[mcavvie]

I have never been able to get the st12 I bought a few months ago to start. The problem is it won't turn over fast enough, like the decompression is working. Well, I took the valve cover off and checked the clearances, the exhaust valve is 0.025", supposed to be 0.020". I checked to see if the compression release is working, which it is, but won't open the valve enough.
Correct me if I am wrong, but to get the right clearance, I am thinking I need to grind the valve and seat. Is this so?

 

[mmccarty]

I doubt .005" valve lift is going to make much of a difference.

What's the history of this engine? Has somebody had it apart? Is the valve timing correct? One tooth out on the valve timing will make it a bear to crank.

When you say it's slow to crank, do you mean by electric start? Does it feel right if you try to rope start it?

 

[mcavvie]

I have no idea about the engine history. I see the lifter coming up to open the valve, it opens the valve a bit, but not enough to release the compression.

 

[Tractor-Holic]

Most small engines dont have adjustible tappets,so yeah,grinding the valve is about the only way to reduce the clearance..but I'd bet the wear is on the camshaft lobe(s) or the base of the lifter,not so much the valve stem..the automatic compression release on the cam opens the exhaust valve only a few thousandths ,so any excess cleaeance will defeat it...

My Suburbans with HH120's spin over quite slow,having starter/generators,but they always fire up,even if they turn so slow you'd think they never would..but I need a good battery thats fully charged to get them going,especially if its cold and the oil is thick..
I dont plan on checking my valve clearances,I am pretty sure they are a bit on the loose side,judging by the clickity clicking they make--after 40+ years I'd expect some wear on the cam,lifters,etc...as long as they start up and run,my motto is "if it aint broke--dont fix it!"..

 

[mcavvie]

Yes, i figure the tappet and/or cam is wore, but just want to be able to start it for now. Planning on using it for my winter backup in case the 19.9 breaks down. I even had my spare starter/genereator hooked to the truck, still wouldn't spin it enough to start. Guess off comes the head.

 

[Tractor-Holic]

Might have a lot of carbon build up on the piston,that can raise the compression enough to make it crank over harder...but its more likely too much valve clearance..getting it back to spec will help ,too bad they aren't adjustable like an OHV Tecumseh,it is a lot of work grinding a valve in a flathead..

 

[mmccarty]

Perhaps you could try shimming the gap with a feeler gauge while starting it to see if taking up the excess clearance actually helps it to crank faster?

 

[mcavvie]

Re: hh120 valve adjust - UPDATE!

Got the st12 going last night. Was playing around with it and spraying carb cleaner in the carb to see if I could at least get a kick out of it, when all os a sudden , it stated to turn over like it should. Still wouldn't kick tho. Pulled gas line of, no gas, couldn't even blow back to the tank. The PO said he had it running to load it onto his trailer to take it to the flea market. I am a little skeptical on that now, the gas in the tank was old, water in the tank and the carb. The fuel pump had water in it and was rusted. Took carb apart, cleaned as best I could and noticed someone lost the springs for the float and float needle valve. Took fuel pump apart and ended up using most of a pump that came off a bolens g10. Anyway, put every thing together, installed on tractor, a couple of shots of gas in the plug hole, and away she went. It will only run on full choke, but at least I know it will run! Now just to see if I can scare up a new carb. Anyone got a spare LME 34 you want to get rid of?

 

[Dude11]

Re: hh120 valve adjust - UPDATE!

It will only run on full choke, but at least I know it will run! Now just to see if I can scare up a new carb. Anyone got a spare LME 34 you want to get rid of?

Unless you have untold wild luck--forget finding one.Get in touch with carbrescue,(he's a member here)--he can do the deed,quite well I might add.