<VV> Looking for some advice on low compression -update
larry at forman.net
Thu Dec 28 03:56:28 EST 2017
Here is an update:
I received an excellent recommendation from Howard Pilon, who is a great
Corvair mechanic located in Vacaville. He is on the CORSA recommended
list of Corvair mechanics. I know that since I recommended him several
years ago when he inquired of our Sacramento Corvair club as he wanted
to start working on his part time Corvair repair business, which quickly
became full time. His normal machine shop in Vacaville recently closed,
but he had used a machine shop in Sacramento, ironically when he did an
engine rebuild for my wife's 1954 Nash Metropolitan, and they did a
great job. This was a difficult machine shop job as many of the parts
were difficult to locate since my wife wanted to retain the original
1200 cc, 42 hp engine that was only used for less than one year on the
first year of the Metropolitans, versus migrating to the larger 1500 cc
engine that was used for the vast majority of the Metropolitan's model run.
When I took the cylinder head in there today, they looked at it and
noticed that there were indications of the #4 cylinder having the jug
hitting the surface of the cylinder head as when the head gasket mating
surface recedes into the head. This is the surface that needs to be fly
cut so the head gaskets mate properly. I am sure that this is what was
causing the low compression on #4 and was pointed out by several of the
VV & UV experts. It most likely was what was causing the low
compression on #1. I should have noticed that myself.
This shop does not advertise and does most of their work for other shops
especially work on cranks.
This shop has about a one week backlog until they can start working on
my head. They have extensive experience on air cooled heads. They will
replace all the valve seats and do a proper valve job.
I want to thank everyone for the great suggestions and recommendations.
I feel I am in good hands now. If this works out well, then we can
recommend this shop for other Corvair head work in Sacramento as the
other Corvair machine shop in Sacramento takes forever to complete the
same work. We really need a capable and responsive shop like this for
this type of work in Sacramento. I will let everyone know how this
works out as I work other issues like possible ring compression on the
Have a Happy and safe New Year,
On 12/26/2017 9:59 PM, Larry Forman via VirtualVairs wrote:
> 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
> 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
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