Hi all,

I am in the middle of transforming a 6 cyl 5 speed manual transmission into a V8 one by using a 3.5 four speed input shaft, constant gear and front cover. I will also be putting reinforced bearings and a second shaft key for the 5th gear pinion on the countershaft.

Unfortunately the input shaft I want to use is scored by 4 thousands of an inch (on the total diameter) where the pilot bearing goes. I was unable to trace a good one and it is discontinued new.

I was told by a professional and also read on the net that I could have the shaft welded then machined back to spec. But two different machine shops have discouraged me to go that way as welding on the shaft would weaken it or could even break it.

I have considered putting a sleeve on it but the cost of machining the shaft then the sleeve is high and the strength of the sleeve would not be the same as the original shaft ending up in scoring again quickly.

I found this Belzona product on the net: http://www.belzonamolecular.com/ProductFlyers/MPT.pdf
Apparently one can fill the scored area with their product and then have it machined back to spec. But I was not able to find any info on how hard this will be and if it will be OK for an input shaft.

Any idea on what I should do would be very helpful.

Thanks in advance!

First,

This only takes load when the clutch is depressed- it's not the most highly loaded. But, you will never be able to restore it to the orginal metalurgical condition and a sleeve... very hard to cut that steel. Tried it before on a chebbie. Welding, chroming etc.. all will be a lower strength (fatigue, and static).

I suggest finding a used donor.


Michael

Well, good donors are not that common. These are 3.5 four speed manual. I got two and both had a scored input shaft. I wonder what causes the scoring in the first place. If it's just the pilot bearing gone bad then some kind of repair may do the trick as long as I put in a new bearing.

The Belzona MPT 1 or 2 looks like it is used in some severe applications and would probably hold up here, but you need to turn it down to spec, With the material and machining costs, it does sound like you'd be better off with another one.

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Prost!

Did you try the MB Classic Center? Also the big MB salvage yards, like Potomac, or Silver Star?

You can certainly weld this back up and machine it to size. I worked in a small machine shop/job shop where we did this kind of thing all the time, mostly on construction and mining and oilfield equipment where the price of a new shaft was $$$$ yikes. To restore the original strength, the shaft would have to be re-heat treated: annealed first and then re-hardened back to spec. It's been awhile, but if I remember correctly, what we did was usually the old shaft was annealed first to soften it and make it more dimensionally stable to minimize distortion during welding. Then shaft was returned to machine shop for weld build-up and machine back to finish size. When complete, then back to the heat treat shop to re-harden. Take it to your heat treat shop first, have them measure the hardness and determine if it is case-hardened or through-hardened, then he knows what to restore the hardness to after the repair is done. Cost of the heat treat I would guess to be $250-ish, welding and machine work probably four hours or so, assuming no keyways or splines are being cut, so there's another $400 or so, so that gives you a really rough idea of cost. For a keyway add another hour and splines add another 2-3 hours.

Thanks for the answers.

73Elsinore, Do you know if I could have only the front of the shaft annealed, welded, machined and rehardened? If possible I would like to avoid the input pinion and associated/inserted synchro teeth on the other side of the shaft out of the process, or would that be just fine to get them go throught the process too?

Otherwise I also came accross this: http://www.southbendclutch.com/kevlarbushing.html and this: http://mustangsunlimited.com/itemdy01.asp?CatKey=Cougar&Category=Drivetrain&T1=N15+01&subCategory=Clutch+%26+Related

These are kevlar pilot bushings that can be used even with scored input shafts. Anybody heared about them, or have any experience with them?

Have you considered having the shaft ground undersize and then making a custom pilot bearing?

I looked at other bearings with a smaller inner race, but the next in size would require grinding too much out of the input shaft and the machine shop guy with whom I was considering that option said the shaft would become too weak and would end up breaking. A custom bearing would be ideal. Are you thinking of a ball bearing, if ever it is possible to have a custom one made, or a composite one?

I didn't realize that it was a ball bearing, many cars use a sleeve bearing. I would not be too concerned about the hardness if using a ball bearing, as there should be a slight interference fit and the inner race should not rotate on the shaft. It seems like a tolerance sleeve would work.

Custom bearings are probably out of the question.

I thought of another solution that would be very cheap and within my capabilities (no machining, heat treatment etc).

The bearing width is 11mm. It goes inside a 22mm deep cavity inside the crankshaft and is kept in place there by a cover ring. See picture below:



I could fit an 11 mm spacer inside the crankshaft (an outer race of a worn pilot bearing for ex.) and then fit the new pilot bearing. This would bring it backwards enough so that the inner race would be on a not damaged portion of the input shaft, while the outer race would still be fully inside the crankshaft. The problem is that I could not fit the cover ring to retain the bearing from sliding back and out of the crankshaft. I could then use one or a combination of both the following two solutions:

1. Glue the outer race of the pilot bearing to the crankshaft. I see Loctite makes products specifically for this application, but I don't know if this alone would be strong enough (though I don't see that cover ring in the original set up retain the pilot bearing with a lot of strength).

2. Fit a carefully sized spacer on the input shaft between the pilot bearing and the bigger spline section to prevent it from sliding back.

A variant is that I could use the 8mm thick cover ring as a spacer inside the crankshaft and add a 3mm spacer between the cover ring and the inner race of the pilot bearing. This would allow the cover ring to compensate for any variation due to heat dilatation (its shape would allow it to work as a "spring") and keep a low pressure on the input shaft bearing, transmission side, while keeping the pilot bearing tightly in place.

This is a long explanation for something very simple. It may not look very "mechanically correct" but would prevent the input shaft from going through various thermic treatments that may well weaken it if not done properly.

What do you think?

http://www.dieselsite.com/index.asp?PageAction=VIEWPROD&ProdID=588

Not quite your 4 thousandths, but maybe they have some ideas

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Prost!

I think the shaft could sleeved to bring it up to size. There's little radial force on it. Or you could bush the bearing.
What is the number of the pilot bearing?

Pilot bearing is 6202.

I could just glue the bearing with some Loctite 638. They say it can take care up to 25 thousands play. I may have some trouble taking the trans out though

This is not a good fix. The pilot bearing supports the input shaft and using loctite will not center the shaft in the bearing.

I forgot to mention that I found a double row bearing that has the same inner and outer diameter but which is 14mm wide instead of 11mm. This would still allow the use of the cover ring. The bearing would be properly centered by 3mm on an undamaged portion of the shaft. The remaining 11 mm with 2 thousands play (each side) would be taken care of by the glue.

I looked at the set-up again and I believe the scoring happened because of too much initial clearance, which is still the case on the good part of the shaft. As a result the shaft turns freely inside the inner race of the pilot bearing without driving it. Using glue may solve that problem. I will also glue the outer race inside the krankshaft. As the surface in contact is greater there the assembly will loosen on the shaft side when I disassemble the trans again, instead of having a glued bearing getting stuck on the clutch disk.