750 crank end float

Hi guys. I'm rebuilding a 72 Combat motor. The bearings have already been done before and upgraded to the superblends. I haven't changed the bearings. I never tested the end float before I dismantled the engine. I've now gone to put the cases together and have found there is no sideways movement at all in the crank so the end float is effectively zero.

The bearings are not C3.

Everything rotates fine - crank and cam. Main bearings are seated in the cases fine. It feels like it's the bearings which are preventing any movement/end float as I noticed when I put the crank into the drive side only there was no play so possibly bearing tolerances too tight?

Would it be ok like this or does there have to be some float with these bearings?

Cheers

Note that the recommended end float increased when the second roller bearing was introduced (from eng. 200000) and not Mk3.

L.A.B. said:

Crankshaft permissible end float

Why did Norton increase their permissible end float for the 850 MK3 from .005"-.015" to a (IMHO) excessive .010"-.024" ??

www.accessnorton.com

Note that the recommended end float increased when the second roller bearing was introduced (from eng. 200000) and not Mk3.

Click to expand...

Thanks for that. It seems the bearings are pretty tight on the inner race so even with the crank inserted into only the drive side case I get no movement. Should there be play? Takes a lot of effort to get it out again too.

I'd read about the C3 bearings being what's needed, maybe this will increase the gap?

Just trying to figure out if and why the bearings are seeming to be the culprits preventing end float? Encountered something like this before?

C3 is the internal radial clearance, changing that will make no difference to endfloat as it's at 90 degrees to endfloat.

kommando said:

C3 is the internal radial clearance, changing that will make no difference to endfloat as it's at 90 degrees to endfloat.

Click to expand...

Ah right. Can rule that out then

The bearings outer is an interference fit in the cases, the inners should also be a interference fit on the crank mainshafts. You can get away with a sliding fit on the timing side as the end nut will pull everything tight but on the drive side the sprocket taper means the end nut does not hold the bearing inner tight so the interference fit is required.

You should not be able to get a feeler gauge between the bearing inner and the crank. If you can the inners are not going the whole way on and you need to find out why.



One check is to look at the inner bearing chamfer/radius and how it compares to the mating radius where the mainshaft meets the crank. If there is a mismatch then the inner cannot go the whole way.

YES, you MUST have some end float.

Since you say you have changed nothing, we must assume it ran OK for some mileage before you stripped it.

This suggests you either have a problem induced by crankcase reassembly, possibly an incorrect assembly, or the problem existed before disassembly.

Are you 100% sure the crankcases are aligned and not putting a load on the bearings?

Historically who knows. But if the inners races have shims installed, they can start to break up. You might logically say that will increase float, but let's ignore that possibility at the moment. You are going to need to inspect the crank either way. The feeler gauge test is a good idea, but you are also looking for signs of the shim metal as well as the gap.

If all is fine you will also need to identify if the outer race has moved in the case at any point, though you note that it is fully inserted, we are only talking a few thou.

I would look very hard at how you are determining that there is no end float. I have occasionally found it difficult to determine, but it is easier to see with cases held to allow the crank to drop vertically, I think Norman White shows this in his book. And of course you need to use a dial gauge to determine exactly what you have, is zero actually 'zero' or just 'very little' ?

At least 4 people are about to attack me! Please read all before the attack

After checking all SteveA and others have said...

1) As the engine heats up the cases expand and therefore the endplay increases.
2) If nothing was changed, then the bearings were shimmed by a previous last person because if not there would be quite a bit of endplay.
3) If everything turns without any restriction anywhere in turning the crank 360 degrees, you are OK and you have at least a tiny bit of end play - more is not required.

marshg246 said:

At least 4 people are about to attack me! Please read all before the attack

After checking all SteveA and others have said...

1) As the engine heats up the cases expand and therefore the endplay increases.
2) If nothing was changed, then the bearings were shimmed by a previous last person because if not there would be quite a bit of endplay.
3) If everything turns without any restriction anywhere in turning the crank 360 degrees, you are OK and you have at least a tiny bit of end play - more is not required

Click to expand...

Attack.....



You mean someone typing a different viewpoint, while safely hundreds, or thousands of miles away?

I've assembled many different rotating assemblies in my life, (not just ICE) and stand quite sure that I could not FEEL .005" PRELOAD on roller bearing end shoulders differing from ZERO clearance with the inertia of the crankshaft at play.

You're safe from attack.
Carry on.

marshg246 said:

1) As the engine heats up the cases expand and therefore the endplay increases.

Click to expand...

Correct as an endpoint, but the initial heating up cycle may heat the crank first especially on a cold morning. If the crank expands before the cases a nil endfloat will cause issue until the cases get warmer. Plus the Norton crank is whippy so some endfloat is needed to allow the mainshafts and bearing inners to bend a little.

marshg246 said:

At least 4 people are about to attack me! Please read all before the attack

After checking all SteveA and others have said...

1) As the engine heats up the cases expand and therefore the endplay increases.
2) If nothing was changed, then the bearings were shimmed by a previous last person because if not there would be quite a bit of endplay.
3) If everything turns without any restriction anywhere in turning the crank 360 degrees, you are OK and you have at least a tiny bit of end play - more is not required.

Click to expand...

Not an attack at all, just an additional point, this time ref Jim Comstock.

Jim suggests that motors built for high rpm can use an extra 5 thou end float, because he says that the crank can stretch with the flex at high rpm.

Does this negate the crankcase expansion, probably not, or at least not 100%. Does this affect the OP, probably not.

But it is why I put in some extra effort, and extra end float, when I recently changed the mains in my race motor.

I totally agree that someone has shimmed the OPs motor before, we don't know where, or with how much shimming.

Bad news for the OP is that he would need to pull both of the inner races and both of the outer races to be 100% sure if shimming is present and how much!

Yes, I can see why he might want to avoid that.

Jim also said that engines which have been shimmed down to 5 or 6 thou end play, by some previous rebuilder, are the generally the ones that have bearing races which are blue in colour.

Glen

Thanks all. I bought the engine as a project with just the bottom end and head. It looked like it dropped a valve(different story) but the bottom end seemed fine. Rotated fine. My mistake was to not check end float before pulling it all apart.

I completely dismantled the cases including bearings for vapour blasting. So I can confirm there are no shims present. Both bearings seeeeem to have seated well when reinstalled - didn't use any product when doing so, simply heat and insert.

The inner race seemed nice and tight against the crank.

Did a test fit with the crank into the drive side case, was definitely a good interference fit. Put it all back together and the crank turns really smoothly as well as the cam. Cam has great end float.

Just waiting on a dial gauge to give me exact reading but using the old mk1 eyecrometer there's no way it has anything near the recommended end float.

It's my first nudge on rebuilding one of these and I bought the motor specifically to learn about them so appreciate all your help

Mensch said:

Thanks all. I bought the engine as a project with just the bottom end and head. It looked like it dropped a valve(different story) but the bottom end seemed fine. Rotated fine. My mistake was to not check end float before pulling it all apart.

I completely dismantled the cases including bearings for vapour blasting. So I can confirm there are no shims present. Both bearings seeeeem to have seated well when reinstalled - didn't use any product when doing so, simply heat and insert.

The inner race seemed nice and tight against the crank.

Did a test fit with the crank into the drive side case, was definitely a good interference fit. Put it all back together and the crank turns really smoothly as well as the cam. Cam has great end float.

Just waiting on a dial gauge to give me exact reading but using the old mk1 eyecrometer there's no way it has anything near the recommended end float.

It's my first nudge on rebuilding one of these and I bought the motor specifically to learn about them so appreciate all your help

Click to expand...

OK, no shims and no end float = something bad wrong. Did you separate the crank? They can get cocked when putting back together effectively making the crank longer (and will definitely make a BIG mess when you start it).

Crank and Cam running smoothly says that the cases are most like aligned - cam generally don't turn smoothly with mis-aligned cases.

Perhaps a pre-200000 crank in 200000 cases? According to Norton Service Release No.68, the double-roller bearing crank was"...of reduced overall width...identified by the letter 'R' stamped onto the timing side crankshaft cheek adjacent to the bearing location."

L.A.B. said:

Perhaps a pre-200000 crank in 200000 cases? According to Norton Service Release No.68, the double-roller bearing crank was"...of reduced overall width...identified by the letter 'R' stamped onto the timing side crankshaft cheek adjacent to the bearing location."

Click to expand...

Ohhhhhh hang on a second. There is an R on the cheek. Case numbers are 204343

Could this be it?

Mensch said:

Ohhhhhh hang on a second. There is an R on the cheek. Case numbers are 204343

Click to expand...

Ok, it seems to have the correct 200000+ crankshaft so disregard my previous post.

L.A.B. said:

Ok, it seems to have the correct 200000+ crankshaft so disregard my previous post.

Click to expand...

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?

I don't know but if the crank and cam are both spinning smoothly when everything is bolted up then I would leave it as it is, for spining smoothly there has to be a little end play, was the old bearings still good when removed.
.005 is not much movement and maybe you just not feeling it when checking but everything as you say is spinning freely.