What Oil Clearance on Mains?

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eekvonzipper

eekvonzipper

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Set New Main Bearings in the 273... Wanna do a Plastigauge test.
I have Red, Blue and Green. What Clearance am I looking for?
Green is .001-.003
Red is .002-.006
Blue is .004-.009

So, Which One?
 
Green. I shoot for .002 - .0025. I'm sure others will chime in with other suggestions.

Have you checked out @krazykuda how to rebuild an engine sticky. Good info there.
 
The general "rule of thumb" for typical performance and reliability usage is .001 of oil clearance for each diameter of journal diameter.
 
What do you do if it's Less than that?

oil.jpg
 
Have a machinist confirm the clearance and turn the crank if it needs more clearance. Plastigauge is only good for a quick final check.
 
Whatever the FSM says. And if you don't have one, why the HECK not? lol
 
Micrometers and dial bore gauges for true measurement. Then, if adjustment is needed, there may be bearing sets available to allow that much adjustment. Some folks talk about running separate upper and lower shells from a set of standard and undersize bearings to make minor (half of undersize) adjustments, but I would rest a lot better having the crank micro polished to correct clearance myself.
 
Just order a set of bearings with the undersize you need to get the clearance you want. But make sure your measuring is accurate.
King will make whatever you want.
2B1F947C-6839-4815-881F-2D4F3C9F302C.png
 
Not sure why that’s so blurry. Here’s the chart closeup.
F37E4261-2E26-4437-B7E1-897BBEFCE8D8.png
 
Were the other main caps tightened down during this test or not? That, can affect results.
 
As Garrett mentioned, I'd have that crank polished a bit more. Make sure you use some oil on the plastigauge and bearings during the test, and torque all the main caps to specs. Take care that the crank doesn't turn or you can get an inaccurate reading.
 
Just a quick word from Clevite;

6E6F891B-2D8C-4E14-A43D-2E4146C9DC90.png

Buy the set of bearings that gets you clearance you want.
 
I'm sure that the fact they want to sell bearings has nothing to do with their recommendation. :rolleyes:
 
cudamark said:
I'm sure that the fact they want to sell bearings has nothing to do with their recommendation. :rolleyes:
Click to expand...
True they are in the business of selling bearings, but it’s also the correct way to establish clearance. Idk but to me removing a crank, taking it to the machine shop, repolishing, reassembling, rechecking, sure seems like the long way around when you can just take a measurement and order a set.
 
You still need to remove the crank, install new bearings, re-install the crank, and check clearances again doing that. You're just saving a trip to the machine shop is all.....and the cost of new bearings.......
 
Just a check, you made sure the bearing saddles in the block and main caps were squeaky-clean with no oil or dust/debris of any kind, right? Anything in between the bearing and saddle can give false clearance readings. Same goes for crank journals, give them a wipe down with lint-free cloth/rag with acetone and blow them off with compressed air.

Also gotta make sure all main caps are torqued to the same spec, noticed you didn't do that... When I recently plastigage'd my 440's mains I put a piece of plastigage on top of each main journal then torqued all the main caps fully to spec. With original factory crank very lightly polished, new standard-size Clevite bearings and original main caps the plastigage was just in the middle between .002 and .003 so I called it .0025 and moved on.
 
Why would you need to torque up all the main caps unless you're checking them all at the same time?
What undersize is the crank?
 
Bakerlite said:
Why would you need to torque up all the main caps unless you're checking them all at the same time?
What undersize is the crank?
Click to expand...

Could potentially push the crank up/down on one end, not likely but 0.001" is a tiny distance to be considering on something that's 2 feet long and 6 inches around. Torqueing fasteners in general also just does weird stuff.
 
Your not going to move the crank up and down, when it's laying in the block..The bearings in the caps, shouldn't even be touching the crank. The only thing that will be in contact is the little piece of plastigauge..
 
Bakerlite said:
Your not going to move the crank up and down, when it's laying in the block..The bearings in the caps, shouldn't even be touching the crank. The only thing that will be in contact is the little piece of plastigauge..
Click to expand...

Probably true, I'm just obsessive-compulsive like that. I've seen some weird stuff happen to parts when they're torqued working in the R&D mech engineering field.
 
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