Pilot bearing to main gear drive fit

[sjhark]

Can anyone tell me how much clearance I should have between the bore of the flywheel pilot bearing and the end of the transmission main gear drive? I have both a new bearing and a new drive, and right now there is only .0003 (three ten-thousandths) clearance between them. I can get the bearing on the shaft, but it requires some persuasion. I'm just afraid that when I'm laying on my back under the car in a snowbank, bench-pressing the transmission up into place and using my foot to shove the transmission into the clutch plate/pilot bearing, that it's not going to want to go.

[SeaSlugs]

you WANT it to be a snug fit - you do not want that bearing center to spin on the shaft what so ever. If it fits with minor persuasion by hand leave it alone. Most people pin prick a used shaft so it presses in tighter.

[BRENT in 10-uh-C]

Originally Posted by sjhark

Can anyone tell me how much clearance I should have between the bore of the flywheel pilot bearing and the end of the transmission main gear drive? I have both a new bearing and a new drive, and right now there is only .0003 (three ten-thousandths) clearance between them. I can get the bearing on the shaft, but it requires some persuasion. I'm just afraid that when I'm laying on my back under the car in a snowbank, bench-pressing the transmission up into place and using my foot to shove the transmission into the clutch plate/pilot bearing, that it's not going to want to go.

0.0003" is awfully tight. I don't think you are going to be able to hone a case hardened bearing 7 or 8 tenths, but you might be able to polish the input shaft some. Verify there are not any nicks or raised areas on the shaft that is causing your fit issues.

[Drive Shaft Dave]

Originally Posted by sjhark

Can anyone tell me how much clearance I should have between the bore of the flywheel pilot bearing and the end of the transmission main gear drive? I have both a new bearing and a new drive, and right now there is only .0003 (three ten-thousandths) clearance between them. I can get the bearing on the shaft, but it requires some persuasion. I'm just afraid that when I'm laying on my back under the car in a snowbank, bench-pressing the transmission up into place and using my foot to shove the transmission into the clutch plate/pilot bearing, that it's not going to want to go.

In my opinion, you should be good with what you have. Be sure to smear some grease on that end of the input shaft.

[sjhark]

Originally Posted by BRENT in 10-uh-C

0.0003" is awfully tight. I don't think you are going to be able to hone a case hardened bearing 7 or 8 tenths, but you might be able to polish the input shaft some. Verify there are not any nicks or raised areas on the shaft that is causing your fit issues.

I was thinking the same thing. I know it's not supposed to be more than .002" clearance, but what I have now is a press fit, for all practical purposes. Am I thinking wrong and the bearing should press on the shaft but slide into the flywheel? Judging by the fit on the shaft, if I try to use the transmission bolts to try to pull the nose into the bearing, I think the bell housing is going to flex before everything ends up where it's supposed to.

[chap52]

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That pilot bearing has to be snug on both the shaft and in the flywheel. A little touch up with emery paper on the shaft and a dab of grease may help the install.
I never thought about clearances on these and somehow managed to assume the needed pretzel position on the garage floor to get them in place.
Last time I installed one I did it from the top (in a 52 F!) and cheated with my engine hoist. Took me 71 years to figure that one out. Fear of getting stuck in the pretzel position was a real motivator.

[Big hammer]

Chamfering or beveling the end of the input shaft will help getting it started, .002 loose fit is what I would work for. Main engine bearing clearance is .0015

[katy]

Am I thinking wrong and the bearing should press on the shaft but slide into the flywheel?

The bearing should be a press fit into the flywheel.

IIRC that bearing is a 6203 which has an ID of 17mm (.6693")

[George Miller]

Should be a tight slip fit on the in put shaft.

[sjhark]

A slip fit is what I was thinking it should be. When I get back to town this weekend I'll chuck it (shaft) up and hit it with some sandpaper. Thanks for your help, everyone!

[PC/SR]

Do not use sandpaper. .002 is too much on the bearing to shaft clearance. With that clearance it will wobble (like a crank shaft bearing will, but they have oil, which the pilot bearing does not.) Keep it snug, the .0003 does not seem excessive tight to me.

[katy]

Note that it only works when the clutch is released, 99% of the time it's not turning.

[sjhark]

When I was checking the fit the other day, I had to use a hammer and brass drift to get the bearing started. I only put it on about half way and had to use a bearing puller to get it back off.
How does one install a transmission if the bearing fits that tight in both the flywheel and on the shaft. It's not going to slide into place using the weight of the transmission alone, and I think using the mounting bolts will distort the bell housing. Or will they?
I've installed a lot of transmissions (granted, newer models that don't have the main gear hanging out there) and the pilot bearing was a slip fit to the shaft, not a press fit that I have now. Am I wrong on this?

[Tom Wesenberg]

Yes, that's too tight. I've never run into that problem, but my first guess would be the bearing size, so I'd try another bearing. It's the same as the front bearing on the generator.

[sjhark]

Originally Posted by Tom Wesenberg

Yes, that's too tight. I've never run into that problem, but my first guess would be the bearing size, so I'd try another bearing. It's the same as the front bearing on the generator.

Thanks Tom. I didn't have a spare bearing, so ended up using the lathe/ sandpaper method. I took an additional .0006" off the shaft and the bearing is a good, snug, slip fit now. It has just under .001" clearance now and fits like I expected it to.

[J Franklin]

That is a trick that some restorers use with a worn input shaft. A new metric ID bearing, and then turn the nose on the shaft to fit.