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Piston ring test

Having a bit of trouble? Maybe we can help.
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SMUDGER

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Piston ring test

PostSun Apr 24, 2016 7:28 am

Ok quick question if a cylinder head is off and I wanted to check piston n rings I know to shine a torch down there and use touch to check for scoring, obviously a compression test should of been done but if I pour petrol into all bores and rotate crank a few times give it an hour if petrol is still staying would this say there fine and if it disappeared obviously they fooked
Or is this a pointless test??

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bloke

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Re: Piston ring test

PostSun Apr 24, 2016 1:53 pm

pretty much pointless as rings need the force from combustion to force them against the bore.
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pch1

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Re: Piston ring test

PostWed Apr 27, 2016 11:00 am

SMUDGER wrote:Ok quick question if a cylinder head is off and I wanted to check piston n rings I know to shine a torch down there and use touch to check for scoring, obviously a compression test should of been done but if I pour petrol into all bores and rotate crank a few times give it an hour if petrol is still staying would this say there fine and if it disappeared obviously they fooked
Or is this a pointless test??

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The rings don't run completely around the piston, so a thin fluid like petrol will easily find a way past the ring gaps.
Put the head on, crank it a few times and check with a compression tester.
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SMUDGER

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Re: Piston ring test

PostFri Apr 29, 2016 7:06 pm

pch1 wrote:
SMUDGER wrote:Ok quick question if a cylinder head is off and I wanted to check piston n rings I know to shine a torch down there and use touch to check for scoring, obviously a compression test should of been done but if I pour petrol into all bores and rotate crank a few times give it an hour if petrol is still staying would this say there fine and if it disappeared obviously they fooked
Or is this a pointless test??

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The rings don't run completely around the piston, so a thin fluid like petrol will easily find a way past the ring gaps.
Put the head on, crank it a few times and check with a compression tester.

So when I turn my bike off everytime what petrol is left in the Chambers go's into the oil pan or are rings left sealed as the chamber is compressed??

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Dooffle

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Re: Piston ring test

PostFri Apr 29, 2016 11:16 pm

When you turn the engine off there won't be any fuel in there. As there is no vacuum to pull through (carbs) or if injection no power. Any tiny amount of fuel will evaporate due to the heat first.
That's pretty much basics of engine knowledge, I do worry.

Another way to check for ring wear is to measure crankcase pressure (blowby) but again you really need the head on. Or remove the rings and measure the gap with the ring part way down the bore.
Check there isn't a shiny area near the top of the bore with a shallow ridge on thrust areas, as this is where excess wear will happen to the bores meaning the rings won't fully seal. Check the honing looks crisp and even.

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