'69 Honda 350 engine rebuild problems

I got this bike a few years ago at a garage sale. Only about 500 miles on
it, but it had sat in a garage for over 30 years with a cross-threaded spark
plug socket open to the air, and missing a few parts.

I gobbed up a tap with grease and cleaned the plug threads, tuned it,
rebuilt the carbs, and it ran for a while (75 miles).

Oil started leaking from somewhere behind the cylinder fins, and I decided
to do a top-end rebuild.

The cylinder walls look pretty good, but as long as I had it apart, I wanted
to check the piston rings and skirts.

Well, the cylinders will NOT separate from the crankcase. I've put upward
pressure on the cylinders (kind of put them in traction from the basement
ceiling) and tapped with a plastic mallet. I've gently heated the bottoms
of the cylinders and tapped again - nothing.

I'm no mechanic, and thought someone might have a trick to obtain
separation.

Thanks for looking.

Rich

 

Try Aero Kroil.

 

Aluminum cylinders will corrode onto the long steel cylinder studs
which also rust. You can drip penetrating oil down the studs and
hopefully it will loosen the cylinders enough to pull them off. A
problem occurs when the cylinders move just 1/8th of an inch and stick
again. Push the cylinder back down and hope that the base gaskets keeps
the next dose of penetrating oil from going down into the crankcase,
carrying dirt and rust with it...

 

you really sure that you have all the bolts out, even the little hidden
ones?
check between the cylinders, at the parting line .
some engines tuck a wee one in.
good luck, sammmmm

 

Speaking of hammering on things, you can drip some penetrating oil down
around the cylinder studs and then use two nuts to double nut the
threaded end of the studs. Use a nut that you can afford to throw away
for the top nut...

Tighten the two nuts together so the top nut doesn't thread all the way
into the stud, leave one or more threads exposed...

*Lightly* tap on the top nut to set up vibration in each stud...

Then see if the cylinder doesn't move easily...

Another idea is to drip penetrating oil down around the studs and hold
a vibrating electric sander (without sandpaper, of course) against the
cylinder...