yeadon_m wrote:Guys,
I’ve also had GT550B (nikasil) motor failures, twice. Once after someone else rebuilt the whole unit but then again after I’d stripped, subbed out & rebuilt it myself.
In both cases, they were ok for a few hundred miles, then got noisier before (in the first failure) seizing its left pot and in the second, nasty scoring in the middle pot.
In all failures, there were vertical scores both in the pistons and bores, more on the intake side than anyo else.
While if you told me this, I’d guess lubrication failure, I’ve visually checked oil delivery in each cylinder intake.
I have no good theory to even begin to explain failures like yours & mine.
Any ideas?
Alan kindly helped me rebuild this time. We’ve installed a top end consisting of first over pistons running in iron re-sleeved ex-nikasil pots ex Kev!
All running sweetly - for now. As we found no cause of the last failure, I don’t yet have much confidence in the motor.
Alan wondered out loud whether full synthetic oil might be unhelpful at this stage. I don’t know. Any thoughts on this or other failure mode theorists?
Cheers,
Mike
Thanks for your input
Mike. I have been keenly following your posts on the iron re-sleeve. I have hedged my bets on two stroke oil and have been using Putoline semi-synthetic for the 10 years I have owned the bike. I have not tested the individual oil lines, although I did undo the banjo feeding the crank on the LH side a couple of years ago and there was red two stroke oil there. The lines are not very see-through so its difficult to see what's going down them. It certainly uses the expected amount of oil and all pots smoke fairly evenly when opened up. In hindsight I had noticed the engine had become a little noisier, though no rattle, during the last few weeks. My feeling is that the general scoring of the pistons and bores has happened over a long period of time. The unidentified piece of metal in the LH bore would seem to be the cause of the bad scoring in the LH bore. The metal is magnetic. Baz has not had a close look yet but it may be a bit of piston skirt. Baz didn't think the rings where broken.
I have learnt from its 2nd owner that about 10,000 miles ago (25 years), it had new rings due to the first owner running it on Castrol R and the rings gumming up. I guess it may have been ridden hard by the first owner who had fitted it with a full fairing, drops, spannies and rear sets. You don't do that and then ride it gently. He had also blown it up at only 1 year old. Having said that it was kept in pristine condition and has not been restored. So it may well be that it its just wear and tear after 20,000 miles, though I would love to know what the metal is that was recovered from the LH cylinder.
Paul