Just assembling the crankcases on a '74 247 Cota and before I fit the clutch just want to make sure I haven't missed something.

Do the crankcase bolts have O rings underneath the washers to stop air / oil escaping past the bolts? I can't recall seeing any when I took it apart although there were traces of silicon under the washers maybe, but I can't really remember, besides, there are usually traces of silicon sealer everywhere on old engines so doesn't necessarily mean anything.

I'd never have thought myself but someone has mentioned there should perhaps be O rings fitted. Or is it just bolts, nuts and washers?

I have a parts book but it only gives part numbers and not what they are and the clymer manual doesn't mention anything either.

Anyone know?

I seem to recall they do, at least under the lower bolts. But then it's been a while since I worked on such an early cota.

Wayne...

Well just put mine back together last week, and it didnt have any before and i didnt fit any this time.

Suppose i'll soon find out if it needs them - just not for a few weeks cos the frames at the powdercoaters at the mo.

Just checked with my old pal Jeff B, and yes they did but not totally necessary. Also the 3 lower screws on the primary cover originally had O rings.

Wayne...

Thanks for that - guess it will be ok without them then. Say thanks to Jeff for me - a very nice chap.

I wish this meant I now didn't have to undo all the crankcase bolts but unfortunately I have. Being the first Montesa engine I've ever worked on, I didn't realise the importance of fitting the oil seal that sits behind the clutch on the selector shaft into its housing in the crankcase before the crank halves are bolted together. I've tried in vain to get it over the shaft and into the housing but it's having none of it. So I have to release all the bolts. open the crankcases a few millimitres to clear the end of the selector shaft, fit the seal and then close them up again. Lessons the hard way as usual....

I speak to him a lot, so I will do that.

Yes he's also got a brilliant memory for all this stuff, and even though he can no longer see to use his knowledge in a practical way he's still got it!

Mind not many people have constantly worked with this stuff from aged 14 to nearly 50, so he ought to know a thing or two!

Wayne...

While you have it back apart, get the o-rings and put them in or at least use silicone under the washers on the clutch side or you'll have ATF or whatever is in your clutch migrating over to the ignition side and fouling your points. Sealing these bolts IS necessary.

Was the traces of silicone you found black? The old o-rings get pretty withered looking.

My 349 has the little seals for most of the crankcase bolts, but most were pretty much perished (ie a gooey mess) and will need replacing....

Steve

While you have it back apart, get the o-rings and put them in or at least use silicone under the washers on the clutch side or you'll have ATF or whatever is in your clutch migrating over to the ignition side and fouling your points. Sealing these bolts IS necessary.

Was the traces of silicone you found black? The old o-rings get pretty withered looking.

Can't remember unfortunately whether it could have been the old O rings squashed and broken or silicon that was there as it was too long ago that it came apart. Probably withered O rings thinking about it. As you say, even if opinions differ, makes sense to fit some as I have to release all the bolts again anyway.

I'll try the importer today to see if they have the original O rings. If they don't, as I'm not too hopeful, do they need to be a particular size?

I have a box of O rings which include some of the right diameter or smaller that will fit over the bolts but I'm not sure about the thickness. They may be thicker than original, but I guess they will squash/compress ok.

Are these O rings fitted to all twinshock Monts, right up to the 330?

My 349 has the little seals for most of the crankcase bolts, but most were pretty much perished (ie a gooey mess) and will need replacing....

Steve

Thanks for that, probably answers my last question in my previous post

You can see a little bevel on the hole where the bolt starts through. The o-ring should compress into it and still allow the washer to bear on the case. Silicone should work too.

Did you get some O'rings Woody? My 330 is still split and I'm planning on putting it together soon. That had o'rings fitted, if you look at the holes in the cases mine has a little countersink for the o'ring to seat into. I tried a couple of different sizes - too big and it'll just rip the o'rings appart. Too small and it'll do no use.

The bolt is about 6.8mm where the o'ring seats. I am planning to use some which are about 9mm (5mm ID) x 2mm thick.

In the pictures are the 9mm and a 10mm - both fit nicely on the bolt without too much trouble.

you can see the 9mm sits a little proud but should compress down nicely under the washer.

I think the 10mm is too proud and will just tear up.

Let me know how you get on,

Steve.

Never had the chance to phone Sandifords in the end today as I was riding a trial today and ended up prepping all morning so I'll try on Monday and let you know. When I was working on the 247 motor I never even noticed the countersink. I must remember to wear my reading glasses now when working on bikes as my focus within the first 2 feet has gone and you don't realise you can't see, or rather don't notice, that things like that are there....

Useful info and pics Steve

I guess some silicon gasket goo would do an ok job as well, as mentioned earlier

- Steve

Just spoken to Sandifords who confirmed that there should be O rings, but only on one side, presumably clutch. They had enough for one set so I've ordered them. When they come I'll measure them and post the size