Not your typical HG question

[Chevy1925]

So in my quest to tighten quench up and do so with HG's, a few friends have raised a concern with my thoughts on running A's.

Right now, my tallest piston is .011 measured at the wrist pin and hits .013 measured at top of the piston with the piston rocked "out". The rest measure .010-.0105. I ran C's before and intake valves average a -.027 depth with the shallowest at -.024 at the outer ridge away from the piston (other end that's over the piston measures .026). Exhaust averaged -.035ish. That was all measured with a deck bridge dial indicator on the valve faces and the old head surface cleaned. My quench was .028 at the tightest based off wrist pin measurement.

I'm looking to go to A's but I do t want the valves to hit the Pistons which were mine and Steves concerns. Based off my thinking, the new heads have the intake valves recessed to an average of -.028 and none over -.0275. Exhaust averaged -.038. So the valves are really close to where the old heads were, if not a bit farther up. So if I ran A's, my quench would be .024 basing off the wrist pin measurement which is still below jons suggestion of no less than .020. Should I worry about piston to valve issues or am I/we over thinking this?

The tallest piston is also .002 taller than GM recommends for an A gasket which again makes me wonder.

 

[WVRigrat05]

So why not just run B's to be on the safe side? Out of curiosity, say you have your valves adjusted to .011, how long before they get a larger clearance? Has anyone ran a motor 10k miles or so after a build to see? If they come out of spec quick I don't see where A's would hurt due to clearances getting bigger, I know my LMM at 30k already had a louder valve train. Hope that question made sense, I'm at work and in a hurry

 

[malibu795]

B's I wouldn't run As too clearance are too tight

 

[Chevy1925]

So why not just run B's to be on the safe side? Out of curiosity, say you have your valves adjusted to .011, how long before they get a larger clearance? Has anyone ran a motor 10k miles or so after a build to see? If they come out of spec quick I don't see where A's would hurt due to clearances getting bigger, I know my LMM at 30k already had a louder valve train. Hope that question made sense, I'm at work and in a hurry

Because I want to know and not just follow off what I did before. Like most, it was just generally said to "just run C's" with nothing backing why. I want to bump mpg back up some if possible and I can give a little help here. My valve lash didn't change over the 40k she was ran. Still the same .011 based off feeler gauges. Just spot checked a few but I never had excessive valve noise or anything

 

[Chevy1925]

B's I wouldn't run As too clearance are too tight

Where and why though? Gimme something to chew on

 

[Ne-max]

I like your thinking. Less material to blow out also.

 

[Huffy67]

It would be extra work but the best way I know to check is put clay? on the piston with a light coat of oil on top of the clay? and bolt the head on without a gasket and turn the engine over. Then cut your clay and measure the thickness, taking into consideration the compressed thickness of the gasket. Then you'll know how much piston to valve clearance there is and set it where you want it with different thickness gaskets.


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[malibu795]

Where and why though? Gimme something to chew on

With As i would be worried about the pistons hitting when they rock over.. I've ran As on the first LBZ I had with fingers. Protrusion was 0 over wrists pins.. Never measures rock though..

I'd be worried runnig As with more then .010" protrusion without micing all clearances especially on a used engine..

Valve timing is a whole nother column, with lash taken into consideration.. One can plot out the top 1/2" of piston travel by crank degrees and plot vale timing by crank degrees. Which is all going to change between hot and cold engines

Tighter the better without going too tight lol

 

[Chevy1925]

It would be extra work but the best way I know to check is put clay? on the piston with a light coat of oil on top of the clay? and bolt the head on without a gasket and turn the engine over. Then cut your clay and measure the thickness, taking into consideration the compressed thickness of the gasket. Then you'll know how much piston to valve clearance there is and set it where you want it with different thickness gaskets.


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That wouldn't be too hard to do at all but the piston will hit the head before I hit TDC and I don't want to hurt something

With As i would be worried about the pistons hitting when they rock over.. I've ran As on the first LBZ I had with fingers. Protrusion was 0 over wrists pins.. Never measures rock though..



I'd be worried runnig As with more then .010" protrusion without micing all clearances especially on a used engine..



Valve timing is a whole nother column, with lash taken into consideration.. One can plot out the top 1/2" of piston travel by crank degrees and plot vale timing by crank degrees. Which is all going to change between hot and cold engines



Tighter the better without going too tight lol

There is .002 increase in protrusion height 90* from the wrist pin where i measured. That's the .013 I posted above so I'd still only be .022 quench with the piston at a full tilt.

I don't know enough about cams to really figure that part out but when and where the valves start coming close to the piston was my concern and just how much space I'd have. I may have to throw the old hg back on and snug a head down with clay between the head and piston to see where I'm at

 

[Huffy67]

Yeah you could use the old gasket and if you know the compressed thickness you should be able to figure it all out


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[malibu795]

Degree the camshaft.. Plot lift at say 5° from zero to zero at the valve.
Then you can say at 10° btdc piston is at A hieght and vale is at B llift

 

[PureHybrid]

I agree, you need to map out TDC lift and use a dummy spring with travel gauge to verify piston to valve clearance. Otherwise put B's in it. And everything I've read on the compressed thickness on these HGs says there's some overlap between the different sets, so you may get a set of B's that are as tight or almost as tight as A's.

Depends on how close you want to cut it. When you open a race engine up and you see the outline of the valve in the carbon, but there's no contact, its perfect

 

[Chevy1925]

Appreciate the info guys! It will be more time and tools I can't play with right now so B's it is. At some point I'll want to play with all that and learn. Might have to get a junk motor to play on