cam bearings

[jadney@vwtype3.org (Melissa & Jim)]

>From: Carlson Bryan J <bjc159s@nic.smsu.edu>

>Remember me?  I'm the one with the cam that locks up upon tightening down 
>the case.  I finally got a hold of a set of calipers.  Here is what I found:
>
>                 New           Old            New          Old
>                  (w/ bearings OD)            (w/o bearings OD)
>Front         1.082"         1.080"           .983"       .983"
>
>Middle        1.082"         1.078"           .983"       .983"
>
>Back          1.082"         1.079"           .983"       .983"
>  (Thrust)
>
>
>Could these few thousands of an inch be my problem, or can this be 
>attributed to wear?  I don't know how many miles this engine had on it, 
>nor do I know what condition it was in prior to blowing (the #2 piston 
>began to desintegrate--it was a basket case engine:  three different 
>brands/types of pistons!).  

I put a set of new cam bearings on a cam here and did my own measurements.  
I come up with 1.082-1.083 down the line, so I don't see any problem with 
your numbers.

Let me suggest some things you could try:  Check the six bearing support 
webs for any sharp burrs that might keep the shells from seating properly.  
Likewise check the thrust surfaces of the cam for burrs that might cause it 
to bind.  Either kind of burr can be removed; use a file or a machinists 
stone (like a whetstone.)  When you install the bearing shells, put each one 
in its place and push down on the two exposed edges to make sure that they 
are fully seated before you bolt the case together.  The exposed edges 
should push down flush, or almost flush with the case mating plane.

Check that the cam will then turn smoothly when lying in either case half.  
Dry each bearing shell face off and color it in completely with a magic 
marker that is non oil soluble.  Then oil everything lightly, assemble and 
turn gently as you tighten up the bolts.  If the interference is still there 
turn a bit and then disassemble and look for the place where the magic 
marker is rubbed off.

If your case had a piston come apart, there is some chance that a piece of 
something got jammed between a moving part of the engine and part of the 
case near the cam bearing web.  This should be obvious due to the large scar 
it would have left.  If this is only slightly distorted you may be able to 
fix it by scraping the offending area down a few thousands of an inch, but 
you should be concerned about other possible areas where the bearing(s) are 
not correctly supported.  If any bearing is not fully supported it cannot do 
its job, and if oil can leak out from behind it your oil pressure will be 
low and you will be unhappy.

I hope this is not your problem, but if it is, it can probably still be 
fixed.  Has it been align bored?  If not, send it to RIMCO; have them bore 
both the crank and cam tunnels and add case savers.  Be sure to tell them 
what size your crank will be, because they supply bearings with the job.

Keep the info coming.

Jim
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       Melissa Kepner                                    Jim Adney
       jadney@vwtype3.org              jadney@vwtype3.org
                             Laura Kepner-Adney
                             Madison, Wisconsin
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