Main bearing question

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Coyote Jack

Coyote Jack

Member #55, I'm old
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I am building up my 340 and I am going to use a 318 steel crank in it. I already have the rotating assembly balanced so that is not an issue.

What I am wondering is, I see main bearings for 318's and I see bearings for 340's listed separately. What is the difference in them? I thought that they shared the same journal size. Is it how they oil? And last but not least, which bearings should I use?

Not a rookie at this but have never swapped cranks like this before.

Jack
 
Difference might be material (harder, softer) of the bearings and whether or not the top shell is grooved for better oiling.

You can get bearings that are grooved in both halves, which will start a huge argument as to whether they are better or weaker.
 
I hear you on the better or weaker argument. The materials should be the same as they are the same C-77 bearings. I will check out the grooves.

Jack
 
the crank will fall in with either set of bearings. im guessing the 340's might be full groove. if not, id order a set of full grooves if its a hot rod. really doesn't seem to be much advantage from one brand to another with whats left out there for bearing availability. correct clearance is the important thing
 
Hey Jack I assume you had the rotating assy. balanced, correct? I mention that because the 318 pistons weigh less than 340 pistons so using a 318 crank in a 340 requires it to be re-balanced, even if it it's a steel crank with the same casting # as a 340 crank.
 
fishy68 said:
Hey Jack I assume you had the rotating assy. balanced, correct? I mention that because the 318 pistons weigh less than 340 pistons so using a 318 crank in a 340 requires it to be re-balanced, even if it it's a steel crank with the same casting # as a 340 crank.
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Yup, it's all been balanced. I changed everything to a forged bottom end. New TRW pistons, New Eagle H-beam rods and the 318 crank.

Jack
 
Yes, they are. I subscribe to the theory that a heavy piston helps to take up some of the shock when the fuel charge ignites. Besides I won't be spinning this engine above 6000 rpm.

Jack
 
Jack, run full groove main bearings as this will also take up some shock on the rod bearings. This provides full time oiling to the rod bearings. The added cylinder pressure from a blower is going to put added loads on the rod bearings. Going to full groove main bearings will provide extra oil and cusioning on the rod bearings.
 
MiradaMegaCab said:
Jack, run full groove main bearings as this will also take up some shock on the rod bearings. This provides full time oiling to the rod bearings. The added cylinder pressure from a blower is going to put added loads on the rod bearings. Going to full groove main bearings will provide extra oil and cusioning on the rod bearings.
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That's they way I was going. Thanks.

Jack
 
Could depend on the year of the block, early (pre74) blocks used different thrust bearing.
 
federal mogul heat treated bearings. Cut larger grooves in the thrust bearing sides. And chamfer the edges of all bearings for oil flow . I have been spinning my 340 to 9000 for three years. Oil pres. is still 30 -40 hot. rod bolts and main studs are a must. Baffled pan and no windage tray. Oil return to pan is just as critical as delivery. Airated oil causes high RPM pressure drop On the big end.
 
...........They are the same diamentions...........340s had a more severe duty bearing than the non performance grocery getter engines.............kim...........
 
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