Parts Advice Required on Engine Rebuild Please

[clive]

I should not despair, if you don't mind about the year of the crankcases they are pretty well interchangeable from about 1949 on I think. I am sure someone will correct me if I am wrong but I think even when the aluminium primary chaincase was introduced they was no change. The only difference I can think of is the bottom front stud hole which increased in diameter. Your frame will have the larger one so if you get an earlier set of cases you simply need to drill them out. Lots of club members will have some cases sitting on their shelves that they will never get round to using. Why not try a wanted advert on the website and in the mag, you may even get lucky and get offered a 56 crankcase. I sold a few pairs of cases a while back when I realised I would never use them. Adverts are free for members.

Ps other changes include the size of the oil pump drive and bronze bush, but you are going to have to change yours and can fit the correct one for the cases. Also the size of the drain plug but it won't affect anything although the later magnetic plug is probably better, they cannot be interchanged as the size of the hole is different.

[Mick D]

Hi

Not sure when the boss was modified but it's no longer there on my 61 G3:

LH Main Bearing.png

What function does it perform on the earlier engine? set the lateral position of the bearing? provide a locator for the inner chain case? If that's all is it really necessary? the engine sprocket will determine bearing position and the three securing screws chain case location ............. won't they?

Where would I find the sectional drawing in the archive please?

Regards Mick

[Johnobirches]

Lots to ponder on here then... I've already bought the new oil pump plunger [not cheap] and any other spare crank cases would need to be closely examined for defects like stripped threads, worn oil pump tunnels and of course lumps machined away. But yes Clive that thought is encouraging and it's appreciated.

Mick, not sure how the years of the engine match up but the drawing I looked at is here:-

http://archives.jampot.dk/technical/Cut ... d_view.pdf

John

[Johnobirches]

By the way Clive your signature "If it ain't broke don't fix" strikes a chord.
My bike had 32 years of "broke" when I bought it but for any members out there who have bought a runner and it's your only bike then ride enjoy it and for goodness sake don't be tempted to take it to bits!
John

[clive]

Lots to ponder on here then... I've already bought the new oil pump plunger [not cheap] and any other spare crank cases would need to be closely examined for defects like stripped threads, worn oil pump tunnels and of course lumps machined away. But yes Clive that thought is encouraging and it's appreciated.

Mick, not sure how the years of the engine match up but the drawing I looked at is here:-

http://archives.jampot.dk/technical/Cut ... d_view.pdf

John

John the oil pump body was standard across a number of years. I have rebuilt engines using at least 10 different crankcases over the years and have not found wear in the pump body to be much of an issue provided there is no obvious scoring. The other threads can be examined, the only other issue will be the state of the timing side phospher bronze bush. Maybe I have been lucky.

[56G80S]

I sold a bottom end a couple of years ago to a Club member for not much money. The fact is I bought it for not much money and decided that I didn't want to build up and slot in a later aluminium primary 350 after all. So I just passed it on - sure there'll be others out there who've done similar things.

Johnny B