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Enduro Engine - 2 stroke Cylinder, Piston, Tranny, Bearings, Clutch, Pipes & Silencers, etc.


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Old 04-22-2009, 06:16 AM
gasgasandrew gasgasandrew is offline
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Default power valve rattle not chain slap

HI have read many members with 2 stroke gasgas bikes with a rattle that seems to come and go my 07 ec250 does this on open trails [ ITS NOT CHAIN SLAP] what i have fould is there seems to be a lot of clearance in the power valve and at steedy speed the center flap slapes from side to side at just the right revs may be pulse in pipe what I would like to no is this a problem or do i just leave it alone as its very hard to get it to do it it just happens now and then at these revs or can i space the outer bearings to close up this clearance as i can close it up by pushing in the left hand bearing under ther power cover any help would be great
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Old 04-22-2009, 08:40 AM
FFRDave FFRDave is offline
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Default No help here, but Misery does love company

I thought it was chain-slap too, and I have been told such in the past. A new chainguide and sliders and a lot of checking the chains' range of motion has pretty much taken the chain-slap theory and tossed it out the window.

You are absolutely right, it just seems to happen at times. For me, it is mostly at high RPM while hauling a$$ across a big sand dune. It just sounds like a rattle in the motor.

I have been able to reduce this noise by putting enough of a bend in the actuater arm to apply a little bit of pre-load, so that at WOT the flapper is pushed more firmly against the stop. It seems like there was enough slop in the powervalve that it could kind of flap (or vibrate) like a reed on a saxiphone. I never thought about side to side motion though.
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Old 04-22-2009, 05:36 PM
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2 strokes 4 life 2 strokes 4 life is offline
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I only ever seem to get this slap or fluttering at low speed in the bottom end or realy lugging the bike.
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Old 04-23-2009, 05:52 AM
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wence wence is offline
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same with me
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Old 04-24-2009, 04:06 AM
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Quote:
Originally Posted by 2 strokes 4 life View Post
I only ever seem to get this slap or fluttering at low speed in the bottom end or realy lugging the bike.
Ditto, I have that at low speed.
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Old 04-24-2009, 06:23 AM
rpduc rpduc is offline
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Quote:
steedy speed the center flap slapes from side to side
Are you confident this is causing your rattle? I have this same sloppy endplay situation but I can't quite envision how it could cause a consistent rattle. There was a washer (#39 on the parts diagram from my '05) missing when I disassembled the PV. I guess that's happened more than once. I ordered the washer from GF but it came wrong. 6mm i.d. instead of required 8mm. The part # size correlation is wrong at Gofasters. Mark was going to check on it so remind him if you order one. The bike ran fine all last summer and I assume also for the P.O. so I reassembled without the washer but now you have me thinking I need to find a washer... the parts list says 8mm x 16mm x 1.5mm
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Old 04-24-2009, 07:48 AM
gasgasandrew gasgasandrew is offline
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Hi pull off the pipe and covers and rock the flap side ways and what you will get is the same noise that you get when it happens when running at the right revs .the noise is not consistent its randome right revs right load sounds like a ball bearing rattling in the camber never happens in single trails or full power only light load on open trails and is very hard to get it to do it and only last for split second and then stops until the next time revs and load are right mostly at steady speed . there seems to be to much clearence we need gasgas to put closure to this as a lot of 06 07 ec are making this noise if its not a problem ok but what damage will it do in the end
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