Piston failure after 600 miles

RDS88 · Apr 16, 2016

Any suggestions on what happened?

Boondocker Turbo Dragon 800 with about 600 miles,
Ran on straight av fuel
8-10#'s of boost depending on the day
EGTs never went over 1250
Ran extra fuel numbers in the mid when need be
Ran 4oz of oil in the gas tank for extra protection

Boston Racing · Apr 16, 2016

Looks like you were detonating. You must have had a lean spot in the map you didn't realize. EGTs can be tricky sometimes because when your detonating the temps can actually go down.

gus bohne · Apr 17, 2016

the evidence is clear, your turbo kit may only have 600 miles but your sled did not.
those pistons show lots of excessive wear on the exhuast ( thrust ) side dome edge. That is from excessive piston to wall clearance and the piston ROCKING. thrust is the exhaust DOME edge and the intake side SKIRT
the polaris already is way to loose from the factory and the fix kits all address this ONE issue.
new forged pistons will end your headache or replate your cyls to properly fit the stock cast piston.
you may have had some det but,,, IT was caused by the rolled edge of the dome getting red hot. that rolled up casting is porous and thin and get super hot initiating pre ignition. your tune was not your problem. piston FIT was.

fix it and forget it.

RDS88 · Apr 17, 2016

Sorry, the engine was rebuilt from top to bottom when the turbo was installed.

Engine had fixed kit installed, with a brand new cylinder, and pistons.

Snowmow · Apr 17, 2016

RDS88 said:
Sorry, the engine was rebuilt from top to bottom when the turbo was installed.

Engine had fixed kit installed, with a brand new cylinder, and pistons.

Any more info your hiding?

RDS88 · Apr 17, 2016

Nope, running boondocker suggested numbers for the elevation I ride.

Snowmow · Apr 17, 2016

So the cylinder was re niked when it was rebuilt?

RDS88 · Apr 17, 2016

Brand new cylinder with reinforced cylinder skirts

skibreeze · Apr 17, 2016

I could never keep pistons in my BD dragon. Finally took off the turbo and got another 800 miles on it before the rod busted a hole in the bottom of the case.

kgra · Apr 18, 2016

I see no sign of fueling or oiling problem. Looks like the piston simply just broke. Either from incorrect piston to wall clearance, bad luck,
Or is that an air pocket in the casting near top center of where the piston broke away?

gus bohne · Apr 18, 2016

my bad, REAL fix kits have forged pistons . Regardless of that. it was a failure from excessive clearance causing piston rock . same problem OEM polaris designed pistons have and have had since the dawn of time. Wrist pin height is too low. This, when combined with loose clearances ( as is the case here ) cause the skirts to crack and fail and dome edge to be exagerated as in this case as well. Forged pistons wont do this .

can only answer the ops questions with truth. if you want to blame the turbo that is your decision, however it is not the truth.

RDS88 · Apr 18, 2016

I wasnt blaming the turbo, just trying to figure out what happened. Like you say piston rock is probably the cause.
The cylinders were beat up as well and will require re-niking

wellfed777 · Apr 18, 2016

send the cylinder to Indy dan sounds like his new coating and finish are very good

ez-ryder · Apr 18, 2016

If the polaris pistons have too low of a wrist pin location.
Why do fix kit Pistons have a lower location than the OEM?
I'm assuming they are lower, otherwise the shim would change port timing not correct it.
These must have been cast m8 pistons of some type?

Or are you referring to wrist pin to dome distance too small?

RDS88 · Apr 19, 2016

Yes they were cast M8 pistons

kiliki · Apr 19, 2016

RDS88 said:
Yes they were cast M8 pistons

not OEM as the stocker do not have the coating on them as the ones in the picture do.

RDS88 · Apr 19, 2016

kiliki said:
not OEM as the stocker do not have the coating on them as the ones in the picture do.

Ya not oem, SPI if I remember correctly

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Piston failure after 600 miles

RDS88

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