My SR (+060 bores, 9:1 pistons, SRM oil pump, SRM billet rods, etc) started to smoke (blue white) really badly.
Before stripping anything down, Checked all the things suggested on this and other forums.
Nothing serious found but did find that the tops of the pistons both sides went from looking normal matt black to wet black and both plugs furry black.
SRM sump plate with removable sump plug installed a while ago so removed plug and about a third of a pint of oil drained out. Fitted magneto cutoff type anti-wet sumping valve.
I have a toolbox mounted cartridge oil filter, also suspect that some oil is seeping back to the sump from that.
I suspected very rich running so moved jet needle down a notch and reduced main jet size.
Didn't help, it just produced weak mix so restored main jet, left needle in new position. Now plugs looking black shiny wet. (Small step forward?).
Still smoking like a steam engine. Decided to take head off, which confirmed piston tops wet with oil.
Checked bores, both showed vertical scoring front and back and also very shiny (like chrome).
Barrels off, both pistons also found to be scored plus signs of over heating around tops, rings looked ok but showing wear. Head gasket showing signs of some cross-cylinder leakage plus slight possible leakage cylinder to push rod tunnel.
Honed out bore scoring and restored both bores to correct honed surface (medium grit stones and oil wash during process), replaced pistons and rings with Gandinis at 8.5:1.
Always thought that 9:1s were perhaps a bit ott for a non-race bike, so 8.5:1s from Fecked seemed a reasonably sensible alternative.
Refurbished head, new valve springs, valves all ok and properly lapped in. Top oil feed banjo bolts looked to have slightly oversized oil holes so replaced with standard bolts.
Engine top end rebuilt (all new gaskets). Oil tank flushed out and filled to line with 'running in oil'.
Dry compression test showing 130psi both sides, repeat as a wet test (WD40 both bores) showing 165psi both sides. (Throttle and air valve both full open).
Noted that oil pressure gauge showing increasing and good pressure during pressure testing.
Good spark both plugs, timing checked and spot on.
Several days of careful work done and wallet empty, tomorrow's 'put some fuel in it and get it started' day.
I'll update you on results, wish me luck.
Hi Greybeard, thanks for the welcome and hello all, Part 2 -
Well, fuel in, started third kick, sounds great and running well, small oil leak from front rocker feed bolt, quick tighten and fixed. Oil pressure rapidly up to 55psi where the oil PRV cut in and dropped it to 50psi.
So far so good but (there it is Greybeard) Unfortunately that's about as good as it got.
Still smoking like a traction engine, - drat!
Had a think and decided to clamp the rocker feed pipe to see if there was any improvement to the smoke situation, Answer no.
Then decided to take the sump plate off add an extension to the sump oil pickup pipe stick the end of that into a jar of oil in a big drip tray and run it again. That showed a lot of combustion blowby (lots of combustion gasses coming out) also huge amounts of oil cascading out.
Conclusions - Clamping the rocker feed pipe probably means that the valve guides are ok.
Blowby and crankcase gasses probably indicating that the bores are now just that bit too big for the new pistons and rings. (Thought I would get away with slightly larger piston to bore clearence and ring gaps, not sure now that it was worth a try).
Volume of oil draining out could mean big end shells need replacement, (SRM oil pump able to push a high volume of oil out through the big ends?)
If crankcase pressure was forcing oil up the bores past the rings not sure why it was still smoking badly when running with the sump plate off, Unless it was residual oil in the combustion chambers.
Looks like another strip down (full this time), replace liners etc, check big ends, and double check everything else.
All very disappointing but lessons learnt and no doubt more to be learnt.
I had an A7 and then A10 GFs back in the 70s, lots of stripdowns in efforts to gain more power (as we did then) and of course as a result of pushing too hard. Never had a single moments problem with the oil systems. Hence this experience being an unwelcome surprise.
Now to start saving up.
