Quits after it gets hot????

[ttw_walman]

I'm coming to wits end here. I have a 79 kitty that quits after 10 -20 minutes of riding. Last year I regeared, bypassed the governor (70 jet no needle change) put on the deep snow kit and small "paddles" on the track. It quit at the end of the season. Turned out that the crank seal under the timing popped out. I replaced the seal but not the one on the gearbox side because I couldn't easily get the gearbox apart. I figured since that seal was constantly bathed in oil it was probrably in better shape than the other. While I was in there I put one of Blasters electronic ignition conversion kits in.
This year the thing runs stronger than ever, for a 10-20 minutes then loses power and eventually dies. I have around 110#s of compression while cold and about 90#s when hot. Is this normal? Since my compression seems good I didn't want to pull the cylinder apart to check it's condition. After it dies I still have good spark. I've had the carb apart several times and don't think it's a fuel problem. It seems more like a heat problem.

Any suggestions would be deeply appreciatted.

Thanks
Walman

[t-dub13]

That sounds kinda low for compression, but these motors might just be designed for really low compression on purpose. Normally, I like to see 130-160#'s or close on other 2 strokes. Might be time for a poor man's rebuild (hone and rings). I think that it loses compression when hot gives it away as being worn out.

Maybe someone will chime in and tell us what stock compression numbers look like...? I'd be interested too.

[kidsperformance]

110 psi is good cold....90 hot that is a lil low...sound like the ring gap has opened up a lil bit and some hot gases are by-passing down into the crankcase heating up the incoming charge and evaporating some of the fuel causing a slow leaning action with a change too the bore of the cyl is oval shaped.....piston top get hot and it over heats...shuts down.............or..........what fuel are you running(87 or 89 or 93?)....what does the plug look like?? If that new ign is stronger than ever you may need to go to a 1 step colder plug....check the timing. there's a rubber insert on the fan shroud and flash a timing light in there...make sure the pointer is in the area of the three marks on the flywheel and make sure it doesn't wander all over the place when you rev it a lil...If the seals blew out I would likely believe my 1st thought....with the hot gases gettin into the crankcase softens the seals.....you need to get the gear reduction apart also....when you push the seals back in put some RTV silicone around the edges.....helps hold them in..........hope this helps

[t-dub13]

It sounds like if the PTO seal is bad, you'll be smokin' something terrible!!! I don't know what's in the gearbox, but it aint no factory Autolube!!!

I'm still leaning towards a ring-job...(did I say that out loud)???

[ttw_walman]

Ok
I just ordered a piston and rings. I never had one of these apart. Can I re-use the head gasket? My Yamaha shop told me they always re-use on the bigger sleds. He said they spray both sides with that copper spray, let it sit a few minutes and slap it together. thats what I plan on doing unless somebody can give me a good reason not to. I'll get the cylinder honed and flat lap the head a little. I'll let you know how things work out.

I kind of figured I'd finally have to go into the jug but had to try everything else first


Walman

[kidsperformance]

Make sure they check for how out-of-round it is.....clearance should be .002.... .006 max If a cyl is really out of round it will never clean up right. and will have the same problem in a short period of time again.....If it just a yard kitty and you never intend to race it there is a .5mm oversize piston for that motor.....Just have(Suzuki Dealer) the guy look up a piston for a TS 50 bike which were built back in the early 70's I hate to see people spend $$ and the problem comes back