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Another clearance question

This is based on checked clearance is ok...

If you are using old springs, or even stock new springs, you are cutting it close because they are more likely to float than if you bump up to stiffer springs.

Also running close no timing chain, gears only.
 
This is based on checked clearance is ok...

If you are using old springs, or even stock new springs, you are cutting it close because they are more likely to float than if you bump up to stiffer springs.

Also running close no timing chain, gears only.

Yup, Leroy's gears here.
 
Yes solid lifter to playdoh for clearance. Someone (Nate maybe?) figured take one apart and flip the piston upside down.

Well, I'm usually pretty good with puzzles but for the life of me, I can't see how a lifter can go together with the piston flipped and make it work.
Any suggestions?
 
 

Sweet!
Yeah, I do remember reading that now, thanks for bringing that up!
 

Got it!
But it wasn't easy, just know that it's a TIGHT fit.

55777
 
Lead wire for measuring clearance.

I seem to have lost my roll of 1/16 otherwise I'd pop some in the mail to you.

Cheers
Nobby
 
CALL COMETIC

Info from Cometic;

Good studs and a perfectly flat surface are crucial for multi layer gaskets.
They have a Viton coating on them that will not be damaged by copper coat, but copper coat will not allow the proper crush on the gasket.
 
Ok, last little bit of info needed...

What is the preferred piston to valve clearance that we are looking for?
I see no specs in my books.
 
I see no specs in my books.

Ok, I finally got a reply from my machine shop that answers this question...

Rather than having a piston to valve spec range like I've seen with other motors, the 6.5 has a negative spec (recessed) for the valve to head surface which is .034" - .048".
Then with your piston protrusion spec of .004" - .006", you have all you need.

When these two are in spec, then the distance from valve to piston is within stock clearances.

I ended up with a max piston protrusion of .016" and my heads were machined within stock spec for the valves (your valves should always be checked after milling the heads) so with .010" over gaskets (or Mahle .010" shaved pistons) I would end up with .006" protrusion so I'm good, right?

Well, I should be but I still had valve to piston contact. If you run into this, check that your timing chain (or my gears) are timed correct. I likely have the cam timing off a bit, when that is corrected, I should be fine. (I'll update when I know for sure)
 
I've not seen that much valve recession before... I can check records but it's more in the .026 - .030 area me thinks... but I will check, I wright this stuff down on each set of heads...

If their was that much clearance their wouldn't be so many valve imprints on pistons even with a wore chain..
 
Found the info, I have it posted here in a different thread....

A little more info..

I checked valve depth from the head surface on a new 6.5 head with the p valves and vice versa the valves that were in the 6.5 head in the p head...

standard valve & standard head = .039" in .037" ex

p valve in p head head = .025" in .026" ex


What I found with these 2 heads was the P head valves are around .010" closer to the head surface..
 
Found the info, I have it posted here in a different thread....

A little more info..

I checked valve depth from the head surface on a new 6.5 head with the p valves and vice versa the valves that were in the 6.5 head in the p head...

standard valve & standard head = .039" in .037" ex

p valve in p head head = .025" in .026" ex


What I found with these 2 heads was the P head valves are around .010" closer to the head surface..

Interesting. Again, I wonder why the difference?

Those numbers above came from the machine shop and I didn't double check them.
However, I just looked in my 1993 Chevy unit repair manual and the specs are:

.045" (1.143mm) for intake
.035" (.889mm) for exhaust

From the Hummer Manual (newer Optimizer):

.0013" (.034mm) for intake
.0018" (.048mm) for exhaust

I saw no spec in the military manual. I suspect because they don't machine, they replace.

So they pushed the valve recess way out on the newer engine.

My main concern is of course valve stikes, but I also want to consider using Harland Sharps later so the higher clearance is what I'm looking for.
At this point, it is what it is on these heads so I'll go check it and see where I actually am.
 
I got some measurements on the passenger head and they were rather odd considering the numbers we saw as spec above.

2 - Intake - .059" Exhaust - .026"

4 - Intake - .045" Exhaust - .026"

6 - Intake - .055" Exhaust - .026"

8 - Intake - .053" Exhaust - .025"

This is an Optimizer head that was machined for flatness and the valves checked for recession but were not touched because they were considered in spec.

I used cylinder number four for my clay test since it is closest to the piston and had the highest (.006") piston protrusion and therefor the highest likelihood of valve strike. It looked fine but I still don't know what numbers that I'm looking for as clearance when measuring the clay.
 
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