<VV> Compression test and TDC

[Western Canada CORSA]

Charles,

I've only been half following this thread, but it looks like you've had
quite a few suggestions on how to find TDC.  I didn't think mine would be
useful because it involves pulling a valve cover.

Anyway, what works for me is pulling the driver side valve cover and
watching I/E on #4.  Its late and I can't remember off the top of my head
it's which valve in which position, but with the order for setting valve
lash in front of me when I'm doing it, the light bulb comes on and it's
always "this HAS to be TDC", and away I go.

Regards,
Joel



-----Original Message-----
From: virtualvairs-bounces at corvair.org
[mailto:virtualvairs-bounces at corvair.org] On Behalf Of Charles Lee
Sent: Wednesday, September 24, 2008 11:56 PM
To: Sethracer at aol.com; virtualvairs at corvair.org
Subject: Re: <VV> Compression test and TDC


Thanks...

I'm not really doing a full compression test here, just one #1 to see which
TDC is the compression stroke.

Looks like I have good compression because it goes to 60 on the 1st TDC,
then 120 where I stopped, because I just needed to see SOME compression to
be convinced I was on the right cycle.

With the "remote starter" cranking the engine, I'd probably be able to feel
the compression with my finger, but not when I was cranking manually though.

Tomorrow we'll see if she fires up - it's been almost 10 years actually,
now that I count the time she's been decorating my driveway !   I heard
some life before the battery died, so it looks good so far.

Later,
Charlie



-----Original Message-----
From: virtualvairs-bounces at corvair.org
[mailto:virtualvairs-bounces at corvair.org] On Behalf Of Sethracer at aol.com
Sent: Wednesday, September 24, 2008 10:14 PM
To: chaz at ProperProPer.com; virtualvairs at corvair.org
Subject: <VV> Compression test and TDC


 
In a message dated 9/24/2008 4:48:30 PM Pacific Daylight Time,  
chaz at ProperProPer.com writes:

On  closer examination, I get 0 on the alternating TDCs, so that must be the
exhaust.

I do get 60, then 120, so maybe it's 60 on the 1st compression  TDC, then
120 on the 2nd time compression TDC ? Seems like good  compression though.


 
Charles - The distributor makes one revolution for every two revolutions of

the crank. Each time the rotor passes the wire for number one it is at the
top 
 of a compression stroke. To perform a correct compression test, all plugs 
should  be removed, and the throttle should be held open during cranking.
There 
will be  a build-up as the piston goes up on each of the 5 or 6 compression

strokes - that is providing the check valve is still in place in the 
compression  tester AND there is some compression in the cylinder! Cranking
it a half 
dozen  times will usually cause the cylinder to reach it's maximum reading
on 
the gage.  If you end up with a cylinder that is low, say 30 lbs less than
the 
others,  chances are you have a problem. If a cylinder is down a bit, the
most 
common  next test is to squirt a little (I mean just a little) oil into the 
cylinder and  see if the compression comes up a bit with another test. If it

does, it is  probably ring wear. If it doesn't, there might be a valve
problem - 
burnt   or bent? The better next step is a cylinder leak-down test. This

involves  putting a known air feed into the cylinder (At TDC) and seeing
what 
percentage  of "leakage" takes place. There is a special device for this. If
20 or  
30% is leaking, not only do you have a problem, but you can probably find
the 
 culprit. The air will exit the motor and you can usually hear it. If it is

coming out the carb inlet, a burned intake valve, out the muffler, burned  
exhaust, if out of the oil filler cap, perhaps a burned or broken piston
-   or 
worse. 
 
Maybe I just have a sensitive index finger, but I have always been able to  
tell when the piston is approaching the top under compression and blowing
the  
tip out. Hey, that's why I call it my Index finger!  -  Seth



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