Claying pistons for clearance

[zaq123]

Clay area for the valve clearance is pretty self explanatory.
What about quench clearance for m20b25 type pistons? Where is the best spot on the piston to put clay to get these measurements? Am I correct to assume that its top ridge is the closest piston's area to the head?
If someone got pics, that would be very helpful.

[ForcedFirebird]

The squish area is angled. The outside ring is where you want to measure, and I have found they like to have .045". Check more than one cylinder if the head has been shaved, sometimes they were warped in the past and have different measurements between them.

Also, I prefer to use electrical solder rather than clay. It will smash down and can easily be read with a caliper.

Typically the piston will contact the head before the valve does - unless you have a high lift cam etc.

[TobyB]

... solder for squish makes sense. Valves might not like it, tho!

heh

t

[nando]

If your valves are sticking out that far that you damage them while doing a clearance check, you were going to have a bad time anyway..

[ForcedFirebird]

... solder for squish makes sense. Valves might not like it, tho!

heh

t

Solder is far softer than your valves. I use this method without any bad results. I have even checked assembled motors before taking them apart this way.

[zaq123]

Solder is far softer than your valves. I use this method without any bad results. I have even checked assembled motors before taking them apart this way.

Yeap, Solder through spark plug works well if one knows what he is doing. Also BH of solder is about 10 vs 85 or so of aluminum head, valves being much harder.

[TobyB]

Solder is far softer than your valves.

Well, yes, but big enough solder to check valve clearance would scare me.
In the gut reaction department, putting metal in the path of an opening valve makes me go 'errr....'
I'm paranoid about bent stems, just because I seem to have bad luck
with 'em. Set a head down wrong with the cam in it, once...

If your valves are sticking out that far that you damage them while doing a clearance check, you were going to have a bad time anyway..

Hmmm? that's the point of a clearance check- you put something in that WILL be
in interference, and measure how much it deforms. I believe John that solder's soft
enough, I'm just too chickenshit (and I do few enough engines) to use it instead of clay.

t

[zaq123]

Well, yes, but big enough solder to check valve clearance would scare me.
In the gut reaction department, putting metal in the path of an opening valve makes me go 'errr....'
I'm paranoid about bent stems, just because I seem to have bad luck
with 'em. Set a head down wrong with the cam in it, once...



Hmmm? that's the point of a clearance check- you put something in that WILL be
in interference, and measure how much it deforms. I believe John that solder's soft
enough, I'm just too chickenshit (and I do few enough engines) to use it instead of clay.

t

I think you guys are talking two different things, quench clearance check and valve clearance check.....so it appears

[ForcedFirebird]

Well, yes, but big enough solder to check valve clearance would scare me.
In the gut reaction department, putting metal in the path of an opening valve makes me go 'errr....'
I'm paranoid about bent stems, just because I seem to have bad luck
with 'em. Set a head down wrong with the cam in it, once...





t

I rebuild m20 heads nearly on a daily basis. I have only bent a couple valves and that was because I was in the hurry and used the old hammer and socket trick to rapidly disassemble one - and that was only because I didn't use the brass hammer to break the retainer/lock seal. Too much of a hurry and that won't happen again. Good thing I have a box full of m20 valves, or I would have been cursing up a storm lol. The bends were so slight, didn't even notice until they were being back cut.

As far as the solder, it's not like you are sticking a 1/2" piece in there - just something close to get it to smash a little. Plus, when turning the engine over slowly by hand, pretty sure you would feel if it were too much and back off (one would hope). It takes a lot of force to bend a valve, a normal sized ratchet/wrench would make that very difficult. You could also use tin foil if the solder made one too nervous. Clay is just far too difficult for me to get an accurate measurement, even with calipers.

[digger]

IMO you dont normally need a very accurate measurement with clay for P to V as most people arent trying to optimise it , rather just check there is enough so clay is good enough.... with squish clay is likely not going to be accurate enough if youre trying to get it accurate within 0.05-0.10mm or so on a performance engine its easy to squish it a bit much with verniers or not enough...

[TobyB]

It takes a lot of force to bend a valve,

See, this is the difference between an occasional mechanic and a pro-
I just don't do it enough to have a good sense of how tough they are.

And yeah, I cussed when I went to cc it and it leaked...

thanks- I learned something today!

t

[zaq123]

my old head gasket got bent and all out of shape. Any reliable way to use anything else/cheap new head gasket to get P/H and P/V clearances?
If new cheap HG is the only way....how should I do it without torquing the bolts all the way? I would like to avoid marring the head too much while compressing the test gasket to its final thickness.

IMO you dont normally need a very accurate measurement with clay for P to V as most people arent trying to optimise it , rather just check there is enough so clay is good enough.... with squish clay is likely not going to be accurate enough if youre trying to get it accurate within 0.05-0.10mm or so on a performance engine its easy to squish it a bit much with verniers or not enough...

[zaq123]

any suggestions?

[e30davie]

Interesting conundrum. What do you mean by "marring the head"?

If you get the cheapest gasket you can find that is the same thickness as the one you intend to use, then just re-use any old bolts for the test that would have to give you a pretty good indication? Sure you arent supposed to re-use head bolts for running, but i reckon they would be fine for the test.

or find a second hand used gasket that is hanging in someones garage. I tend to hang my old head gaskets in the garage, dunno why...

[zaq123]

Interesting conundrum. What do you mean by "marring the head"?

If you get the cheapest gasket you can find that is the same thickness as the one you intend to use, then just re-use any old bolts for the test that would have to give you a pretty good indication? Sure you arent supposed to re-use head bolts for running, but i reckon they would be fine for the test.

or find a second hand used gasket that is hanging in someones garage. I tend to hang my old head gaskets in the garage, dunno why...

typically, when you tighten the head, gasket's metal rings dig into softer aluminum surface of the head, slightly marring it. If I'll use new gasket, it won't give actual compressed height since it's not compressed till the final torque is applied.
I can just assemble it with new gasket and subtract uncompressed height from the final measurements. I just wanted to know if there are any tricks/ideas from experienced folks who've done it a few times.