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  1. #1

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    Unhappy R&D Powervalves all started to rub and touch pistons and rings (no piston scuff) WHY?

    R and D valves do not need wave eater clips, right? After re-reading the R and D catalog, it says that you never have to worry about these powervalves coming loose or hitting pistons like stock ones did.

    I have a 2000 GRR with D-Plate, stock carb choke plates and accelerator pump removed, 41CC Riva 92 octane or above heads, Riva water cooling block, exhaust water valve, Stock 80mm Pro X (A) pistons and rings, Millinium rechromed jugs, Full stage 2 Riva, R&D ignition/powervalves (2002 model year valves)/power plenum intake, I pre mix Amsoil Dominator at 40/1, and dynafly pump and impellor.

    I have rebuilt this engine 3 times and have finally figured out to make sure that number 3, back jug and piston get extra fuel due to that cylinder getting less water than other 2 jugs. I just took off my heads after 2 years of regular duty riding (no racing) and found that the R&D billet powervalves came into contact with the piston and rings. #3 powervalve completely broke off at the stem and has seem to dissappear (not in exhaust or water box that I can see or find). # 1 and 2 powervalve barely touched piston just enough to slightly ding up jug and head area. I have called Bubba at Riva Yamaha, Dale at Dales Performance in TX and they say they have not seen this happen as best to their knowledge. It is possible the valve stops have worn down from 12 years of use or that when the valve got very hot (possibly from ethanol detonation) expanded enough to touch the piston? There was a nice "wash" pattern on the top of all 3 piston tops and none of the pistons overheated enough to touch or scar the cylinder bores.

    If the pistons didn't expand far enough (even during a short overheat) to touch the cylinder walls, how did they touch the powervalve guilitine at all? I was told to make sure that the guilitine is at least .020 thousands clearance to piston and ring which I thought I did 2 years ago. Just wondering if anyone out there has seen this before and what should I do to prevent it on this rebuild? Dale suggested that there is so much bad fuel out there that ethanol could have lowered the premium fuel octane due to water separation/absorption and maybe detonation was happening even though I didn't hear or see it on the tops of any of the pistons (I had a seize up in the past where part of the piston head was destroyed by detonation but I believe I have that problem resolved due all 3 pistons look great without any scuffing of cylinders except of course near where the powervalve scrapped near the exhaust side. Any help would be greatly appreciated! Do these valves wear out due to being bombarded by even slight detonation or from years past of more severe detonation? Hope to hear any plausible theories or ideas before rebuild, Thanks, Steve.
    Last edited by scoobie6916; 09-08-2012 at 04:29 PM.


  2. #2
    Almost's Avatar
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    Paragraphs? That's very hard to read, you might want to try breaking it up for better responses.

  3. #3

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    Sorry, about not breaking up the sentences.

  4. #4
    Almost's Avatar
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    All is good, I hate to be the grammar nazi. I'm sure some one will chime in soon.

  5. #5
    how many hours on the PVs? i think they (updated style) have a good service life of 75 to 100 hours,,,after that i think they are on borrowed time.

  6. #6
    mudslanger's Avatar
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    Possible cause could be the power valve cables out of adjustment causing the power valves to close too much. and over time and wear on the stops the valves push into the side of the piston. the stroke force on the valve is enough to break the stem and if your lucky enough for it to go into the exhaust wile it is breaking up. on the down stroke it can go out the exhaust if the water box doesn't catch it. but with my luck it usually destroys the cylinder and piston. i have worked on skis were something similar happened without getting the cylinder but ruined the piston and the power valve was missing and the pin came out of the stem.

  7. #7

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    R and D Power valves probably have 500+ hours on them after riding 10+ seasons and at least 3 top end rebuilds due to number 3 cylinder always having issues with heat due to less cooling water the way the Riva cooling block is set up. I will either try to find the gas valves at a discount or buy 3 new R and D valves. Any one who knows who has a set of used Gas Powervalves, let me know, thanks, Steven Jones.

  8. #8
    caliburn's Avatar
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    I am trying to learn every thing I can and have a question for you on this detonation, what exactly is detonation and so you can even hear it on the water running? and also about the power valves, I cleaned mine up a bit, and you stated the cables can get out of alignment how to check this to make sure that they are or not? I noticed that after cleaning mine and running it seemed to be dragging/lagging befor they kick in,befor put the covers the covers on I sprayed some fogging oil in each valve to help lube them up, hope I did not do something wrong. thanks for any imput.

  9. #9
    pokplalya22's Avatar
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    Has anyone else have had this problem with the R&D valves? I have a set waiting to be put on, and now thinking twice. Do the cables need adjusting when switching over? Should I be concerned?

  10. #10
    mudslanger's Avatar
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    The cables usually don't get out of adjustment they are usually installed and adjusted wrong by someone working on the ski.

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