Rod Bearing Clearance
12-05-2012, 09:57 PM
#1
Rod Bearing Clearance I am reassembling my engine and there is between .0025-.003" clearance on my rods. The big end of the connecting rods check out right on size and the rod journals are within tolerance. I'm using King Bearings and can only figure it's the bearings. They are for a .010" under journal. Should I be concerned with .003" clearance?
12-06-2012, 12:07 AM
#2
It's a little loose for a n/a engine, but if you plan to spray it, I'd leave it. My bearings on the rods are .0027 clearance. Clevite h series, but I plan to spray mine.
You can either leave it, or you can order -.001 bearings to tighten it up to .0015-.002
You can either leave it, or you can order -.001 bearings to tighten it up to .0015-.002
12-06-2012, 07:22 AM
#3
That's pretty loose unless you plan on making some serious power. It won't hurt the engine, but the oil pressure will be low. Since you're already .010" under, ACL makes an .011" under bearing which will get your clearance tighter, but I don't know if King does.
As the saying goes, "Too loose and only you know it. Too tight and everyone will know it."
As the saying goes, "Too loose and only you know it. Too tight and everyone will know it."
12-06-2012, 05:56 PM
#5
I am reassembling my engine and there is between .0025-.003" clearance on my rods. The big end of the connecting rods check out right on size and the rod journals are within tolerance. I'm using King Bearings and can only figure it's the bearings. They are for a .010" under journal. Should I be concerned with .003" clearance?
Very true sir.
12-07-2012, 12:00 PM
#6
For future reference, when you have to grind a crank down, you can mic the bearing ID and have the crank ground to whatever diameter gives you your preferred oil clearance. That way you avoid the problem you're having now.
12-07-2012, 12:02 PM
#7
That's pretty loose unless you plan on making some serious power. It won't hurt the engine, but the oil pressure will be low. Since you're already .010" under, ACL makes an .011" under bearing which will get your clearance tighter, but I don't know if King does.
As the saying goes, "Too loose and only you know it. Too tight and everyone will know it."
As the saying goes, "Too loose and only you know it. Too tight and everyone will know it."
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12-07-2012, 12:20 PM
#9
In that case you could have the bearings coated. It will get your clearance down and act as a sacrificial layer in case something bad happens. I use PolyDyn here in Houson, but there is also Swain and Calico.
For future reference, when you have to grind a crank down, you can mic the bearing ID and have the crank ground to whatever diameter gives you your preferred oil clearance. That way you avoid the problem you're having now.
For future reference, when you have to grind a crank down, you can mic the bearing ID and have the crank ground to whatever diameter gives you your preferred oil clearance. That way you avoid the problem you're having now.
12-07-2012, 12:50 PM
#11
I'd be more concerned with a .0005 inconsistency across the measurements if you really are getting .0025-.003. What method are you using to measure tolerance?
I am reassembling my engine and there is between .0025-.003" clearance on my rods. The big end of the connecting rods check out right on size and the rod journals are within tolerance. I'm using King Bearings and can only figure it's the bearings. They are for a .010" under journal. Should I be concerned with .003" clearance?
12-07-2012, 01:14 PM
#12
This may sound dumb, but I assume, you want the bigger clearance on high power applications so that you have a greater oil cushion for the bearings? Never really read an in depth discussion on here for choosing bearings based on application. I am sure its on here and I missed it over the years.
12-09-2012, 08:21 AM
#13
I used a couple different methods. First, I measured the rod bearing diameter with an inside mike(2.092) and the journal diameter(2.0885) with an outside mike. This gave me a .0035" clearance. I also measured the connecting rod bore and subtracted the bearing shell thickness x 2 - the rod journal diameter. That method gave me a clearance of .0027. I'm a little upset with the the guy that did my bottom end machine work. He asked the shop that reground my crank to grind it to 2.0885 instead of 2.089 and then when he reconditioned the rods I specifically asked him to leave the rod bores at 2.2267 which is the low measurement. He went to 2.2272 which is the high. Obviously when you do the math this is where we ended up with the extra clearance. If he would have went with the factory specs I would have been right at .002 with the latter method of measuring clearance. I not supercharging or spraying this motor. I ran the living hell out of my stock bottom end with stock clearances and clean oil without issue. Long story short, I'm assembling the engine with a melling 10296 HV oil pump and hoping everything will be ok. Maybe I'm overthinking this because I do machine work for a living. lol.
12-09-2012, 10:13 AM
#15
I used a couple different methods. First, I measured the rod bearing diameter with an inside mike(2.092) and the journal diameter(2.0885) with an outside mike. This gave me a .0035" clearance. I also measured the connecting rod bore and subtracted the bearing shell thickness x 2 - the rod journal diameter. That method gave me a clearance of .0027. I'm a little upset with the the guy that did my bottom end machine work. He asked the shop that reground my crank to grind it to 2.0885 instead of 2.089 and then when he reconditioned the rods I specifically asked him to leave the rod bores at 2.2267 which is the low measurement. He went to 2.2272 which is the high. Obviously when you do the math this is where we ended up with the extra clearance. If he would have went with the factory specs I would have been right at .002 with the latter method of measuring clearance. I not supercharging or spraying this motor. I ran the living hell out of my stock bottom end with stock clearances and clean oil without issue. Long story short, I'm assembling the engine with a melling 10296 HV oil pump and hoping everything will be ok. Maybe I'm overthinking this because I do machine work for a living. lol.
Everything will be alright. Like said, your oil pressure O
May dip down pretty low, but you will be fine
12-09-2012, 12:48 PM
#16
12-09-2012, 12:58 PM
#17
Rotella 15w40 for the break in (higher zinc content) no additives, and VR1 20w50 because my only options with VR1 are 10w30 or 20w50, and Amsoil is order only around here (I don't want to have mail order oil changes). I set my rods to .0027 and my mains to .0029 (.0025 on the thrust bearing). My journals were all dead on 2.5585 and 2.0994.
12-09-2012, 05:25 PM
#19
Bww3588, I work with tolerances this tight all day long using carbide cutting tools and CNC equipment. They do not cut rod housing bores to finish size with a cutting tool. They use a honing process for reconditioning rods which is a very slow but precise process of removing material. You can hold .0001" with a rod honing machine if you have precision measuring equipment which is why sunnen put a dial bore gauge right on the machine that is graduated to the tenth of a thousandths. Obviously the dial bore gauge has to be precisely set. I pretty much know the engine will run but I was looking more for someone who runs these clearances and what type of oil they use and where the oil pressure is at.
12-12-2012, 09:41 PM
#20
