Date:         Wed, 15 Sep 1999 13:04:24 +1000
Reply-To:     Dom <dmoon@METZ.UNE.EDU.AU>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dom <dmoon@METZ.UNE.EDU.AU>
Subject:      Re: Align-boring?
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----- Original Message -----
From: <JKrevnov@aol.com>
To: <dmoon@metz.une.edu.au>; <vanagon@gerry.vanagon.com>
Sent: Wednesday, September 15, 1999 11:53 PM
Subject: Re: Align-boring?



>dmoon:
>Thanks for your reply.  I have had a variety of experiences with field
>machining and cannot fault the results of the most unlikely rigs when set
up
>by a true master.  I had a friend (God rest your soul, Tom) who would
>routinely rebore 10-ft diameter steam cylinders in place(obviously).  And I
>certainly don't doubt the capabilities of any prime mover, especially if
its
>a 1" Ingersoll-Rand air drill backed up by a deadman.  Whereas, the only VW
>case prep I have seen was featured in a VW rag and according to the text
and
>photos the operator simply used the existing bore to pilot his cutting
tool.
>While I agree, the C/L of the opened-up holes probably coincided, I saw
>nothing done to assure perpendicularity to the cylinders.  What is done to
>provide for this important geometric relationship?
>Richard


I sure hope some listee's who do this for a living chime in on this one. I
cannot myself understand how one can effectively ensure anything at all
using the technique you saw in the VW rag. An example directlty related to
this I can cite is Stan Pobjoy. He is a rebuilder over here and perfected
his art as an apprentice building up engines based on VW 1600's for
aircraft. He explained the process of setting up his self designed rig as
basically many gruelling hours of measuring, adjusting, measuring etc.
getting it so that when he SECURED his case into the jig it would bore to
his required tolerance. I remember him specifically citing perpendicularity
as his primary concern . He builds primarily race engines taking 1600cc out
to 1916cc and has won both state and national hillclimb titles (AUS). For
him I would say by taking the capacity out so far, fine tolerance is big
bucks if he gets it wrong. For a standard engine, a bore which is not
straight still means the pistons are driven at an angle resulting in
immediate power loss and abnormal wear . As well, oil can leak excessively
from the main bearings which may result in lost pressure. The C/L of the
opened up holes probably do coincide but what is equally important is that
this allignment as a whole is in line with the centerline of the case. If it
isn't, you get the perpendicularity problem. If you want a quality rebuild
which will reward you in longevity I would have this done correctly.

Dominic :)