Tom M'Guinn

Thought I would post up some pictures of this diagnostic tool I am trying on the head gasket -- it is a pressure sensing film that turns color based on how much pressure is applied. First picture is before head was torqued, and the second shows the pressure applied by the head. See the website here:

http://www.pressurex.com/

http://www.sensorprod.com/static/bolted_joint.php

I will be sending it in for their computer analysis, but already can see some variations in the clamp force. Time will tell if it has value as a diagnostic, but thought I'd try something new. The o-rings in my block make checking with a straight edge more difficult than normal.

theedge

Hmmmm interesting. How much does the whole process cost?

beentherebaby

Where and what problems are you experiencing? Perhaps the o-rings are preventing the head from applying normal pressure against the block and head gasket?

Techno Duck

Tom, that is very cool. Can you describe how you check for flatness using a straight edge on the block? What type of feeler gauge do you use?

I am experiencing some external leakage from the headgasket which i believe may be attributed to me running the #2 intake gasket upside down for some 10k miles. I am thinking it may have warped the head or block slightly causing the small external leak which is only apparent after running the car very hard. The head is o-ringed so i am thinking that may be stopping coolant from entering the cylinder.

When i pull the engine this winter i plan to redo the headgasket and id like to check the block prior to bolting the head back on (which will be rebuilt at a machine shop).

Tom M'Guinn

Brian, it costs about $100 to do the top and bottom of the head, all in.

Jon, you need to start with a true percision straight edge, such as those sold by Snap-On. A ruler or t-square, etc. will not work. I think the factory manual actually shows the test -- basically you put the straight-edge on the deck and check to see if a feeler gauge can be slipped under the straight-edge anywhere. Use the thinnest feeler gauge you have -- my thinnest is 1.5 thousands of an inch, but hoping to find an even thinner one. You want to try this with the straight-edge running kity-ccorner across the block (and head) and parallel down the block at various point. You're just looking for any low spot. The manual actually has specs listed for out-of-flatness.

Beenthere -- long story, been having a hard time holding more than 15psi on my 3L. Most recently my boost controller failed and I boosted to 30+ psi before I figured out what was going on...

333pg333

Tom, well done. Should prove very interesting at worst, conclusive at best.

Thanks.

theedge

Not a bad price. What pressure range did you get, I guess the 70-350PSI one?

Chris White

Keep in mind that as the block and head expand as they come up to temp things will change….but this test can indicate some issues.

BTW – when using a straight edge you can get a pretty good idea by putting a light source behind the edge and looking for how much light comes though. While not a measurable standard you can see the variations quite well.

Van

Fantastic idea. I guess if you'd done it without the head gasket, you'd get just the o-ring contact area. I wonder how much the head gasket deforms and distributes the load?

Looks like a great test (although it's not quite wide enough) for an MLS gasket.

Van

A machinist friend of mine checks to see if a piece of cellophane from a cigarette pack can slide under the straight edge...

333pg333

What about just using the smoke?

toddk911

Is there such a thing as a malleable hg?

That would help for any low spots, head lift, heat/cold expansion/contraction, etc. etc.

Van

Copper?

Duke

Nice. At least there's nothing that show problems with cyl 4 clamping force while cold.
Generally it seems to have less force at the intake side? But perhaps it's marginally.

944V8inDFW

Would a Zig Zag work the same?

All kidding aside is there a called out factory spec for flatness on the block?

I have seen several on the head but dont recall seeing one for the block.