Definitely not more than I wanted to know!
I think there'll be a couple of people here that won't mind learning this,
so I'll post the reply to the list, as well.
Thanks John - This is exactly the kind of thing I joined the list to learn
about. Well, she's with "Dr. Lou" right now, so I'll let you guys know what
happens...
Cheers,
Steve
(1968 SR311 Solex)
WorriedROC, PensiveROC, etc. etc.
>From: "John F Sandhoff" <sandhoff@csus.edu>
>Reply-To: sandhoff@csus.edu
>To: "Stephen McCartney" <sgam@hotmail.com>
>Subject: Re: Valve seals (was: SadROC --->Noroc?)
>Date: Tue, 12 Dec 2000 17:25:56 -0800
>
>You wrote:
> > Hmmm... Compression tests haven't been done, yet. She goes in today or
> > tomorrow for a good solid look. I won't be doing the work, but what's
>the
> > difference between a "wet" and "dry" test? How does the difference
>point to
> > various problems?
>
>Short answer:
>If the test pressure of a cylinder is significantly higher after a
>tablespoon of oil is squirted in, that cylinder's rings are worn.
>
>Long answer:
>In a nutshell, to do a compression test:
>1) Warm up engine. Make sure battery is charged. CHECK VALVE
>CLEARANCE if accuracy is important.
>2) Disconnect coil primary, pull plugs
>3) Block open throttle.
>4) Install compression gauge, crank at least 3 compression strokes
>(you can hear the engine 'lug' and the needle will jump up each time).
>Note reading. Repeat for remaining three cylinders.
>5) Squirt about a tablespoon of engine oil in cylinder. Repeat test.
>Watch for oil splashingout the spark plug holes :-) This is the 'wet' test.
>6) UNBLOCK THE THROTTLE.
>7) Install plugs, reconnect coil.
>
>What you learn:
>All cylinders should be about equal, hopefully within 10% of each other.
>If valve adjustment is off, may vary a bit more. Pressure will typically be
>120-140, AS I RECALL. Below 90-100 and you have a restricted intake,
>well worn engine, incorrect valve timing. Above 150-160 and you have
>excessive carbon buildup or a head/block that's been severely milled.
>Two adjacent cylinders low = probable bad head gasket. One cylinder
>near zero and you may have a hole in the piston.
>
>If you have one or more low cylinders and the valves seem to be adjusted
>OK (check the cam lobe for flat spots, excessive clearance, etc), you
>have a bad head gasket, burned valve, or bad rings. That's where the
>wet test comes in - if the pressure came up significantly when you
>added oil, it's because the oil temporarily sealed the rings - bad rings.
>If the pressure did NOT increase by much, it's a valve or gasket problem.
>Apply compressed air thru the sparkplug hole while at TDC compression
>stroke and listen for hissing out the air cleaner or tailpipe: bad valve.
>
>More than you wanted to know, right?
>
>-- John
> John F Sandhoff sandhoff@csus.edu Sacramento, CA
>
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