While tearing down our Dirt Track B-Mod motor we found #8 rod bearing wore to the brass. All other bearings, including #7 looked really good. The crank looked good as well. No signs of heat. No signs of any other problems. Clearances were good. We only ran 12 nights and the motor performed great! No oil pressure issues. We never noticed anyting abnormal in the System 1 Filter. One reputable Mopar builder said the lack of full groove mains is the problem. The motor was professionally built but of course they build mostly GM. This is an X block with all the normal oil modifications. Callies Dragonslayer 3.58 crank. Eagle I-beam rods(due to rules), King Main Bearings, and Clevite Rod Bearings. Any opinions woud be appreciated! Thanks, Bob P.

Have you checked the big end of the rod for proper size & egg shape? Do the bearings have the proper chamfer? I'll assume you have a high volume oil pump.

Rods checked good on size, The wear was consistant across and around the bearing. What baffles me is that the problem is isolated to #8 bearing. The other 7 look good. I might add that I am running a Champ Pan and Pickup. The HV pump was ported and blended to the block.

#8 is the only rod fed from the rear main. This is where I would look.

Is your crank crossdrilled to oil the rods from two different holes? Otherwise you are only pressure feeding the oil circuit to #8 half the time. Check the crank and make sure there is no problem in the hole from #5 main to the #8 rod bearing.

Leon

I appreciate the suggestions. The motor is now tore down. I will be going back down to look at it on Saturday. THANKS!

Having #8 rod bearing issues is rare-----but anything can happen in an oval track engine. As said, the #8 rod bearing is only fed by the rear main bearing----that's where you need to look. Go back and check the passages in the block to the rear main, many X (and R blocks as well) have obstructions(passages only partially drilled for example). Make sure they are the correct size. Then, look at the oiling hole in the rear main, does it give full flow or is it partially restricted. I have no experience with King bearings, Clevite is fairly good----but I always modify the main bearings to improve flow to the rod passages in the crank. And while you are looking (checking), look at the crank---passages are not always perfect as well.

You didn't state what the max RPM is nor if the lifter bores were tubed or sleeved. Improper tube installation can cause flow restrictions also.

You have a "building" problem, probably not an "assembly" problem.

Thanks, 40ford, I used what I believe is your post (on another Mopar site) as "bible" when I started this project. I will double check all of the passages tomorrow. The motor turns 7200-7400 rpm. The lifters bores are not sleeved, but the right side oil passage hase been tubed. It is a restricted (2bbl) motor with a flat tappet cam. 425-450HP. Motor carries 60-70 psi oil pressure on the track at 190-200* water temp. We change oil every 3 races with Valvoline 50w. I run a remote System 1 oil filter with #12 lines (15-18" long) plumbed directly into the block. The full groove bearings is a big question for me. I have heard reputable people claim that you have to run them, while others say do not run them. The first motor I did open up the oil holes in the main bearings, this motor I did not....Bob

Check the tube on the right side oil passage-----make sure the tube does not partially restrict the oil passage to the rear main. Also, make sure the threaded plug in the end of the passage is not too deep in the block. That could also restrict the oil flow to the rear main.

On the subject of main bearings----I am not a big fan of full groove. On high torque applications, the full groove don't provide as much support to the crank as a half groove. And, the NASCAR guys don't ever use full groove because it isn't needed.

Let me know if you find anything during your inspection.

yep never seen a need for full grove bearings that's why some company's don't even offer them.

I went down for an inspection on disassembled motor. All oil passages in the block were free from obstructions. We did find that the #5 main bearing hole lined up perfectly in the block, but is 1/2 off from lining up with the hole in the crank. Everything else looked good. Three engine builders from two different shops were there and all agreed that chamfering the crank and the bearing would be the best route to go. One recomended that cross drilling the crank could be benificial as well. My builder is going to contact Callies for their opinion.

Any misalignment of the oil holes in the crank and bearing is serious. If you only have 1/2 alignment, you effectively have on about 30% oil flow to the rod bearing. That's the reason I like to elongate the hole in the bearing into a slot but widen the oil hole as well(from 1/4" to about 5/16"). Elongating the hole into a slot gives much longer dwell for the oil to get into the crank to feed the rod bearings.

In the "olden" days when Dodge was very active in Nascar racing(1970s), Clevite produced a main bearing with wide slots. That stopped about 1980 when Dodge withdrew from Nascar. The same was true for hemis but they continued the special mains several years longer.