Adrian: A cold leak down or compression test won't be accurate. Engines
are made to be run at temperature.....as they heat up they tighten up. Also
the leak down test should be done air going into the cylinder and the piston
just coming to TDC on a compression stroke. That way the rings will be in
the position they are in when the sparks fly.
Another tip for leak down tests: with the air from the compressor going
into the cylinder, listen at the carbs, at the tail pipe, and at the
crankcase ventilation port. Air noise will tell you if the leak is intake
valve, exhaust valve, rings respectively.
I don't understand the instructions for the leak down test that you provide.
My tester has two gauges and a "calibrated orifice" (ahem). You pump 80lbs
of air in and hope that you get 60 or better on the low side (at least on an
aircraft engine!!)
It would seem that since all your readings are roughly the same, and
considering the cold engine that you are in pretty good shape. I'm sure
I'll be corrected though.....
Geoff Branch
----- Original Message -----
From: "Adrian Jones" <adrianjones747@earthlink.net>
To: <spridgets@autox.team.net>
Sent: Sunday, January 14, 2007 12:19 PM
Subject: Leakdown test and compression readings
> Hi Folks,
>
> I'm still pondering the rust problems with the 1275 restoration.
> Meanwhile, this morning I played around with a Cylinder Leakdown Tester -
> on sale from Harbour Fright for $40.
>
> (This consists of a valve and pressure gauge that is used with you
> existing air compressor. You pump air into one cyinder with a plug hole
> adapter and adjust the pressure so that the % leakdown is 0%. Then you
> hook it up to the other cylinders and see what they show for leak down.
> If one cylinder is bad (for whatever reason) it can be identified.
> Someone jump in if I have this wrong.)
>
> Anyways, I tried it out and basically I can adjust the pressure on one
> cylinder and then all the others come out between 0 and 4% leakdown, all
> with an indicated pressure of 70 psi. I'm thinking the cylinders are
> pretty much in the same mechanical condition and that is all I can
> determine from this test.
>
> OK, so I get out the compression tester (Cal-Van) and here are the
> results: 157, 154, 155, 150. Woo-hoo!
> With a tablespoon (15 ml) of oil, the readings shoot up to: 205, 190, 205,
> 200. Boo-hoo!!
>
> Not sure if it matters but a week ago I had put in a tablespoon in each
> cylinder and done the same a couple of days ago - prior to seeing if the
> engine would even turn over. Surely the oil would have drained down past
> the rings before the test I done this morning?
>
> I should also mention the engine is stone cold for all these readings.
> The engine has not been started in over 4 years. I think I need to at
> least dismantle the carbs and give them a good clean before I fire it up
> for real.
>
> Any thoughts? I'm puzzled - could an engine have 150 psi on all cylinders
> and still have bad rings?
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