Subject: Re: [Fot] Odd compression?

From: Scott Janzen <[email-masked]>
Date: Thu, 23 Aug 2012 18:47:21 -0400

Hi, Ed
Sounds to me like you have a warped head, non-level block and/or studs that are stretched to the point where they've lost their elasticity (my engineering materials courses are 35 years in the rearview mirror, sorry if the terminology is wrong).  Too long is not an issue unless you are running out of thread to tighten the nuts.
Anyway, I'd suggest getting some new studs from ARP or another good supplier, and getting the both the head and block checked by a good machinist to make sure they're both flat, and getting the valves and valve seats re-cut.
Leakage along the outside of the pushrod galleys is not unusual - I usually assemble with a bit of black permatex over there, but not between the combustion chamber and the pushrod galleys.
Length of pushrods, etc - sometimes you can have these shortened, depending on the design.  Basically, you need to install and see if, when the camshaft travels through the lift cycle, the rocker travel across the tip of the valve is pretty close to centered.  If it's off, you'll get too much side load on the valve and wear issues.  There are lots of aftermarket pushrod mfrs who can supply new ones to the right length, or your machinist may be able to shorten the ones you have.

On Aug 23, 2012, at 5:21 PM, Edward Dunn wrote:

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: Vince G <[email-masked]>
Date: Thu, 23 Aug 2012 19:14:44 -0400

On this engine the leaking head gasket from the fuel pump side of the block is
a classic symptom I starting your torque sequence in the wrong side ( I've
made that mistake.

Have the valves and seats been recently done?

I've rebuilt 4 of those exact engines and never had to replace the stick bolts
but that is not to say yours are ok

You can check the head for flat/true by cleaning everything good then without
bolts or head gasket set the head into the engine block an use a .002 gauge to
check for gaps between block and head everywhere.  If you have a proper metal
straight edge you can lay it across block and head to further check if you are
of a mind to "do it  yourself" and this is a stock rebuild.

The machine shop is of course the best answer if it hasn't already been there
just prior to your recent assembly.

Best if luck

Sent from my iPhone

On 2012-08-23, at 6:47 PM, "Scott Janzen" <[email-masked]> wrote:

> Hi, Ed
> Sounds to me like you have a warped head, non-level block and/or studs that
are stretched to the point where they've lost their elasticity (my engineering
materials courses are 35 years in the rearview mirror, sorry if the
terminology is wrong).  Too long is not an issue unless you are running out of
thread to tighten the nuts.
> Anyway, I'd suggest getting some new studs from ARP or another good
supplier, and getting the both the head and block checked by a good machinist
to make sure they're both flat, and getting the valves and valve seats
re-cut.
> Leakage along the outside of the pushrod galleys is not unusual - I usually
assemble with a bit of black permatex over there, but not between the
combustion chamber and the pushrod galleys.
> Length of pushrods, etc - sometimes you can have these shortened, depending
on the design.  Basically, you need to install and see if, when the camshaft
travels through the lift cycle, the rocker travel across the tip of the valve
is pretty close to centered.  If it's off, you'll get too much side load on
the valve and wear issues.  There are lots of aftermarket pushrod mfrs who can
supply new ones to the right length, or your machinist may be able to shorten
the ones you have.
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