Main Bearings Seating Depth/inner race seating

OK. Got the inner races pressed on the crank ends today at a local shop. Look good. Heated up the gas grill and dropped the outer races in the 2 cases and they seemed to go in fine, although the timing side was tighter, but as I got them close to bottom, they seemed to just drop in. Heated them to 350F for about 10-15 minuets. Installed the new crank studs/nuts in the crank (not torqued yet), installed in the covers, and as I tighten 3 or 4 bolts around the crank cases, the crank gets tight in the bearings and will not turn. 2 new superblends NJ306E.M1.C3. Going to try to heat the cases and see if the outer races will go in any more. As far as I can tell the races are bottomed on the crank cheeks. The drive side seems to stick out of the case more than the timing side. Should they both be the same? Needless to say, I'm pissed. Any ideas?

Dave
69S

Dave,
Having recently built up a '71 750 motor, I can only make a couple of suggestions - Are the cases a matched pair? i.e. off the same original motor? Next, did you pre-install the mains and do an end float check? Both bearing outer races should be flush with the rim of the cases, no lip protruding. End float shims fit between the crank cheeks and the inner races, which means you do the fit up twice - 1st check end float, measure , remove inners, add shims. 2nd refit inner races, bolt on con-rods and prepare for final install with sealant on cases. There is some conjecture about how much end float to permit, certainly the factory was pretty slack on this, my 850 has visible end float its that much, but hell its still runs like a train. Popular thinking is around 0.020" to 0.030" is acceptable.

Mick

Cases are the original 69 pair, removed and cleaned up. Mating surfaces were not touched. This is my trial fit for the shims with the roller bearings, but I am not getting any clearance at all. I'll take it all apart and make sure everything is pressed in completely again. The bearings outer races do not go in the cases to be flush with the case surface at all. I don't know if this is an early issue (69-70)? I haven' t compared the old bearing depth to the new ones, I'll do that.

Thanks,
Dave
69S

DogT said:

Cases are the original 69 pair, removed and cleaned up. Mating surfaces were not touched. This is my trial fit for the shims with the roller bearings, but I am not getting any clearance at all. I'll take it all apart and make sure everything is pressed in completely again. The bearings outer races do not go in the cases to be flush with the case surface at all. I don't know if this is an early issue (69-70)? I haven' t compared the old bearing depth to the new ones, I'll do that.

Thanks,
Dave
69S

Click to expand...

You took a picture of the old bearings in the cases before you took them out, right?

I have the old bearings. But I just drifted in the drive side outer race into the case with a piece of wood and now I have clearance. Funny, when it was hot, it felt like it went into the bottom, but it didn't. Haven't measured it yet, but all I can say is: Static between the earphones as usual. Looks like it is going to sort out.

Thanks for listening to my useless rant.

Dave
69S

Not useless at all. I learned a lot from it to store away until I get to do the same. Thanks. (we are all bozos on this bus)

A bit OBE now, but still maybe of interest to someone. I just measured the races in a set of MK3 cases that I recently put new bearings in. The drive side race is exactly even with the crankcase surface, and the timing side is .007" above the surface.

Ken

This talk of drifting in mains is a bit worrying. It only takes the smallest burr on the housing to cock things up.

The cases should be heated until spit balls up and bounces off (don't let your wife see you spitting in the oven though )

If they're hot enough and you drop the bearings in square, they should seat with a definite unmistakeable 'clunk'. If you don't hear the sound then it isn't fully home. I don't know if you're using Loctite but that can cause the bearings to grab before they're fully home.

I pre-heat my oven to 250, and pop the bearings in a plastic bag inside the freezer's ice tray.

Then, I heat the cases for 10 or 12 minutes.

Bearings ALWAYS drop right into place, all the way home.

Measure end float, shim, re-fit, verify.

Done.

I heated both cases, one at a time on the outside gas grill so the boss would not whine, for about 15 minuets at 350F. The drive side dropped in with a bit of coaxing to get it straight and I heard it clunk and I gave it a tap on the 4 quadrants just to make sure. The timing side seemed to go in a bit tighter, but it did the same, once it got started straight, I heard it clunk and again I gave it a tap with a piece of wood to make sure. I think the timing side went in fully, but surprisingly the drive side did not. I put it on a piece of wood, cold, used the old bearing as a plate and with a nice old transmission shaft, I tapped it on in until it was nearly flush with the case face. Just for drill, I did the same with the timing side, but it didn't go in any further.

Anyhow, it seems to have sorted. I have about 0.015" of crank play, so I am going to order the OB under the outer timing bearing shim kit unless someone has one left that is 0.008 or so. It is within the less than 0.020 Norton specification, but as I am this far, I'll like it less. I need the tab washers for the crank anyhow. They didn't come with the Norvil kit.

Dave
69S