Date: Sun, 12 Nov 2006 23:09:50 -0500
Reply-To: ROBERT DONALDS <donalds1@VERIZON.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: ROBERT DONALDS <donalds1@VERIZON.NET>
Subject: Boston Bobs type 2-4 engine comments was <no subject>
Content-type: text/plain; format=flowed; charset=iso-8859-1; reply-type=original
the air-cooled type 2 engine has more issues than being a flat 4 engine. I
have never seen egg shape wear in any cylinder I meausred honed or rehoned
after use. The cylinder has a taper widest at the top of the ring travel and
almost no wear below the ring travel. The air-cooled engine unlike the water
cooled WBX engine sees higher temps and shorter engine life. The ability of
this engine to maintain a reasonable head and oil temps is key to the life
and wear of the internal parts. I would never reuse a set of air-cooled
pistons due to the top ring grove wear this increases oil consumption and
blowby. my rebuilt engines have new piston and cylinder sets that I have
rehoned the cylinders to increase the skirt clearance as advised in a VW
tech bulletin in May of 1990. I have also gotten to the point I use new AMC
heads that I have reworked to eliminate the shortcomings of the valves stem.
I also recommend using an aditional external oil cooler to prevent the oil
from reaching 225 F. The 225 F. oil temp is the saturation point of oil and
when this happens head temperatures spike if the increase in load continues
as in a hill climb.
The type 2-4 block in my opinion needs to be align bored if it been in a bus
or van and has had the usual hours and miles. The cams need regrinding or
replacing and the crank needs to be ground and is often bent to the point of
binding in the block if reused as is. I am also hand fitting the center main
bearing to allow the freshly align bored case to touch as the new bearings
will hold the cases apart. Not only do they hold the case apart but when
measured the center main bearing ID can be out of round as much as .005ths
this is due to the bearing being to long. When filed at the mating surfaces
enough to provide some crush and allow the case to touch it needs to be
remeasured. Now the main bearing to crank clearance can be as little as
.0005ths and at this point is now also round. It is then that I have the
crank ground to reflect the size of the bearings that have been fitted to
the case and have the proper oil clearance .
To my skeptics just bolt a center main bearing into a case and shine a flash
light at the case seam before you reach for the keyborad to respond to my
comments.
I have said it before and I will say it again there is a big differance
between reassmbling an engine and rebuilding an engine
rebuilding requires restoring the clearances and to do that you need to be
able to measure them
I remain
Bob Donalds
Boston Engine Exchange
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