Main cap question?

[Mike 340]

Can you use 273 main bearing caps on a 340?
I have a person that wants to do this and I don't want to sell him the wrong parts.

Thanks
Mike.

 

[perfacar]

they will fit, use 273 bolts though, as caps are shorter.

 

[Mike 340]

Thank you, I thought that there was a difference.

 

[perfacar]

block will have to be align bored though. torque is same for 273 and 340 bolts

 

[Mike 340]

I am thinking that he will need a line bore to use these caps or any other caps.

He might be better off to get 340 caps.

 

[perfacar]

doesn't matter which caps, still needs to be align bored. the 273 caps are strong enough to support crank. also have to find a set of stock caps, from another block. stock caps are not available as new,

 

[grimreaper]

The 273 caps are approx. 1.996 tall and the 340 caps will be approx. 2.247 tall. Same bore, but they may not line up exactly so if the fit is close they will need a line bore. The 340 caps are usually a few thousandths wider on the outside. Bolts are different length and 340 had special bolts for windage trays. The rear cap is the one that usually has the largest alignment difference so any swap of main caps can be problematic.

 

[Mike 340]

Thanks for the information, he also wants to buy the crankshaft as it is a steel one. But I warned him that he would need to get it balanced for his assembly.

 

[Jadaharabi]

For my 2 340 blocks I tried the used 318 and 340 cap. Wound up buying new 4 bolt main sets and cutting off the the outside bolt hole on the 3 middle caps.
The problem with the used caps is they may be side shifted at the factory and won't line up with your block.

 

[cudamark]

Thanks for the information, he also wants to buy the crankshaft as it is a steel one. But I warned him that he would need to get it balanced for his assembly.

As for crank interchange....the forged 273 cranks have the small converter register, so, that could be an issue with using the later converters. Either machine the hole larger, or, build a custom converter with the smaller button. If it's going into a manual trans car, you may need a conversion bushing (bearing actually) if the 273 crank doesn't have the final machine work done for the stock pilot bushing. An engine rebalance will be necessary too.