Oh dear GT550 Engine not sounding good

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Harrymail
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Oh dear GT550 Engine not sounding good

Post by Harrymail »

Well after 10 years of riding my GT550 I think that I have an engine rebuild round the corner. Yesterday I did 85 miles to Willingham Woods and back, bike running really good. 2 miles from home I noticed a rattle from the left side of the engine. Backed the throttle off and it stopped, throttle back on and it rattles. Kept riding but the rattle got louder so stopped. At tickover it sounder more like a clatter, certainly not good at all so shut the engine off quick. Got it back home in a mates van, tried starting it but the clatter sounded so bad I switched it straight off. Not has chance to look at it properly, but my guess is its a crank shaft bearing. Its running on all 3 pots, clutch is fine, have checked behind alternator cover and all is fine there. Not sure if there is much else I can check without a fair bit of dismantling.

Any thoughts anyone ?

Harry :( :( :(
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barney01
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Re: Oh dear GT550 Engine not sounding good

Post by barney01 »

Hi Harry. My plan of action would be to get the head off and look at piston crowns. Then if that was all okay I would lift the barrels off and check the cylinders. It sounds to me to have happened too quick to be a crank bearing. I once had a piston seize half way up the bore and the rod tore the bottom half out and the clattering was the conrod rattling around.
Just a thought do you have the early starter clutch that has been known to fall apart?
NO SMOKE .......NO POKE
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Alan H
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Re: Oh dear GT550 Engine not sounding good

Post by Alan H »

Head & barrels off and check pistons and little ends for starters.
Errr, there is oil in the oil tank?
Proof that four strokes are over complicated
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Harrymail
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Re: Oh dear GT550 Engine not sounding good

Post by Harrymail »

barney01 wrote:Hi Harry. My plan of action would be to get the head off and look at piston crowns. Then if that was all okay I would lift the barrels off and check the cylinders. It sounds to me to have happened too quick to be a crank bearing. I once had a piston seize half way up the bore and the rod tore the bottom half out and the clattering was the conrod rattling around.
Just a thought do you have the early starter clutch that has been known to fall apart?
Thanks Barney, starter clutch is in the right area I think. The clatter is from the left hand side as far as I can tell. The starter does work though. As I did start it briefly when I got the bike home, but the clatter was too bad to leave it running more than a few seconds. Not sure if it is an early starter or not, but being an A model I presume its not an early starter.
Currently without a GT, but looking
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Harrymail
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Re: Oh dear GT550 Engine not sounding good

Post by Harrymail »

Alan H wrote:Head & barrels off and check pistons and little ends for starters.
Errr, there is oil in the oil tank?

Hi Alan. Yes plenty of 2T oil in the tank, and it does use it. Though that does not gurantee all oil lines are working. Will have to start from the top and work down. I'm ok with removing head and barrels if needed. Will have a look up the exhaust ports for any clues first. Looks like a busy weekend.

Harry
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Harrymail
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Re: Oh dear GT550 Engine not sounding good

Post by Harrymail »

Well initial investigations have begun and straight away I have a small piece of metal on the spark plug of the left hand pot. Also the piston rattles in the bore if pushed about with a pencil down the spark plug hole. So looks like its top end. Head and barrels off tomorrow then, see what the damage is, then try and determine the cause :(
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Alan H
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Re: Oh dear GT550 Engine not sounding good

Post by Alan H »

I might have barrel/piston spares if required - depending on type of course!
Proof that four strokes are over complicated
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Harrymail
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Re: Oh dear GT550 Engine not sounding good

Post by Harrymail »

Alan H wrote:I might have barrel/piston spares if required - depending on type of course!
Thanks Alan. Its chrome barrels. The piece of metal on the plug is magnetic, so its not a piece of Alloy. I have just taken the LH exhaust off and had a look. Big groove down the back of the bore from the inlet port upwards. A few more bits of metal on top of the piston.

Sods law I have a NOS barrel in the loft. Just had a look and its Right Hand, and its my Left one that is damaged.

Garage time tomorrow so I should find out more. Piston will likely be damaged I would think.

Harry
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BATTS
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Re: Oh dear GT550 Engine not sounding good

Post by BATTS »

Piston ring breakup? perhaps following piston skirt damage? I have found a firm that will make and fit an iron liner to SCEM barrels retaining the improved porting such as the one's Mike Yeadons' just fitted. It costs about the same as replating £150 per bore but means you can use normal pistons and rings at a fraction of the price of SCEM ones and rebore in the future.
Chris
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Harrymail
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Re: Oh dear GT550 Engine not sounding good

Post by Harrymail »

No going back now. Will have the engine out tomorrow. I have looked more closely at the damaged lh bore and it looks bad. A deep groove near the inlet port. Its at about 1mm deep so I presume the barrel is scrap.Other two barrels appear ok, but there is a lot of wear on the RH piston. LH piston is damaged by the broken ring. My thoughts are that it is time for a full overhaul and repair of the engine. With chrome bores I'm not sure what the options are. Bottom end will need inspecting as well. May be time to hand the engine to Baz and pay an expert to sort it out :(
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Currently without a GT, but looking
2003 Yamaha Fazer 600 Blue
2020 Triumph Street Twin Red
1968 BSA Bantam Sports Red
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