Pilot Bearing Question

[gw]

The pilot bearing does not fit snugly on the trans input shaft. Measuring shows that the shaft is .002 smaller than the pilot bearing. Is this a problem? If so, could a brass shim ring be used?

[Werner]

Hallo gw,

if the shaft can move inside the bearing seats, this is not a good thing because the main bearing wears out faster. A brass sleeve is difficult to manufacture because the wall thickness is too small.

I minimized the movement by glue a steel strip (0.1 mm) round the pilot stump (Locktite).

[Patrick L.]

I wouldn't worry about .002"

[Tom Endy]

During a transmission overhaul it is common to find most input shafts with the nose end worn. I take them to a local repair shop where they machine the nose down and press on a drill bushing of the proper size.

Tom Endy

[Russ/40]

Tom, your fortunate to be able to get those kind of services done for you. I suspect the volume of your work makes that more worthwhile for a machinist. Always enjoy seeing your posts.

[Joe K]

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I would say 0.002 IS worth worrying about. One of the reasons for "jerky" engagement and walking the 3rd gear internal gear "off" the input shaft. (i.e. slipping out of 3rd back to neutral)

Best would be to turn it down, bush it back a tad oversize, and with emery cloth go for a "tight" fit.

Cheap insurance.

Joe K

[Werner]

Originally Posted by Tom Endy

... I take them to a local repair shop where they machine the nose down and press on a drill bushing of the proper size.

Tom Endy

I was advised against that. Due to the thinner turning, the nose loses strength and can break due to torsional stress.

[1928Mustang]

Any good machine shop can fix it. One way is to tig weld it up and turn it to size so bearing just slides on. I have done many this way.

[Mulletwagon]

Originally Posted by Patrick L.

I wouldn't worry about .002"

I'm with Pat. Clearance of .002 is little more than a sliding fit. Not sure the mods described are warranted. For serious slop a new input shaft/pilot bearing would be more cost effective IMHO.

[Chuck Sea/Tac]

They make a smaller inner diameter 6203. Metric I think. Turn the nose down and use that bearing. I’m rebuilding my transmission after 40,000 miles of this bearing. It’s worn a little more now, so were I to reuse the otherwise good input shaft, I would turn and sleeve back to standard, as Tom mentioned.

[1ton]

.002 clearance is fine but the pilot on your input shaft looks to be worn. How can you get a good measurement on that?

[goodcar]

Originally Posted by Patrick L.

I wouldn't worry about .002"

As long as you have the transmission removed, fix it. .002 problem or not, shaft will continue to wear. Find a good machinist to weld and turn down or use a sleeve. Pulling and installing the transmission is no fun.

[Jim Brierley]

I agree with Pat L and mulletwagon. .002" is miniscule, and the only time that brg. is turning is when the clutch is pushed down and the car isn't moving. Don't worry about it!

[Patrick L.]

.002" is half thickness of a human hair and that of an engine crank bearing clearance.

[Ranchero50]

Gotta have some clearance or the input to bushing fit will seize while sitting at a stop light with the trans in gear and the clutch held.

[Patrick L.]

While most vehicles use a bushing for a pilot 'bearing', most Model As use a ball bearing. I have seen a couple old Fords with a bushing though. A properly oiled oil-lite bushing would work just fine. As you mention, some extra clearance would be necessary.

[Werner]

Originally Posted by Ranchero50

Gotta have some clearance or the input to bushing fit will seize while sitting at a stop light with the trans in gear and the clutch held.

For sure? I think the rolling movement when pedaling the clutch is taken over by the roller bearing?

[rotorwrench]

Push fit is anywhere from .001" to .0015". .002" is good for a rotational clearance that doesn't need to be a push fit. I've seen the V8 flywheels with the old phosphor bronze bushing worn egg shaped and they were still working albeit not as well as they should. Now if it was more than .002", then I'd start to get concerned. The input shaft bearing has clearance too or the bearings would last very long.

Rotating bearing fits have to have some clearance or there can be galling from excessive temperature built up. The only time the pilot really turns is when the clutch is released. Folks that stand on the clutch too long will experience more wear. Put the transmission in neutral and release the clutch.

[Werner]

That's true, if rolling bearings run under tension, they are quickly destroyed.

In my case, the worn undersize is 0.007"! This is extreme and the new main ball bearing would wear out quickly again.

[Roger V]

I agree with Joe K (#6 post). Now is the time to correct the issue since it’s out. The shaft is going to turn in the pilot bearing as it has already so it’s going to wear smaller yet. As mentioned, getting it turned is easy for any machine shop. Also it seems most machinists have their own lathes at home and may do it for you. I’ve had them turned to 5/8” by a retired tool and die maker. The bearing originally was metric at 17 mm. That few thousandths will clean-up most shafts and has never been a problem strength-wise. You can buy bearings at most bearing shops. I get mine on Amazon Prime.

[Ranchero50]

Originally Posted by Patrick L.

While most vehicles use a bushing for a pilot 'bearing', most Model As use a ball bearing. I have seen a couple old Fords with a bushing though. A properly oiled oil-lite bushing would work just fine. As you mention, some extra clearance would be necessary.

Mine has a bushing, wasn't aware that they had bearings at one time.

[katy]

Here's what they look like:

[100IH]

Werner, we have a company called "speedy sleeve." They make hard alloy thin wall sleeves that can be installed with a press fit and/or locktite. Made just for repair of worn surfaces. Somewhere in Germany there must be something like that. I made my own thick wall sleeve to repair my input shaft after turning it down to an under size. The radial load is minimal and the speed differential is also slight and momentary. just needs a good shiny surface with clearance.

[rotorwrench]

Speedy sleeves are primarily for worn seal surfaces.

Most of the shafts I've had repaired for the helicopter transmissions were surface ground on the worn journal then plated back up with hard chrome or Chromalloy. The shaft then went through a relief process to prevent hydrogen embrittlement. It was then surface ground back to its original dimension. This was all a very expensive process but the cost of a new shaft was a lot more. The cost of an input drive shaft for a Model A is likely less than those type of repairs at around $225 US. I guess it depends on how long a person wants to keep running the parts. No matter what, it will cost time or money. I think I'd look for an undrilled phosphor bronze bushing blank and cut it to fit the worn stub. The bronze bushings last better than a lot of folks give them credit for and they won't gall.