Posts
7
Joined
12/8/2022
Location
Highlands Ranch, CO, USA
Edited Date/Time
2/6/2023 6:04pm
My son lost power midway through his last moto yesterday and immediately pulled off the track. I removed the cylinder today and noticed large amounts of oil on the top side of the power valve diaphragm. The PV blade is stock but it loosened up at the threaded stem near bottom. Do you think fixing the PV is enough or is it likely the RH crank seal is leaking (oily diaphragm)?
The diaphragm, PV and stem, piston, ring and cylinder all look unharmed. Crank is nice and tight, too. Plan to replace the top end while it's off. Thanks!
Is exhaust spooge working it's way back through the hose from the expansion chamber? Check that hose and make sure it's clear and open and clamped well at both ends with no cracks anywhere.
Hose was tight at both ends and no cracks. Yes, some oil making its way back inside.
Replace w aftermarket valve or use red loctite to reassemble the valve
Our 2014 65 def ends up with "some" oil on top of the diaphram even after fresh rebuild, its not much but definitly not "dry". I think it comes both via exhaust port and non-perfect sealing around the shaft. Its never affected powervalve functionality, but I wipe it out every once in a while too.
The Nihalo PV is a quality piece of kit but I'm not sure its necessary versus just locktiting.
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Thanks VetStuff.
There was about a capful of gray viscous oil on top. I could easily cover two fingertips with it. The top of the piston and bore had only a trace of red 2T premix, otherwise "dry." Transmission oil is still golden, only a few hours old.
I'm wondering if when the the PV blade and its stem loosened, the blade couldn't fully lift past the exhaust port under load (~3/4 throttle), while vacuum from intake continued and sucked a crank seal, pulling oil up there. My kid said it bogged severely before losing all power and coming to a stop off the side. I'll have to take a deeper look under the engine side cover later this week.
If the valve doesn't open at high RPM it def will bog and usually foul the plug at the same time. Now that I think about it, a fellow moto-dad had an issue one that there was a fine tear in the rubber boot that was no obvious without close inspection that allowed blow by to the top of the valve under pressure. If you have it apart anyways, give that boot a little stretching with your fingers just to make sure its good before you reassemble.
You are referring to the diaphragm? I'll take a closer look at that, too. Makes sense.
The plug was black but not oily. Usually runs dark brown. I did start the bike up with one or two kicks immediately after with what felt like low compression but heard an intermittent rattle (the valve) so shut it down right away. Wasn't sure if he broke a piston or ring; all of that is good though.
Thank you!
Sorry - was typing faster than brain was thinking. Yes I mean the diaphram for a small tear, not the powervalve itself.
Post a reply to: KTM 65sx - oil on top of PV diaphragm