Bearing Clearance Issue - Chevelle Tech
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post #1 of 75 (permalink) Old Jul 11th, 20, 8:41 PM Thread Starter
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Bearing Clearance Issue

Im Building a street 454.
I had the crank ground .010 under mains and rod journals.
I bought .010 under bearings.
I used plastigauge to check for oil clearances.
I am only reading .0015 clearance for oil on the rods and 0021 for the mains.
I would be happier with .003 for clearances.
I have a starrett outside micrometer. The rod journal measures 2.189.
I do not have a bore gauge.
Is plastigauge crap? First I used the red. Then I tried the green. I got two different clearances with the two colors.
Is the oil clearance supposed to be ground into the crank or is the .010 bearing actually.009 or something?
Thank you.
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post #2 of 75 (permalink) Old Jul 11th, 20, 9:54 PM
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Re: Bearing Clearance Issue

You didn't put any oil on the bearings when you checked it?

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post #3 of 75 (permalink) Old Jul 11th, 20, 10:26 PM
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Re: Bearing Clearance Issue

HI
What you doing with the engine ??
Sounds like u have tight clearances. These need to be verified with dial bore gauge and micrometer.
If they measure up slightly bigger then I would say your good to go . Was the crank [assuming stock cast] unit checked for straightness ?
Some bearing makers offer +.001 /-.001 +.011 / -.009
Then u can use half sets eg half std,,, half under/over size . This gives a .0005 change
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post #4 of 75 (permalink) Old Jul 11th, 20, 10:38 PM
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Re: Bearing Clearance Issue

I would have someone with a dial bore guage measure the main and rod bore 1st then install the bearings and measure. A good engine machine shop can do that for you for a few bucks
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post #5 of 75 (permalink) Old Jul 11th, 20, 11:12 PM
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Re: Bearing Clearance Issue

To get the total picture you also need to know if your rods are sized tight, in the middle, or on the loose side. There is a .001 tolerance for their sizing. However knowing that will not change what clearance you have.

I would get .009's for both. That will get you another .001 clearance. I would also get Clevite or ACL bearings. ACL the best on consistent sizing of anything I have used.
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post #6 of 75 (permalink) Old Jul 12th, 20, 11:48 AM Thread Starter
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Re: Bearing Clearance Issue

Quote:
Originally Posted by swampy 6x6 View Post
HI
What you doing with the engine ??
Sounds like u have tight clearances. These need to be verified with dial bore gauge and micrometer.
If they measure up slightly bigger then I would say your good to go . Was the crank [assuming stock cast] unit checked for straightness ?
Some bearing makers offer +.001 /-.001 +.011 / -.009
Then u can use half sets eg half std,,, half under/over size . This gives a .0005 change
Just a street 396 block from 1968. original 1968 cast Nodular crank .010 on mains and rods. This engine has original 375 horse forged pistons from a 402! I just ordered a dial bore gauge from amazon to check the clearances. They seem too tight with the plastigauge.
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post #7 of 75 (permalink) Old Jul 12th, 20, 11:49 AM Thread Starter
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Re: Bearing Clearance Issue

Quote:
Originally Posted by sleeper View Post
To get the total picture you also need to know if your rods are sized tight, in the middle, or on the loose side. There is a .001 tolerance for their sizing. However knowing that will not change what clearance you have.

I would get .009's for both. That will get you another .001 clearance. I would also get Clevite or ACL bearings. ACL the best on consistent sizing of anything I have used.
I agree with you. .009 will be right. I ordered a dial bore gauge to double check first.
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post #8 of 75 (permalink) Old Jul 12th, 20, 11:54 AM Thread Starter
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Re: Bearing Clearance Issue

So does anyone know which is supposed to have the clearance? When you have a .010 crank journals and order .010 bearings. Which is supposed to have the clearance? The bearings, or is it supposed to be ground into the crank? I will correct it with .009 bearings but somewhere theres supposed to be clearance.
If you have a stock crank and order stock bearings,which one has the clearance?
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post #9 of 75 (permalink) Old Jul 12th, 20, 11:55 AM Thread Starter
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Re: Bearing Clearance Issue

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Originally Posted by 77 cruiser View Post
You didn't put any oil on the bearings when you checked it?
I wiped off all the oil from the bearings first before I put the plastigauge to it.
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post #10 of 75 (permalink) Old Jul 12th, 20, 2:18 PM
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Re: Bearing Clearance Issue

Quote:
Originally Posted by MisterMicroscope View Post
So does anyone know which is supposed to have the clearance? When you have a .010 crank journals and order .010 bearings. Which is supposed to have the clearance? The bearings, or is it supposed to be ground into the crank? I will correct it with .009 bearings but somewhere theres supposed to be clearance.
If you have a stock crank and order stock bearings,which one has the clearance?
Unfortunately there is more to it than that
You have a nominal spec, a low & hi limit for the crank journals,,,
Bearings that can vary within the same manufacturer & especially in different brands,,,,
The rod & main housing bores also have a low & hi limit
So,,, you add or subtract all these possible differences & this is why you sometimes end up with goofy clearance numbers & have to juggle bearings or possibly redo the housing bores or crank

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post #11 of 75 (permalink) Old Jul 12th, 20, 2:18 PM
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Re: Bearing Clearance Issue

I am going to play the devil. Factory specs for a 1970 Corvette 454 are

Rods : .0012-.0037"
Mains: .0007-.0032"

So you are just about in the middle for the mains. Rods "might" be on the tight side but to be honest with you I dont see how you can use plastigage on rod bearings. they move around too much when you torque them. So the rods are probably more clearance than you think. In my opinion .003 is too much for rods anyway.

As far as "which has the clearance" the bearing or the crankshaft, there is a tolerance range for both. There is a full thousandth range on the crank. So if you get a crank that is on the large side of the range and a bearing that is on the thick side of its range you end up with not enough clearance. Exactly what does your crankshaft measure ? How about the bearing.

If your rod journal measures 2.189 then it is right at the small end of the spec and you should have enough clearance. If you want to verify your checking method, put a set of bearings in one rod and torque it together. Then measure the rod journal with your micrometer and lock the mic so it cant move. Take the rod and the micrometer down to your machine shop and ask them to set the gauge on their Sunnen rod machine using your micrometer and measure the rod assembly and tell you what clearance you actually have.

I would do that before ordering more bearings.

Personally I would have no problem running a street engine with the clearances you showed in your first post.

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post #12 of 75 (permalink) Old Jul 12th, 20, 3:19 PM Thread Starter
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Re: Bearing Clearance Issue

Quote:
Originally Posted by Wolfplace View Post
Unfortunately there is more to it than that
You have a nominal spec, a low & hi limit for the crank journals,,,
Bearings that can vary within the same manufacturer & especially in different brands,,,,
The rod & main housing bores also have a low & hi limit
So,,, you add or subtract all these possible differences & this is why you sometimes end up with goofy clearance numbers & have to juggle bearings or possibly redo the housing bores or crank

Welcome to the wonderful world of engine building 101
I see. Makes sense.

Lets say a brand new chevy engine from GM is measured today. Where is the clearance left on a factory engine?
Lets say a 5.3L vortec. The rod journal diameter is supposed to be 2.100. Is it really 2.098? Im too confused at this point.

Im also building a 600hp 496. I was told by the crank manufacturer to leave .0035 clearance for the high horse application. Looser is better they said. I think it was Scat.

To test out your theory, I do have another brand .010 under bearing set for a different engine, Bearings made by made by King. I am going to try the king bearings and report back here.

Thank you for all the insight! Fun learning process. Kind of trial and error.
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post #13 of 75 (permalink) Old Jul 12th, 20, 3:49 PM
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Re: Bearing Clearance Issue

Quote:
Originally Posted by MisterMicroscope View Post
I see. Makes sense.
Im also building a 600hp 496. I was told by the crank manufacturer to leave .0035 clearance for the high horse application. Looser is better they said. I think it was Scat.
On your 600 HP build you should aim for .0025" on the mains and .002" on the rods (assuming steel rods).

The "looser" you leave the brgs (mains and rods) the more issues you MAY encounter when the unit is idling!

I would put this "tip" here also for anyone contemplating grinding a crank to any undersize, first procedure is to confirm ALL hole sizes are within the recommend limits, THEN install ALL the brgs (mains/rods) and very accurately measure the hole size, THEN, have your crank cut to give you the desired clearances. We've been doing it this way for over 50 years now??

Thanks, Gary in N.Y.

P.S. We have a 3000 HP unit (ride in my signature) running .0025" on the rods (steel) and .003" on the mains, NEVER one single brg issue so far!
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post #14 of 75 (permalink) Old Jul 13th, 20, 9:01 AM Thread Starter
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Re: Bearing Clearance Issue

Quote:
Originally Posted by GOSFAST View Post
On your 600 HP build you should aim for .0025" on the mains and .002" on the rods (assuming steel rods).

The "looser" you leave the brgs (mains and rods) the more issues you MAY encounter when the unit is idling!

I would put this "tip" here also for anyone contemplating grinding a crank to any undersize, first procedure is to confirm ALL hole sizes are within the recommend limits, THEN install ALL the brgs (mains/rods) and very accurately measure the hole size, THEN, have your crank cut to give you the desired clearances. We've been doing it this way for over 50 years now??

Thanks, Gary in N.Y.

P.S. We have a 3000 HP unit (ride in my signature) running .0025" on the rods (steel) and .003" on the mains, NEVER one single brg issue so far!
Wow. Ive had so many different opinions on bearing clearances so far. Im going to take your advice. Your advice seems to be in the middle of the road of others opinion.
Another engine builder said to aim for .0027 to .0032 for mains and rods.
A different builder said .0035 is good.
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post #15 of 75 (permalink) Old Jul 13th, 20, 9:07 AM Thread Starter
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Re: Bearing Clearance Issue

I went ahead and tried a different brand .010 bearing set. King brand. Got the same results. Plastiguage shows only about .002 clearance for the rods and .0015 for mains.
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