Plating Main Bearing Races for Fit

Not that this forum needs anything mor obscure than we already post, but I couldn't restrain myself on this one. I recently had occasion to copper plate the inner race of a pair of Commando main bearing to get a tighter fit on the crankshaft. It's not my favorite solution to the problem of worn, or polished undersize in this case, main shafts. I'd prefer to have the shafts hard chromed, but the only local plater who does that quoted $650 to do the job, and that wasn't in the bike owner's budget. The next best solution would have been hard chroming the inside of the races, but that would have also been expensive. We settled on the copper plating because it can be done at home. It's a solution I found in Phil Irving's wonderful book, "Tuning for Speed." He didn't like it as well as hard chrome or nickel, because copper is softer, but said it was still an acceptable solution for those without access to (or funds for) commercial platers. This was my first shot at it, and I'm pleased (and surprised) that it came out right the first time.

This is one of the finished races.



The race wired up with safety wire for an electrical connection, dipped in wax to mask the bearing surface, and trimmed.



The plating setup



After plating



Plating thickness was about .0005" for one side and .0015 for the other to get the fit back within the fatory specs. Pretty easy to control the thickness by time in the bath. Total plating time was around 20 minutes per race. I pulled them out of the bath to check the bore diameter periodically. It also requires some care in positioning the race and the copper electrode in the bath to get a uniform thickness around the bore. The races went on the shaft with a light press fit that felt just like fitting them on a stock crank.

Ken

Isn't electro plating fun? It works too. And you can do it right on your bench, if the part is not too big.

Dave
69S

Wouldn't bearing-fit Locktite do the same job?

I've tried using the Locktite high strength stuff designed for studs and cylindrical bearings and bushings, but it didn't hold. I tried it twice, on two different race bikes, and when I tore them down later the race was loose again. I've heard the same results from a couple other Norton racers who tried it. I had the same results when I tried using Locktite for outer races that were loose in the crankcase. Locktite and similar miracle goops are great stuff, and I use them a lot, but Norton main bearings don't seem to be one of the places they work. The last time I had to do this was with a new Nourish crank back in the '80s. It came with the drive side mainshaft undersize by a small amount, .001" or so, if I recall correctly. I had it hard chromed to build it up by that amount, and it has worked perfectly ever since. It was so little material buildup that no grinding was required, and because it was in the tank such a short time, there was no hydrogen embrittlement issue. I was hoping to do something similar with this one, but had one plater turn it down because it was nitrided, and the other quote that ridiculous $650 fee. Times change, and the enviromnental regulations have driven most of the electroplaters I used to use out of business. The remaining ones are way more expensive now, at least here in Southern California. Besides, the copper plating was something new to try, and kind of fun, and I think it will work just fine. Did I mention that it is also really cheap?

As an aside, when I had race engines with the inner race loose on the mainshaft, it never caused any damage. Might have worked fine even longer, but I was just never comfortable enough to try it. Then again, the engines might have fragged if I kept running them. Could have been an expensive experiment.

Ken

I never got loctite to work on the main bearings when they were loose in the case. I put that down to the fact there is a fair bit of expansion between the alloy case and the steel bearing.

For steel on steel as in fitting a bearing to a crank, I would have expected it to work OK....it's holding the steering head bearing into my BM racer!

Icrken, I asked you about dellorto carbs in the 2 into 1 thread.

Yeah, I expected it to work too. That's why I tried it a second time. I dont have any theories on why it didn't work. Sometimes things just don't turn out the way you expect.

Ken

Lcrken,
thanks for sharing this with us.
You reckon it could work on the outer ring of a gearbox sleeve gear bearing as well?

slimslowslider said:

Lcrken,
thanks for sharing this with us.
You reckon it could work on the outer ring of a gearbox sleeve gear bearing as well?

Click to expand...

I think it would, but with a ball bearing like that, you'd have to figure out how to mask it so there's no leakage. Otherwise, you end up with copper plated onto the balls and races. The bearing almost always seems to loosen up in the gearbox shell eventually, so even plating would only be a temporary solution, until the bearing works its way loose again. Still, temporary could mean years, depending on how hard the bike is used.

In normal use, a loose sleeve gear bearing doesn't seem to have much effect. Almost every high mileage gearbox I've taken apart has had a loose sleeve gear bearing, and has been cracked between the sleeve gear bearing and the layshaft bearing. Most of them were still working normally before I took them apart.

Ken