<VV> 69 Monza Low Compression Miss - The Rest of the Story!

[ChiefTAM@aol.com]

Ok ya'all, many of those who helped me to try and diagnose the problem in my 
69 Monza, and there were many of you, had asked me to let you know what I 
found.  So, here goes:

First, a recap.  I moved from Minnesota to Texas about six months ago, and my 
brother brought two of my Corvairs down from their winter storage when they 
came down for the NASCAR race at TMS the first of April.  The trailered my 65 
Corsa Turbo Vert. and drove my 69 Monza Convertible.  The car is 3388, LeMans 
blue, 110hp, 4-speed with just under 50,000 miles.  They left Northern Iowa and 
headed south.  In southern Kansas, while driving, the car developed a miss.  
They drove another 100 miles and stopped in Oklahoma for the night.  I went up 
the next day to pick up the car with a rented trailer.  I couldn't find much 
of a miss in the cold engine, and didn't notice any smoke.  They noted that 
one of the cylinders just seemed a little off.  They thought it was #6.  Several 
weeks ago, I bought a compression tester and ran a compression check.  All 
cylinders were 150 to 160 except #4, which came in at 60 lbs.  I later sprayed 
some oil in #4 and the compression went up to 90 lbs.  I borrowed a compressor 
and pressurized #4 cylinder.  At first, I heard air out the carburetor, but 
after I loosened the rocker arms, I could only hear air out of the oil filler.  
Obviously, we had a problem, and you all agreed it had to come apart. Most of 
the early guesses centered around a valve seat that was thinking about coming 
out, or perhaps an old fashioned burnt valve.  After the pressurizing test, 
many thought it was a holed piston.

Today, with the help of Carl Coulter of the NTCA (many thanks) we pulled the 
engine apart. (I know you all say the Corvair engine is easy to work on, and 
it may be in itself, but, man do you have to spend a lot of time taking off 
shrouds!  Seems easier to tear apart a 60's small block!)

The head checked out OK, the seats are all in, and the valve are sealing all 
the way around on #4.  A little carbon buildup, but not bad, and only a little 
wear in the valve guides.  We did have 3 studs pull out, all on the exhaust 
side of the cylinders.  I couldn't get to two of them with vice grips, and one 
just pulled out anyway.  On the positive side, no aluminum threads came out 
with them, so I think we can just screw them back in after we get the nuts off 
and clean up the threads.  So much for having Acorn nuts and using PB Blaster!

After putting some copper pipe over the studs to hold the other two cylinders 
on, we pulled off #4.  There, we found the TOP TWO rings broken in two.  
There was some scoring on the inside of the cylinder.  There was also three small 
gouges, about 1/4" wide in the top side of the piston, but not all the way 
through the top side of the piston down to the top ring groove.  After taking off 
the blower housing, we took out the #4 piston and rod.  We found a little 
scoring on the crank bearing, with one small, maybe .002 groove in the bearing.  
This all appears to be the some total of the damage.  

Our plans are to tomorrow to polish the crank journal with some emery paper, 
and then to mic the journal to see what size it is.  We will then send the 
offending parts off to one of our wonderful Corvair vendors, and probably get a 
new cylinder with a piston and rings attached to a connecting rod, and new 
bearings, and put it back together.  I can't find any marks on the piston or the 
bearings, so I believe that the piston is standard.  

So...some questions.

1.  What would cause TWO rings to break?

2.  What would cause the small gouges on the top/side of the piston?

3.  Any thoughts on our plan to repair the engine?   

Again, thanks very much to everyone on this web ring who are willing to help 
those of us who are less experienced.  This is what is keeping our Corvairs 
running and popular!

Todd Miller
Corvair Minnesota and now NTCA too
Dallas, TX