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Piston colour, is it normal?


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Hi people.

I put a lovely new exhaust and reduction gearbox on my H+E today, with the new harness I put on the other day it looks like a new machine, apart from the bent cage :roll:

Whilst doing the exhaust I had a look at the piston through the exhaust port, the sides of the piston were quite brown and scorched looking in places with verticle scratch lines, the lines were not scores just smooth lines. Is that normal or has it been too hot or close to seizing up to cause that colour and those lines? :?:



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Hi Whitters

The ball joint does wear without grease and will start to squeek annoyingly. There is a thread on here which talks about using a silicon based product used to assemble motorcycle exhausts with a detailed how-to. Honda bond was it?

the springs will have a factory recomended tension but I wouldnt have a clue what it is and doubt it is critical.

Not an expert but dont like the sound of the piston. There is a guy called Tony Lawrence who doesnt come here anymore who is very knowledgeable on 2 strokes. I will try and find his email and pose your question.

Also Martin but havent seen him around lately either. I expect there are more.

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iam not sure weather u r asking for my advice but i do know alittle about

engines.... my advice from what u said its normal for the marks down the sides.

but if u have the time take barrel off. then check scoring from inside barrel

for any scratches.any chips....etccheck the piston rings wear can be seen if the

overall thickness of the ring is adnormal...meaning its worn.also while looking

from inside exhaust barrel look at piston rings while turning drive belt over by

hand and watch the gap from the piston to the barrel. as the piston moves yuoll

be able to see slack too much slack is no good and means its worn... the piston.

and you get less powwer and compression.if u take piston out and renew always

lightly score inner barrel with fine emery paper so new piston will bed in

good......regards tonyfor those who dont know i race mx bikes and engines are

alike even thou mx are race engines


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The scorched piston skirt is a result of the combustion process burning past the piston rings, this is caused by the bore becoming glazed and/or the piston rings worn. A good remedy would be to remove the cylinder and hone the bore & fit new rings and/or piston & rings. The vertical lines are caused by impurities entering the cylinder or partial seizing, look at the top of the piston, ideally it should look a dark brown colour or just black here and there, any lighter than this and the mixture could be a bit lean

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As confirmed by Mario Mohle

First thing to check for are stuck rings. A common occurence long before they

wear out.

Carbon deposits will eventualy prevent rings from moving in their groove thus

reducing ring to cylinder contact and allowing pressure leaks. These are the

brown marks seen on the piston sides, worn off at spots where piston rubs

against cylinder walls.

This situation normaly shows up with a loss of compression, thus engine power. A

good cleaning of ring grooves may be all that's needed. Refit rings in same

position as they were.

PS Thanks for your top rate advice on the bus brakes Phatboy, going in for MOT next week.

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mario is correct. but.....if thast was the case piston rings sticking.while

running engine white smoke and excess oil would be spurtting from exhaust

ecessively and spark plug would be wet.regards tony

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