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914World.com _ 914World Garage _ Compression: can it be tested old & cold?

Posted by: Bruce Allert Jun 16 2005, 12:09 AM

I've had this 1.7 for 2 years sitting on the shop floor. The guy I got it from prolly had it a few years sitting on his shop floor and it had oil in it when I got it. Looked clean too. (oil that is)

I checked compression tonight by rotating the engine by hand. Did 4 - 5 rotations for the peticular cylinder being tested. The results were a consistant 30 PSI in each hole.

The only oil I've added is some Marvel Mystery Oil thru the plug holes and most of that squirted out the exhaust valves. There should be some oil in the sump. I know quite a bit came out onto the floor when I was moving it but it ain't dry!

I'm just not sure if I want to go thru putting this engine in the car and have it not run or have no more than 30 PSI.

Any ideas?

Anyone know if compression will come up once it's running?

I even adjusted the valves to be sure nothing was open.

........b

Posted by: groot Jun 16 2005, 06:28 AM

30 psi???? If that measurement's correct, don't bother installing that engine in anything short of a lawnmower.

I think the Haynes manual says the lower limit is 90 or 95 psi, with no delta greater than 5 or 10%.

Posted by: groot Jun 16 2005, 06:30 AM

I've tested my compression when the engine's cold. Engine sits for a while and then I use the starter to get 4 pulses.

I would only expect the compression to get worse once the engine warms up.

Posted by: Bruce Allert Jun 16 2005, 08:30 AM

QUOTE (groot @ Jun 16 2005, 05:28 AM)
30 psi???? If that measurement's correct, don't bother installing that engine in anything short of a lawnmower.

I think the Haynes manual says the lower limit is 90 or 95 psi, with no delta greater than 5 or 10%.

I find it rather strange that I'm getting the exact same reading across all 4 cylinders. I wouldn't expect an engine to wear uniformally as this.

Maybe I'm doing something wrong???

No HE's, no intakes, valves adjusted and turning it over with a socket on the center bolt of the fan.

..........b

Posted by: ! Jun 16 2005, 08:36 AM

Best to do a leak down when an engine is out and cold. Craftsman and a few other tool companies have the set ups.

If you can get it to run on a bench you can get it warm....not hard if you have a trans, a stand, a starter and a temporary fuel tank.

Trekkor did it when he test fired his sixer that came out of the dune buggy. Dig up his thread...it's in there someplace.

Posted by: SLITS Jun 16 2005, 10:31 AM

You can't turn it fast enough to get real numbers by hand. Hook a tranny & starter to it.....then check the compression.

Posted by: Bruce Allert Jun 16 2005, 11:07 AM

QUOTE (SLITS @ Jun 16 2005, 09:31 AM)
You can't turn it fast enough to get real numbers by hand. Hook a tranny & starter to it.....then check the compression.

I was hoping this was the case. Gives me a better outlook for the rest of the day!

........b

Posted by: SLITS Jun 16 2005, 11:12 AM

We used to do it wet & dry to determine the condition of the rings (kinda).

1st test...hook it up and spin it.

2nd test....shoot a couple of squirts of oil in the cylinder..hook it up and spin it. Compression will usually increase....if it increases a lot...the rings are worn (maybe).

Have fun...last engine I tested cold...hadn't run in 3-4 years...130 PSIG on all cylinders.

Posted by: Bruce Allert Jun 16 2005, 11:17 AM

Thanks Buddy I'll send ya som'o dat DeathStar Gold!!!

.....b