need help figuring out quench
10-30-2011, 06:55 PM
#1
need help figuring out quench
I got my engine (22r) back from the machine shop last week and assembled the short block, everything went well until I realized my pistons are +.020 out of the block. The block was bored .020 over and the crank was polished but not ground and the block was not decked and never has been. I have read that +.006 is best but how much is too much?
Before I realized that I was even supposed to measure the height of the pistons
I torqued the head down with an OEM head gasket, when I removed the head the gasket measured .057 thick at the fire ring, does this mean I have .037 quench or is the HG compressed much more than that when installed.
Should I have the pistons shortened .010? What about the .020 thicker lce headgaskets?
I am using the ITM components that the shop sold me and an engnbldr street/rv head. This is my first engine build so I am not really sure what to do.
Before I realized that I was even supposed to measure the height of the pistons
I torqued the head down with an OEM head gasket, when I removed the head the gasket measured .057 thick at the fire ring, does this mean I have .037 quench or is the HG compressed much more than that when installed. Should I have the pistons shortened .010? What about the .020 thicker lce headgaskets?
I am using the ITM components that the shop sold me and an engnbldr street/rv head. This is my first engine build so I am not really sure what to do.
10-31-2011, 06:25 AM
#3
Registered User
First pistons don't get cut to change quench values. Rods are cut if too much positive quench and if too much negative quench then blocks get shaved. Usually re-builders' pistons are already "cut" due to the fact of how many blocks and/or heads are cut during rebuild. But not all. They are almost never "taller". Not quite sure your measuring correctly. That value is supposed to be measured with the headgasket in place and not "squished" or without the headgasket in place. I can't remember, but either way a .020" value has got to be way out of whack unless the bearings aren't correct or you got other issues going on.
Engnbldr a while back on another forum had a very good writeup explaining this. Might try google for it.
Engnbldr a while back on another forum had a very good writeup explaining this. Might try google for it.
10-31-2011, 07:26 AM
#4
These are supposed to be OEM height pistons, not destroked and the bearings are standard size and they plastigauged within spec so I would think that they are ok. The only way it seems that they could be too tall is if the pistons are thicker than stock, are these crappy pistons?
I am measuring the height with a straightedge across the piston and sliding a feeler gauge underneath without the headgasket in place. Is that the proper way to measure?
I will be calling engnbldr and my machinist this morning.
I am measuring the height with a straightedge across the piston and sliding a feeler gauge underneath without the headgasket in place. Is that the proper way to measure?
I will be calling engnbldr and my machinist this morning.
10-31-2011, 07:32 AM
#5
they said they decked .006 off the block, and their chart shows a .032 max protrusion spec for all 22r's...way more than anything i've seen posted. machinist also claims that a headgasket is only compressing about .003 leaving about .053 or so of gasket thickness, thus a head/piston clearance of about .019...wonder where all these specs come from. Ted @engnbldr has alot of experience that results in his preferred quench spec of 0-.006 which is what I am/was going by. My shop says I will be fine with stock gasket, I am curious how I will be upon first startup.
http://www.4x4wire.com/forums/showfl...fpart=all&vc=1
Last edited by MudHippy; 10-31-2011 at 07:39 AM.
10-31-2011, 07:34 AM
#7
Registered User
here is that article I was talking about:http://www.4x4wire.com/forums/showfl...fpart=all&vc=1
EDIT: Dang Mudhippy slightly beat me to that article. It apears that he's measuring without the headgasket in place as he references block and not HG.
EDIT: Dang Mudhippy slightly beat me to that article. It apears that he's measuring without the headgasket in place as he references block and not HG.
*******
One very important step is to verify the quench before final assembly, which is often overlooked. Quench is the close collision of the piston head to the flat part of the combustion chamber. Nearly all aftermarket pistons are destroked by about .3mm or around .012" or so. This varies a tad between brands, so installing a new piston set will probably reduce the piston height. Then if your machinist resizes the connecting rods, you just lost even more deck height because they clip the cap and rod to do it. (Well, they do if they are doing it right.)
********
There is only one real way to check for quench, you must assemble the short block and measure. So you will need one spare set of connecting rod bearings, they are cheap since all 1975 to 1995 take the same part, only the undersize varies depending on if your crankshaft is machined or not.
Then if the machine shop regrinds the crankshaft, you really could end up with 4 different deck heights in the same engine, unless they index the crankshaft stroke and most simply do not. By the time they get to, say, .030" undersize and have resized all of the connecting rods, it can stack up to a lot, and this just kills power output.
So "dummy" up the short block, and measure how close the piston is to the top of the block. A straight edge and a feeler guage makes this easy. We want it to be zero deck, or as close to that as we can get. Stock, the piston does protrude by about .006" or so, if yours does, this is fine.
The goal here is to get them all to as close to the same as possible and up where they belong.
If this measurement shows the piston is down from the top of the deck at TDC, you will need to disassemble and correct this by having the block decked. Tight quench means you can run proper ignition timing without pinging. A sloppy quench will create more pinging at less timing that the tighter compression ratio will, the blast effect of the close collision atomizes the mixture and distributes it better across the chamber.
Be sure to keep track of exactly how much is surfaced off the engine block, this is important I will get to why later.
One very important step is to verify the quench before final assembly, which is often overlooked. Quench is the close collision of the piston head to the flat part of the combustion chamber. Nearly all aftermarket pistons are destroked by about .3mm or around .012" or so. This varies a tad between brands, so installing a new piston set will probably reduce the piston height. Then if your machinist resizes the connecting rods, you just lost even more deck height because they clip the cap and rod to do it. (Well, they do if they are doing it right.)
********
There is only one real way to check for quench, you must assemble the short block and measure. So you will need one spare set of connecting rod bearings, they are cheap since all 1975 to 1995 take the same part, only the undersize varies depending on if your crankshaft is machined or not.
Then if the machine shop regrinds the crankshaft, you really could end up with 4 different deck heights in the same engine, unless they index the crankshaft stroke and most simply do not. By the time they get to, say, .030" undersize and have resized all of the connecting rods, it can stack up to a lot, and this just kills power output.
So "dummy" up the short block, and measure how close the piston is to the top of the block. A straight edge and a feeler guage makes this easy. We want it to be zero deck, or as close to that as we can get. Stock, the piston does protrude by about .006" or so, if yours does, this is fine.
The goal here is to get them all to as close to the same as possible and up where they belong.
If this measurement shows the piston is down from the top of the deck at TDC, you will need to disassemble and correct this by having the block decked. Tight quench means you can run proper ignition timing without pinging. A sloppy quench will create more pinging at less timing that the tighter compression ratio will, the blast effect of the close collision atomizes the mixture and distributes it better across the chamber.
Be sure to keep track of exactly how much is surfaced off the engine block, this is important I will get to why later.
Last edited by xxxtreme22r; 10-31-2011 at 07:40 AM.
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10-31-2011, 08:40 AM
#8
Ok, so I read all that and it seems that I am measuring right and my pistons really are +.020 which is too much so how should I fix it?
Is there anything on assembly that I could have done to cause this?
It seems my options are thicker HG or recrown pistons.
Is there anything on assembly that I could have done to cause this?
It seems my options are thicker HG or recrown pistons.
10-31-2011, 09:55 AM
#9
well this is what I heard from Ted, pretty interesting
"Hi.
Well, that is part of why we do not supply ITM products, we have had some of the same issues with those pistons and even worse with their cylinder heads.
But we have also seen .020" piston protrusion and ran them that way, premium fuel usually becomes a requirement though.
Factory pistons specs for early (to circa 1989-90) was .939", average of .010" to .015", the factory reduced that to .925" which is about zero to .006" protrusion with all else stock.
Note variations in the figures that do not quite come out, the reason is the factory deck on the blocks was all over the place, something I am sure of having measured probably literally hundreds of them.
Our piston sets are destroked to allow room for decking, (.913") that is a possible option for you but of course additional cost. That should put you at about minus .006" which is just fine, the difference between that and zero would not be noticeable as far as power is concerned.
Or you could bolt her up and run her the way she is, if you avoid any overheat situations she should be all right.
Hope this helps,
Ted(engnbldr) "
"Hi.
Well, that is part of why we do not supply ITM products, we have had some of the same issues with those pistons and even worse with their cylinder heads.
But we have also seen .020" piston protrusion and ran them that way, premium fuel usually becomes a requirement though.
Factory pistons specs for early (to circa 1989-90) was .939", average of .010" to .015", the factory reduced that to .925" which is about zero to .006" protrusion with all else stock.
Note variations in the figures that do not quite come out, the reason is the factory deck on the blocks was all over the place, something I am sure of having measured probably literally hundreds of them.
Our piston sets are destroked to allow room for decking, (.913") that is a possible option for you but of course additional cost. That should put you at about minus .006" which is just fine, the difference between that and zero would not be noticeable as far as power is concerned.
Or you could bolt her up and run her the way she is, if you avoid any overheat situations she should be all right.
Hope this helps,
Ted(engnbldr) "
10-31-2011, 04:04 PM
#10
After talking to my machinist, ted and an LCE tech I ordered a .072 head gasket. I also remeasured my pistons using a makeshift deckbridge and came up with +.023 on all of them, this probaby isn't exact but I think it is more accurate than my feeler gauge.
With the thicker HG and +.023 that gives me an estimated quench of .049.
I will post back when I get it up and running, thanks for the help!
With the thicker HG and +.023 that gives me an estimated quench of .049.
I will post back when I get it up and running, thanks for the help!
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