Hi All,
I'm a bit baffled by my first experience of trying to balance the crankshaft on my 62 B40. I've acquired a +20 high compression piston, so assumed it would be out a bit.
It seemed way off and in fact balances almost perfectly with just the gudgeon pin in place. Admittedly the new pin has 2 1/2 times the wall thickness of the old one, but that still leaves 367g of piston and rings to account for, which feels like an awful lot to be taking out.
There are already six big holes in the flywheel, though none quite opposite the big end.
Does anybody know whether this is truly excessive, or have any wisdom to offer?
Many thanks
you only need a percentage for the balance . This explains it . I think it is the same for a 4 stroke . https://www.youtube.com/watch?v=0hoE_MuFpPI
Aha! I'm now much more educated. I'd watched another YouTube which showed the crank balanced with the piston etc. in place.
Many thanks.
50% seems to be the magic number for a road bike . High revving or other than 90 degree engines require different % .
Thanks chaps. Now I've played with it a bit more I'm beginning to think it may have to go off for a rebuild anyway.
At first inspection everything seemed smooth and nice. No play (but it's a 41-181 so I assume it's a roller bearing)
I cleaned the whole thing, emptied the sludge trap (very little in it) and squirted a bit of oil through, which duly appeared around the big end.
Once I had it in a couple of bearings to balance it I found that if I grab hold of the conrod and spin it over, it goes for about six or eight turns then tightens up considerably. If I reverse the rotation or squirt some more oil through it it loosens up again, but that doesn't feel right to me. Also, either I'm getting paranoid or I can now feel a bit of lumpiness when turning the con rod by hand.
With most bearings, you can take them out and investigate their condition fairly rigorously. Unfortunately, you can't do that very effectively with a big end bearing and, if there is any doubt about its condition, it's best to replace it. That said, I recently replaced a big end bearing because there was a distinct possibility that it might have suffered damage due to corrosion. It turned out the old bearing was ok but at least it was worth the cost to give peace of mind.
Yup, that's pretty much what I was thinking too. I'm replacing all the other bearings and most of the bushes, so it makes sense. It's just a pain that it's the only one I can't do and consequently ends up as the most expensive.
On the upside, it means I'll get it professionally aligned and balanced too.
And so to the next question... where do I find a big end?
It's the Alpha B-24, but the only ad's I can find on the web say useful things like "late C15 or B40" which could mean any one of three as far as I know.
Cheers
https://www.ebay.co.uk/itm/BSA-C15T-C15SS80-C15S-TRIALS-SCRAMBLES-BIG-END-BEARING-26/392005435263?hash=item5b45583f7f:g:ieUAAOSwz3JaFBb5
check yourself but i think thats the one
;)
You could try Alpha Bearings directly;
http://www.alpha-bearings.com/
Thanks Derek. I just spotted that one too. A bit painful for the wallet, but I've bought it anyway. Next option looks like it would have been getting one from the USA, but with postage and import duty I think it would have been about the same.
Cheers
Quote from: Dabbist on 02 Apr, 2018, 13:56
Thanks Derek. I just spotted that one too. A bit painful for the wallet, but I've bought it anyway. Next option looks like it would have been getting one from the USA, but with postage and import duty I think it would have been about the same.
Cheers
i hope its the right one then! ;D
You could hunt about and save some money probably, but sometimes best to bite the bullet and just get it and get the job done.
derek
Well, Rupert says it's the right one and I'm not going to argue with him ;D