May have found my problem...

[usmcdoc]

Duh! Found my problem?.... For those that remember I was having MASSIVE amounts of blow by from my vent tube.....to the point it was almost a Geiser ...and the crank would be bone dry after 3-4 miles. All to often we just just 'jump' into what we think is the problem without analyzing what happened. Well......That very day on the way to the store I noticed it was hard to start and lacked power(like when the valves need to be adjusted)....so when I got home I checked and did that since both valves were tight(could not even get a .00015 in feeler in them? Did the adjust and prob was still there. Returning from a 3 mile ride I noticed oil dripping from airbox and crank was empty! Refilled the engine with 750 mil of oil....removed vent tube from airbox and another 3-4 mile ride. Once home crank was empty and oil had blown all over the CVT cover!! Tried everything including using a check valve and an engine tear down and many other things advised by folks here(For which I thank you all! That is what this site is all about.....helping others!)
Yesterday I decided to remove valve cover to see how much was really spraying from the rocker arm cover. Cranked it over with cover off and plug wire pulled.... About 5 short cranks I saw the oil start to dribble from the rocker arm assembly. The ODD part was that I noticed a vapor.....air/fuel vapor hovering around and occasionally wafting from the intake valve area! Is this normal..or has anyone seen it?... Tells me it must be leaking..since the lash is set at .005in it should be fully seated....but not. Hence the difficult cold starts...and loss of power when warmed up. So I ruled out stem seals and piston rings since it burns no oil. Leading me to think a bent valve...or intake valve needs to be lapped. As I mentioned..on the stand at 6,000 rpm for 5 mins I saw very little oil.....HOWEVER.....while driving(where there is a load on the engine) The oil blew all 750 ml in 3 miles. MY best guess now is that the compression stroke blows by the intake valve seat....pressurizing the valve cover..and poof....the oil blow by. Odd part is that the engine still runs..albeit not as well.
Does anybody think an intake valve leak could cause the 'over pressure' problem?... It seems reasonable to me(but as I said..I am a retired military combat medic/paramedic...not an ASE mechanic)
Growing up on the farm I have lapped lawn mover and small engine valves....would this be any different in the procedure.
I totally appreciate all the help and input from ya'll here so far. I would just replace the head.....but being the rare and oddball "QMG GY6 100 engine....built on a 150 short case engine" No such luck finding one ANYWHERE!...

[90GTVert]

If compression blows by the intake valve when it's supposed to be closed, it would pressurize the intake tract and you should have fuel spraying out the inlet of the carb I'd think. It must pass by the valve seal or it can't pressurize anything but the intake path. If you plan to try the valve lapping, which is the same process as any other small engine basically, then I would replace the seal as well if you can find one. Like you said, a whole new head would be better, but we aren't sure what you can use on there.

[usmcdoc]

90....hm....possibly a valve stem leak would cause that as well?

[90GTVert]

It would have to be both if it were this. Like I said, otherwise it wouldn't be able to pressurize anything but the intake path. I'd think you'd see some sort of evidence of this on the valve or stem if it were leaking. If it leaks, it leaks all of the time so it should be getting hot in places it's not usually hot and there should be some sort of difference in color or something. I dunno for sure, I'd just think there'd have to be some evidence.

[Deleted]

Dec 19, 2011 9:55:29 GMT -5 usmcdoc said:

..possibly a valve stem leak would cause that as well?

highly unlikely. valve stem seals usually cause oil to seep into the combustion chamber while the engine is off then when cranked it will billow blue smoke.

i have asked this several times and from what i recall you were having trouble with your gauge but a compression test will clear up a lot of this guesswork. i bought one of these now that the threads on my old one are worn out:
www.ebay.com/itm/220867835051?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_2624wt_1037

[jmkjr72]

91b all the way
i was 91b and 19e
and what do you mean not a mechanic i spent so much dam time in the motor pool when i was in a fsb it wasnt even funny

[90GTVert]

I thought he said in the other thread 140psi. FFR : it's way easier to update one thread IMO. Keeps all the info around if someone wants to go back through it.