800 Rave Clearance

[Michael73]

In my seadoo manual it says that seadoo only offer a .25mm oversize piston because of clearance problems with the rave valve, I know SBT only goes up to 1mm oversize.

My engine is .5mm oversize, and I am trying to find out what the recomended clearance is if you put a straight edge over the exhaust port and measure the rave valve clearance with a feeler gauge.

I know the engine was running previously with these pistons, they dont appear to be hitting, I just want to be sure that the clearance is correct, due to the fact that the rebuild has already cost me FAR too much, so I want to avoid any possible catastrophies (?).

Thanks, from Downunder!!! :D

[Bryan Glynn]

I don't know how much but I believe you do need to grind the valves back a touch for .5mm os pistons.

[Bill O'Neal]

Using a half round file, file off .010 from the face edge of the valve. I have seen valves catch a ring if not filed when going to .5mm OS, or more.

[Michael73]

So then what sort of clearance would I be looking for if I use the feeler guage and a straight edge over the exhaust port/ rave valve.

If you cant answer how much i should have, it might be easier to ask what is the maximum I should have before blow-by starts to become an issue???

Thanks

[Bill O'Neal]

Blow-by is not an issue, as the valve is in the exhast port, not the clyinder, and has nothing to do with the rings. Blow-by is gasses passing the rings and entering the cases.

You need at least .015-.020 clearance to allow for growth of the piston and valve when heated.