Use a table ban saw to hack off the 340 piston crown .

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J

Jessearent

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340 piston in 360 block : take off bout 0.10" from piston crown if it's thick enough, add a 0.080"head shim on the engine side with a standard 0.038" thick head gasket gets you 0.118" to work with. Subtract from the 0.27" sticking out....you need to shoot for the perfect 0.030 squish/ quench @tdc for the turbulence it creates in your combustion chambers...measure carefully and take in to account your rpm, stroke, stretch at the high end...
 
And how do you determine if 'the crown is thick enough'? What input would you use to determine a safe minimum?
 
Absolutely a poor idea on several areas. Chuck them in a lathe if you need to trim them down, but only if they are a solid dome. You can tell from looking at the inside of the piston.

Skip using a .080" spacer and buy Cometic head gaskets in whatever thickness you need them in.

However before you go to all the trouble just sell the domed 340 pistons and buy the set of 360 pistons you need.

Keep it simple for when, or if you need to repair it later down the road.

Tom
 
Here is an equally smart move:

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1 laugh 4.jpg
 
Yea , I thought I would get a good laugh...we here in Alabama like doing it on the cheap... No money's for the machine shop if we can help it.
 
Okay I looked up the KB 243, which is a flat top piston. You called it a crown and I was thinking dome in my first reply. There is no way you can cut .100" of the top of that piston even

lathe cut and expect it to live. I've cut really thick old forged TRW pistons off in the lathe and ended up with .110" top thickness when I was done. Those KB 243 pistons are

Hypereutectic and they aren't nearly as strong as forged pistons are. You're going to do as you like, but I am still doing to say it's a bad idea.

Good Luck,

Tom
 
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Yes, I believe your correct, but now I know some poor fella / youngster out there who has an old set domed forged piston laying around and wants to build his engine with no money and use what he has will go and borrow his neighbors table ban saw and enjoy doing it.
 
Jessearent said:
Yes, I believe your correct, but now I know some poor fella / youngster out there who has an old set domed forged piston laying around and wants to build his engine with no money and use what he has will go and borrow his neighbors table ban saw and enjoy doing it.
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Sell the pistons you have and buy some 360 pistons. No reason to reinvent the wheel now a days with all the choices that we have for parts.
 
Where are the rings gonna end up relative to the deck?
and will they survive there?
Recheck your math;
A friend of mine did this with used factory pistons, (don't know which ones) without spacers. It's been a strong street-runner nearly as long as mine has (since 1999)
 
Jessearent said:
Yes, I believe your correct, but now I know some poor fella / youngster out there who has an old set domed forged piston laying around and wants to build his engine with no money and use what he has will go and borrow his neighbors table ban saw and enjoy doing it.
Click to expand...
Band saw. Aw what the heck, use a bench grinder.
 
PROSTOCKTOM said:
Absolutely a poor idea on several areas. Chuck them in a lathe if you need to trim them down, but only if they are a solid dome. You can tell from looking at the inside of the piston.

Skip using a .080" spacer and buy Cometic head gaskets in whatever thickness you need them in.

However before you go to all the trouble just sell the domed 340 pistons and buy the set of 360 pistons you need.

Keep it simple for when, or if you need to repair it later down the road.

Tom
Click to expand...

^^^^^^^^^^^^^^agree , I did turn down a pent roof set of hemi prostock trw`s , to legal superstock specks , back in the day ...
 
I prefer a Harbor Freight cut off wheel to do all my critical work. Good luck with your project and please give us a follow up.
 
Dartswinger70 said:
How about a "belt sander...?" :)
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I use a band saw. The OP has a ban saw. You can try a belt sander if you wish. I would have mine machined on a lathe or a mill. Or better yet, just buy the right pistons to start with. I have a couple of things that were done on my 273 that were made to work but I would change if I had to do it over.
 
as above sell the 340 pistons, buy the right 360 pistons. too expensive you say? don't forget shimming the head off the block will need to buy longer custom pushrods and the intake will need shimming too. doesn't make the difference between selling your pistons and buying 360 ones seem so bad now does it. no shims to buy, for heads or intake and no custom pushrods to buy. and you can still be happy you didn't give money to a machine shop :rolleyes:
 
You need .187 or so for material thickness on the top of the piston if I remember correctly. This was a set of TRW's but it's been 25 years.

Make a simple fixture to keep it consistent and way to scale your pistons. It won't win awards from most but I did it and that motor is probably still running today lol.....
 
****, I just throw them in the engine and dykem the decks; belt-sand until flush. If you want the pistons out of the bore, just use an old scrap head gasket as a spacer.
Use a flashlight to make sure the pistons aren't too thin. If you can see light through them, get out the electric glue gun and add some metal where you need it.
 
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