Engine Compression after Build

mike kojima choaderboy2 at yahoo.com
Thu Apr 29 01:27:08 CDT 2004

Ok there are a couple of different posibilties here.
One the engine was severly overheated when it was
stolen and abused.

I have a theory that a severly overheated SR will
never be right unless it is sleeved with thiock Darton
sleeves due to perminte distorsion of the thin steel
liners.  Sure you can bore it but soon the cylinders
will warp again in a short period of time.  I have
seen this a couple of times.

Second the SR being closed deck really should be bored
and honed with a transmission bellhousing and a torque
plate bolted up to it.  You can see the cylinders
shift up to 0.0012 or so due to torque distorsion.
This is most apparent in cylinder 4 so maybe your
engine is not suffering from this.

Third, the cams may have some base circle runout. A
sign of this is an engine that does poorly in a
compression test, sometimes has a poor idle but makes
perfectly normal power at higher rpm and does not burn
oil.  If the engine is rotated by hand a few times,
leakdown test numbers decrease. Cam base circle runout
variation of less than 0.001" can cuase the lifters to
slightly pump up and just bairly crack the valve open
at idle and while cranking.  At higher rpm the dynamic
losses are very small so power does not suffer.

These are three things I have experianced that are
weird asskickers but fairly common with SR20's.  They
can puzzle a good professional engine builder.


--- "Richard A. Haney Jr." <rahjr at cox.net> wrote:
> After putting some 1500 miles on the engine, another
> series of tests were
> performed with the following results:  Dry
> Compression Test yielded Cylinder
> #1 = 135 lbs; #2 = 150 lbs; #3 = 115 lbs; #4 = 150
> lbs; Wet Compression Test
> yielded Cylinder #1 = 150 lbs; #2 = 155 lbs; #3 =
> 140 lbs; #4 = 155 lbs; and
> Leak Down Test yielded Cylinder #1 = 5% to
> crankcase; #2 = 2% to crankcase;
> #3 = 5% to crankcase; #4 = 2% to crankcase.

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