i think i used federal mogul on mine gotta check the box to be sure though.

Interesting. How did you know they were worn out? Did they spin, or just oil analysis data?

--Ian

Despite some level of "research", I'm not as knowledgeable as I'd like to be on this subject, but I don't think it's as simple as "oh, they're race parts so they must be high performance with short life". Please correct me if I'm wrong, but I believe that in comparison to the oem bearings something like an ACL race bearing is just plain better. Furthermore, under the high load of a boosted engine they should last significantly longer?

Pits and scoring of the bearings was said to be from overload acording to King. Rod bearings #1 and 4 were along with main #1 were the worst. Motor was taken apart because of burnt exhaust valve.

Exhaust valve that was burnt was in #1 hole that had started becoming wet with oil. Scores were in the cylinder walls as well on all cylinders.

What I don’t understand is what is imbedded in the side of the pistons above the rings. I think this is what scratched up the cylinder walls enough to cause the oil consumption.

I did not notice any pitting on the top corners of the piston that looked like detonation that I have seen before.

Bob

I believe the ACL bearings are undersized by .001" to open up clearance a bit - my bearing clearances came in at just under the allowable OEM maximum on both motors. I don't know quite enough about the subject to comment on whether that would harm longevity, but I can't imagine it helping.

My oil clearance was a good bit above recommended, but still within maximum range. I'm about 30k miles in and no issues yet. Maybe it doesn't effect longevity too much, hopefully. These were mains. Mazda specs said .0007-.0014 with a limit of .004. Mine were .00175. So not too bad for a 110k mile crank/block.

They have a race bearing part number, and then another part number that ends with an "X." They state that the X set is undersized for .001" more clearance. I did some light reading on short block assembly and according to a few SBC builders you can mix the standard and the X sets to get .0005" more clearance.

I dunno how ACL race "standard size" bearings are sized compared to OEM, or slightly worn OEM, but when I pull my motor to do the rods & pistons Imma plastigage the stock bearings before teardown so I have a reference point.

Why would you assume that?

How do I go about choosing the size of the rod bearings I need? FM sells OEM as well as over-sized ones.

You'd have to disassemble the rods from the crank and mic the journals. If there's no damage (scoring, etc) and they mic to the stock specs, you order stock size bearings. If there's damage, then your machine shop will have to grind the journal to make it smooth again, and they will grind off a specific amount for which bearing sizes are commonly available. If they grind off 0.25mm, you order the .25 bearings.

OEMs. 10,000 miles, so far so good. The guy who machined my block recommended the oems as opposed to a race bearing. I told him it was a daily driver and he said the race bearings run a little on the loose side and the oems being tighter, do a better job of keeping oil in the bearing.

I'll admit, I never researched this for myself but he builds a bunch of race motors, so I figured he knew what he was talking about. The local NMCA builder sends all his machine work to this machinist. He's a pretty reputable guy.

I'm doing a refresh when I install my rods so I will have some hard data.

Im currently using Calico teflon coated rod bearings in my 1.6 build.
I believe they are ACL bearings and are undersized with the teflon coating making up for the difference.

Im using the good ol' ACL race bearings for the main's and thrust though

Thanks for the info. I wanted to just put in a set of aftermarket rods, should I go about and replace the crank bearings at the same time, or can I just leave them untouched? I've never built an engine before, but I do know how to follow instructions and crank a wrench. I also don't want to turn this into a major engine overhaul or extreme build.

I'd replace them while you're in there, especially if you're planning to abuse the motor a bit after. I mean, bearings are a wear item, albeit a very long wearing item. My feeling is you might as well do it while the block is out of the car and torn down. The cost isn't that much. A full set of ACL race bearings (rods, mains, and thrust washers) is in the ballpark of $120. If there's no damage to the journals you're "probably" okay to buy stock size bearings. If you want to know for sure, mic the journals before ordering the bearings. Either way, you'll want to plastigauge the clearances on reassembly to verify everything's kosher.

This seems to be the most appropriate place for this question so...

What is the typical Crank machining cost for undersized main and rod bearings. My crankshaft has pretty bad scoring so I'm going to go with 0.25 undersize bearings and was wondering what most competent machine shop charge for that work.

I'd say depends on the shop but the costs are trivial if you're doing a full build. Once they are done they can advise you on what bearings to get I do believe.

When I needed my crank to be reground, the estimate I was give was $150-200. It had to be sent out to a different shop as my machine shop could not do it. I ended up just finding a new good crank, as it was the cheaper faster option.

the plan was to buy bearings and measure and give the machine shop the spec since they can hold a very high tolerance rather than the other way around.

ACL all the way on mine. Also had the mains align honed for the ARP main studs and got the crank journals polished before I reassembled.

This is backward. You don't know how much material needs to come off the crank to clean it up. Let the machine shop tell you what bearing thickness you need.

depending on your goals, turning the crank should be fine. However, if you're going for a lot of power and want logetivity, I'd look for a good crank that doesn't need turned. You lose the hardened surface when you turn it.