340, 318 main cap difference

[68fsh]

Does anyone have pics of the 340, 318 main caps? I heard the 340 ones are taller. I want to purchase one but what to make sure it is the 340 main caps before I purchase it

 

[krazykuda]

Both engines use the same main bearing caps, and both have the same main bearing journal diameter. The main cap bolts are the same length...

You will have to get the caps align bored if you change them from the originals that came on the block.

 

[Locomotion]

FWIW, here are pics of a Direct Connection P4007249 Pearlitic main cap for #1, 2 & 4 mains. I realized I had a caliper nearby after I took the pic with the ruler, but the cap is 1.014" wide and 1.250" tall.

I thought 318 caps were less beefy and/or shorter than a 340. But I never had the 2 to compare side-by-side or needed to compare them. :dontknow: Always open to learning something new. :iconbigg:

lol...Some people must be just being nice, but I meant to say "2.250 tall"

 

[AJ/FormS]

The part thats taller is the bolts, to allow fitment of the oem windage tray. The retaining screws, screwed into the main-bolt heads

 

[NC Engine Builder]

Both engines use the same main bearing caps, and both have the same main bearing journal diameter. The main cap bolts are the same length...

You will have to get the caps align bored if you change them from the originals that came on the block.

This is 100% WRONG. the 318 caps are shorter than 340 caps.

 

[NC Engine Builder]

actually, the bore size is the same, and yes also to line boring for diff caps

 

[AJ/FormS]

They must be taller, cause when I put the windage tray and 340 main-bolts onto a 318, years ago, it seems to me I had trouble with the bolts bottoming before the caps were tight. Seems to me I double washered them.I was a kid then so we did what ever worked.

 

[NC Engine Builder]

They must be taller, cause when I put the windage tray and 340 main-bolts onto a 318, years ago, it seems to me I had trouble with the bolts bottoming before the caps were tight. Seems to me I double washered them.I was a kid then so we did what ever worked.

correct

 

[1970Duster]

Just buy a good aftermarket set. They'll be stronger than the originals and you have to line hone/bore the caps anyway. It's also a great to have the caps machined flat in case you what to run/use a stud girdle.

 

[krazykuda]

This is 100% WRONG. the 318 caps are shorter than 340 caps.

Ok then. Show me...

 

[NC Engine Builder]

340 cap is just about exactly .250 thousanths taller. Bolts longer as well, I will try to attach a pic

 

[NC Engine Builder]

A couple more

 

[mderoy340]

Learned something new today. Thanks

 

[NC Engine Builder]

A quick measurement looks like the 318 cap is 1.996 tall and the 340 cap is 2.247 tall. The 340 cap is a few thou wider, but not much. Bolts are different also, and not because of the windage tray.

 

[krazykuda]

A quick measurement looks like the 318 cap is 1.996 tall and the 340 cap is 2.247 tall. The 340 cap is a few thou wider, but not much. Bolts are different also, and not because of the windage tray.

I wonder why they did that...


What's the difference in the bolts, just length?


Is there a difference between the 318 and 340 caps in the locating width (for the channel)?

 

[NC Engine Builder]

I wonder why they did that...


What's the difference in the bolts, just length?

yeah, the bolts are just a lil longer, same head, thread ect. I guess they figured the 340 was a "performance" engine, intended to be more heavy duty, more rpm ect.

 

[NC Engine Builder]

Is there a difference between the 318 and 340 caps in the locating width (for the channel)?[/QUOTE]

No, they locate the same, and are completely interchangeable as long as you use the correct length bolts.

 

[krazykuda]

Is there a difference between the 318 and 340 caps in the locating width (for the channel)?

No, they locate the same, and are completely interchangeable as long as you use the correct length bolts.[/QUOTE]


I wonder if they built them on the same assy line at Mound Road, or on different lines...

They used to build the 3.9 L and 5.2 L on the same assy line in the late 90's. The 360's were made in Mexico then....

 

[NC Engine Builder]

If I am correct, I think ALL the 340s were built in Canada. But I still think it was a HD
thing

 

[krazykuda]

Is there a difference between the 318 and 340 caps in the locating width (for the channel)?

No, they locate the same, and are completely interchangeable as long as you use the correct length bolts.[/QUOTE]


I thought that they were interchangeable, but didn't know the heights were different...