Subject: [Fot] Odd compression?

From: Scott Janzen <[email-masked]>
Date: Mon, 20 Aug 2012 09:02:28 -0400

I had a similar experience with my GT6 a few years ago (though a different initial cause). Could be gasket or rings or a warped head, but for my car it was leaky valves that needed to be recut.  I had lapped them and my machinist had thought they looked fine too the first time when we resurfaced the head.   My first advice is to get a leakdown tester from Summit Racing or somewhere.  Pretty cheap and a great diagnostic device.  Especially with the manifolds off, you can readily identify the source of the leaks by the air whistling!  You'll probably have to run the test without your rocker assembly on, depending on how radical a cam you have.  The compression tester tells you that you have a problem - the leak down tester tells you where.

Payen gaskets are trouble free for me.  I'm guessing you are using stock head studs - with ARP if memory serves I'm torquing to 65 or 70 lbs.
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From: Jack Mc <[email-masked]>
Date: Mon, 20 Aug 2012 10:40:52 -0400

Not relevant to your question, but I wouldn't be to quick to conclude somebody
just didn't put that screw in - unless you've already searched the oil pan for
it - I have found that screw on a magnetic oil pan drain plug

Cheers,
Jack Mc

Sent from my iPad

On Aug 20, 2012, at 4:29 AM, Edward Dunn <[email-masked]>
wrote:

> He found
> that the engine builder had not installed the set screw that keeps the
rocker
> shaft in line with the oil feed hole in the upright.

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From: Edward Dunn <[email-masked]>
Date: Thu, 23 Aug 2012 14:21:54 -0700

Did a leak down test on the GT6 motor. Retorqued the head to 75 lb ft.
Performed test, and cylinders 1-5 were leaking through their exhaust valves.
All cylinders were also leaking through the head gasket, but ONLY on the left
side (opposite intake/exhaust ports).  Pulled the head, and the intake/exhaust
(right) side of the gasket looked fine, but the left side had oil and water on
the gasket, both top & bottom of gasket.

So, it's got leaky exhaust valves, and head gasket leak. Possibly the head
studs are too long, since the head has been machined who knows how many times?
Perhaps the studs are stretched? Also, one pushrod is a touch shorter than the
rest.  I think this can be adjusted for, but it would make the geometry a bit
off, correct?  The pushrods are also a slightly different design than on my
spare engine.  With the head milled a bit, still use the original length
pushrods?

This is all puzzling to me and my non-professional but competent mechanic
pal.

Ed Dunn

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From: Edward Dunn <[email-masked]>
Date: Thu, 23 Aug 2012 16:03:30 -0700

Thanks,  we'll check it out more tonight. Will likely order a set of ARP head
studs.  Guess I'll take the head back to the cylinder head shop to have them
check the exhaust valves.  The engine was rebuilt last winter, and had a very
good race weekend before it failed. Did not retorque after the initial race
weekend. When doing a leak down test, how much time do you use per cylinder?

Ed

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From: Vince G <[email-masked]>
Date: Thu, 23 Aug 2012 19:17:00 -0400

Race engine, ya sounds like machine shop time to be safe :)

Sent from my iPhone

On 2012-08-23, at 7:03 PM, "Edward Dunn" <[email-masked]>
wrote:

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