800R Blown Motor (Why)

[steelroe]

I have just stripped down my 800R motor and the inside is like a bomb went off. Reason for strip down is loud bang on last outing, ski will not start and 0 psi on rear cylinder

Motor has the following mods.

Riva Head and Domes
K+N Air Filters
reed Stuffers
Running on premix with primer fitted.
Motor interior ported and polished.

damage

Rear piston in pieces. Hole in casing. reed valves damaged. Skirt on bottom of cylinder snapped off.

What could cause such a catastrophic failure of the motor.

Service carried out 3 weeks age and all seemed fine, including good compression on both cylinders.

[RDH]

POWERVALVE!!!!

PV clips should have been the first thing you did, before anything...

the exhaust side of the piston crown is broken right?

[steelroe]

Power valves are fully intact and have not slipped down.

[TRuBLuE01]

Did u swithch to a deeper dish piston, it looks like u had a a rod bearing failure which caused all your havic, how did they look. Ive had tons of blown motors come in with the same problem

[RDH]

Power valves are fully intact and have not slipped down.

really?

in that second shot the crown of the piston looks phuked up...

[stingray152003]

you should take some picks of the power valves

[IrishGpr05]

From experience and from seeing other skis with the same damage. When the top of the piston breaks off like that on the edge, it's from be wayyyyyy to lean which causes detonation which makes everything really hott and then the piston breaks off.

If your lucky like I was the piece will go out the exhaust and you wont destroy the motor but in your case it looks like the piece that broke off stayed in and possibly fell down one of the ports and then the crank started beating it around until you got what is pictured.

I may be wrong but thats what it looks like.

Take some pics of the underside of the piston crown. If they are black in the center you were running lean.

With the mods you have...did you go through the carbs and re-jet them?

If you didn't..that's what caused you whole problem right there. Also there possibly could have been an air leak from re-installing the cylinders or carbs.

Did you pressure test the motor once it was built this last time? This is different than a compression test.

-Jon