Any piston readers out there?

billyslad
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billyslad
Edited Date/Time 4/6/2016 12:52pm
I have a 99 CR 125 with a Gorr 144 that I tore down yesterday
I am pleased with what I found apart from I think I am running too rich although it may be too much oil
I have run Castrol 747 at 32.1 and the piston has been in for half a dozen practice session and I have raced 6 super evo meetings
The bore still looks immaculate and the ring gap was 35 thou



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billyslad
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billyslad 4/4/2016 11:29pm
4/4/2016 11:29pm
There is a bit of wear over the exhaust bridge and a bit on the skirt from what I can see
I am running on 97 petrol with v force reeds and a 38 mm air striker
Paw Paw 271
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Paw Paw 271 4/5/2016 7:34am
4/5/2016 7:34am Edited Date/Time 4/5/2016 7:36am
What does the underside of the piston look like? If it is black you have a leaking crank seal.
Your ring end gap is too big.
What color is the tip of the spark plug?

Paw Paw
Skerby
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Skerby 4/5/2016 8:43am
4/5/2016 8:43am
That was the old ring though right? I always thought rings were supposed to wear, hence big gap in old ring.

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Paw Paw 271
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Paw Paw 271 4/5/2016 9:50am
4/5/2016 9:50am
Skerby wrote:
That was the old ring though right? I always thought rings were supposed to wear, hence big gap in old ring.
Yes that is true, but that end gap is way beyond the service limits.

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billyslad
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billyslad 4/5/2016 10:56am
4/5/2016 10:56am
Ok I picked up a new ring and put that I and measured at 30 thou

billyslad
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billyslad 4/5/2016 10:57am
4/5/2016 10:57am
Spark was black with no deposit on underside of piston
Paw Paw 271
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Paw Paw 271 4/5/2016 12:25pm
4/5/2016 12:25pm
With that much ring gap on a new ring, it would suggest that the cylinder is worn or there was a poor fit on the original bore size.

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TJ 755
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TJ 755 4/5/2016 2:42pm
4/5/2016 2:42pm
Paw Paw 271 wrote:
With that much ring gap on a new ring, it would suggest that the cylinder is worn or there was a poor fit on the original...
With that much ring gap on a new ring, it would suggest that the cylinder is worn or there was a poor fit on the original bore size.

Paw Paw
would also explain why that GP piston still has all the black on it.
In my experience that stuff goes away.
billyslad
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billyslad 4/5/2016 11:36pm
4/5/2016 11:36pm
Ok so what are my options ? I don't think that I can get a B size piston so would a recoat of the barrel be enough ?
Paw Paw 271
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Paw Paw 271 4/6/2016 2:15am
4/6/2016 2:15am
Try your ring end gap measurements ( three places) in the areas the ring travels in the cylinder and not down at the bottom where they never go as in your photo.

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billyslad
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billyslad 4/6/2016 9:27am
4/6/2016 9:27am
Paw Paw 271 wrote:
Try your ring end gap measurements ( three places) in the areas the ring travels in the cylinder and not down at the bottom where they...
Try your ring end gap measurements ( three places) in the areas the ring travels in the cylinder and not down at the bottom where they never go as in your photo.

Paw Paw
Thank you for your patience I have measured in 4-5 places up the bore with the new ring and it is between 0.35 and 0.40 mm
Paw Paw 271
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Paw Paw 271 4/6/2016 10:55am
4/6/2016 10:55am
There seems to be something wrong in those numbers. You see .40mm = .0015" ....
I think you are using a guage that is in inches and you have a .040" ring end gap which is very large.

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Paw Paw 271
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Paw Paw 271 4/6/2016 12:52pm
4/6/2016 12:52pm
Your correct, as I mis-spoke.
So you are at about .015" and you should be at about .007".
It may be time to have the cylinder checked as something is not correct and the ring end gap on the new ring is about twice it should be.

Paw Paw

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