bretb
New Member
Posts: 6
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Post by bretb on Dec 2, 2006 8:07:19 GMT -5
I have just completed rebuilding a 79 SR. I stripped the top end and replaces valve stem seals and lapped the seats. The bore and rings checked out fine. It was a one owner with only 23K. The problem has been when first started, after sitting overnight, it blows enough smoke to fill the garage. I have pulled and stripped the motor a second time and rechecked everything. I put it back together and the same problem. When it warms up it is fine. Has anyone experienced a similar problem ?. I don't want to pull the motor a third time without a idea of what it is. Any help would be very welcome.
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Post by SRwillie on Dec 2, 2006 10:14:05 GMT -5
Hey Bret, a couple of questions come to mind. Did it do this before the teardown? 23K is quite a few miles. Has it been bored? Lastly are the ring gaps staggered correctly? You may want to try a new set of valve guide seals on the chance you may have one that ripped or was bad to begin with.
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bretb
New Member
Posts: 6
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Post by bretb on Dec 2, 2006 16:32:54 GMT -5
It has 23000kms, I stripped it as soon as I bought it, so I don't know if it was blowing smoke initially. It had been in storage for 17 years. I replaced the valve stem seals, lapped the valves, replaced the top end gaskets. The bore looked fine (could still make out the hone marks!!). Piston and rings were excellent and spotless, no sign of blow back. There were no carbon deposits in the combustion chamber.
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Post by SRwillie on Dec 2, 2006 21:24:56 GMT -5
When you re-assembled, did you stagger the ring end gaps properly?
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Post by wotavidone on Dec 3, 2006 17:55:22 GMT -5
Hi.
I have a story for you which may help you. Next time you go out to the garage to start this bike, check the oil on the dipstick before you do anything else.
If it is down, and comes up after you run the bike, it may indicate an entirely different problem.
I have a friend who is a masochist - in that he loves British bikes.
Years ago, he bought an A10 BSA which looked absolutely immaculate, but blew oil badly on cold starts. Owner had given up so my friend got it very cheap.
I asked him why he bothered and he said, "because I reckon I know what the problem is. The oil scavenge pump non return valve is leaking oil back into the sump. The bike is wet sumping on start up - this is a problem for bikes which are left to sit for a long time or have a very worn pump."
The XT I bought the other day had absolutely no oil on the dip stick until after I ran it for a few seconds - it was all down in the engine. This bike sat for two years.
May not be the problem in your case, but definitely worth looking at, especially since it doesn't do it when it's warm and you have replaced the valve stem seals already.
Mick
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Post by wotavidone on Dec 3, 2006 17:57:26 GMT -5
PS, if its just a non-return valve leaking back, it might come good on its own.Anyone out there know if the scavenge pump actually has a non-return valve?
Mick
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Post by miker on Dec 4, 2006 12:33:19 GMT -5
My SR occasionally blows smoke after sitting a few days, I'm sure it's a wet-sumping thing. The non-return valve is a ball, spring, and seat in the right side case.
miker
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