P/V clearance... Just Clay'd... At .010

[korn]

Ok. Should I use the new HG (2.05) to measure or the old used one?

[ForcedFirebird]

That will gain you .011"

Use the same head gasket you already did and clay the piston where the crown is.

[E30-325iS]

Probably telling you something you already know, but make sure your cam is installed and timed correctly when measuring the the PTV clearance.

[Som]

I went through the same shit last year. I had an over-decked head that I measured at about 4.901" at the lowest (it wasn't easy getting consistent measurements). The machine shop said they'd taken out 0.028, though. From a never-before-decked head (~4.925", which is also what I measured before sending it in), that would put the head at about 4.897".

I reassembled the head with the 2.05mm (.080") head gasket -- trusting my measurements. That's a 0.011" increase over stock. If I believed the machine shop numbers + my original deck height measurement, that would mean I was running at about a 4.908" equivalent (0.001" under spec'd minimum height). If you believed my post-deck measurement of 4.901", I was at about 4.912" and should have been fine.

Started the engine and got knocking.

PV clearance was more than ample. This was the piston hitting the head.

Took it apart and clayed. I measured the #6 cylinder around 0.017" -- buuut, I used shitty Crayola kids clay because I was in a time crunch and it's all that was available at Target that night. I couldn't be sure that I wasn't dipping the gauge into the clay and compressing it a little, or if I was distorting the clay when pulling it off the piston.

Anyways, the recommendation to me was "minimum 0.030", but 0.040" is recommended". I was originally going to buy a 0.098" MLS gasket from Cometic -- the extra 0.018" would bring me to 0.035 clearance based on my clay measurement. But then I decided that I didn't trust my clay measurement enough to warrant the compression ratio hit if I was overestimating.

The lowest possible head height I could have was a 4.893" head. That would be a starting head height of 4.921" (I believe it's stock 4.925" +/- 0.004") -- and the machine shop saying they shaved 0.028". Adding 0.023" (0.092" MLS - 0.069" stock) would bring me to 4.916" -- well above the minimum 4.909". So I "gambled" and got a 0.092" MLS instead.

Reassembled with the 0.092" MLS gasket -- knock was gone.

The 0.030/0.040" numbers given to me was the recommended piston-to-head clearance. From how it was explained to me, there wasn't really even a concern for piston to valve clearance with the stock configuration. Also, I'm running the stock cam. Not sure if the 272 could make that much of a difference, though.

Som

[korn]

Ok: re-claying tomorrow AM.

SOM- those numbers are fresh in your head for a year ago!! Thanks for that detail. Really close to what I'm dealing with. And short of dremelling the Pistons I just may have to go get the MLS gasket.

[Som]

Haha, yeah... it was an intense few weeks leading up to a race weekend. :)

Som

[korn]

how is the MLS gasket holding up? I have some slight pitting on my head, I hear that they can eprone to seeping...

[korn]

Ok. So it took me 4 tries to get a decent clay that would not pull apart... The photos speak volumes. When lifting off the piston these would tear, so measuring the areas that are piston to head clearance, right where it tore, I can measure up with .025 clearance.

So. Can I make this work with 2.05 head gasket. Should I get the Drexel out and tweak the high areas?

[korn]

Additional photos

[korn]

Additional photo

[korn]

More

[korn]

https://en.m.wikipedia.org/wiki/Hair%27s_breadth

[korn]

So. On that last pic, the clearance on the exhaust side of the piston was really difficult to measure. The top side was .030 +/- .005.

If I dremel the lower piston ridge down a bit on all cylinders, just "round it off, and slightly deepen the pockets of the valves. I should be able to bump the clearance up to .040. Added to the larger gasket...

Anyways; that's my plan- thoughts?

[jeffnhiscars]

I'm curious about the measuring process here.

Clearly if you line up the timing marks without a belt, there may be just one cylinder in synch to measure since you can't rotate anything. If so which one ?

How are you tightening the head ?

Since you are not precisely duplicating a final install is there a standard amount of "fudge" or is this a best guesstimate ?

Any details on best practices are appreciated

[jeffnhiscars]

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