<VV> Looking for some advice on low compression

[Larry Forman]

Hi All,

I recently purchased a nice 65 Monza Vert PG at Hot August Nights car 
auction with about 80 K miles on the odometer.   It was claimed to have 
had a recent engine rebuilt about 5K miles ago (now about 7K miles).   I 
measured the cylinder compression and got the following readings:
cyl 1: 100 and w/ oil at 115          cyl 2: 120
cyl 3: 125                                      cyl 4: 90 and w/ oil at 95
cyl 5: 125                                      cyl 6: 125

As luck would have it, it just dropped an exhaust valve seat on #2, but 
fortunately the valve seat remained whole but wallowed out the valve 
seat mounting area and gouged the piston top.   I will smooth out the 
piston top so there are no sharp edges where it was gouged.

The cylinders show the cross hatching evidence of a recent rebuild.   I 
have not yet measured the cylinders on the driver's side for taper.  I 
have only removed the driver's side cylinder head and am not planning on 
removing the passenger side since the engine is still in the car.

I am not too impressed with whatever Reno area shop did the rebuild 
since they did not do ANY head deflashing, which likely contributed to 
the dropped valve seat.  That same shop also rebuilt the carbs and left 
out one power enrichment needle, which explains why I had trouble 
getting the carbs balanced until I redid the carbs and found that 
problem.   I have now done a proper head deflashing on both heads so 
hopefully once the engine is back together it should be more reliable.

I am now looking for a Sacramento area air cooled engine shop who can do 
a proper valve seat repair and check the head out for any other issues 
or possible loose valve seats.

My question is: What are the recommendations for determining why the #4 
cylinder compression is low?   And what should I do to make the best of 
the current situation?

I assume I should check cylinder taper, ring conditions and orientation, 
and look for any valve issues on #4.   Any other recommendations?   I 
have not yet determined if the pistons have been replaced from the stock 
ones that can lose their tops.  I certainly hope so.

Any recommendations would be very welcome.

Thanks in advance and have a Happy New Year,

Larry Forman