The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: xib34 on 27.01. 2014 19:01
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Pappy here, what I thought my old user name was doesn't work so I made a new one. My A10 got major rebuild some years ago, but then even after many break in miles it always had a lot of oil in the right side cylinder, fouling the plug eventually. Checked cylinder bore for scoring, tightened up valve stem clearances, replaced head gasket, top end oil supply looks ok. No change. Then I left the gas tap on last winter and the thing seized, so I took it to the same mechanic as did the rebuild long ago and he honed cylinder and replaced the rings. Now the thing has excess oil in the LEFT side cylinder! Leaks oil out the exhaust to cylinder had joint, and also oiling the plug. Right side is ok. Took the head off, no sign of a leak path under the head gasket from oil passages to combustion chamber. Valve stem clearance is in spec. Valve guides are not lose. Rocker box moving parts look fine. Ideas? Defective rings? But has anyone ever actually experienced defective new piston rings? Twice? In all the cylinders in car engines and bike engines I have done myself I never have. Should I just send the thing to SRM?
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well I've bought new pistons and rings and found the rings to have a much bigger gap than should be, meaning the purchase of another set of rings.
Lots of variables to consider though
Was the rebore correct or maybe a tad slack
Is it the rings or the piston
I think it's the rings, these days they come ready gapped. think I would prefer they came in need of a file *conf*
On the left / right cylinder oiling, this seems common (at least among by biking friends) mostly the left but can also be the right, popular felling is it's to do with how the engine stops and which ex valve is left open or valve guide allows oil down into an ex pipe where it burns off for the first few miles then clears
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G'day Pappy.
Yes I've had new dud rings. What make of rings? When your mechanic did the left side, did he replace both sets of rings?
Alloy or iron head? Valve guides may appear tight when the head is off and cold. Heat head to 150 C, guide should stay put with a good push by hand. At 200 C it will come out with a good tap.
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New rings both sides both times. Not sure what make of rings. Alloy heads.
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If you are too gentle with running a motor after a hone, you may glaze the bores.
What kind of oil scrapper rings are you using? one piece oil rings are often problematic. the 3 or 4 piece oil rings typically work much better.
Mind you if it was simply the rings I would expect you to be burning oil (out the exhausts) rather than fouling plugs.
So does suggest valves.
That much oil should be leaving a trace.
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I don't know what kind of rings were installed, I need to ask the mechanic that installed them if they were one peice or three piece oil rings I guess. I may have to pull the cylinder off some time to check.