AJS & Matchless Owners Club

Good morning everyone.

I have put my engine back together, but I seem to have come across another problem. When I tighten the front sprocket/rotor nut, the crank gets very hard to turn.

I have replaced the bearings with new units, but, the ones I found fitted are a standard roller bearing which are LJ 7/8. Am I right in saying that they should be a two-piece bearing such as an LRJ 7/8?

I don't appear to be getting any endfloat which I suspect is down to the main bearings being the wrong ones. If they were the two-piece type, they would allow a slight amount of movement either way without clamping the balls to their races.

Would one of you be able to confirm my suspicions and the correct bearings to be fitted?

Thanks in advance,
Regards
James

The inner bearing should be a two-piece type, yes. When assembled correctly (with the front sprocket nut tight), you should not have any end float.
You did remember to fit the breather rotor?
http://www.jampot.com/forum/viewtopic.p ... 30#p188884

You should have around 0.020" end float in the crank BEFORE you fit the sprocket. Once you tighten the sprocket the end float should disappear as it pulls the crank towards the LH side of the engine which gives some space between the crank and the timing bush at the other end to allow for expansion. The crank should still turn freely though

Thanks for your replies guys

I have ordered the correct LRJ two-piece bearing, so I'll have to take it apart... I won't say "again" as it was in bits when I got it lol.

It threw me a bit as I had a spare crank thrown in. My casing had a standard roller bearing fitted, one crank had the remains of a two-piece bearing and the other crank had a standard roller bearing. As I didn't have the track of the two-piece, I just assumed I needed two standard bearings.

We all know what assumption is don't we? Lol

Oh well, hopefully it'll be sorted by Sunday so I can put it back in the frame.

@Clanger9 - yep, breather thingy is all present and correct

Thanks again.
James

Ah, that makes sense. Even though the engines were originally fitted with two identical roller bearings, it's not clear how the heck they assembled them like this at the factory without the bearings nipping up. My guess is they fitted both drive-side roller bearings to the crankpin, then just whacked the left-hand case on fresh from the oven. I guess if you were quick to do up the front sprocket nut (before the casing cooled), then the bearings would 'kinda sorta' line up correctly.

It makes far more sense to use the later two-piece inner bearing. At least that way, you can be certain there's no axial stress on the bearing when you do up the sprocket nut...

Hi Clanger9. I did have a thought about warming up the casing to seat the crank bearing, but when I started reading another thread on here about cranks and endfloat, I realised there were a few other bits that I didn't have, e.g, shims. So I thought I'd get the right bearing and rectify it all in one go.

I'm pleased I did too. I got the engine back out of the frame and stripped down last night and I have found that one end of the big-end pin is rubbing the inside of the crankcase - and that is before the end-float will be taken up.

It's only just sitting proud, so I'll give it a touch with a grinding stone to reduce its height.

Of course, it's entirely possible that I managed to take up the endfloat and that it was the pin that was stopping the crank turning and not the bearing. Saying that though, I didn't have the shims for the sprocket either, so the crank would've been pulled in too far.

Cheers
James

Just to clarify, the sprocket shims (if fitted) are only there to line up the primary drive sprockets correctly. There's no "setting" of the endfloat on these engines - there isn't any!

The entire crankshaft assembly is held laterally by the outer ball bearing. It's a slightly weird setup and the absence of any sort of thrust bearing means AMC were putting quite a lot of faith in that outer bearing...

Here's a diagram that shows how (I believe) it's meant to work:

@ Clanger9

Thanks for posting that diagram I have got all the right bits now, so will be putting it back together today and tomorrow (if I don't get any calls - I hate standby )

I will keep you all posted.

Thanks again
James

I realise I forgot to show the breather stator in the diagram - I'll add that in...