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I just finished measuring the clearance for the main bearings in my 406. I used plastigage, so the last digit is my estimation based on eyeballing the difference between the plastigatge and the paper strip chart. (I'm planning on double-checking these numbers with my cheapie measuring tools, but frankly I trust the plastigage more.) The info that I have says it should be .002-.003, so they look OK to me, but...thought I'd ask you folks for a second opinion:

1 - .0025
2 - .0028
3 - .0023
4 - .0021
5 - .0022

I'm a little worried about 3, 4 and 5, especially considering some of the references I have say 25-35 thou for a performance application.

Do these look OK?

Thanks!

Pat
 

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Little snug for my taste. I normally try to shoot for 0.0028" as a minimum. Always better to be too loose than tight.:rolleyes: :D

You might want to look for some "X" series bearing halves to correct #4 & Thrust bearing.
 

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Just a thought but did you check your crank for any runout? If you have any runout at all it could move the plasti gage readings. I found, for me, plasti gage always read tighter than the dial bore gauge/micrometer method I use now.
 

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Mike Goble said:
Here's an article on bearing clearance as it relates to oil flow, bearing temperature rise and load capacity. Callies likes .002" to .0025".

http://www.chevyhiperformance.com/techarticles/4380/

Mike that article was very interesting...thanks for the link:)

BTW would a standard oil pump (non HV pump) be more then enough if you kept the bearing clearances in the above mentioned 002" to .0025" range?
 

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Discussion Starter #7
OK, they say 20-25 thou for the bearings (they didn't clarify if they were talking about main or rod...although all the stuff pictured is related to mains) and "Generally, an extra 0.0005 inch is added to the No. 5 thrust bearing to ensure plenty of oil gets to the thrust surfaces." That would be 25-30 for the #5 bearing. Going by that, 1-4 are fine, 5 is too tight. Looks like I need to order an X set for #5, and I will probably get another set to play with the #4 as well while I'm at it.

Are the bearings all 'the same', or is it worth trying to swap the existing bearings between the #2 and #4 journals to try to equalize those a bit?

As for runout, I don't remember what it was offhand (have it written down somewhere) but I do know it was OK. The packing job that was done on the crank (from the factory!) was a bit...umm...sparse. I checked the runout as soon as I could to make sure it had survived the shipping...it was fine.

Thanks everyone!
 

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Remember, we're working with ten-thousandths of an inch, not thousandths. 25 thousandths would be a lot of clearance. You could also swap halves on the 2 and 4 bearings, might go up 3 on one and down 3 on the other.
 

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Discussion Starter #9 (Edited)
By gum, you're right. ten-thou. That's what I get for posting late at night.

I'll try switching bearing halves from #2 to #4 to see if that makes a difference.

A couple of problems on #5...The X series bearings are +.001, which would put my #5 bearing at .0032 (assuming it really changes exactly .001) which is a bit bigger than the article suggests. OK, so I use half of the .000 and half of the .001, and that should do it. Except...1) the crank is .010, and I don't see any listings for combinations of off-sizes. I see .010 (H10) and .001 (HX), but not .011 (H11 or H10X)...and 2) I only see X bearings listed for connecting rods, not mains.

Assuming that I shuffle #2 and #4 pieces to (hopefully) get both of those to .0024, it seems like 1-4 are OK. The #5 still seems tight though. How can I correct that?
 

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Equalizing bearing clearance often requires juggling shells. Bearings vary by small amounts. If you don't use precision tools you won't be able to detect the small variations in thickness.
I use a ball mike and measure the actual bearing deviation and mark it on the back. Then I juggle the shells around until the clearance evens out. In a lot of cases I have to check several sets to get shells that give me the right clearance.
You can also buy shells that are 1 thou over or under and use one half to get 5 tenthou. So a clearance that's .0021" could be truned into .0026" or a .0032" could be .0027"

I'll show the process on Kev's build up soon
 

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Call up Jerry over at Calico Coatings. He will be able to answer all of your questions with part numbers and or price. Sure it sounds like a sale for him but the best thing I like about Calico Coatings is that I get to speak with the same guy "all" of the time (as long as he's not talking to someone else). They sell both ACL and Clevitte, coated and un-coated.

Not to get off-subject but that is one of the reasons why I like the family level style of business. Some businesses have gotten so embedded into the corporate level that the customer becomes a caller and not someone with a name. Ok..done rambling...:shh:

You are correct in swapping halves. This may show a difference. Also double check your torque values and whether or not you're checking them with lubricant or ARP Moly lube. This will effect your readings. Good luck.
 

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i wasn't aware of bearings being sold in .011-.012 undersizes


std, .001, .002, .010, .020 etc...





are they made in .011 under ???
 

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In most cases the plus or minus shells are for standard sizes not undersizes. Normally, when a crank is ground the clearance can be made correct during grinding. this is why you measure your ID's before you have your crank ground so you can specify clearances.
Crank grinding has tolerances and they can make the clearance too tight or too loose and still be within production specs. ".010 under" could come out as .0097" or .0012" and still get an "AOK" at some shops.

What you have to determine is your variation in the OD of the journal or the ID of the bearing. If the OD is too large by a bit, you can have it polished to your spec. If it's ground slightly too small you'll need to find a slightly thicker bearing.
If the ID's are varying you might have a main cap problem.

Half a thou may sound like it isn't much but it can make the difference between a regular engine and a blueprinted engine.
 

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Setting bearing clearance is why I paid to have my bottom end put together. I'll buy just about any tool I need. But the cost of machinist tools, skills to use them and buying 2-3 sets of rod and main bearings to get exactly where they needed to be helped make my decision.
 

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the Flyer said:
i wasn't aware of bearings being sold in .011-.012 undersizes


std, .001, .002, .010, .020 etc...





are they made in .011 under ???
Yupp. They actually come in .009", .010", & 0.011". I don't believe they have a 0.002" version. Like I said Jerry or David over there can handle all of your bearing needs, Clevite and ACL.

~Ty
 

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9SecAntique said:
Yupp. They actually come in .009", .010", & 0.011". I don't believe they have a 0.002" version. Like I said Jerry or David over there can handle all of your bearing needs, Clevite and ACL.

~Ty
do you know if they have the same spec range for the .020 and ,030 undersize bearings too???...for example....019", .020", .021".....029", .030", .031":)
 

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9SecAntique said:
According to my chart they don't. Most cranks we run don't see life after 010/010. I normally sell them off past that point.
Cool...thanks for the info:)
 

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Plastigage is not for measuring tenths. It is just for a quick check to make sure the micrometers were read correctly.
 
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