Issues with main bearing clearance

[TexasRoadRunner68]

I made it to the from the 5th to the 2nd main bearing before reaching an issue on the main clearances. I calculated a minimum clearance of 0.0026-0.0027 for the 400 mains. The first 3 were all 30-31 thousandths. This one is measuring 23-24 thousandths. I took it apart and retorqued it, but got the same result. Even more frustrating, the top bearing shell popped loose from the main cap and marked up the lower bearing shell. I’m assuming this now needs to be replaced, which I also assume means a full set. Do I need to go up a size to grant proper clearance? This was align honed…I figure if anything it might be loose.

 

[zyzzyx]

Two things you need to do: Measure the crankshaft journals. All of them. Mains and rods. This will
tell you which undersize bearings you need. If the machine shop line-honed your block, they should
have measured the cente-to-center distance between the cam and the crank. If the hone took out
too much stock on the upper part of the bore, you'll need an undesize timing set.

 

[69Bee]

They only make: Std, 0.010", 0.020", 0.030", 0.040". You won't find any 0.0011" or 0.0012" out there. If you buy another set, you are going to have the same thing as you do now. You don't say how you are measuring the clearance, but unless you are measuring a micrometer and bearing micrometer or a micrometer and bore gauge, plastigage only gives you a "close" approximation of the clearance. The clearance spec for the mains is 0.0011" to 0.0036" which you fall into, albeit on the high side. Sometimes shells are thicker or thinner, so you can move them around to get the best clearance. If it were mine, I would use a HV pump and run her!!

 

[69Bee]

Two things you need to do: Measure the crankshaft journals. All of them. Mains and rods. This will
tell you which undersize bearings you need. If the machine shop line-honed your block, they should
have measured the cente-to-center distance between the cam and the crank. If the hone took out
too much stock on the upper part of the bore, you'll need an undesize timing set.

While this is true, a line hone cannot control where the stock is taken from, only a "Align-Bore" can. The height of the cutter mandrel can be adjusted to take more material from the cap while a hone mandrel is only going to follow the bore. The align hone will theoretically take an even amount from cap and block to make the bore round again and to size, but other influences can affect that. I cut the caps to reduce the height between 0.0035"-0.0045" and when the bores are finished, you should have theoretically only moved the crank 0.00175" to 0.00225" towards the crank which is not a lot. In all of my years, I have only needed to get a -0.005" chain set once, and more believe that it was due to chain/gear inaccuracies being made in china.

 

[TexasRoadRunner68]

I have measured the journals with a micrometer that measures down to the ten thousandth, set the dial bore gauge that is also accurate to a ten thousandth and then measured the difference once in diameter on the installed bearing. Repeated measurements show the front two bearings having a tighter clearance of 23-24 thousandths.

Main Journals:
M1: 2.6232
M2: 2.6233
M3: 2.6234
M4: 2.6232
M5: 2.6233

Bearing clearances:
M1: 0.0023
M2. 0.0024
M3: 0.0030
M4: 0.0033
M5: 0.0031

Using the 0.001 per inch of journal like with rods, it appears the front two are tight. Or is there a different rule for mains? I just figured I’d see closer to 30 thousandths.

 

[Fran Blacker]

I'd want to know why the bearing popped out. 400 blocks have smaller mains than RB blocks right? Have a set of U/S .001 RB mains. Try King bearings they have U/S .001 for RB I believe maybe they have'm for 400's.

 

[TexasRoadRunner68]

I'd want to know why the bearing popped out. 400 blocks have smaller mains than RB blocks right? Have a set of U/S .001 RB mains. Try King bearings they have U/S .001 for RB I believe maybe they have'm for 400's.

It seems tight after removing and reinstalling it. I’m not sure how it got tweaked when removing the main cap.

I guess the other question being, if 0.0024 is good enough…is a scratch in a soft bearing a big deal? Or run it?

 

[69Bee]

...Using the 0.001 per inch of journal like with rods, it appears the front two are tight...

There is no such rule, and I am not sure where you read that. The spec is what the manufacturer puts in their service manuals for their requirements. Chrysler says that they want to see 0.0011" to 0.0036" for main bearing clearance and 0.0009" to 0.0034" for rod bearing clearance. While I like to see 0.002" to 0.0025" for the mains, I wouldn't be afraid to run up to 0.0035" for the mains.

I have seen that rule for piston clearance, but even they give the actual amount to multiply by bore size to determine the clearance, AND if you are using any "power adders", that number changes.

 

[2quick]

Ran into this problem on my 454 marine engine with an eagle crank. Clevite HX series, The X means thinner than standard for .001 in. extra clearance.

 

[2quick]

They only make: Std, 0.010", 0.020", 0.030", 0.040". You won't find any 0.0011" or 0.0012" out there. If you buy another set, you are going to have the same thing as you do now. You don't say how you are measuring the clearance, but unless you are measuring a micrometer and bearing micrometer or a micrometer and bore gauge, plastigage only gives you a "close" approximation of the clearance. The clearance spec for the mains is 0.0011" to 0.0036" which you fall into, albeit on the high side. Sometimes shells are thicker or thinner, so you can move them around to get the best clearance. If it were mine, I would use a HV pump and run her!!

Clevite HX series is .001 thinner for .001 added clearance...

Clevite H-Series Rod Bearings CB-527HXND​

CHRYSLER Clevite Engine Parts CB-527HXND Clevite H-Series Rod Bearings | Summit Racing

These are the rods and it doesnt look like summit has the mains but they can be ordered thru Mahle.

 

[dvw]

A couple of things. The .001" per inch of journal is a very close rule of thumb. It's been used with success for years. No way I would ever build a performance engine with .0011 main clearance. First, 3 items affect clearance. Crank journal size. Bearing housing bore dimension. The bearing itself. Are all the journals the same size? Have you swapped the bearings into a different location? The bearing bore has a tolerance. You may have some on the high side, some on the low side. Or they may be out of spec. If the first two items are ok the bores are most likely different diameters. If this is a street car the tighter clearances will be fine. On a racecar I'd like to see the tight two larger.
Doug

 

[69Bee]

Clevite HX series is .001 thinner for .001 added clearance...

Clevite H-Series Rod Bearings CB-527HXND​

CHRYSLER Clevite Engine Parts CB-527HXND Clevite H-Series Rod Bearings | Summit Racing

These are the rods and it doesnt look like summit has the mains but they can be ordered thru Mahle.

His problem is his clearance is on the high side, and using HP "X" series bearings is going to exacerbate that problem! Going back and looking at his original post to determine crank size, he NEEDS to grind the crankshaft R10/M10 and fix his worn crank, The worst (smallest) size main journal is 0.0013" BELOW spec.

 

[69Bee]

Texasroadrunner68, get your crank ground, put new 0.010" OS rod and main bearings in, and you will be fine. I didn't really pay attention to your original post to see that the crank was std and not ground. You did half of the job properly, now grind the crank 10/10 to finish up and your clearances will be proper.

 

[2quick]

His problem is his clearance is on the high side, and using HP "X" series bearings is going to exacerbate that problem! Going back and looking at his original post to determine crank size, he NEEDS to grind the crankshaft R10/M10 and fix his worn crank, The worst (smallest) size main journal is 0.0013" BELOW spec.

Ohh sorry, I didnt think these clearances where loose. I thought the 23 might accually be tight. But I'm working with 600+ hp motors..I shoot for 3 thou on the mains.

Bearing clearances:
M1: 0.0023
M2. 0.0024
M3: 0.0030
M4: 0.0033
M5: 0.0031

 

[69Bee]

Ohh sorry, I didnt think these clearances where loose. I thought the 23 might accually be tight. But I'm working with 600+ hp motors..I shoot for 3 thou on the mains.

Bearing clearances:
M1: 0.0023
M2. 0.0024
M3: 0.0030
M4: 0.0033
M5: 0.0031

Yes, and I agree with you, non-stock HP motors are GOING to require more clearance. According to the pic he posted of the "uncoated-stock" bearing, his build should be a stock build. And honestly, all you would need to do to open up the first two for your HP application would be to polish the two crank journals a little more to arrive at the desired clearance.

 

[69Bee]

OP, you are only working with the mains at the moment and having problems due to the std crank. I will guarantee you will have more issues with the rod bearing clearances as the thrust dimension (6 & 12 O'clock) usually has more wear that the 3 & 9 O'clock dimension.

 

[TexasRoadRunner68]

OP, you are only working with the mains at the moment and having problems due to the std crank. I will guarantee you will have more issues with the rod bearing clearances as the thrust dimension (6 & 12 O'clock) usually has more wear that the 3 & 9 O'clock dimension.

This is all brand new from 440 source. Rod bearing clearances seemed to check out. Brand new scat I beams and clevite bearings. I’ll have to measure again on the last 2 mains, as I don’t see why I would need to polish a journal on a brand new crank.

 

[69Bee]

The measurements you gave for the crank mains do NOT match a new crank, unless it is defective. I would expect to see the crank measure 2.625" on the mains and 2.375" on the rods" Re-measure and contact 440Source if there is an issue. The minimum main dimension for a stock crank is 2.6245", and every NEW crank I have worked with were ground to the max dimension.

 

[Wietse]

Like Doug suggested... swap the tightest and the loosest bearings and measure again to see if they balance out to a close average.
All dimensions have a tolerance, with a journal being against the lower size tolerance and a bearing that sits on the high side of the tolerance you get and a larger clearance.
Playing around with them you will mostly find a sweet spot for all of them.
Depending if you are building a streeter or a racer, the guys here will tell you you are ok or not.

 

[dvw]

OP, you are only working with the mains at the moment and having problems due to the std crank. I will guarantee you will have more issues with the rod bearing clearances as the thrust dimension (6 & 12 O'clock) usually has more wear that the 3 & 9 O'clock dimension.

The thrust dimension of what? The crank? It wears oval? We don't even know if the crank is the cause. Have you ever run a motor with loose bearing clearance? If so you would know what the results were, Zip, Nothing, Nada. As long as the housing bore and crank are with-in spec there isn't a serious issue here. As stated before 1&2 are a touch tight for an all out race motor. For street, I'd run it. Line honing is tricky. It takes skill to get all the bearing bores the same. We are talking .000X"
Doug