Subject: automotive engine boring on a mill
From: (Leigh Knudson)
Date: 06/12/04 02:47 GMT Standard Time
Message-id:

When I was a kid I bored both single cylinder Briggs & Stratton and
four cylinder Crosleys on my Dad's 11" South Bend. It was quite an
exercise as the boring bar he had was simply a big stout boring bar
with not calibrations. You adjusted the bar by loosening the tool and
tapping it gently then made a test cut. Usually took a couple of
evenings to do a Crosley to +/-.0005. I have some Crosley engines to
do right now and you can bet I will be doing them on a Bridgeport type
mill. They don't work well with the standard automotive boring bars as
they have nondetachable heads and you have to have a rigid downstop.
BTW: To the fellow that suggested you use a boring bar sysem that
locates on the top deck of the engine, NO WAY! Good boring machines
locate on the crankshaft centerline.

I'm not aware of any normal boring machine that locates on a crank centreline.
Either the block stands on its sump face on the machine table or the machine
bolts to the top of the block. V engines can sometimes be tricky to jig up if
there is no readily available flat face to mount on so they can need a jig that
bolts into the crank saddles. That isn't a function of the boring machine
though. It's a function of the jig that bolts to the machine table that is
hopefully true to the boring head.

Provided either of those faces is as true to the crank centreline as needed
then both methods work fine. I always put a light skim on the head gasket face
before using my bolt-on boring machine to make sure the head face is true.
There's no guarantee that a sump face will be true either though.

However it's a crock of **** to think that tiny errors in the bore's
perpendicularity or centrality to the crank make any real difference to an
engine's power output. In fact if the error in the original bore was very big
you'd never be able to correct it anyway without going to a very large overbore
size.
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)