340 rod bushing conundrum

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BIGLOVE

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picked up my 72 340 from the machine shop, 340 .030 over speed pro l2316 pistons, 341865 rod castings, eagle cast crank. The rods i sent were not bushed for floating pins so i asked him to verify. Well i pick them up no bushing. took it home and measured pin at .984od and the .986 id on the rod. i asked him about it he said to run them. It seems that this is a divided subject would like to get some opinions from yall. should i take them back and have them resized and bushed or just send it.

Thanks
 
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First off, how did you measure it? A caliper ain’t much better than using a tape measure for stuff like that.

Second, you can run them unbushed and floating. I’m just not sure on that much clearance, but again...not questioning your skills or anything else...I’m just saying without a micrometer and a bore gauge you have no real idea what the clearance really is. Unless the machinist told what the clearance is.
 
Yeah I just used a caliper to measure. I assume my machinist checked them since he said to run them unbushed seemed like if people were running them steel on steel the clearance was.0007 ish
 
BIGLOVE said:
Yeah I just used a caliper to measure. I assume my machinist checked them since he said to run them unbushed seemed like if people were running them steel on steel the clearance was.0007 ish
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I can buy the .0007 clearance. Somehow you need to verify that though, unless you really trust the machinist.
 
Unbushed factory rods are usually run as press fit, not floating.

Steel on steel floating....... I’m not a fan....... at all.
 
PRH said:
Unbushed factory rods are usually run as press fit, not floating.

Steel on steel floating....... I’m not a fan....... at all.
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Me either, but I’ve seen it done so many times I can’t count, and I’ve never seen a failure. Even with uncoated pins.
 
Steel on steel is not a problem for Nascar, F1, Porsche, Ferrari and others.
 
Cuz that stuff all uses the exact same materials for the rods and pins as what’s in a 70’s 340.

I’m sure Mopar added the bushings just to waste money.

FWIW, I’ve torn motors down with the steel on steel floating situation(circle track stuff from the 80’s-90’s when there were “stock rod” rules in place) ....... several of them had the pins seized into the rods from the rods and pins exchanging material.

It’s a def “no thank you” for me.
 
^^^^^I agree, either bush them properly (like stock 340's were from the factory) or press fit them. For street and mild performance use with stock rods, I'd bush them.
 
It's a cheap mod to bore rods for bushings and add them. How much would a seized piston pin cost?
 
If the pin just seized on the rod, you probably wouldn't even notice it. If it seized both on the rod and in the piston....that could be catastrophic.
 
cudamark said:
If the pin just seized on the rod, you probably wouldn't even notice it. If it seized both on the rod and in the piston....that could be catastrophic.
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And it would. How flippin hot do you think the pin would be when it seized to the rod? It'd weld itself to the piston.
 
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