Crankshaft repair, advice sought.

On the drive side main bearing on the crankshaft of my Commando, the inner bearing will spin on the crankshaft i.e. it is not an interference fit, and it is possible to rotate it by hand.

It was like this three years ago when I rebuilt the engine, but as I was by then in a hurry to get it built and not miss the good weather, I used a Loctite product to lock the bearing inner to the crankshaft after taking advice from Loctite (can't remember which one without consulting the garage), but on dissasembly of the engine this week, I have found the inner bearing again to be spinable on the crankshaft, so the Loctite hasn't lasted.

I intend to effect a proper repair this time whilst the engine is down, and wondered what was the best method to effect repair.

My own thoughts of repairing by preference and in descending order are;
1. Take to a metal sprayer and get the shoulder on the crank built up, before turning down to correct diameter.
2. Get the shoulder hard chromed, and turned down ........
3. Peg the bearing inner to the crank.
4. Machine it down and get a sleeve heat shrunk onto the crank.
5. Get a Steve Maney crankshaft ££££££££

But as I am not an engineer, I would welcome your thoughts on the best method to use, and welcome any recommendations of companys that can do any work recommended. Anywhere in the UK is OK.


Thanks in advance

First of all don't bother with Loctite, it always comes loose.
Make sure your bearing is not oversize, it has been known.
It does sound like your crank is u/size though, I would be inclined to speak to Mick Hemmings.
I have put a few bearings on or in crankcases with .001" shim around the shaft or bearing, but it is a sod of a job on cranks.
If you get another crank, sell me that one cheap!

Flo wrote;

001" shim around the shaft or bearing

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How does that work? I'd appreciate it if you could explain as I've never heard of this before.

I think you're right, Mick Hemmings would probably be the man to ask. I just wondered if there were any no brainer recommendations, where I could access services locally.

I've used a speedy sleeve in similar circumstances, i woulder if they have one for you?

http://www.bimmerboard.com/forums/posts/458355

Wrap .001" thickness x 1/2" width shim around the crank & cut off so it does not overlap. Heat up bearing & put over the shimmed shaft. I think I have done this about 3 three times, the last time on my freinds 650ss. It did work, but it is a bloody awful job.
If the bearing is loose in a casing, putting shim in the bearing hole & heating the casing before dropping the bearing in is a lot easier, as the aluminium expands better.
I would contact Mick Hemmings myself, you will probably get Angela on the phone, she is a good laugh.

Greetings,
I am not sure about the hardness of the crank, but you could ask a machinist about having the bearing area "knurled" slightly. You could do it by hand with a chisel (make sure no ones watching).

GB

A good crank guy could always weld it up a bit and turn it down. That going to cost a couple bucks though.

Although welding would build up the journal in question, I wouldn't do it. The weldment area will be brittle. Bad deal on the drive side. The .001 wrap doesn't sound too bad.

Metal spraying isn't a bad idea, but the crank still has to be turned down to start with, the shim idea suxs eggs in my opinion, I was thinking you may be able to get the journal copper plated, your hard chrome plating idea should work to ,but a bit more work.

Too bad the bearings weren't more common , you could just get an undersize.

You really must get the bearing and shaft measured to;
Firstly find out which is wrong, perhaps the bearing has been honed out to allow end float checks;
Secondly to to find out by how much. If the clearance is very small I don't think you've got a problem as the bearing is, or should be clamped firmly into place.

Cash

I've spoken to Mick this morning (via Angela) and he recommended Loctite 638 as the cheapest option which I have tried last time but has failed (possibly operator error), and the next best option but significantly more expensive is metal spraying. So I will locate a local metal sprayer and fix it properly this time I think. Thanks for all of the advice everybody.

Just out of interest Flo where would I get a metal shim for this job, as I am intrigued as that sounds a possible cheap fix?

You didn't mention if this is the same bearing from the last rebuild or a new one, or if that bearing was new when you rebuilt it engine the last time. I agree with Cash, you need to mic the crank to find out what's going on. How far are you from Mick? Why not take the crank and your bearing up to him. He can mic them both and sell you a new bearing, which you're going to need in any case if the race has been spinning anyway. And he might have better luck with the Loctite. Did you use activator/primer?

Measure the crank and then get the bearing inner plated to give back the fit you want, best done with a new bearing plus the disadvantage is that any further replacement bearings will need the same fix. Plating can be put on a single surface by covering the non plated areas with a resin, this could also be done to the crank but theres a lot more work involved. Plating could be hard chrome or copper.

Removed wrong info given on crank, been working on too many BSA's recently :roll:

kommando said:

Measure the crank and then get the bearing inner plated to give back the fit you want, best done with a new bearing plus the disadvantage is that any further replacement bearings will need the same fix. Plating can be put on a single surface by covering the non plated areas with a resin, this could also be done to the crank but theres a lot more work involved. Note as you are doing it on the driveside the rotor nut pulls the bearing inner to the crank anyway, so an interference fit is not strictly required, a good sliding fit with no freeplay is sufficent. Plating could be hard chrome or copper.

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The nut on the rotor is bearing down on the taper of the sprocket/crank so there's nothing locking the inner race to the crank, unlike the timing side. Most bearings need the crush on the outer race and the stretch of the inner race to get the fit within the bearing elements into spec. Until the crank journal is measured there isn't much point in actually doing anything. I like the lower primate approach myself. Get a new race in one hand and the crank in the other and shove. If it goes on you have a problem; if not, yer golden.

This is a problem I have seen several times. Locktite will not fix it for long. I usually turn the crankshaft down about .040 and fit a hard stainless sleeve. Then grind the sleeve down to the correct size. A decent machine shop can handle this without any problem. I have done it with just a shim but getting the shim to stay in place when installing the bearing can be pretty tricky. Plus the shaft tends to wear out of round so the fit isn't so good. Jim

I have corrected my post ref the driveside bearing, still John Hudson (not Nelson) recommended reducing the fit to a siding fit on both sides on the main bearing journals to allow for easier subsequent dismantling as detailed in the NOC Commando Notes.

kommando said:

I have corrected my post ref the driveside bearing, still John Nelson recommended reducing the fit to a siding fit on both sides on the main bearing journals to allow for easier subsequent dismantling as detailed in the NOC Commando Notes.

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I'm sure you meant John Hudson?

The bearing fit on the drive side needs to be maintained at an interferance fit. Working down the crank to make a sliding fit for the bearing results in a bearing that will turn on the crank and will cause wear and become loose in a short time. Jim