18hp.Vanguard, burned valve?

RustyBucket

I am installing a rev kit in my Vanguard and was using air pressure to hold the valves open while I had the springs & retainers off. I did the front cylinder--- yeah the keepers were a pain--- and it was fine. I put air pressure on the rear cylinder and air was blowing out of the carb. Has to be an intake valve problem, right? I don't have any vanguard experience. Would this be a burned valve or do the seats come loose sometimes. The engine runs good, makes lots of power and doesn't use any oil. I HATE to have to take it apart.......OH YEAH, I took the cover off of the Comet clutch and I think it was stuck closed a little bit on some dirt but seems to be ok now. Thanks!

BGW

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rib33024

Sounds like You need to turn the motor a little to colse the valves, sounds like the cam is holding one valve open

morepower

Agreed! If you had a valve burnt it would run like crap. Intake valve was still open causing the hissssss.

wrenflyer

Could be a small piece of debris holding the valve open. With air on it and the spring still on, pop it with a hammer to crack it open quickly and see if it seals off then.

RustyBucket

...the rocker arms, pushrods and valve springs are removed. I put some little tie wraps in the keeper groove on the valve stems to keep 'em from falling in and took the air pressure off. I pulled the intake open and closed by the stem and twirled it around. Hooked the air back up and it's still blowin'.
BUT!! It just ran TOO GOOD to have much wrong with it. Starts, idles, good throttle response. I have a TinyTach on it and at about 3900rpm. the GPS said 23mph. with about 500lbs. of people on it. That's 350+ for me and 125 or so for my Daughter. I'll mess with it again this afternoon and probably pull the rear cyl. head off if I can't figure it out.

RustyBucket

tryin' to post a pic of my buggie......... couldn't figure out how to get rid of the night time shot of the house at Christmas time.... sorry

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Mark L

Was the engine hot when you did this? Any time you do a cylinder leakage test or a compression test the engine should be close to running temp. This makes things seal up a little better because of expansion. Just a thought.

RustyBucket

No Mark, it was cold. The front cylinder seals up good but the rear one's intake valve is leaking some. I'm gonna put it back together...... don't have time to pull it all to pieces right now. thanks, Howard

RustyBucket

I'm not sure my Comet clutch problem is cured but the engine ran so badly that I took it out of the cart this evening. It wouldn't idle and kept backfiring through the carb. I pulled the rear cyl. head off and scrubbed the combustion chamber clean with brake cleaner and a little brass brush. There's a crack between that runs between the intake and exhaust valve seats. I stood the head on it's side and poured mineral spirits in the intake port and it dribbled out through the crack. I did a search on this site and apparently it's not a common problem on Vanguards. Are the heads on the vertical shaft engines the same as mine? Lots more vert. shaft's than horiz. 'round here. Wonder why mine did this.. lucky me. Is there a better deal on a gasket kit than getting HOZED by the lawnmower shop? At least I know why air blew through the carb. while I was putting the rev kit in and why it ran so crappy. Tom at CPP offered to look at the clutch if I'd send it back to him. Think I will while the engine's apart.