750 crank end float

Mensch said:

Ah yes. Re-read your post. I have what I'm meant to have


I'm probably going to have to split cases and triple check all bearings again. I don't think new bearings will make a difference?


I'd read on here somewhere about someone using a bit of leverage on the crank cheek to help check float. Hesitant to go that path as I'm assuming this should all be done by hand? Would heating cases also help?

Click to expand...

Done carefully with a suitable tool it's fine to do that. I did it with a tyre lever! Gently!

End float is measured cold, so no heat.

But of an update. End float with a dial gauge shows absolutely nothing.

I've kind of traced it to the inner and outer bearings

When I put the crank into either side case on its own. It really struggles to go in and then to separate the crank out of the case I have to use a soft face hammer on the crank. This is for both cases

Is this normal. Should they slide in and out a lot easier than this?

Have you tried heating the cases up a bit? I have seen situations where the interference fit of the outer races in the cases tightens things up when cold but this can disappear when some heat is applied.

Mensch said:

But of an update. End float with a dial gauge shows absolutely nothing.

I've kind of traced it to the inner and outer bearings

When I put the crank into either side case on its own. It really struggles to go in and then to separate the crank out of the case I have to use a soft face hammer on the crank. This is for both cases

Is this normal. Should they slide in and out a lot easier than this?

Click to expand...

As was mentioned at the beginning of this thread, C3 bearings have more clearance and are specified for this engine. As you do not have C3 bearings I would assume that some of your issue above may be related to that?

Seems you have 3 issues:

1. Lack of end float
2. Tight bearings
3. Incorrect bearings.

Given where you’re at in this rebuild, and the price of new bearings vs the cost of main bearing failure down the line (in time and money), I’d suggest new correct main bearings should be your next step.

I also think the problem would be solved with C3 clearance bearings. A while ago I fitted a set of CN so called Superblends to a 750 engine & the crank was grabbed by them & had no float. It was difficult to insert & remove the crank & therefore would not show any endfloat. I removed the bearings & fitted C3 type & all was well. Also I have an old bearing inner race on which I ground the bore out by a thou, so it is a sliding fit on the crank. I use this to set the endfloat to make fitting shims easy on a trial basis.

Mensch said:

Ah yes. Re-read your post. I have what I'm meant to have


I'm probably going to have to split cases and triple check all bearings again. I don't think new bearings will make a difference?


I'd read on here somewhere about someone using a bit of leverage on the crank cheek to help check float. Hesitant to go that path as I'm assuming this should all be done by hand? Would heating cases also help?

Click to expand...

On most of the Commando engines I've worked on (with double Superblends, that is), it has taken a bit of gentle prying between cases and crankshaft cheeks to get the crank to move side-to-side in the bearings when measuring end float. I use a large screwdriver for the purpose. It seems to not want to move, and then just sort of gives up and slips sideways. Presumably that's because the force finally overcomes the static friction, and it moves more easily once you are in the sliding friction mode. Not talking about a lot of force here, but I've rarely (if ever) seen one that will slide back and forth freely with only pushing or pulling by hand.

Also, as others have mentioned, I don't think you will ever find a case where you have no end float with matching stock cases and crank, no shims on either case or crank, and the bearings and races correctly installed,

Ken

Fast Eddie said:

As was mentioned at the beginning of this thread, C3 bearings have more clearance and are specified for this engine. As you do not have C3 bearings I would assume that some of your issue above may be related to that?

Seems you have 3 issues:

1. Lack of end float
2. Tight bearings
3. Incorrect bearings.

Given where you’re at in this rebuild, and the price of new bearings vs the cost of main bearing failure down the line (in time and money), I’d suggest new correct main bearings should be your next step.

Click to expand...

Thanks mate. That's what I was leaning towards. Just wanted to double check before forking out.

It is a practice engine I'm working on so want to make sure it's all perfect. I'll order the new c3 bearings and report back

Does make me wonder if whoever installed these current NJ306E non-c3 bearings ever checked end float or if the tolerances lessen over time

An update on this one in case anybody finds this in the future.

New bearings from Andover Norton and I now have end float of 0.021"

So I'm all set!

The bearings that were originally in it were NU306E and inner race was NJ306E

As soon as I've put the correct Andover Norton sourced bearings I'm away.

Cheers for all your help