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Another clearance question

Hink

Hink

Overkill Is Underrated
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Location
Stevenson, Wa.
Again, mostly from lack of hands on experience with these motors but also from lack of a definite clearance spec or confusing numbers, I'm unsure of where I'm at with another clearance.

The best numbers for a piston protrusion spec tha I can find is .0039" - .0059" but I've seen it also stated that .009" is fine with standard gaskets.
I had some corrosion milled from my deck and also had my heads milled a bit to flatten. Now I'm looking at .018" that, with my Victor Reinz .010" thicker gasket will, of course, be .008".

Would this be acceptable?

My understanding is that Cometic can make a gasket of any thickness but I can't even imagine what that would cost, not to mention the time involved.

Thanks!20190131_210910.jpg
 
Last edited:
You need to lay a used gasket down,put a wide strip of putty where the valves will be, install head & torque down, install 2 pushrods & rockers, then rotate the motor slowly 2-3 revs, remove everything and measure the thickness of the putty... their is a putty that drys fast so it can be pulled up and measured but I can't remember what it's called... report back with measurements.

That much protrusion is a lot, deep risk of a valve touching... one reason I made some pistons with reliefs...
 
Copy that on the putty. I know it's been used for that but I've never used it myself.
I'll see if I have a used gasket still around.

Yeah, that's why I want a set of those! : )>

I have an email out to my machine shop on the specs and amount milled from heads but no reply yet so it looks like I'm waiting another few days to move ahead with this engine.

And I'll check Cometic to see about the availability.
 
So Cometic does, indeed have multiple thicknesses available (although it does say made-to-order) with the smallest size at .045" compressed thickness.
Does anyone know the compressed thickness of a stock gasket? We all know of the .010" thicker, but thicker than what?
 
Hink said:
So Cometic does, indeed have multiple thicknesses available (although it does say made-to-order) with the smallest size at .045" compressed thickness.
Does anyone know the compressed thickness of a stock gasket? We all know of the .010" thicker, but thicker than what?
Click to expand...

Answered my own question, but man they don't make it easy for crying out loud.

Fel-pro spec for stock gasket is .040" - .0440". so the first Cometic offered is the stock thickness.

And they have 7 different thickness options all the way to .098" which would give you 0.053" thicker!
Pretty impressive amount of options.
 
Long time back I had some problem with cometics on 6.2 or 6.5. Can’t remember for the life of me what it was. Precup sealing comes to mind because of heat -but not sure. That was so long ago.
 
Yeah @NVW is correct. Her custom thickness Cometic's failed on her decked engine. I was somewhat involved in replacement block efforts.
 
I am pretty sure my issue was heat from the precups against the gasket surface. Their materail is good, but inconel is crazy hot.
Maybe coat the face of the precup? The ambient heat will still make the precup work. Inside the precup will be hot since the fuel and air saturation occurs their first. Just using coating as an insulation to protect gasket.

CALL COMETIC

Maybe Missy and I each did something wrong. There are some WAY serious builds running them successfully.

Expensive option- annealed copper. It will fight with water jackets, but there is supposed to be treatment now that take care of that. You won’t find a better head gasket on this planet than these. Nothing else stand up to nitromethane, and I think just maybe they have a tad more pressure and heat than us. Haha.
 
Also, rods.
John of Unique Diesel redoes 6.5 rods. He does larger rod bolts and sells them as match length sets. Obviously not going to do that without all the basic checks too.

Maybe talk to him and see if he has a nice short set?
If you already had your assembly balanced, just make sure the new rods are balnced to match.

I know this isn’t the primary option, but look at all possibilities does hurt.
 
Hink said:
Again, mostly from lack of hands on experience with these motors but also from lack of a definite clearance spec or confusing numbers, I'm unsure of where I'm at with another clearance.

The best numbers for a piston protrusion spec tha I can find is .0039" - .0059" but I've seen it also stated that .009" is fine with standard gaskets.
I had some corrosion milled from my deck and also had my heads milled a bit to flatten. Now I'm looking at .018" that, with my Victor Reinz .010" thicker gasket will, of course, be .008".

Would this be acceptable?

My understanding is that Cometic can make a gasket of any thickness but I can't even imagine what that would cost, not to mention the time involved.

Thanks!View attachment 55720
Click to expand...
Btw, I'm surprised and disappointed that no one corrected me on the fact that the reading on that dial is .017", not .018"

Come on guys, I need you to call me out on my dumbassery!
 
Ok when was the last time that cheap China tool was calabrated? :facepalm: Have you cross checked it to make sure it's in the ballpark?
 
WarWagon said:
Ok when was the last time that cheap China tool was calabrated? :facepalm: Have you cross checked it to make sure it's in the ballpark?
Click to expand...

Stop picking on me!
I'll have you know that I borrowed that from someone who builds aeronautics for our US military, so you all oughta feel safe.

And yeah, I used the straight edge/feeler gauge method as well.
 
One frustrating thing in measuring this is the piston rock.
Trying to make sure it's level in the cylinder is not easy.
 
Twisted Steel Performance said:
You measure it on the side above the pin to eliminate as much rock as possible...

Have you had time to try the clay method yet?
Click to expand...

Not yet, I have some clay coming in a few days.

Thanks for pushing me in that direction, I was trying to resist going that route but it really is the right way to go.
And this way we can see what kind of results that we can expect with .010" gaskets and .017" protrusion.
 
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