classic motorcycle forum
Motorcycle Discussions => Japanese Bikes => Topic started by: Ianc2929 on March 02, 2009, 12:13:03 PM
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After a big end collapsed, I rebuilt my Superdream engine with a secondhand crank & rods. It runs fine, but has a huge oil leak, apparently from the cylinder base. At first, I thought this was the o rings on the ends of the cylinders (they were pattern parts), especially when I came to replace them with Honda parts, which were noticeably thinner. It still leaked oil though. A more careful examination showed it was coming from just above the lowest cylinder fin, not below it. Stripping the top end (again!), I see there is a groove machined on the LH cylinder between each inner head bolt hole & the central tunnel the cam chain runs up. The 4 inner head bolts are partially exposed & have copper washers to stop oil leaks, but oil can get out through these grooves. Now maybe I've done something wrong & there's excess oil pressure, too much crankcase pressure or something, but I still can't understand what these grooves are for & why oil didn't escape there before - the engine was oil-tight before I rebuilt it. Anyone help ?
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With a bit of luck, Ive attached a picture of the centre rear of the cylinder where it mates to the crankcase. The 2 inner rear head bolt holes are shown, with the groove visible on the right (left cylinder - it's upside down). There is another groove at the front. The inner bolts are exposed between the top & bottom fins where the cylinder has a gap to allow cooling air past the inner surfaces. Until I understand what these grooves are for, and why oil didn't leak out before, I can't figure out what i've done wrong to make it leak now.
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Hi,
did you get this sorted, I have the same problem with my 250.
When I stripped it there was a rubber sleeve on the head bolt, I think that's what needed to fix the leak, trouble is, I can't find any for sale!,
help!!
thanks. :-[
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Hi, I think the rubber seals you mean go on the two outer rear bolts - they actually go on the steel locating sleeves. Oil passes up these bolt holes to lubricate the cam. There are also copper washers on the 4 inner head bolts to stop oil leaking down the bolt holes. I re-used the copper washers, but I got new rubber seals from David Silver. The part number is 12909413000.
Unfortunately, I don't think these are causing my problem....
Regards, Ian