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balanced compression

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tl1965

Posts: 18

Joined: Sun Oct 28, 2001 1:01 am

Location: Logansport, IN USA

Post Sun Sep 29, 2002 3:46 pm

balanced compression

I checked my compression on my 45. I'm averaging ~35 on the front and ~43 on the rear. It dawned on me that when I had the head milled after a blown head gasket I raised the compression ratio. How much the shop took off precisely I don't know. The gasket surface was pocked with pits before they started and it came back smooth. Will the unbalanced compression cause any problems down the road and is that why I seem to be fouling the rear plug? (I'm using D-16 plugs and no intake leaks at this time) I've put 1000 miles on since the head was milled and It has ran fine.

[This message has been edited by tl1965 (edited 29 September 2002).]
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HOOTER

Posts: 1319

Joined: Sun Feb 25, 2001 1:01 am

Location: State College, Pa.

Post Sun Sep 29, 2002 6:02 pm

Do a leakdown test to better determine the condition of your topend.
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George Greer

User avatar

Posts: 961

Joined: Wed Aug 28, 2002 12:01 am

Location: Markt Einersheim, Germany

Post Sun Sep 29, 2002 6:15 pm

Hey Hooter,
What is a leakdown test? And how do you do it?
George
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HOOTER

Posts: 1319

Joined: Sun Feb 25, 2001 1:01 am

Location: State College, Pa.

Post Sun Sep 29, 2002 7:48 pm

That's a pressurized test of the combustion chamber. With the gauges you can get a percentage of leakdown of each cylinder when the valves are shut. Up to 7% is normal, above 15% you might want to think of tearing it down to fix, 20%+ better rebuild. this test tells you the condition of your topend. It will also let you know where a problem is just from air gushing out of whatever port you hear it from.

HOOT
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tl1965

Posts: 18

Joined: Sun Oct 28, 2001 1:01 am

Location: Logansport, IN USA

Post Mon Sep 30, 2002 2:34 am

Thanks for the reply, Hooter. How much air pressure should I pump in and how much time should pass after the cylinder is pressurized?
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Boogiemanz1

Posts: 896

Joined: Mon Mar 06, 2000 1:01 am

Location: Bixby,OK, USA

Post Mon Sep 30, 2002 5:06 am

As the leakdown test works on percentages, you set one guage at a standard presssure (determined by you) and the difference in the reading of the second guage needs to be converted to a percentage of the first guage.....a very easy thing if you use 100lb on the first one.
It is much easier to do with a leakdown tester, but there are designs for homeade testers...but the results may not be as repeatable or comparable.

[This message has been edited by Boogiemanz1 (edited 30 September 2002).]
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Boogiemanz1

Posts: 896

Joined: Mon Mar 06, 2000 1:01 am

Location: Bixby,OK, USA

Post Mon Sep 30, 2002 5:12 am

You may want to visit this site for the long suit answer http://www.geocities.com/dsmgrrrl/FAQs/leakdown.htm

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