72 340 short block

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340 8BBL

340 8BBL

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today i picked up a 72 340 short block for 50 bucks.the bearings appear to be in good shape,and it has no ridge.but the bores have surface rust and the piston are 40 over stamped with L2316 .040.does any body know if these are cast or forged,and what the comp ratio is?also what is the over bore limit for this year 340?is it possible to clean the block and re-hone it and re use the pistons?thanks -wade
 
L2316 Sealed power hyperuertics or whatever they call them.Better than cast,not quite forged.9.8 to 1 on my motor,deck height and heads will change that though.

At .040 over your almost maxed,clean up the bores if possible,have the block sonic checked to make sure if you need to go farther.They should clean up if not too badly rusted.
 
L2316 are an old trw and seal power part number they are forged pistons.
 
L2316F at least used to be the TRW number for the 68-71 Hi compression forged replacement piston. Depending on actual deck height, actual combustion chamber cc's, depth of the valve notches if deepened over stock, and thickness of the head gaskets used, exact stroke of the crank, and rod length, all affect the compression ratio.
You could have anywhere form the mid 9 range all the way up to almost
13-1.
Better get some help measuring to be sure what you have.
A 340 for $50 is still a good deal. Congrats.
Alan627b
 
mygwenevere66 said:
anybody know the overbore limit?
Click to expand...

Ever block is different only a sonic check will tell you. Some blocks can't go pass .030 others can go much higher..I hear of .090 on a few GM blocks...only cause more racers are using them.

Rumor is the first 360 blocks were really cast as 340 and those blocks can be opened up alot from the 360 bore size.
 
.060 is safe, just have it sonic checked for thickness.

sounds like TRW pistons, I have a few sets.

When you rebuild it, look at KB243 pistons, they fairly light and cost little.
 
Yup, old forged pistons... If it's +.040 then it's at the factory recommended limit. I've found the 72=73 blocks to be better in terms of core shift so they may be fine to go larger even for a stroker. If there's rust, I'd plan to have it sonic tested and plan to over bore. It's an ok price but the choices for use now are limited without checking it.
 
I've known people that have lightly honed and re-ringed if there is very light rust. Its not ideal, but if you get someone good, with a good honing machine and a nice finish on the walls it may be fine. The surface finish is important. Assuming the cylinders were honed straight and correctly the last time.
My 273 wasn't rusty, but the last person to bore and hone did a very poor job on the final surface. It burned almost 4 quarts of oil in 200 miles. It had new pistons so my boss at the time cleaned up the cylinders for me at work. He has done many, many performance builds and knows a good hone. I reassembled it with new rings etc. It used under a quart of oil on my 3,500 mile road trip last month.
 
If you are looking at just "surface" rust as in a light coat of it with very little to no pitting in the metal itself...I would just clean up the cylinders.
I have been doing it for years,you would be surprised to see some engines I have brought back lol.
I had and engine that sat in the weeds for years with no spark plugs and valve covers off and exhaust manifolds off,pistons were locked from rust,pulled it all apart and had pretty bad rust but I brought it up to par and it didnt smoke or use a drop of oil.
It all just depends on if you know what your doing I guess.
I normally take some light emory cloth strips and knock down the rust until its kind of dusty smooth I guess you would say.
I then hone it out, I have used bead hones and block hones but the bead style is harder to find and if you work a spot to long you can "egg shape" the cylinder slightly.
A nice block hone with some good sharp stones and some WD-40 will make them look like brand new after knocking the rust off with emory.
Load it up on the drill and start off slow and spritsing it with WD-40 while its rotating and keep working your way back and forth (don't hold one spot or you can create a ridge).
As you go along you feel less drag and visibly notice the difference in the cylinder and you can gradually speed up the drill and towards the end you will be going full speed and in and out of the cylinder non stop.

The end result should be a nice glass textured cylinder.
You can atleast try this first and see what you think and see if you can save the cylinders.
It sure is alot cheaper then having to have the block bored and sonic tested and buying new pistons and rings and everything else....when you could just be looking at what it will cost you to hone it and toss rings on the pistons you have already! Something to think about any way ,good luck!
 
thanks guys.ill let you know how it turns out,now all i need is another a body to put it in .damn it.
 
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