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Main Bearing caps - Not an exchangable item !!!
Posted: Thu Feb 21, 2002 1:45 am
by C Sherriff
Message text written by "Jim Buell"
>My first message may not have gone out, so this may be a repeat - sorry.
I am in need of a set of main bearing caps for an XPAG (TC) block. If you
have a set you are willing to part with please contact me off list. Thanks
Jim Buell
Re: Main Bearing caps - Not an exchangable item !!!
Posted: Thu Feb 21, 2002 3:30 am
by Badger
> I am in need of a set of main bearing caps for an XPAG (TC) block. > Jim
Buell > ============================================
Jim,
Mixing and matching bearing caps and blocks is not only unfashionable and in
poor taste, it is also inadvisable from an engineering standpoint and is
fraught with serious pitfalls which are nonetheless, overcomeable
(overcomeable?) via various methods, assuming you want the crankshaft to
actually turn once bolted into place. One method is the use of a rubber
crankshaft or alternatively, you could use the original steel crank but with
the main journals turned to an undersize to allow approximately 1/8 to 1/4
inch clearance between the crankshaft main journal surfaces and the inner
bearing shell surfaces. While both the aforementioned methods will
successfully allow the crankshaft to turn in the block, they may introduce
other problems farther down the "road". A more successful approach would
probably be to have a competent machinist fit your "rogue" caps and then
"line bore" the block and caps as a single unit however, it should be noted
that, as there have always seemed to be many more capless blocks than
blockless caps on the open market, it may be preferable to start with the
caps and then locate a suitable block to fit on top of them rather than the
other way around as you are attempting to do.
I trust the forgoing will be of some assistance.
Re: Main Bearing caps - Not an exchangable item !!!
Posted: Thu Feb 21, 2002 6:45 am
by Robert Grunau
Clive is sort of correct, the caps are not readily interchangeable. Badger
is his useful self suggesting finding blocks to fit caps etc.
The real truth is bastard caps can be made to work fairly easily on an XPAG
block. First step is to fit the caps to the block and check the step in the
crankshaft bore between block and cap. Measure or estimate the bore step and
note which side it is on, then move the cap sideways to reduce/eliminate the
step. Aim for no step between the cap and the block. This will require
grinding/milling material off one side of the cap edge where it sits into
the block recess. When you get the bores fairly close with minimal or no
step, add a sheet metal shim to the cap edge on the opposite side so the
cap is again located securely in the block recess. Braze the sheet metal
shim to the side of the cap. Or, use a small set screw or pin to hold the
shim in place. You may possibly have to elongate/enlarge the main bearing
stud holes in the cap to allow it to slide across to match the bearing bore.
The "new" cap is now located sideways by the block recess and fits tightly
into the recess. Now take the block to a good machine shop and get the final
line boring done removing minimal material from the block. Moving the cap
sideways greatly reduces the final line bore amount. Using this method can
save a rare T type block.
Another option is to mess about with only the rear cap which has the oil
return lip and cork seal recess. Hard to replicate this cap. Get the rear
cap to match the block. Then make new steel front and center main caps as a
new pair with undersized bore. Fit all caps to the block and get the block
line bored removing minimal material from the block. Install bearing pins in
the new caps as required. Remember to relieve the center main cap outer
edges to allow the trust bearing flange to clear. Match mark the caps to the
block so they can be reinstalled in the same orientation the next time you
or the next custodian takes the engine apart.
It works, Frank Mount and I are running/building TC race engines using
blocks with bastard caps. I would surely rather have a TC with a bastard set
of caps on a TC block than a replacement TD/TF engine. It just makes it
right.
Bob Grunau
I am in need of a set of main bearing caps for an XPAG (TC) block. If you
have a set you are willing to part with please contact me off list. Thanks
Jim Buellhttp://www.grisoft.com).
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Re: Main Bearing caps - Not an exchangable item !!!
Posted: Thu Feb 21, 2002 12:37 pm
by C Sherriff
Message text written by INTERNET:
cgrunau@pathcom.com
>Clive is sort of correct, the caps are not readily interchangeable. Badger
is his useful self suggesting finding blocks to fit caps etc.
The real truth is bastard caps can be made to work fairly easily on an XPAG
block.
Some of these caps are way off when you put thim in another
block - proceed with great caution if you are playing this
dangerous game!! !
Clive