AJS & Matchless Owners Club

A good idea Shaun. Yes, you could have slips of paper (not a continuous ring) outside the circumference of the O ring and do the test. This would prove the O ring can seal even with a 1 thou gap.... No rush, will be interesting to see any results you get. I was impressed with the results you are getting with the RTV....

Took the oil filter out today and checked the internal space to see if there was room for an expedient fix...Sadly, there is only a couple of millimetres spare around it, so the idea of installing and internal tube anchored in with Loctite 581 can't be done but makes me think it might have worked. I was tempted to smear a band of Araldite around the internal join line but decided not to and put the filter back in. Re torqued the front stud and went for a 10-mile blast in the high heat of the day...Just a small dribble down the front but not bone dry...such a pity; the engine is bone dry oil tight everywhere else. By the way, looking into the filter tunnel was quite a reminder of how little metal there is surrounding the tunnel. Also, the two sides don't line up perfectly as there is a slight step between each side. This will mean the O ring has to be spaced a little further away (Bigger OD) to make sure it sits not too near the tunnel inner edge mismatch.

I was going to try and get a 29mm ID x 1mm thick, which I think was the size Poul used. So 30mm ID x1mm would go up 0.5mm a side, probably easier to get hold of too.
I'm surprised there's a step inside the filter chamber, I thought when Bill said about the wall thickness's being slightly different, that would have been the step you can feel on the outside.
I'll see what is available.

What is it that lines the two crankcase halves, is it a good fit on the centre bearing plate or are there dowels on a couple of the bolts?

Could possibly go up 1mm but probably creating a weak point outside the seal?

shaunstaples wrote: ↑Sun Oct 08, 2023 8:58 pm I thought when Bill said about the wall thickness's being slightly different, that would have been the step you can feel on the outside.

The cases I measured for wall thickness are separate and stripped bare, but aligning them with just a couple of bolts the step inside is minimal / hard to detect. Doesn't really tell us anything though, as would need whole thing assembled properly to verify.
Did AMC bore the tunnel with the cases bolted together, or one by one? Who knows, but some do say that halves can be mixed and still match, although I have never tried because I have never had to.

I suppose really if your cutting with a bush then the o ring will be central and be able to go closer to inner edge, it’s just if the plain side covers it fully?

shaunstaples wrote: ↑Sun Oct 08, 2023 8:58 pm What is it that lines the two crankcase halves, is it a good fit on the centre bearing plate or are there dowels on a couple of the bolts?

The cam follower spindles (011626) align the cases.

Replies: Shaun and Groily: Regarding the step. I reckon the chamber tunnel was produced mostly in the casting process and a quick drill through/ream to clean it up. There was no need for perfect accuracy for a filter so not reamed in line bolted together. I'm concerned about guessing on this forum (we have sarcastic people watching. Ho ho) but I think it has the flange on the drive side, can't remember if it had dowels but maybe it has but not really important for us. Regarding the size I would get it further out to the centre line of the surrounding edge metal, certainly 30mm looks better than 29mm. I personally would aim for an O ring central to the surround...this is the strongest position IMO. This would also ensure the joint mismatch was not too near the inside of the groove on one side. By the way as said above by me you want the outer diameter of the groove the same as the O ring OD BUT....you want the groove WIDER than the O ring thickness to allow for the squash and to leave space to achieve only 85% volume fill (15% unfilled)...IE: with a 1mm thick O ring you must not have a 1mm groove width! This is because O Ring rubber does not squash, it simply deforms sideways under pressure and needs somewhere to go..PS: Just noticed Duncan has supplied the method of location of the 2x halves...Thanks.

Are we thinking of using Viton O rings which will withstand higher heat?
Dave.

I would choose Viton Dave, As far as I know they are "better"?