[428GTO70]

I just got an Eagle Forged 4340 Crank and have a question about rod bearings.

I have found the info that says to use the narrower CB758HXN bearings to clear the large radius on these forged cranks. Is this THE rod bearing to use for this crank? As in there are no other drop in options?

I also found this part number available CB758HN but not sure what the missing X stands for in the part number? It seems the difference may be the thickness of the bearing wall? .0614 on the CB758HXN and .0619 for the CB758HN. Seems that CB758HXN would have more oil clearance, So would CB758HN be more desireable for a street motor? Sorry if this has been answered before but I didnt find any info on the CB758HN bearings anywhere.

Any help would be appreciated, this is for the engine combo in my sig.

[428GTO70]

Ok I have confirmed that the X stands for .001 more oil clearance. What would be more desireable for my street engine? I just ordered a set of standard size 3/4 groove main bearings, Sealed Power 151M which are listed as "performance" bearings. Which of these rod bearings would match those better? the standard or .001 clearanced set?

Again as always any help is greatly appreciated!

I really want to get this stuff in hand and get this thing together already!

[mrennie]

It is difficult to answer your questions about clearance unless you know what the journals are sized to and what oil clearance you are looking for. As I have learned (the hard way!), it is sometimes better to buy bearings and install them, then mic the bores and determine what size the journals have to be ground to to get you desired clearance.

If the crank you have it already ground and ready to go, then you will need to buy a set of bearings that you think are correct, install and torque the caps, then mic the bores and compare to the journal diameter of the crank and see if the resulting clearance is what you want. You should also mic the journals and compare to the published blueprint specs for that particular journal, which would give you some sense of whether or not you might need a thinner bearing like the X style, in case your crank is ground at the high end of the range and the bearing bore is at the low end. The resulting clearance is affected by all 3 (bearing shell thickness, bearing bore ID, and journal OD).

At that point you can determine if the brand/style of bearings will work, or if you might need to try a different brand.

I am going nuts trying to get the clearances I wanted with a reground OE crank that I bought thinking that it would be a drop in since all journals were within "the range". So far I have bought *5* sets of main bearings as not one set has had the same thickness of bearing shells and there are significant variances within the sets themselves. In hindsight it would have been better and cheaper to plan to regrind the crank and just go with the next undersize, buy a set of bearings, mount them and measure, then send the crank out to be ground to the specific dimensions I was looking for.

It's entirely likely that your clearance will be fine, but you really won't know until you buy a set of bearings, install and measure.

Federal Mogul also makes rod bearings that have the large bevel or are narrower to work with large radius cranks (I think they are part # 87050CH).

[428GTO70]

Thanks for the info, I think I will go ahead and get the standard sized bearings and go from there then. Hopefully I can actually use them, since I already ordered standard main bearings.