Subject: automotive engine boring on a mill
From: Anthony
Date: 06/12/04 23:51 GMT Standard Time
Message-id:

(Dave Baker) wrote in
:


Provided enough material is honed out to remove all tooling marks it
matters not a jot what the quality of the original bore is like. It
can have 4 thou deep chatter marks as long as you hone out 8 thou on
diameter. Not that anyone with any sense would want to do that.




Sure...but what *quality* of bore do you have? What is the roundness and
straightness? Yes....it might work....but for how long? What kind of blowby
and ring wear are you going to see? A hone, to some extent, is going to
follow the bore that exists. This is true of most any finishing operation.
The quality of the previous operations will almost always influence the
quality of the finish operations, to some degree. It is a matter of to
what precision you wish to measure, and how accurate you wish the final
product to be.

The whole point of rigid stone honing is that it doesn't follow imperfections
in the original bore. The most it follows is the general direction of that
bore. A good honing machine removes all taper, ovality and lack of
straightness. Provided sufficient material is left in place to allow a perfect
cylinder to be created after the original boring operation it makes no
difference what quality that boring operation was done to.

As for measuring equipment, my own bore gauge is a Mercer dial bore gauge
reading to 0.0001". Most commercial engine reconditioning operations use 0.001"
gauges which are adequate for the general -0/+0.001" tolerance on piston
fitment. My work needs to be infinitely more precise, and is!

I have two honing systems. A Snap-On 5" stone system which is best for
achieving perfect bore straightness because the stones are longer and a
Delapena 4" stone system which is better for removing taper from the bottom of
bores where the crank saddles prevent you "through honing" as far as you would
ideally like. Choice of stone grit and speed and feed then lead to the perfect
surface finish and cross hatch angle.

I have to conclude that if you think that honing can't create a perfect bore
regardless of imperfections in the boring operation then this isn't an area of
machining that you have actually been involved in. In fact I'll ask. Have you
ever actually used a professional rigid stone engine cylinder honing system?
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)