Engine bearings
#23
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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?
#24
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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
#25
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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?
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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.
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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.
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.
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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.
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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.
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.
#33
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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.
#34
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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.
#35
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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.
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.
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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.
#40
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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.