy. If the clutch speed is higher than redline of your engine, you end up having issues... Clutch speed is completely independent of flywheel weight. When you shift down to 2nd the rpm of the input shaft is accelerated and when you engage the clutch, this rpm is transferred to the flywheel and crank. If anything a heavy flywheel will have a larger inertia and therefore more resistant to increase the rpm transferred from the gearbox. Of course this is just a few milliseconds difference in the real world and the drivetrain rpm (or more precisely the rpm of the input shaft of the gearbox) WILL be transferred to the crank and thereby over rev the engine...

i am my best friend and worst enemy in this case

[solstice]

Money shifts usually happen when you downshift two ore more gears since you need to be at very high rpms in for example 3rd gear going to 2nd to over rev the engine. You would be in the mid to upper range of the power band in 3rd having both max acceleration if that's what you want or strong engine braking available, there would be no reason to downshift.

I suspect your friend went from 5th to 2nd...

[rsr racer]

Originally Posted by Boss330

So now your "friend" has become just friend... Your first post looked like it in reality was you that drove your own car...

Anyway, the weight of the flywheel doesn't matter here. If you engage 2nd gear while the car is travelling too fast, it's the clutch speed that is your enemy. If the clutch speed is higher than redline of your engine, you end up having issues... Clutch speed is completely independent of flywheel weight. When you shift down to 2nd the rpm of the input shaft is accelerated and when you engage the clutch, this rpm is transferred to the flywheel and crank. If anything a heavy flywheel will have a larger inertia and therefore more resistant to increase the rpm transferred from the gearbox. Of course this is just a few milliseconds difference in the real world and the drivetrain rpm (or more precisely the rpm of the input shaft of the gearbox) WILL be transferred to the crank and thereby over rev the engine...

i am my best friend and worst enemy in this case

[rsr racer]

Originally Posted by solstice

Money shifts usually happen when you downshift two ore more gears since you need to be at very high rpms in for example 3rd gear going to 2nd to over rev the engine. You would be in the mid to upper range of the power band in 3rd having both max acceleration if that's what you want or strong engine braking available, there would be no reason to downshift.

I suspect your friend went from 5th to 2nd...

def 6500 3rd to 2nd. unquestionable.

just a dumb mistake and obviously shitty heel / toe blip with entirely wrong shoes on as well.

[solstice]

Originally Posted by rsr racer

def 6500 3rd to 2nd. unquestionable.

just a dumb mistake and obviously shitty heel / toe blip with entirely wrong shoes on as well.

He obviously wanted to shift, why 2nd? Was the intention an upshift to 4th? I don't get it. I never attempted a downshift at 6500 rpm in over 30 years of driving. There is no reason ever to do that.

[Boss330]

Originally Posted by rsr racer

def 6500 3rd to 2nd. unquestionable.

just a dumb mistake and obviously shitty heel / toe blip with entirely wrong shoes on as well.

If you went from 6500rpm in 3rd and downshifted to 2nd, there is no way you could have salvaged anything even if you where the world's greatest heel-toe shifter

It's not about rev matching (since no amount of throttle blipping could raise the rpm to the rpm the input shaft had in 2nd at that point...).

In the F8x MT 3rd gear is 1,542:1 and 2nd gear is 2,315:1

This means that 2nd gear is approximately 1,5 times higher numerically than 3rd gear. So as the input shaft did 6500rpm in 3rd, that speed can be multiplied by 1,5 to get the rpm of the input shaft (assuming the car is still moving at the same speed and no braking is done during the shift).

6500rpm x 1,5 = 9750rpm

So, if the clutch was even just connected for a short while the engine might have seen RPMs very close to 10.000rpm... That surely cannot have been very good on the internals...