Oh dear GT550 Engine not sounding good

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Harrymail
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Re: Oh dear GT550 Engine not sounding good

Post by Harrymail »

barney01 wrote:Thanks Harry. I have had 2 catastrophic seizures in my bike which I have owned for 25 years. Both in the early days before I understood these engines. You did the right thing in recognising the rattle was serious and getting a lift home. I tried to limp home and the left piston seized mid bore and the conrod ripped the bottom of the piston out and it punctured the crank seals on the first one. It was caused by oil starvation. I think a blocked oil feed banjo. The second was a timing drift effectively overheated right spark plug so much it melted a hole in the piston crown. (This is why I now have Newtronic ignition) as I switched the bike off there was that awful sounding click as it seized. That was 20.000 miles ago and touch wood no problems since. Good luck with your rebuild it's cartainly in good hands with Baz.

Cheers Barney, good to know I'm not the only one who has had a bit of a disaster. ;)
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yeadon_m
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Re: Oh dear GT550 Engine not sounding good

Post by yeadon_m »

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
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Harrymail
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Re: Oh dear GT550 Engine not sounding good

Post by Harrymail »

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
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willowden
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Re: Oh dear GT550 Engine not sounding good

Post by willowden »

Hello , do you think the offending piece of metal could possibly of originated in your exhaust & been sucked into your engine ?
Are your exhausts in solid rattle free condition. If a baffle or exhaust internal is degrading this can happen . Just a thought worth checking.
Regarding oil , I only use comma mineral. I don’t think forty year old tolerances suit full or semi synthetic oils.
Good luck.
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Harrymail
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Re: Oh dear GT550 Engine not sounding good

Post by Harrymail »

willowden wrote:Hello , do you think the offending piece of metal could possibly of originated in your exhaust & been sucked into your engine ?
Are your exhausts in solid rattle free condition. If a baffle or exhaust internal is degrading this can happen . Just a thought worth checking.
Regarding oil , I only use comma mineral. I don’t think forty year old tolerances suit full or semi synthetic oils.
Good luck.
The exhausts are solid, no rattles. I have taken a picture of the bits of metal. The bit on the bottom right was stuck inside the spark plug. Looks like the scrapings from the bore. The other bits were in the exhaust header. There is some bronze colouring to the metal. The rings on Nikasil bores are mixed metal I think ? The pieces look the right size to be broken piston ring. Any thoughts welcome ? :?

Paul
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martyducati

Re: Oh dear GT550 Engine not sounding good

Post by martyducati »

I thought the plated barrels used iron rings(magnetic) and the Pistons were aluminium ( not magnetic) I don't think the engine can suck exhaust material/debris back into the motor,where else can ferrous metal come from in the combustion chamber/crank inlet area on a motor? Hopefully you/we get an answer,could something have entered the air box and made its way into the motor?
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Harrymail
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Re: Oh dear GT550 Engine not sounding good

Post by Harrymail »

martyducati wrote:I thought the plated barrels used iron rings(magnetic) and the Pistons were aluminium ( not magnetic) I don't think the engine can suck exhaust material/debris back into the motor,where else can ferrous metal come from in the combustion chamber/crank inlet area on a motor? Hopefully you/we get an answer,could something have entered the air box and made its way into the motor?
I am pretty sure you are correct Marty. All the bits of metal are magnetic. The bad scoring lines up with the inlet port.
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Alan H
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Re: Oh dear GT550 Engine not sounding good

Post by Alan H »

Could be bits of bearings - little ends favourite.
Proof that four strokes are over complicated
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mizzytheman
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Re: Oh dear GT550 Engine not sounding good

Post by mizzytheman »

Alan H wrote:Could be bits of bearings - little ends favourite.
We’ve heard about your favourite little end :lol:
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canaletto5
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Re: Oh dear GT550 Engine not sounding good

Post by canaletto5 »

mizzytheman wrote:
Alan H wrote:Could be bits of bearings - little ends favourite.
We’ve heard about your favourite little end :lol:
I was wondering what that video clip reminded me of :P
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