B33 valve split cotters

Started by Cardiboy1, 02 July, 2024, 21:42:24

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Cardiboy1

Seeking some guidance from the collective fount of knowledge. My recently acquired 1959 B33 was leaking oil from the pushrod gland, and to fix that it's 'off with its head'. This revealed much evidence of oil burning in the combustion chamber, so much that something had to be done about it. I lifted the barrel which revealed a couple of tiny scores but a piston and rings in excellent condition... and thankfully no detectable play in the rod. I proceeded to strip down the head and sure enough the valves were in poor condition- seating well but wobbly in their guides. All this explains why the compression was good and the bike ran well when I rode it! I never saw any smoke behind me. Now for the rub, It was difficult getting all the parts required for the head job. However, slowly I've acquired the guides and valves, springs etc. I have NOT been able to get hold of exhaust valve split cotters. And parts lists are very confusing, suggesting that they are the same on both the inlet and exhaust valves. This is not the case. The valves have slightly different stem diameters, the exhaust thicker than its mate by about 1/32in. Now, my questions for the wise are- 1) Does anyone have some exhaust cotters for me? 2) If I can't get hold of some, will it be safe to put the old ones back in... they look in good condition? 3) Will the split cotters from another make or model fit? The inlet cotters do not fit. A pair sent me by a trusted supplier don't fit either valve!

neil1964

I'd re-use the old ones, assuming that they fit properly, unless you've put a HC piston and hot cams in of course.

Cardiboy1

I've had some professional advice today. It's ok to re-use the existing split cotters. That was the good news. He examined the barrel and strongly advised  rebore. Ouch. That almost certainly means a new piston and rings.

neil1964

Oh, dear.
I guess if you have it apart then seems sensible if there is doubt.  If you only use it occasionally you could as someone to clean the bore uo as best they can (still a bit like a rebore vs a hone, which can cause its own issues) and use new rings.
Personally  if going for a rebore I'd go for the very slightly higher compression 7.5:1 vs stock 6.5:1
This is the crown shape:

They are Gandini and you can buy them from a few sellers (Draganfly, Feked, Classic Bike Bits).  Assuming not modded yours will be the short rod version (pre 53 is long rod where gudgeon pin sits next to lowest ring).. Yours will have a few mm between top of pin and oild control ring.
Good luck

Cardiboy1

Thanks Neil64. Yes all that was discussed with the specialist currently doing the valves. He said the bore would be ok for just a few sunny days and Sundays, but there was a danger that it would nip up and seize, resulting in another round of expensive work. Better to deal with it all now and be sure. My B33 has a short rod engine, the piston currently fitted probably original- a BSA marked one, part no 65-1661. It looks exactly like the one in your picture so is probably already a 7.5:1 compression. I initially thought it was in good condition but each time I look closer at it I see signs of wear! Maybe I'll be happier with a new one anyway. I took it off this afternoon- easier than I thought after warming the piston top with a hairdryer. Hopefully tomorrow it and the barrel will go to the workshop in Newark for assessment. The present piston has no marking that indicates it's oversize, so hopefully a first stage rebore will go up just +20thou, cure the bore and eliminate the scratches. I've swallowed hard and am prepared for the new piston and rings costing about £200 !