Stepped piston hitting head, options and advice needed.

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popinsmoke

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Gentlemen,

I am going to try to give you the readers digest version of my situation.

I bought a 408 stroker short block that due to my own error I did not catch the fact that this short block must be used with open chamber heads.

Shortly after taking delivery of the short block I have to have shoulder surgery on both shoulders 4 plus months recovery each side, so the short block sat for the better part of a year.

So last week I install the oil pump, pan, cam XE268H, and timing cover, mock up a head and clay they piston to check my piston to valve clearance and it hits me like a big bucket of stupid the piston hit the the head Doh!

The piston is a stepped KB with a raised quench pad that sticks above the deck, my heads are RHS LAX heads with a closed chamber just like the manufacture said not to use had I caught the warning.

So now I am looking at options and or solutions?

Do I dump money into a set of open chamber 596 heads that I have on the shelf?

Do I pull the rods and pistons out and have the quench pads milled?

Run a custom really thick head gasket?

Buy the Edelbrock heads that have the .60 machine into the chamber to clear the above deck pistons found in the 68-71 340's?

Start a shop fire and collect the insurance (kidding mostly)?

I am still kicking myself for not catching that the short block would not work with closed chamber heads which I already had.

Thanks for reading this far any advice is appreciated.
 
Where is the flat of the piston? Close to zero deck? Then mill the quench pad off the piston and rebalance the rotating assembly.
 
Would a thicker gasket do the trick?

I order up a Cometic gasket @.075.
 
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Wait just a flaming minute! A stroker piston with a quench pad? Who makes those? I've got a stroker with the dished pistons .010" out of the hole. But that is because the machinist goofed up. That was solved with a .051 thick gasket.
 
Icon / keith black pistons have a quench dome that can be removed or partly removed. It should be fairly close to zero on an uncut deck. If using a .039 gasket the deck would have had to be cut .040 or more ?????? . A thicker head gasket is the easiest answer . Are you sure its the pistons hitting the heads and not an incorrectly installed timing chain allowing the pistons to hit the valves. Also make sure the pistons are installed correctly as they are small / large valve oriented.
 
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If a thicker gasket doesn't do the trick, build the open chamber heads you have
That cam will keep your power hand down low, so heads don t need to flow a ton, I doubt it will ever rev past 5500
 
I had a similar issue and the machine shop milled the Pistons down. No problems and didn't cost much.
 
what about stacking the head gaskets you got...
check p-v clearance.
then decide, cut pistons or purchase cometic gaskets,

Hate to see you cut the pistons, then not have enough p-v clearance
 
first some carefull triple measureing to see how much interference there is (be aware of piston rock) & how much SCR you are after/will have when done & can you achieve quench. I would try to resolve it with the custom Cometics & they I believe need a smooth(er) deck/head surfaces. If you do mill the pads weigh the pistons before/after (HF has a $9.95 digital scale that is just as accurate as my buddys high dollar one!) & if needed check into this: reportedly OE 273 pins are real heavy & could possibly be used to make up the milled off weight difference (drill out the pin ID till the weight matches what you need) to save you from rebalancing. The wall thickness on em was way thicker than normal cuz Ma used em for a similar (rebalancing) purpose.
 
Rapid Robert said:
first some carefull triple measureing to see how much interference there is (be aware of piston rock) & how much SCR you are after/will have when done & can you achieve quench. I would try to resolve it with the custom Cometics & they I believe need a smooth(er) deck/head surfaces. If you do mill the pads weigh the pistons before/after (HF has a $9.95 digital scale that is just as accurate as my buddys high dollar one!) & if needed check into this: reportedly OE 273 pins are real heavy & could possibly be used to make up the milled off weight difference (drill out the pin ID till the weight matches what you need) to save you from rebalancing. The wall thickness on em was way thicker than normal cuz Ma used em for a similar (rebalancing) purpose.
Click to expand...
Yep, check compression mathematically as if you milled a part of the dome and use a bit thicker gasket, or go as far as needed to get .035 to .040 quench AND the right compression ratio for your combo.
On my stroker I needed to cut .005 to get exactly what I wanted for quench and compression. The result was a motor that made max power at 30 degrees on 100 octane gas.
 
popinsmoke said:
Gentlemen,

I am going to try to give you the readers digest version of my situation.

I bought a 408 stroker short block that due to my own error I did not catch the fact that this short block must be used with open chamber heads.

Shortly after taking delivery of the short block I have to have shoulder surgery on both shoulders 4 plus months recovery each side, so the short block sat for the better part of a year.

So last week I install the oil pump, pan, cam XE268H, and timing cover, mock up a head and clay they piston to check my piston to valve clearance and it hits me like a big bucket of stupid the piston hit the the head Doh!

The piston is a stepped KB with a raised quench pad that sticks above the deck, my heads are RHS LAX heads with a closed chamber just like the manufacture said not to use had I caught the warning.

So now I am looking at options and or solutions?

Do I dump money into a set of open chamber 596 heads that I have on the shelf?

Do I pull the rods and pistons out and have the quench pads milled?

Run a custom really thick head gasket?

Buy the Edelbrock heads that have the .60 machine into the chamber to clear the above deck pistons found in the 68-71 340's?

Start a shop fire and collect the insurance (kidding mostly)?

I am still kicking myself for not catching that the short block would not work with closed chamber heads which I already had.

Thanks for reading this far any advice is appreciated.
Click to expand...
KB356 Pistons..?
I run kb356 in my 410sb, they are a d cup quench step head style. I milled the quench pads to a positive .046, or ".046 out of the hole"... which flushed with the compressed thickness of the gasket. I run open chamber j heads. I did not re balance anything and it's smooth. Youre taking weight off, like about a gram or so, if that....but that's a new topic for debate in some other thread...possibly called "to balance or not to balance"..lol
Those pistons ootb will only work with stock chamber j/x head for a quench of around .040. The stock 70-74 heads were about .080 deep on that side. Everything else requires some milling to work and or raise the compression from 9.1
Pull the piston and rods, mill piston. I believe they are .080 tall.
Should be just you time and about 65-80 bucks for the milling.

Or....you take matters into your own hands and get a bench mounted belt sander and do it yourself.
You can weigh the cost of balancing against redoing other open chamber heads if you want...but unless you port them, they wont do the hp the RHS will.

Mill pistons, "consider" re balance , it will be cheaper than recon heads with porting.
 
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IQ52 said:
Wait just a flaming minute! A stroker piston with a quench pad? Who makes those? I've got a stroker with the dished pistons .010" out of the hole. But that is because the machinist goofed up. That was solved with a .051 thick gasket.
Click to expand...
Okay, yeah, what is it, KB236? Mill down the quench dome.
 
I agree with milling the piston down. Seems the best way.
 
MOPAROFFICIAL said:
Youre taking weight, I don't amount like about a gram or so, if....bit that's a new topic for debate in some other thread.
Click to expand...
Correct..... you're talking a bit over a gram for .040" off of this quench pad. That will effect bobweight by an equal amount, and only the most highly revved engine (like 6 or 7kRPM and above IMHO) would need a re-balance for a change of 1+ grams in bobweight.
 
A person could cut a piece of paper in the shape of the step then cut that piece up into pieces to where you can lay/fit em together in a circle then measure the circle diameter & 1/2 of that for the radius then get the area "(A) =Pi x radius squared" for square inches then multiply that number by the thickness you wanna mill, say .035" to get cubic inches then multiply that number by 16.387064 to get cubic centimeters and aluminum weighs 2.699 grams per CC. then you will know exactly how much the piston will be lightened. This is my OCD talkin! OR you could call KB as I'm sure they have dealt with this before but that is too easy! (& whats the fun in that).
 
i did the same to my KB356 Pistons....put them in a lathe and turned down the quench pad to use with the closed chamber heads. No Problem, way better than using a thicker gasket in my opinion.

Michael
 
Rapid Robert said:
A person could cut a piece of paper in the shape of the step then cut that piece up into pieces to where you can lay/fit em together in a circle then measure the circle diameter & 1/2 of that for the radius then get the area "(A) =Pi x radius squared" for square inches then multiply that number by the thickness you wanna mill, say .035" to get cubic inches then multiply that number by 16.387064 to get cubic centimeters and aluminum weighs 2.699 grams per CC. then you will know exactly how much the piston will be lightened.
Click to expand...
Or just LOOK at the pix of the piston in question, make a good estimate of the area based on its standard shape and well-known geometric formulas and the known piston diameter, and work out the numbers.....oh wait.... I DID that when I gave my number: a bit over a gram for a .040" cut. (I don't usually put out numbers without already working it out.... LOL.)

Measuring after the milling is A-OK if you want the answer, but I would like an idea of the answer up front BEFORE pulling everything apart.
 
MoparLeo said:
Don't start cutting and grinding on your engine. Just put the proper heads on and be done.
Click to expand...
Wasn't implying to so it while assembled.
That's another option, sell the rhs...to buy open eddy, but even still the pistons come out .080 and @ 9.1 or 9.5 with the average 68-65cc...you need 60cc chamber for 9.99/10.1 compression. And say .030 quench distance, so the head needs to be that depth on the shallow quench side.

Could the RHS be machined for an open .065 deep chamber on that side to accommodate that ootb quench pad.... id look into that cost.
 
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MOPAROFFICIAL said:
Wasn't implying to so it while assembled.
That's another option, sell the rhs...to buy open eddy, but even still the pistons come out .080 and @ 9.1 or 9.5 with the average 68-65cc...you need 60cc chamber for 9.99/10.1 compression. And say .030 quench distance, so the head needs to be that depth on the shallow quench side.

Could the the be machined for an open chamber ....id look into that cost.
Click to expand...
Better yet, fill the valve notches with clay, turn the motor over till the piston is exactly .500 down in the hole, use grease to seal the piston to bore, measure the volume with alcohol, and subtract it from the bore square area times .500. If you have a 4.030 bore, then 2.015x2.015x3.1416 x .500= 6.378 cubic inches, or 104.5 CCs. Divide the difference by 16.387 for the CCs You can divide the dome height into the CCs of the dome, and multiply times the cut for the amount of volume removed. There are formulas for the weight of aluminum if you search for them. Go to United Engine and Machine web site for a compression ratio calculator that allows quick changes for gasket thickness and piston dish volumes to get ypou the answers you want. That is how I did it.
 
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