The machinist says it's okay to buff the jackshaft bearings, not as
critical as the crankshaft. Used a dremel tool to take down the high spots.
Then used a roll of electrical tape, removing tape until the diameter
matched the inner diameter of the bearing. Wrapped a piece of crocus cloth
around the roll, and rotated it until it until the bearing was smoothly
polished. The jackshaft rotates cleanly without binding.
Also a problem with the crankshaft thrust bearing. The mains were taken
down ten-thousandths. The new undersize bearings had the proper clearance,
but the thrust bearings were too wide to fit the saddle. The machinist told
me what to do. Using a sheet of glass as a flat surface, I set a sheet of
240 grit sandpaper on it. Set the thrust bearings together and sanded them
down, applying even pressure on the sandpaper over the glass. Every so
often measured the thickness with a caliper to be sure it was even all
around, and did both sides. I then went with 600 grit, and finished with
1500 grit. I did this until the thrust clearance was proper. The book says
between 2 and 7 thousandths, although the machinist says he does it 6 to 8
thousandths.
Reminds me of my computer work. I listened to older guys with unorthodox
methods, but they worked. In the old days, as a programmer sometimes I
would mount my own reel tapes if the operators were busy. Often the tape
headers would go bad, and the drives rejected the tapes. Costly to make new
tapes. One old guy showed me how to slap spit on the tape guides, and the
tape would work! Not in the book. I miss those days, as all our cartridge
tapes are now mounted by robots. Point is, a lot of answers are not in the
shop manuals!
Fred - So.SF
----------
> From: Toby B <toby@wolfenet.com>
> To: a roadster list <datsun-roadsters@autox.team.net>
> Subject: Re: Engine bearings
> Date: Thursday, June 17, 1999 10:07 AM
>
> The short answer with modern bearings is
> yes, it's bad to scrape them. They have a limited amount of 'bearing'
> material, with a harder base underneath that. They're designed to
> provide a pretty specific oil-flow pattern and rate...
> Of course, the camshaft/jackshaft bearings don't take as much of a
> beating, and aren't as hi-tech as crank and rod bearings. But I'd worry
> that the bearing surfaces might not be in alignment (now OR before, if
> it bound) which would add quite a bit of stress to the jackshaft. Let
> us know what the machinist says...
> Toby
>
> Fred_Katz@ci.sf.ca.us wrote:
> >
> > Is it okay to buff rough spots on engine bearings?
> Either the bearing is not
> > standard size, or the press-fit wasn't done right by the machine shop.
> >
> > I polished out the scrape, and now the jackshaft goes in all the way.
Does
> > anyone know what the bearing clearances are supposed to be for the
> > jackshaft?
> >
> > I'm going to the machinist for an opinion on the polished bearing. I'm
just
> > curious whether removing any surface material is bad for the bearing. A
> > long time ago a mechanic friend told me that he shimmed bearings on his
> > Chevy with aluminum foil without problems, so maybe bearings are pretty
> > rugged.
> >
> > Fred - So.SF
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