Question about 1987 Yamaha SDR

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Bravo 250 I have an old 86 bravo engine that i am going to try to mount in an 85 citation, The rings are good but one side of the piston is scored fairly deep, what could be causing only one side to score? i want to fix the motor on the bench b4 it goes in the sled

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Can be from seizing due to overheat or lack of oil...
best replace the piston and rings

Posted on Nov 01, 2009

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Posted on Jan 02, 2017

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1 Answer

What is the compression readings for a 1979 c10 i6 250

normal compression readings will be in the 150-165 psi range
There is a permissible 10% differences between adjacent pistons
anything below 120 psi is considered worn engine
really low readings on 1 cylinder indicates
broken ring
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low readings between adjacent pistons indicate a head gasket

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1 Answer

Replaced rings and honed the cylinder but its scored up again and the rings were stuck in the piston and were hard to remove

Your description indicates when the engine started the piston wasn't receiving any lubrication or maybe the rings were too tight or both and the engine suffered pre-seizure.

It is well to observe the basics with these sort of things and take nothing for granted. Prior to fitting piston rings it is important to check the ring end gaps. Most popular repair manuals will have diagrams about this and the recommended gap for your engine which is likely to be something like 4 - 6 thou per inch of bore. Quite often the piston ring ends must be filed a little...

In addition it is important to ensure the piston ring grooves have been thoroughly cleaned of carbon and the rings fit well with a side play of 0.0015 inch. A little more is permissible and perhaps as much as 4 thou for the top ring but more than that and the piston should be replaced.

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I have a Honda GC160 5hp that I just rebuilt but will not start

did you check the piston to bore clearances? did you check the ring end gaps? did you hone the cylinder and check it for roundness?

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Scorched pistons in a STIHL chainsaw - and its not the fuel mixture

What side of the piston is scored? If it's the exhaust side, it's running too lean, ergo, it's the mix ratio.

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1 Answer

My 16 year old son ran straight gas in blower for approxiamately 5 min. until unit shut off. Piston has not seized up in cyl. head. It's trying to run but won't. Without tearing it down, what parts...

Yep , Sounds like the rings have probable seized to the piston. It will probably be on the exhaust side so you may be able to take off the muffler and look inside the cylinder there to see if there are any score marks. Good luck.

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Probably going to be a paired piston&cylinder
you will need to replace both.. remove your muffler and see scorched(black streaks) piston, fused rings. Remove air filter and carb to see scored cylinder wall(on hot side)

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I'm about to rebuilt my RGV 250 VJ21a top end but I don't know wich rings I should use,cylinders are stock size but I had too little compression less than 85 psi. should I use rings at the 25 measure will...

hi buddy the standard piston and rings will be the ones you need if its still below 85psi your barrel must be out of shape or you are leaking air in the gasket or in the coolant also when you put a new piston kie in get new gaskets my kx85 new ring and piston went to 185psi

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2002 honda CR125R

sounds like you might have broken a piston ring. Sometimes a small piece will break-off and cause the loss of compression and if you look down the cylinder you wont see it. But it's enough to cause a problem.

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Was driving my o6 kx 85 . was at full speed and it cut out and refused to start and when i try to start it , it would backfire i think its getting a spark but no starting . does anyone know what the...

sounds like you might need to rebuild the top end and check the rod bearings remember when doing a top end always change piston and rings and use new base and head gasket

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