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flywheel pilot bush

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71tr

71tr

Jedi Warrior
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Just installed a new aluminum flywheel and noticed that the new pilot bush is a tight fit. The old pilot was nicely polished after 30yrs and fit in place freely, while the new unit is a snug match. Any thoughts on this, or concerns. Does this bush rotate with the flywheel or will it eventually rotate freely on its own?
 
They are designed so that the input shaft turns inside the bushing. The bushing usually intact with the flywheel. A lot of "bushings" have been replaced by needle or roller bearing cups. Technology marching on.
 
If using a bushing it needs to be a press fit in the crank and the pilot shaft needs to spin freely.

If the pilot shaft is too tight it can make shifting into a gear from neutral difficult because the transmission pilot shaft will tend to spin with the crankshaft. Ask me how I know!
 
Do I remember these should be soaked in oil overnight before installation? I guess the bush is somewhat porous and the oil keeps it lubricated.

Rob.
 
We just replaced the clutch in a club members TR250, and ran into the same thing. The old bushing just fell out, and the new one was an interference fit.

Wonder what makes them get loose?? /bcforum/images/%%GRAEMLIN_URL%%/confused.gif
 
Whenever that happens, you want to take a close look at the input shaft of the transmission. There is a good chance that the bearing became stuck to the bushing and it was actually turning in the flywheel.

The tell tale sign is a black or dark brown ring around the tip of the input shaft, where it fits into the pilot bearing. Eventually after all of the spinning, it works loose of both and may just fall out.

A major cause of TR6 and other cars "clutch squeal".
 
From what I found out when replacing the pilot in my 3A, the bushing is supposed to be able to spin inside the crank.

The bush is soft and will never abrade the crank if it spins and serves the purpose of keeping the input shaft aligned.

It should not be a press fit item although a new one might have some degree of interference fit. ISTR that the TR3-4A pilot is the full depth of the crank recess and the TR6 pilot is much shallower so a slight interference would keep it from pushing inside the crank recess when you install the gearbox.

To remove the old one, squirt some grease through the pilot into the hole in the crank recess. Then use a dowel that is the same size as the hole inthe pilot to hydraulically push the old bushing out (wear goggles). Insert the dowel and pop it, and the grease will push it out and cover your face with grease!
 
Okay, good info I feel a bit more comfortable. I'll check the fit of the tranny input shaft with the new bush before installing. What are thoughts on lubricating the bush prior to install?
 
If it's bronze, an overnight soak in oil. Some small amount of grease on the input shaft "nose" initially on transmission install as well.
 
Where most of the installs go wrong or bad is when the installer doesn't use an alignment tool and has to keep trying to force the transmission into the bell housing and the bushing gets all beat up from the input shaft beating against it.

If you have the clutch disc and pressure plate aligned properly and add a small amount of grease to the slight bevel or radius leading into the pilot bearing and also on the inside of the bearing, you should be fine.

Just keep any grease away from the contact face of the flywheel and clutch and pressure plate faces as well.
 
PeterK said:
From what I found out when replacing the pilot in my 3A, the bushing is supposed to be able to spin inside the crank.

The bush is soft and will never abrade the crank if it spins and serves the purpose of keeping the input shaft aligned.

It should not be a press fit item although a new one might have some degree of interference fit. ISTR that the TR3-4A pilot is the full depth of the crank recess and the TR6 pilot is much shallower so a slight interference would keep it from pushing inside the crank recess when you install the gearbox.

To remove the old one, squirt some grease through the pilot into the hole in the crank recess. Then use a dowel that is the same size as the hole inthe pilot to hydraulically push the old bushing out (wear goggles). Insert the dowel and pop it, and the grease will push it out and cover your face with grease!
Click to expand...
Peter,

I have to disagree with you on this one. The pilot bushing is a press fit into the crankshaft. The input shaft should spin inside of the crank bushing. The standard bearings are also 'oil-impregnated' so no lubrication of any kind is needed.

An old bearing may get loose inside of the crankshaft due to wear from the input shaft wobbling in the pilot bore and just plain old age.

Years ago I spent some serious $$$ on a Snap-On pilot bushing driver set... I wouldn't have spent the money if I could just plop a bearing into the crank.
 
I agree with YankeeTR it should be a tight fit, it is NOT supposed to spin inside of the crank. It should rotate freely on the trans pilot shaft But not loose as to wobble. Lube it lightly with some lithium grease {not too much tho, you dont want grease to get on the clutch surface.}

Brosky has a very valid point:
you want to take a close look at the input shaft of the transmission. There is a good chance that the input shaft became stuck to the bushing and it was actually turning in the crankshaft.
When instaling your trans, an alignment tool is a MUST HAVE item. It prevents you from buggering up the pilot bushing thus making it too tight a fit on the trans input causing the bushing to spin inside of the crankshaft.
If it isnt a tight fit in the crankshaft then M.H.O. is it isnt the right bushing for your application.
Just my Pennys worth
Kerry
 
To the best of my knowledge, there is no pilot bearing designed to spin inside the flywheel. They are designed to be stationary and the pilot shaft turns in side the bearing.

Every pilot bearing that I have installed or seen being installed had a press fit that kept it in place. I would not suggest that you install a bushing or bearing that is loose inside the flywheel unless you enjoy removing and replacing transmissions.

Sorry that I missed this in the first go around.
 
On both of my TR 4-cylinder cranks, the pilot fit is precise but slips in with after soaking in oil for 24hrs.(actually I have to check my HVDA manual to see if I soaked it or not), no tapping. I thought it should be a tap in fit too so I used some loctite green made for holding bearing races and such.

I talked to everyone about mine slipping in when I changed it. All the auto guys said no press fit too. Then I called Herman VDA about it and he said, torch it out (needed heat to break the loctite green bond), the bearing should not be locked in. True at least on a TR3-4A where the bearing fit the crank recess fully pushed home.

So after removing the pilot, cleaning up, I inserted with a little lube as Herman instructed. A nice smooth precision fit that I could stick my little finger in and move out and in. The pilot is soft bronze so neither the crank nor input shaft get worn from the bushing spinning. When you think about it, it really makes no difference as long as the input shaft stays centered. Maybe it doesn't spin, maybe they both (pilot and input shaft) spin, maybe just the input shaft. Who knows - we can't see in there to tell?

I also have a TR6 bearing and that thing is only like 3/4" thick, the TR4 bearing is about 1-1/4" long, same diameter as the 6. I've never seen the back end of a TR6 crank so I don't know how deep the pilot hole is. So the 6 might need the interference to keep from falling in if it's as deep as a TR4.

edit
btw - it's working and I'm not taking it out unless I have to!
 
PeterK said:
On both of my TR 4-cylinder cranks, the pilot fit is precise but slips in with after soaking in oil for 24hrs...
Click to expand...

Same thing on mine (precise but not interference), but again that's a 4-cyl TRactor.
 
The original bushings were a porous ('oilite' or sintered- created from a powder) bronze. You can see the pores especially with magnification. A lot of later replacements were bronze but made from cast or extruded metal with no pores. So the soaking doesn't help. though it should still be oiled. I never was quite sure what to use and have tried some greases, but have no truly long term results to relate. You find it (porous bronze that is) also in the generator/ starter bushes. It is a push fit in the crank. As long as the old one is not rattling around I don't see a problem with reoiling and reusing it.
Tom Lains
TS8651 & 58107
 
OK, I'm confused. I just looked up the install of the "spigot bush" in the Bentley. They don't mention pressing in the crank, in fact just the opposite:


Quote from the Bentley:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Fit the spigot bush into the back of the flywheel ensuring that it is a loose fit[/QUOTE]
 
My flywheel seems to confirm the Bentley quote above. The engine side of the flywheel has a nice recess that fits the bush perfectly. Not sure if the end of the crank has a similar recess or not, the engine is at the garage.
 
Not to confuse or belabor this question, but when I said remain stationary, I did not mean to infer that it was a press fit with a lot of pressure. Just a slight bump with a wooden handle of a hammer to secure it, has always been my rule of thumb with GM cars and my TR6.

But then again, I thought, maybe I'm wrong, so I looked it up and here it is. I stand corrected, for the TR6, at least.

Right out of the original TR6 manual:
 
Paul,

Just to make you feel better, I also saw a writeup on the 6 that said to knurl the ouside of the pilot so that it doesn't spin. So the judge will declare a mistrial on this one.

But like I said, as long as it keeps the input shaft of the gearbox centered (presumeably to keep the input shaft bearing intact), it really doesn't matter if it spins.


PK
 
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