what pistons for 340???

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74dusterman

74dusterman

74dusterman
Joined
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I have decided to rebuild my 340 for the 2nd time. It dropped a valve after the first rebuild.... don't ask.:banghead: The block is fine but the head is shot and so is the piston. I was wondering what everyone was running for pistons in their 340? I was considering Keith Black KB243 pistons. The block is bored .030. A little info on the rest of the motor and car- 1970 block, comp cams XE268H cam, Edelbrock Airgap intake, 750 Holley carb, The heads were J heads completly redone with 2.02/1.60 valves and new seats and guides. I don't know if I am going to have another head redone or buy budget aftermarket cast iron heads. The motor is going in my 73 Duster with 833 4 speed and centerforce clutch and 3.23 geared 8.75 posi. I want a good street motor that will fry the tires for 3 city blocks and leave the brand X people in the smoke cloud.:prayer: I am on a bit of a tight budget right now but all of the machine work is already done to the block. Thanks for the help.
 
I have KB 243 in my 340 with about the same build you have.
If you only need one piston, just buy the one piston from the manufacture, it will save on re-balancing the motor.
Why did the motor drop a valve, might be cheaper to fix the head or replace it with a identical head.
Pictures would be useful.
Also take all the oil gallery plugs out and flush all the metallic particles out, they will be every where, with a piston comming apart it needs a complete tear-down.
 
Then engine is completly tore down now. I planned on putting all new bearings in and cleaning the block again. Not sure what the pistons that are in it are. I used the pistons that were in it when I built it the first time. I will feel more at ease with all new pistons and rebalancing the motor than taking a chance again. Have enough money stuck into it already. It dropped a valve as a result of the piston kissing the intake valves because of a rookie mistake.
 
Make sure to measure the cylinder wall diameter and verify it's what it's should be to obtain the correct clearance for the pistons you choose cause not all pistons use the same wall clearance. If the cylinder bore is too large (either worn or honed too large) you may need to take it to .040 over. Another thing to remember is KB hypereutectic pistons take a specific ring gap and need to have the rings file fitted to each bore
 
I love my Ross racing pistons in my 340. It's not that much to have it rebalanced.
 
I'm using Mahle 10.5-1 .40 0ver pistons . So far 15,000 miles and no troubles . Lighter than stock , forged and coated . They were not expensive for what you get .
 
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