GP800 Power Valve Piston Contact

[98YamahaGP]

I'm rebuilding the engine on the GP800 I bought.

When I tore it down, I determined the power valve in one of the cylinders made contact with the piston top. Power valve was shaved shiny from it where contact was made. Piston top was hammered, top ring broke up into little pieces and was pretty much gone.

When I pulled the power valve caps, I was expecting to see that the pin had walked out of the side of the factory keeper. It hadn't. Pin was secure in the valve top still. So I'm wondering what caused the interference.

The connecting rods feel right, minimal side to side play and basically no up and down play.

I've always read it was the flawed keeper design that caused interference. I'm trying to get away with just a top end build. But worry I'm missing something that caused the PV interference.

Don't want to bolt it back together to have it happen again.

Thoughts?

[98YamahaGP]

Super helpful forum so far. All threads so far-crickets. Noobs get treated really well.

[K447]

Super helpful forum so far. All threads so far-crickets.

Noobs get treated really well.

It is wintertime across many of the regions where these machines are used. Many members are not visiting the watercraft forums this time of year, or not as often.

Eventually someone who can answer your questions might notice this thread and respond.

In the meantime, you might find some helpful info using a site focussed Google search.

Include the command site:greenhulk.net along with the keywords you are looking for.

[Jonesyfxr]

Likely the PV was out of adjustment, causing the contact. Look in the manual for torque specs and adjustment procedure.

Pro tip: grease all gaskets to aide in sealing.

[98YamahaGP]

Likely the PV was out of adjustment, causing the contact. Look in the manual for torque specs and adjustment procedure.

Pro tip: grease all gaskets to aide in sealing.

I've got the FSM. I will refer to it when installing the new PV's. Grease? I'll be applying copper spray to the exhaust gaskets and high tack to paper gaskets.

[steve45]

Super helpful forum so far. All threads so far…crickets. Noobs get treated really well.

Gee, you wait only 7 hours for a response before complaining, on a Saturday night no less...

[Jonesyfxr]

No copper spray!!!
No RTV!!!
Use grease on the base gaskets and nothing in the exhaust. Copper spray will gum stuff up… trust me.

[98YamahaGP]

Gee, you wait only 7 hours for a response before complaining, on a Saturday night no less...

Yep must have been having a bad night. Apologies.

[steve45]

You're good. We all get antsy when we can't figure out the answer to a problem.

[WFO]

Likely the PV was out of adjustment, causing the contact. Look in the manual for torque specs and adjustment procedure.

Pro tip: grease all gaskets to aide in sealing.

Good tips... also the power valves have a "stop" made into the guillotine and it may be worn out. The plastic coupler between the linkage is probably shot. I always recommend installing the waveeater style clips and coupler when servicing power valves

[Adam]

The power valves have a stopper on the shaft that makes it impossible to hit the piston, also the power valve cannot physically go past the stops on either side of the power valve groove . Any damage is usually caused by piston material hitting it on the way out the exhaust port .

[98YamahaGP]

Good tips... also the power valves have a "stop" made into the guillotine and it may be worn out. The plastic coupler between the linkage is probably shot. I always recommend installing the waveeater style clips and coupler when servicing power valves

I purchased new power valves with the improved design and the wave eater kit for the linkage. So hopefully everything will be solid.

[WFO]

I purchased new power valves with the improved design and the wave eater kit for the linkage. So hopefully everything will be solid.

good deal

maybe post up a photo of the damaged valve to try to figure out what happened

[Jonesyfxr]

I had a PV and drop, nicking a piston in our 1200R. Use loctite and torque everything

[Myself]

The power valves have a stopper on the shaft that makes it impossible to hit the piston, also the power valve cannot physically go past the stops on either side of the power valve groove . Any damage is usually caused by piston material hitting it on the way out the exhaust port .

Negative Ghostrider.....I've seen it many times. That 'stopper', or shoulder on the valve, will in fact wear down and allow the rings to start taking bites out of the valve.