Seeking Advice: piston to head clearance. (1 Viewer)

[FitzPR]

Some time ago, i posted Overheating Problem has me stumped.
Spoiler alert: it was the HG.

I had my head surfaced (it’s straight), and my block needed resurfacing as well.

I told them to do a minimum pass, and they did great, the locations of the deepest pits are still visible, but completely flat.

Even so, my pistons now protrude slightly at TDC.

I measured how much using the edge of my calipers as a straightedge, along with a feeler gauge. I consistently got .008 readings, unless i put the caliper edge on the cylinder number stamping, since the metal was slightly displaced when they did that.

Some searching on here suggests that OE style gaskets compress to .052-.053, which would give me .044-.045 of clearance, a number I saw @landtank aimed for on a build.

How confident can I be that it’ll be fine?

(I don’t have the details of my gasket kit with me here in the lunchroom at work, the small parts place i got it from assured me it was from the OEM what made it for Toyota in the first place)

 

[dallen341]

Curious but did the machine shop indicate how much the block was decked?

 

[FitzPR]

Curious but did the machine shop indicate how much the block was decked?

My receipt appears to say .006, but the old guy who wrote it wasn’t the guy who ran the machine. It’s also possible someone was in here before me.

I’m most likely going to put it together in the morning. The old guy at the machine shop suggested putting the head on, but not fully torqued, (10 pounds under) and releasing a rod cap, so as to use a dial indicator on the rod bolt to measure the clearance. I might do that, but I’m leaning towards not

See no evil, and all that

 

[White Stripe]

You can put a piece of clay on top of the piston where the valves would possibly kiss it. Lightly bolt the head on and timing chain, hand crank it over. Pull head and measure the clay thickness. You can also go to the hardware store and buy really weak springs, install it as a valve spring for exhaust and intake valves on one cylinder. Lightly bolt the head down, then when the valve is full open you can move it further by hand to see how much further it will go to hit the piston. These methods are all over the internet. You did not post how much the head was decked, nor post a pick of the pitting left over.

 

[Kernal]

Would an MLS head gasket work in this situation??
Mill the piston tops??

IDK

Interesting read:

Ask Away! with Jeff Smith: Figuring Piston-to-Deck with Protruding Pistons

I’m building a Chevy 350 engine for my son’s circle track race car. I started out with a 0.040-over block that I think has been severely decked but I’m not …

www.onallcylinders.com

 

[Shipwreck]

When I installed my new short block, I reused my original head which had been decked twice. (Once at 130K when the head gasket went and the second time for installation on the new block.) I used a Cometic MLS gasket which made up for the amount that was machined off the head. The amount machined was recorded in my records as well as the machine shop that did the work. I ordered the appropriate thickness gasket based on those measurements. All is well 40k miles since the work.

 

[Saito]

.035 to 0.041 is about ideal for quench height and what I’ll be shooting for when I put mine together. Those two pads on the piston match the ones on the head and push the mixture out into the combustion chamber as the piston reaches TDC. It’s a very important thing.

 

[FitzPR]

You can put a piece of clay on top of the piston where the valves would possibly kiss it. Lightly bolt the head on and timing chain, hand crank it over. Pull head and measure the clay thickness. You can also go to the hardware store and buy really weak springs, install it as a valve spring for exhaust and intake valves on one cylinder. Lightly bolt the head down, then when the valve is full open you can move it further by hand to see how much further it will go to hit the piston. These methods are all over the internet. You did not post how much the head was decked, nor post a pick of the pitting left over.

The valve clearance wasn’t something I was worrying about, though maybe I should have.

My uncle had suggested a similar clay procedure for finding the piston to head clearance, without a gasket, before he found out my pistons protrude, obviously if there’s no gasket and the pistons stick out then contact is inevitable.

And if the gasket isn’t compressed, then it’s not possible to know what the clearance will be when it is.

I should have taken a picture of the top of the block. There’s no detectable pitting remaining, except visually. The marks that can be seen cannot be detected with any tools that feel the surface

I don’t know that this engine has ever been apart before. I don’t known that it hasn’t, either…

The update is that it’s together now. Valve clearance seems to be AOK, as the cam installation procedure has the intake valves on #1 open as the cam is put in, and i already had the engine at TDC #1. When i turn it over by hand with no plugs, there’s no resistance anywhere beyond the constant tightness of the mechanisms. All the cylinders seem to seal, and the engine makes a pleasant fluting noise out the plug holes.

These suggestions are all pretty good basic ideas, but what i was really after was confirmation on the gasket’s compressed height.

If it really is about .052, then I can expect a quench gap of .044, and if that works for @landtank, it ought to work for me.

 

[PIP]

A little less than stock quench height is usually a very good thing for most gas engines. When I was a broke 17 year old drag racer I was able to run a SBC at 11.2:1 compression on 92 octane by decking the block just right to get to get the bare minimum quench height.

The problem with running minimum quench height is that the tolerances of all the parts in the valvetrain and rotating assembly stack up and you can have piston heights that vary and deck heights that never were straight with the mains.

Knowing what I know now I'm amazed that engine took 7500 RPM shifts and no f**ks given burnouts in drive as a daily driver for a 17/18 yo kid for 2 years.