Clutch Plate Bolt question
 

I have a 1928 35A which has a 3 fingered V8 pressure plate with a machined flywheel. I have just replaced the pilot bearing and have started to re-assemble.

Of the six bolts that attach the pressure plate, five tighten as they should. One however just turns. Taking the bolt out, the thread is intact but there are pieces of metals shavings attached.

Of the possibilities, I have thought that this is waste left over from the machining. I would not have thought that a bolt could normally strip metal from the flywheel itself, but it is possible that in the tightening and torquing this has occurred. I have also considered that the hole was not drilled deep enough. I have cleaned out what I can but still I cannot tighten to torque the bolt.

The options as I see it are:

• Just tighten to specs the other five and don't worry about it too much,
• Use thread tape and Thread Lock,
• Tap the hole a tad deeper and use a longer bolt, or
• Something else I haven't thought of as yet! :D

I guess the question that I have is this. If this was your car, what would you do; preferably something that does not involved taking off the pressure plate itself?

Thanks
John

Re: Clutch Plate Bolt question
 

There is no shortcut here. Take the pressure plate off and examine the defective threaded hole. It is likely stripped. In which case use a helical coil insert (Helicoil). Consider installing the inserts in all the other threaded holes too. Be careful to drill the pilot hole for the insert in the correct location and perpendicular to the surface.

The threads can strip if a high strength bolt is used, especially if they were damaged or not cut correctly.

Re: Clutch Plate Bolt question
 

The flywheel is cast iron, so it is easily stripped if the bolt is over tightened.

If installing a Helicoil or similar insert use the pressure plate for an alignment guide when drilling.

Re: Clutch Plate Bolt question
 

The flywheel is cast but not cast iron. They are cast steel, a totally different alloy. The threads have more than likely been stripped from over tightening, bolt being cross threaded, or some other reason for the threads to be stripped. I would repair it with a Helicoil as recommended. Be sure the tap is perpendicular to the surface.

Re: Clutch Plate Bolt question
 

the original V8 bolts had a shoulder used to center the pressure plate ,a s a slight counterbore effort he threads.
One of the stripped thread strategies I use is to take a bolt with threads all the way, put a nut on it tighten the bolt into the remaining threads at the bottom of the hole then run he nut down and cut off the excess above the nut— this s about all you can do without taking it apart.

Re: Clutch Plate Bolt question
 

oldspert, thanks for the correction.

Re: Clutch Plate Bolt question
 

Sorry, but A flywheels are NOT cast steel!!! They are cast iron.

Re: Clutch Plate Bolt question
 

Wouldn't make sense to use steel on a flywheel anyway. Steel is for tensile strength. A flywheel just needs to be big and heavy.

Re: Clutch Plate Bolt question
 

Model A, B, and Burtz flywheels are cast iron. More modern more high performance engines do have steel flywheels and even aluminum flywheels with steel inserts.

Re: Clutch Plate Bolt question
 

UPDATE:
Many thanks for the suggestions. I followed the sage advice and removed the flywheel. In checking out all the bolt holes, I cleaned crud out of all the holes. Plus metal shavings from the problem hole and one other. After all were cleaned , I measured the depth of all the holes with my trusty calipers. The two with metal shavings were about 1/8" less in depth than the other four. From that I would suggest that after the flywheel was machined down and the pressure plate holes drilled, someone was a tad careless about the depth when doing the job. When I tried to tighten down the bolt, it had no where to go; it just stripped and spun.

I guess that is a lessen learnt; If I had checked before hand, perhaps an extra washer under the bolt head would have worked.

Re: Clutch Plate Bolt question
 

Now that you have it apart, I would agree to put Helicoil inserts in all the holes. Make sure to drill all to the same depth with the matching Helicoil drill before threading with the Helicoil tap.

Helicoils are avaliable in different configurations, assorted lengths, with or without thread locker on the outside and a choice to have a helicoil that locks the bolt ( similar to a locknut).

Done correctly, it will be the end of your trouble as it is considerably stronger than new!