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Engine Rebuild Business

Subject: Engine Rebuild Business
From: (Allen Bachelder)
Date: Fri, 24 Feb 1995 15:42:39 -0500 Midget book says a 500-mile break-in with top speed of 45 mph
is called for in the case of a new Midget motor as well.  Of course, 45 mph in
a Midget is closer to 3000 RPM....  Funny the recommended max. speed is the
same for two differently-geared cars...


Michael Chaffee

Michael -
Now you're reminding me of the part I didn't discuss:  is that 45 mph limit
for  B's with, or without, overdrive?  In fact, the last engine I rebuilt
was in an overdrive car - so I did cruise it at 2500 rpm - which in
overdrive is more like 55-57 mph.  In fact, I ran a tad faster than that
for fear of lugging - more like 2700-2800 rpm.  Actually, I'd never load a
B engine at 45 mph in 4th gear OD.

Is it the rpm that is critical, or is it some combination of rpm plus the
amount of work the engine has to do?  The engine has got to be working
harder to move a car @ 57 mph in OD than to move it 45 mph out of OD, even
tho rpms might be about the same.  It should be hotter and parts expanded -
differentially yet - inducing different wear patterns.  So I have no idea
what the ideal should be.  Maybe Abingdon was just trying, rather
subjectively, to get us to "take it easy" on those new engines. A guideline
like that sorta keeps one from redlining it at every stoplight, anyway.

When I rebuilt my '76, I tweaked it just a bit - with 9:1 pistons,
Schneider cam and HS4s.  My son's '85 Plymouth Horizon, at 156,000 miles,
will still blow its doors off, but it is nevertheless a definite
improvement over a standard unmolested Z-S '76 B.  Naturally, I couldn't
resist the temptation to stick my foot way down the carbs every
once-in-awhile just to see what's there.  Definitely a violation of
break-in protocol, but at 16,000 miles I have yet to notice any ill
effects.  That's hardly enough, however - I'll have to report back in
another 80-90K.

BTW, a friend of mine says that if you've done something wrong in a
rebuild, it will usually show up in the first few hundred miles - so I
figure that after 1,000 miles the rebuild must be OK.

Allen Bachelder

 "I just know that if I take the trouble to remove the head from my current
rebuild, I will not find any more rice in it.  If I don't, I will!"

Allen H. Bachelder, Associate Professor of Trumpet
Department of Music, Virginia Tech, Blacksburg, VA 24061-0240
E-mail:, Phone: 703-231-6713,  Fax 703-231-5034

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