Re: Oliver valve adjustment leads to more work!! P

Posted by Hobo,NC on February 03, 2007 at 20:12:05 from (71.29.34.192):

In Reply to: Oliver valve adjustment leads to more work!! Pic posted by wagsw900 on February 03, 2007 at 18:05:29:

A runing compression check would have nailed it, the reason it did no on a crank"in check izz the compession sealed the valves and only needed to have enuff spring tension to hold"em till the compression took over.

The volumetric efficiency test or running compression test
is a very good test to use any time you have a engine miss
that can"t be traced to ignition or other basic systems or
when there is a lack of power.

Step 1. Perform a cranking compression test with all plugs
out and the throttle open.

Step 2. Record your cranking compression readings. Make

sure the charging system was up to snuff so all cylinders
were tested under the same conditions.

Step 3. Install all plugs but one. Install a standard
compression gauge in the remaining hole with the shrader
valve in place.

Step 4. Start the engine. Yes, it will run but will be
missing on the cylinder with the compression gauge. Burp
the gauge and allow the reading to stabilize. It will be
bouncing around at about 50 to 60 psi. (the throttle is
causing a restriction and the piston is moving fast
compared to cranking speed causing only a partial fill of
the combustion chamber).

Step 5. Snap the throttle wide open and return to idle. The
gauge will hold at the peak reading. This reading is higher
than idle because the peak comes at the instant the
throttle restriction is removed and the piston speed is
relatively slow.

Step 6. Record your readings for running snap compression
for all cylinders. The running compression reading should
be approx. 80% of cranking compression. (example: cranking
compression = 150psi running compression should = about
120psi)

If your running reading is below 80% of cranking
compression, the intake system is causing a restriction. If
the running reading is above 80% of cranking compression,
the exhaust system is causing a restriction. If the problem
is in one cylinder you either have a problem with a worn
camshaft, broken spring/rocker, carbon build up, etc. If
the problem is on all cylinders look for a restricted
intake system or clogged cat/muffler. The 80% spec is a
ballpark spec and should be used as such. Remember that
cranking compression is a measure of cylinder seal while
running compression is a measure of volumetric efficiency
or the cylinders ability to draw the air/fuel mixture into
the combustion chamber

Also what a cranking compression test tells ya and remember its only a place to start, if you have problems you will need to do a cylinder leak down test to trace the leakage.

the first stroke of the compression (assuming it is not starting on an open
valve condition) indicates valve sealing capabilities. Generally, it should
be about 2/3 of the total compression. The first stroke is the valve
sealing, and each stroke afterwards, whether you do 4 total, 5 total, or
absolute total compression

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