What is a 342??

bart said:

...is it just a 347 crank without boring for the pistons??? educate me on this.

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Yep, u got it. 4.00 bore/ 3.400 stroke.

Yeah your keeping the stock 302 bore...people usually get the 342 over the 347 to keep machineing prices down...

My new engine combo I'm putting together is a 342 . My reasoning for not boring is since I bought a more expensive block, I'll be able to bore it down the road when I wear out the 4.0 bore. My pistons and bore are actually about .002 over just to make sure I have a perfect bore with the main studs and girdle installed and torque plates installed.

bart said:

yeah, this would be me. what about the pistons?? i bought a nice set when i rebuil the 302. i wouldnt have to replace them would i??

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I would think you would keep the same piston (assuming same skirted ratio - side of piston)...

bart said:

yeah, this would be me. what about the pistons?? i bought a nice set when i rebuil the 302. i wouldnt have to replace them would i??

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Yup, say goodbye to those pistons they will not work. 302 pistons wont work with a 3.40" stroke crank. I'll be using probe srs forged pistons in my 347 with a 1.175 compression height with the 5.315" probe light weight forged I beam rods.

bart said:

well ****, if i gotta buy new pistons then i might as well bore it. well unless there is a major difference in price between the 2 pistons. the boring cost wouldnt be much more anyways. my builder owns one of those BFE machine shops. 80 bucks to work heads as opposed to 600 for the same in a big urban area.

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Why bore? If you keep the stock bore, you'll have enough left for an extra rebuild. I don't think there is a different price in pistons but I never checked.

qplk11 said:

Why bore? If you keep the stock bore, you'll have enough left for an extra rebuild. I don't think there is a different price in pistons but I never checked.

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I'll go easy on this one

The reason for reboring as with any need for something to be machined is that it loses its shape. With regards to an engine block and its reciprocating parts ala the crank, the bore wears in an oval shape (as do cylinder heads) What happens in a lot of cases if this is not corrected is that you get anything from poor sealing, uneven seating, loss in compression, horsepower loss, blowby, oil consumption, and so on. Reboring isn't spoken of as an option, it's about as common practice as machining a flywheel with a new clutch kit. If you are a lucky one that has a decent or low amount of miles, and everything checks out, then you may just be okay with new seals, gaskets, bearings all around, pistons, and rings. If not, with a bore gauge, a mahcinist will be able to say how much of a bore is necessary to make the bore straight again. One does not just pick a number like .030 over - it must be measured and calculated.


With regards to the piston, if you rebore or you go either of the two major stroker routes, you will need a new piston. If you just do a bandaid engine slap together, then your pistons (4.000") will still work.