Main Bearing Clearance Questions

Because of quarantine, i decided it would be a good time to start putting my engine together. Today i was doing my bearing clearances to make sure everything was good. Rod bearings checked out good all came back the same measurement, within spec. The Main bearing clearances were a bit confusing to me because there are different tolerances for each journal. I am using King bearings, standard size, and a brand new sti nitrated crankshaft.

The tolerances i looked up say:

1. STD 0.003 - 0.030 mm

Limit 0.045 mm

2. STD 0.012 - 0.033 mm

Limit 0.045 mm

3. STD 0.003 - 0.033 mm

Limit 0.040 mm

4. STD 0.012 - 0.033 mm

Limit 0.045 mm

5. STD 0.010 - 0.031 mm

Limit 0.040 mm

I was using plastigauge, so not that accurate, and some of the tolerances are smaller than the plastiguage can measure. Im probably going to get some bore gauges and a micrometer tomorrow to get some more accurate measurements.

What i got is:

1. Alot bigger than 0.025 mm (Meaning tighter clearance)

2. Little bit bigger than 0.025 mm (Meaning a little tighter)

3. little bigger than 0.038 mm (Meaning a little tighter)

4. 0.038 mm

5. 0.025 mm

Do these clearances seem alright, or do i need to buy another set?

Ill add some pics for comparison.

Because of quarantine, i decided it would be a good time to start putting my engine together. Today i was doing my bearing clearances to make sure everything was good. Rod bearings checked out good all came back the same measurement, within spec. The Main bearing clearances were a bit confusing to me because there are different tolerances for each journal. I am using King bearings, standard size, and a brand new sti nitrated crankshaft.

The tolerances i looked up say:

1. STD 0.003 - 0.030 mm

Limit 0.045 mm

2. STD 0.012 - 0.033 mm

Limit 0.045 mm

3. STD 0.003 - 0.033 mm

Limit 0.040 mm

4. STD 0.012 - 0.033 mm

Limit 0.045 mm

5. STD 0.010 - 0.031 mm

Limit 0.040 mm

I was using plastigauge, so not that accurate, and some of the tolerances are smaller than the plastiguage can measure. Im probably going to get some bore gauges and a micrometer tomorrow to get some more accurate measurements.

What i got is:

1. Alot bigger than 0.025 mm (Meaning tighter clearance)

2. Little bit bigger than 0.025 mm (Meaning a little tighter)

3. little bigger than 0.038 mm (Meaning a little tighter)

4. 0.038 mm

5. 0.025 mm

Do these clearances seem alright, or do i need to buy another set?

Ill add some pics for comparison.

 

 

You don't have any over the limit if I read that right. If you have any under the limit you'll need to polish the crankshaft to open that up and meet the factory giidlines. Or just run em and let the crank self clearance lol. I have no personal experience, but I would say either don't measure it at all or measure them and make them right with machining the crank.

 

Something you could try if the variation is the bearing size is to swap the bearings around and re measure. Eg take the biggest and smallest clearance numbers and swap them.

Personally if you have standard size bearings and a standard size crank that isn't giving proper clearance ( eg too tight) I'd want a refund for defective bearings. If they say no you can offer to run them, trash the engine, and then send them the bill for an entire engine.

I would suggest you PM member "m sprank" he will know the answer to your question.

You don't have any over the limit if I read that right. If you have any under the limit you'll need to polish the crankshaft to open that up and meet the factory giidlines. Or just run em and let the crank self clearance lol. I have no personal experience, but I would say either don't measure it at all or measure them and make them right with machining the crank.

 

Something you could try if the variation is the bearing size is to swap the bearings around and re measure. Eg take the biggest and smallest clearance numbers and swap them.

Personally if you have standard size bearings and a standard size crank that isn't giving proper clearance ( eg too tight) I'd want a refund for defective bearings. If they say no you can offer to run them, trash the engine, and then send them the bill for an entire engine.

 

I'm sure they are fine, I'm just very cautious as I don't have money to build this engine twice. I went to harbor freight and got a set of cheap bore gauges that should do the trick. Once I get home from work, I'll try and get some measurements and post the results here

I wouldn't trust harbor freight for precision measuring, but if you can move them around to get your clearances within spec run it.

I would suggest you PM member "m sprank" he will know the answer to your question.

 

What's to answer? You have clearance tolerances set by factory. You must meet those tolerances. If your new parts don't meet the manufacturer spec, get a refund.

 

What questions remain?

 

If the crankshaft mics out correctly and the case hasn't been modified, then the bearings must be defective.

What's to answer? You have clearance tolerances set by factory. You must meet those tolerances. If your new parts don't meet the manufacturer spec, get a refund.

 

What questions remain?

 

If the crankshaft mics out correctly and the case hasn't been modified, then the bearings must be defective.

 

I was just thinking the clearance would be more consistent across the board like the rod bearings. It's seemingly like that's not the case. I just heard people talking alot about bearing consistency.

 

About the harbor freight tools, it's not a dial bore guage, it's just a t style bore guage. So it's not actually doing the measurement. You put it in the bore, lock it and then measure it with some calipers. I think they will be fine as long as my calipers are calibrated correctly.

**Update** I will admit when I'm wrong, harbor freight gauges not as accurate as I thought they would be, plus it isn't easy to get to the inside bearings. But the only journal I was concerned about was the first one since it was out of the measurement range of the plasigauge. With a little finess I got a mesurement of 0.01 mm so it is within spec. Thanks everyone for the help. I think I'm just going to run it with these, should work just fine.

Post up a first start video, so we can celebrate with you

Post up a first start video, so we can celebrate with you ��������

 

Will do , I can only hope it will be a celebration.