Engine questions

R

Rex_A_Lott

Well-known member
Normally I try to never drive this little truck in the rain, because a lot of it iis wooden, and home made, but the running gear is all stock.
Any way, as luck would have it, I recently got caught out in a thunderstorm, at night, to boot...no big deal, except the radiator sprung a big leak and it blew most the water out of it and it ran hot. Because of the rain, I drove it on home, because I didnt notice the water or the steam.
Just before I got home it took a bad skip, which I attributed to the rain. Wrong! After a little diagnosing the case, I decided it had a blown head gasket, because 1&2 were dead, even after cleaning all the plugs and switching them around. So I pulled the head.Wrong again.
Turns out, I had valves stuck open. Mild pressure with my thumb and they snapped shut, so the springs arent broken. So far, I havent pulled the valve cover yet, having a coffee and thinking. I suppose that is the next logical move. I dont know if it has the split guides or the one piece.
I'm thinking at the least I should pull all the valves and check for galling and check the springs. I dont have a spring checker, so I'd have to buy or borrow one...or should I just buy a new set and forget about checking the old ones?
Also I noticed the pistons are stamped STD. Was this normal? All the ones I've taken apart before were bored at least one oversize, and that's what was stamped on them.
My buddy did a lot of work to this little truck, but I didnt think he completely rebuilt the motor. I've heard of people sleeving one back to standard, but I would be real surprised if that's the case here.
This is not a fresh build, its been running for years, nor has it been sitting up, I drive it a good bit. I also try to run non-ethanol gas. Any guesses why the valves stick now? Its not consistently every time, but just rolling it over with the crank, they occasionally stick open, mostly on #2.
Thanks for any feedback.
 
With it running, just mist a little of your favorite "top oil" through the carb, if it runs O.K. then, just forget about it.
Bill W.
 
Have you put oil on the stems? Do it for all 8 valve stems, then roll it around with the starter or hand crank and see if any are still sticking. If none stick then you should be good to go. If they stick, then now is the time to remove the valves and clean them up or replace the guides and valves as needed.
 
My experiences have been with intake valves not seating because of carbon caking on the underside of the intake valve head, and on the upper part of the intake valve stem.

Causes of the carbon caking in my opinion have been:
> Excessive motor oil drawn up a worn intake valve guide / valve stem. This occurs on the intake stroke, and the motor oil cakes on the extremely hot parts of the intake valve in its valve chamber.
>Other contributors to motor oil caking are thin edge valve heads which causes them to run hotter than normal, a scored cylinder wall and oil leakage past the piston rings;
> Excessively rich fuel mixture due to air filters and improper use of the GAV;
> Oil base additives put into the gas tank.
 
I agree with oiling the stems. Just squirt some on the stems while the valve is up/open. No need to remove side cover if the sticking stops.
Look it over good while head is off to look for any cracks, they can be hard to see. A torch helps with any suspicious spots.
If all seems good, Button it up and drive it, see what happens.
 
BILL WILLIAMSON said:
With it running, just mist a little of your favorite "top oil" through the carb, if it runs O.K. then, just forget about it.
Bill W.
Click to expand...

Probably what I should have done first, but I didnt realize the valves were stuck until after I pulled the head off, so that was out.

Tom Wesenberg said:
Have you put oil on the stems? Do it for all 8 valve stems, then roll it around with the starter or hand crank and see if any are still sticking. If none stick then you should be good to go. If they stick, then now is the time to remove the valves and clean them up or replace the guides and valves as needed.
Click to expand...

The two worst ones had burrs on the valve stem, but I'm saying it was guide material, softer, not hard like the valve stems. A small honing stone took it right off, and I polished the stems with some fine sandpaper.
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I also used the fine sandpaper to take the galling out of the guides, was just left with some gouges in the upper part. A little lube and they slide free.
I figured since I was into it this far, I might as well hand lap the valves/seats.
Thanks to all who replied!
 
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If they are exhaust valves they probable pulled some metal and it built up on the stem from the extreme heat. You could take a chance on put some top oil in the gas. It may work, or you could take the valves out and check the stems and valve face and seat. It would cost a gasket and some time.

You should also check for cracks in the block at the valves from the heat.
 
you can test spring pressure by putting a bathroom scale in your drill-press table, put a spring on it and bring to installed height. reads in direct pressure.
 
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