Posted by David Sherman on June 10, 1998 at 22:33:43:
I have an army 5kW genset with a hercules ZXA series 4 cylinder
flathead motor in it. It doesn't have alot of hours on it but it
sat out in the rain for a long time. When I fired it up, some rust
got stuck in the exhaust valve, so to make a long story short I
pulled the rusty head which resulted in breaking and having to drill out
some of the studs. This resulted in a couple of the holes in the
block being extremely loose. Put back together it ran okay for a
couple hours and then started running horribly. I swapped magnetos
with another genset powered by a continental 4-cyl and I dissected
cleaned and tweaked the simple carburetor many times. I got new spark
plugs and wires. The compression is iffy and I'm wondering if A) A valve
is sticking or leaky or B) the head gasket is leaking due to the couple
of marginal studs.
So my questions are: Is it save to tap out the hole in the block for the next
bigger size stud (and drill a bigger hole in the head)? If so, how should
I torque the larger stud relative to the specs for the smaller ones?
If I pull the head again, do I have to get a new head gasket (not easy to
find) and can I grind the valves in place using one of those little suction-
cup-on-a-stick gadgets or do I have to remove the engine, crank, pistons, etc
and take the block to the machine shop? Remember, this is a 65 cu in flat-head
that I think is spec'd at 20 hp. It's not a racing machine. Also, any opinions
on using any type of gasket sealer (permatex copper-filled, etc) on a head
gasket?
I know this isn't an M37 question, but the motor's kind of a small version of
the one in my M37 so I thought maybe the same advice would apply.