Mike,
Yes! I went through that in the last month. It's necessary to replace the
jackshaft bearings because the hot-tanking will destroy the old ones.
Order/buy all the components up front before the rebuild, so you won't get
delayed during the rebuild. (Some parts are getting hard to get.)
My U20 motor was really gunked up not only because it was dirty to begin
with, but it sat for over 20 years in my garage. But that isn't the only
reason to hot-tank it. That will clean out a lot of rust crud in the water
jackets, as well as contaminants elsewhere. The caustic solution will
destroy the pressed-in jackshaft bearings. Another thing I found out, is
you need to hone the cylinder walls before installing those new piston
rings. Do not re-use old rings. I found out after I hot-tanked, so I had to
do extra work to clean the sanding particles from doing the honing.
Have a machine shop press in the new jackshaft bearings. Also have them
polish up the crankshaft journals, and do any required head valve work. One
thing to watch out for - don't force the jackshaft into place. One of my
jackshaft bearings was a tight fit, and I had to polish it in the
interference areas to get it within proper clearance. The machinist assured
me this was okay as long as you don't take off too much material.
Here's another tip I got. Use an old radiator for the first 200 miles. Then
install a recored radiator. Leftover gunk from the rebuild will clog part
of the radiator. Might as well clog it before a recore, and not clog a
newly recored radiator! Fortunately, I have both old and recored radiators
on hand, but you may not.
Fred - So.SF, Calif.
BADROC
>
>I haven't heard anyone mention when to replace the jackshaft
>bearings. I'm rebuilding the motor now and need to know if its
>necessary.
>
>Mike
>Hayden Lake, Idaho
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