340 Rebuild And Machine Work

[plymouthman72]

Back in May, I asked the question of stroking my 340 motor and got a lot of great advice on how to go about it. Link below:

http://www.forbbodiesonly.com/moparforum/search/2855076/?q=340&o=relevance&c[node]=20

I am finally at a point to where I can start putting money into the engine so I disassembled the motor this weekend and found some scratches in the bores that I wasn't expecting to see. After looking back at the old receipts from long ago I did find that my dad did indeed bore the motor .030 over and sleeved the number 8 cylinder. Before I take the block to a shop and have them machine it, I wanted opinions on whether or not the block is worth saving or not. The machine shop thinks they can get by by machining to .040 over but I don't even know if pistons are made to 4.080 on the 340. Here are some pictures of the cylinder holes.

 

[plymouthman72]

Here are the other 4 bores.

 

[PurpleBeeper]

In my opinion, I would just price out your options. If the block is numbers-matching to your particular car and that is important to you, then keep the block. Also, decide if the pistons you have are the pistons you want to run. Are they?

As I see it, your options are:
1. Buy a new 340 block.
2. Buy a used 340 block that can be bored .030" & re-use the pistons you have.
3. Re-sleeve the block you have & use your current .030" pistons.
4. Bore the block you have .040" or .060" and replace the pistons.

Since you're talking about stroking the engine anyway, you'll definitely need new pistons anyway. Based on that, I suggest you keep the block if you can get stroker pistons of an appropriate size, re-sleeve the block if you can't get stroker pistons in .040" or .060" AND it's numbers matching to the car, and find a different block if the first two paths don't work out.

 

[plymouthman72]

In my opinion, I would just price out your options. If the block is numbers-matching to your particular car and that is important to you, then keep the block. Also, decide if the pistons you have are the pistons you want to run. Are they?

As I see it, your options are:
1. Buy a new 340 block.
2. Buy a used 340 block that can be bored .030" & re-use the pistons you have.
3. Re-sleeve the block you have & use your current .030" pistons.
4. Bore the block you have .040" or .060" and replace the pistons.

Since you're talking about stroking the engine anyway, you'll definitely need new pistons anyway. Based on that, I suggest you keep the block if you can get stroker pistons of an appropriate size, re-sleeve the block if you can't get stroker pistons in .040" or .060" AND it's numbers matching to the car, and find a different block if the first two paths don't work out.

Thanks for the advice. It is not the original block and I plan on doing a ground up rebuild with all new parts so I am okay with boring it out if it can be. The machine shop said sleeving us a last resort because its so expensive. I will take it in to them and see what they say if it can be done cost effectively, I will do that. I am however, committed to keeping a 340 block so if I have to find another, I have to. I only want the 340 block since that is the engine that came with the car.

My main thing was to see if the scratches in the pictures looked really bad or something to be expected on a car. Thanks again for the help.

 

[moper]

Best thing to do is to have your block sonic tested. I just did this for a FABO guy over Thanksgiving. His block is not suitable for his plans as a result. Not that your's is perfect - but a 4.08 piston is a custom unit and more moeny, and if you have thin cylinders sleeving them is extra money too. Between those up-charges it might be easier to just start with a better candidate block. So I would start with a high quality sonic test.