engine and drivetrain Pressure plate bolts bottoming out, problem or feature?

[rlobdill]

Question:  I just had my (OEM) flywheel resurfaced. I think this is the second time.  Yesterday I was installing a new pressure plate (Sachs, OEM) and noted that just when the bolts were starting to tighten up, it also felt like the bolts were just bottoming out in their mating holes in the flywheel.

 

My assumption is this is due to the fact that the flywheel is now slightly thinner than it used to be and I should now use some slightly shorter bolts.  It would seem odd to me that it would have been designed to bottom out -- but I've been surprised before.

 

Would you agree that the correct approach is to install new slightly shorter bolts?

 

Thanks, 

Rich

 

 

[avoirdupois]

Doesn't sound right.  Are you using washers under the bolts?   PN: 07119933241

 

 

 

[rlobdill]

Hi: Thanks,  I used washers under the bolts but they are flat washers not lock washers.  That was what was there when I took it apart, don't know what would have been original.  I suppose i could use a flat+lock washer combo, that would probably make room for the bolt.

 

Rich

[Son of Marty]

The split washer is the one that's used with the clutch don't use it with a wave washer under it you'll defeat the way ether washer works mechanically and the clutch is a real bad place to have a failure. if need be I think I would go with bolts that were a thread or two shorter but no more. 

[rlobdill]

Thanks Son o' Marty:

 

What was on the car was neither a wave nor split, simply flat. My experience has been that BMW typically uses wave washers instead of split.  So as it sits I do not have any type of locking washer on the bolt, just a flat washer.   In any case, my sense is that having the bolt bottom out is incorrect. So I need to address that.

 

One of the main reasons I took the transmission apart in the first place was that the clutch chattered nastily. I wonder if maybe the bolts had bottomed out for the PO and he thought that was fine. In that case it is possible that the pressure plate was a bit 'loose'.

 

Rich

[M3M3M3]

bolts should not bottom out.  how much has been taken off the flywheel?   

 

shorter bolts....or the flywheel has been thinned beyond spec and should be replaced.

[jimk]

33 minutes ago, rlobdill said:

What was on the car was neither a wave nor split, simply flat. My experience has been that BMW typically uses wave washers instead of split

I have only seen split lock washers on these cap screws.

[avoirdupois]

The pictured washer is the style recommended for securing the pressure plate to the flywheel.  Your washers could be much thinner.  But even if that were the case, I would think the standard length bolt would work even on a resurfaced flywheel.  Unless, as Marshall postulated, the wheel is below recommended thickness or is custom.  Come to think of it, are the bolt holes blind?

 

Could it be that when the flywheel was machined, the threads were somehow buggered, causing resistance that only seems like the bolts are bottoming out?  Old threadlocker/rust/debris left in the threads?  How much torque before the bolts stop turning? 

 

 

 

 

 

 

       

[rlobdill]

I didn't measure finished thickness of the flywheel. I brought it to a well respected machinist here in the North Bay Area (Best Machine) and I counted on him to know if the flywheel could stand for another resurfacing.

 

The threaded holes are blind, that is why they are bottoming out. The bottoming out is very obvious compared to other types of binding. Things go along nicely as you are tightening the bolt and then -- bamm -- everything stops, no amount of torque is going to make the bolt budge. It could be that there is some shavings that fell into the blind holes but in that case I think I'd have different bolts bottoming out at different bolt depths which does not seem to be the case.

 

I will probably take a two pronged approach. I'll get some proper split washers (which I think are thicker than the flat washers I presently have) and I will see if I can find some bolts that are 2 or 3 mm shorter. If the split washers tighten up nice I'll use the original bolts. If not I'll use the slightly longer bolts.

 

Thanks for the help guys.

 

Rich 

[JayMac]

There are shorter bolt listed on real oem. 28mm and 22 mm

[halboyles]

T

20 minutes ago, JayMac said:

28mm and 22 mm

Those bolts are for the flywheel to crank attachment on the 215 and 228mm flywheels.  The pressure plate to flywheel bolts are m8 by 16 or 18mm.

[JayMac]

12 minutes ago, halboyles said:

T

Those bolts are for the flywheel to crank attachment on the 215 and 228mm flywheels.  The pressure plate to flywheel bolts are m8 by 16 or 18mm.

I stand corrected. Pardon me while I turn my "Idiot Light" off. I was doing some research on this as I will be having this done shortly. On the flywheel I have the bolt holes go all the way through but are only partial threaded so I guess they could be tapped deeper if needed. Off to the penalty box...