OT: Questions about Hard Chrome Plating to salvage a shaft journal

A friend of mine named Bud Provin- a name not unknown to some of you who ride Airhead BMW motorcycles- has an oldtime motorcycle repair garage in Vermont. He works on a mix of mostly older "Airhead" BMW motorcycles and some of the old British motorcycles. A few days ago, Bud called to pick my brain about a problem he ran into. Bud is rebuilding the 5 speed transmission on a customer's BMW Airhead bike. Fifth gear has clutch dogs on one face, and otherwise free-spins on the output shaft of the transmission. There is no bushing or bearing in the hub of this gear. It is a helical gear, none too wide. The problem Bud encountered is the bore of the gear and the portion of the output shaft (journal) it turns on have become worn with some scoring. The problem of lubrication may have been a factor in that the shaft the gear is on has a spline immediately next to the journal. My belief is any oil film is probably none too good and prone to collapse via the grooves in the spline. However, there is no real load on this gear when the dogs on it are disengaged and the shaft spins free in it.

The problem is these motorcycles are around 40 years old. Some new parts are available, but a new shaft and new gear would be around 800-900 bucks. Add the cost of bearings and seals to go thru the transmission and labor, and the bill to put the transmission to rights would be up around $2,000.00.

Bud called me to ask about salvaging the fifth gear and output shaft. We kicked a few ideas around. One, which seemed the easiest and least costly, is to send the shaft out to have the journal ground under and hard chrome plated, then finish ground to slightly larger than original diameter. Bud has a good assortment of Sunnen Hones and a honing machine, so he could then re-size the bore of the gear to run on the hard-chrome plated journal.

I have no experience with hard chrome plating other than on journals which had spun in roller bearings. My own concern is the hard chrome plating might not hold up as a "running journal". My other question is how thick a deposit of hard chrome plating is needed to get a good solid journal with an allowance for finish grinding.

Bud is going to get back to me as to whether the gear is through-hardened or hard all over (surface hardened, but same difference from my perspective). Bud asked my thoughts on putting a bushing into the hub of the gear. My first thought was that if the gear is hardened, there is no boring it out for a bushing. If the gear hub is not hardened (which I think is unlikely), I had thought of boring and shrinking in a hard bronze bushing, something like an aluminum bronze and possibly pinning it. The ideal bushing would be a "floating bushing" as is used on heavier gears is this same transmission, but this gear hub design may not lend itself to that.

The bushing idea struck me as having more potential problems than the hard chrome plating of the journal/honing the bore of the hub to suit. I pretty much ruled it out at this point.

The easier and surer fix, at least to my way of thinking, is the hard chrome plating of the journal. Having no experience with hard chroming a running journal, let alone in a hard-steel on hard-steel application, I would appreciate any insights members of this board could give us.

The shaft journal is not all that large, perhaps 11/16" diameter, and the shaft can go in a USPS flat rate box, so it is not a big job. If anyone can recommend a good hard chrome plating shop who also does the precision grinding, please let us know as well.

Thanking you-
Joe Michaels

All of these repairs: chrome, spray weld, etc will work for a while. They are a compromise between replacing the parts and scraping the whole machine. They will not last as long as the original parts.

Some of the gears in that gearbox, do run with bronze bushings inside the bore, from the factory. So this might
be a good choice. The gear in question will most likely be not just case hard. It will be hard through and through
but could possibly be bored with the correct tooling.

My experience with hard chrome for bike parts is limited to press-up fits where a ball bearing is now a sloppy
fit on a bearing seat, the section of the shaft where the bearing seats is ground undersized and plated up, and
ground to size. Not a running fit of course.

My personal suggestion for this is to contact somebody who might have the correct shaft in good condition, from
a used gearbox. I have the contact information for such a source in the western MA area. Also I am currently
in contact with a man for some other bmw parts (NOS) and will raise the issue for this gear and shaft when I next
speak with him.

I first met Bud when he, his mom, and his dad delivered my first BMW to my house, from vermont. This was around
1989 or thereabouts. I doubt he remembers this but I recall his shop in vermont, vividly. It was a cool place.

Hard chrome lasts well with no peeling on cylinder shafts, under substantial sliding load through the gland. Also works in engine cylinder sleeve bores. I would not use it as running surface for a rolling-element bearing, with 100x the contact stress, but for a plain journal, done well, I would expect success. Unfortunately I can't recommend a plater. I'd hone the gear bore out, if too hard to bore, for a bronze bushing. IMO that combination should be better-than-new.

Upon further inspection.

Turns out I have this exact gearbox in pieces in my shop right now. Basically I keep a spare on hand, this is the
spare that needs re-build. (this one has a bigger issue, the second and third gear need replacement on the intermediate
shaft, and supposedly you can't get there from here...)

The items on Bud's gearbox that would be replaced with new, if possible, would be the small helical fifth gear, and the
output shaft, which it rides on. The remainder of the parts on the output shaft can be moved over.

The shaft itself has a steel thrust washer that blocks the fifth gear away from the splines farther aft on the shaft. So
the fifth gear is captured on a smooth portion of the output shaft between the front ball bearing (pressed on the
end of the shaft) and that steel washer. It would be pretty easy to mask off the rear portion of the shaft and hard chrome
the surface the gear runs on. Because it's at the very end of the shaft (except for the smaller diameter bearing seat area)
it would be not to hard to grind to size. Also this could be finished oversize without harm, if the gear hub were honed
oversize to round it out and eliminate bell-mouth.

The gear in question indeed has no turning load on it ever. It's either floating if in some other gear, or locked to the dog
plate to the rear if it's in use. The only real reason to tighten it up I think would be to improve the shift behavior of the
gearbox, unless there is a LOT of wear.

Best: brand new fifth gear and output shaft.
Better: source good, used parts.
Good: go the plating route.

We would question the chrome plate in a rotating environment so it may fail.

Crankshafts have been built up by welding then ground to size for years.

This could be done here.

Look for old school engine shop, worked at one back in the day and this was a common 3 times a week task.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk

Just a thought so please don't shoot me.

I couldn't quite picture the situation so ...........

What is the possibility of grinding that section of shaft just so it cleans up (size doesn't matter) , and boring out the gear and fitting a HARD bronze bush (press and Loctite the works) then bored to fit the cleaned up shaft?

No heat, no distortion, and all work in your own shop done under YOUR control.

Tony Quiring said:

Crankshafts have been built up by welding then ground to size for years.

This could be done here.

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Not entirely applicable. In repairing a crankshaft, the damaged journal is ground, then welded, then straightened, then all journals are ground to the next smaller size. If the crank has been ground to it's minimum size, all journals have to be welded and much $ is spent.

Similarly here, one cannot weld just the affected area and hope not to disturb the rest of the shaft. Hard chrome and spray weld are done because they happen at a low enough temperature to minimize that effect.

Thanks to everyone who responded. I know hard chrome plating has been used with success on crankshaft journals, so ought to hold up in service on this transmission shaft journal. Thanks to Jim Rozen for the anatomy explanation.

Limy Sam:
Bud and I had both thought of the hard bronze bushing route. My only concerns were whether there was enough meat in the gear hub to bore out for a bushing; whether the gear was through-hardened; and what length/width ratio of the bushing would be. My first thought when Bud Provin called me was to suggest boring and bushing with a hard aluminum bronze bushing. My thought was to use a heavy shrink fit to lock the bushing into the hub.

It remains to determine if bushing the gear hub is possible, though the hard chrome route should be less costly and a whole lot easier.
I tend to think like an oldtimer, so bushing the hub was my first thought. Bud said some other Airhead motorcycle mechanics have gone the hard chrome route to build up this particular journal and honed out the gear's bore, but he did not have any experience with it of his own. Bud called me to bounce ideas off me and see what my thinking was. I bounced the ideas of this group to see what the experience-based wisdom is.

My gut sense is a funny thing, in that it does not comfortably accept the idea of a hard chrome plating job holding up as a running journal and possibly peeling off into a running transmission... with a real bad failure resulting. On the other hand, hard chrome plating is used in industry in countless applications and does hold up handily on things like hydraulic cylinder piston rods on things like heavy construction machinery. I am probably being overly cautious without a solid foundation for the misgivings my gut is telling me about.

Thanks again to everyone who has responded to my post.

Chrome plating is quite suitable for running journals. Googling "chrome crankshaft" will turn up a bunch of shops that do locomotive and marine engines, including one called "Chrome Crankshaft". Seems to be the preferred repair for EMDs

I've had experience of chrome plating for rolling bearing journals, gear seats etc. It worked fine but this was on big shafts and nothing was rotating on the shafts.
We worked on a maximum of 0.020" thickness of chrome or 0.040" on the dia.

Regards Tyrone

Call 314-781-6631 and ask for Jim Vishion. They do this sort of thing every day. They routinely do shafts that have to be loaded on the grinder with a forklift. Tell him an old guy on an Indian told you to call him.

Bill

Joe, if you look at the parts breakdown for this sub-assembly, you'll see that the first gear on the output shaft,
is set up with a bronze bushing from the factory. I've actually replaced that bushing in more than one gearbox
that was up for re-build.

I do not however understand why that one gear has the bushing and none of the others on that (output) shaft
have a bronze bushing. Teutonic engineering, etc.

I have looked at a variety of sources for the parts in question (fifth gear, output shaft) and the overall impression I get
is NLA. No Longer Available.

I will attempt to contact my source for a used gearbox. I need an intermediate shaft. He needs the two other parts.

Jim

I have hard chromed valve stems, crank shafts and gear box shafts without a lick of trouble. If you want your valves and guides to last more than 15-20,000 miles in a Triumph Trident chrome the valves and use aluminum bronze guides. I machine the guides for Fiat 128 valve seals. I have a few of them out there with over 50,000 on the valve job, still running great. That is saying something for an engine with the worst rocker geometry I have ever seen.

I recently was trying to find someone to build up a hard chrome spindle. The bearing surface showed about .015" of score on the bearing surface.

Most places doing hard chrome these days wanted a LOT of money to build that back up, on the order of $1200-$1500.

If you can get it done at a reasonable price, more power to you.

What I ended up doing was (and it's not done yet), send it out to a machinist to hard turn the diameter and grind to size, then make new bronze bushings for it that are slightly smaller on the ID to accommodate the newly turned bearing surfaces. In this case the machine already had bronze bearings (South Bend 10L), so new ones with a slightly smaller ID was not too big of an issue.

There was a place that a lot of South Bend owners used to have hard chrome the spindles, Miller in IN or IL. He had an outdated web page, but the phone worked and I spoke to the owner. He quit doing them several years ago as it became too costly to hard chrome. What used to be a couple hundred is now close to $1000, and since he used to send that out to a hard chrome shop, the price went through the roof so he quit doing the spindle.

If you can get it done at a reasonable cost, which probably translates to not too thick of a buildup, it might not cost you very much. I would check and price that out first.

A couple of years ago, in the early 1960s my first job as an apprentice was at a shop that rebuilt Diesel Engines, injectors and the like. This was pre-EPA so they had their own Hard Chrome shop and always had a large batch of parts in the tanks usually over the weekend.

In addition to injector pintels I remember one item that had a couple of hardened steel gear/shaft assy that rotated at high speed in bronze bushings. Shafts were about 1/2" in diameter and after grinding the worn area they masked the gear and hard chromed the shafts oversize. I remember them adding as much as 0.100" or more of hard chrome to some parts. After cleaning up we took care of the finish grind back to factory size.

Several things I remember well. The chrome was very hard but dull in appearance and it was microscopically porous so it retained oil well. The finished items always lasted longer that original parts. I would highly recommend hard industrial chrome over spray weld and regular weld. The big issue now is where to find a good Hard Chrome shop.

Walter

Walter A said:

A couple of years ago, in the early 1960s my first job as an apprentice was at a shop that rebuilt Diesel Engines, injectors and the like. This was pre-EPA so they had their own Hard Chrome shop and always had a large batch of parts in the tanks usually over the weekend.

In addition to injector pintels I remember one item that had a couple of hardened steel gear/shaft assy that rotated at high speed in bronze bushings. Shafts were about 1/2" in diameter and after grinding the worn area they masked the gear and hard chromed the shafts oversize. I remember them adding as much as 0.100" or more of hard chrome to some parts. After cleaning up we took care of the finish grind back to factory size.

Several things I remember well. The chrome was very hard but dull in appearance and it was microscopically porous so it retained oil well. The finished items always lasted longer that original parts. I would highly recommend hard industrial chrome over spray weld and regular weld. The big issue now is where to find a good Hard Chrome shop.

Walter

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Thanks to the epa it is next to impossible to find anyone doing chrome anymore.

moonlight machine said:

Thanks to the epa it is next to impossible to find anyone doing chrome anymore.

Click to expand...

True enough but as I remember that Plating room was pretty nasty smelling when plating was being done. These were open tanks full of Chromic Acid smoking away and the only vent was a 4ft exhaust fan sending it outside. I do not remember what happened when they had to drain a tank or where the used up lead went.

It wasn't as bad as a couple years later when I had to do some work at a tallow plant but still nasty.

Walter