787 Rave Piston Thread Failures

[etemplet]

I have a wrinkle on one of my 787s. Threads are being destroyed on the Mag side rave valve. I measured the rave housing and it was a take worn. I'll have to take a measurement on a new one. I saved some housings with the intention of installing a bushing to tighen up the clearances. I'm thinking the valves just rattle around too much for the plastic piston. The same engine exhuast piston is just fine. Strange. I ordered some aluminum pistons.

Being a machinist type I've considered aluminum welding the rave valve so they are not quite so loose in the cylinder slot. Anyway... input is appreciated. Strange problem but I know it isn't just me or this engine.

 

[tobytd]

Been there done this. I’ve had rave valves screw up the threads in aluminum pistons. search: sluggish 787 July 13, 2021, post 8, 9 and 10.

 

[etemplet]

I've replaced the housings with "NEW" and found them opened up to the previous "Worn" size in 2 hours run time. Back then I decided to install a brass bushing with a tigher clearance which I did not do cuz I hardly ever ride the ski. Obviously the blades are hammering around inside the cylinder slot and that is the main problem. Strange that both are loose but only the MAG blade is causing problems.

I have a plan. and I'll post pictures when I get R did. It will solve the problem.

 

[JJinSC]

@etemplet , any progress or results in this?

 

[etemplet]

@etemplet , any progress or results in this?

Nah off season for me no riding. I do have the aluminum pistons.

 

[JJinSC]

@etemplet did you ever observe or determine what the wear tolerances should be before needing replacement? I know I read a lot of measuring going on. I added mine to that other thread with the measuring.

 

[etemplet]

I can take some measurements. The Brand new rave housings that I rode for ONE HOUR were a larger size in ONE HOUR than the old rave housings I removed. Incredible to believe. Has to be looseness or turbulence allowing the blade to shake rattle and roll thus wearing out the aluminum housing. Doesn't make sense but the RFI cylinders are a MUCH tighter fit for the rave blades than the carb 787. I tried to measure the housing slots and couldn't get a decent size. All different sizes everywhere I checked. Jet ski mechanics don't much go into the why they just replace parts. Currently this is happening only on my jet ski and only on the MAG cylinder rave. Strange.

 

[JJinSC]

The blade I had break, broke in the middle and the only other issue I found on that valve was that the threads were stripped. Trying to find some commonality in all of this. I just cannot come up with what would cause a blade to snap in two in the middle of the blade (not the stem).