Main bearings and clearance...

[64PI]

Working on the assembly of my 451" after the cam bearing dilemma. Light polish on the crank. Mic'd the journals up and they are few tenths under. Torqued the caps down with 125M bearings. My clearances are coming in around .0018-.0022. The last time I put the engine together using the same brand bearings they came in at .0025"-.0027".. I know bearing MFG's allow a .0005" tolerance.   Has anyone had any experience with another brand bearing that tend to run on the looser side? I hate to buy another set of 125M and have them be the same. Anyone have experience with Cleveland bearings? I know you have to remove the tang. What is the part number for a 3/4 groove Cleveland bearing to allow .001" more clearance?  Fred

[blykins]

Are you checking with a mic and bore mic?

[64PI]

Mic'ing the crank journals and using a bore mic to check the bores.

[blykins]

Good.

Do you have a good crank grinder near by who could touch grind the journals for you?  You could do that or switch to Cleveland 145M/146MX bearing halves, or 146MX halves mixed with your 125M halves. 

[64PI]

Thanks, Brent. I was trying to avoid having to grind the crank.. I will look up the bearings and weigh my options. I was hoping to open up the clearance to .003". Fred

[blykins]

Wouldn’t need much, it’s not like you need to go to .010” under.  Sometimes cranks need adjusted this way.

I do agree, I’d rather see somewhere around .0028-.003”.

[My427stang]

Absolutely agree with Brent, but you polished the crank and are now .0005-.0007 tighter?  You'd expect the opposite if all the parts are the same.

Are you using the same procedure that you used with the first build?  Have you rechecked your mic?  Same block?

I'd make sure the locating tabs are clean, check your mic against the standard, and if you have the old bearings around, remeasure. 

Brent's probably laughing right now because in my garage, unheated at night, this winter I was getting all kinds of odd numbers on 390 4V during the course of the day and it was driving me bonkers, but when measuring down to that variance all kinds of stuff can change your numbers

That being said, if the numbers are repeatable, then they are what they are

[GerryP]

... in my garage, unheated at night, this winter I was getting all kinds of odd numbers on 390 4V during the course of the day and it was driving me bonkers, but when measuring down to that variance all kinds of stuff can change your numbers

That being said, if the numbers are repeatable, then they are what they are

I keep my mics in the house in a stable temperature environment.  For moveable parts, like a crank, I move that indoors for 24 hrs to stabilize before measuring.  If the part can't be moved indoors, then I move the mics to the same environment.  You're right, though; If the number repeats, then that is the number.

[Ranch]

Your Mics should be in the same Temp. Humidity conditions as what you are measuring.  Precision measuring tools are usually 'Stored' in climate controled rooms 'along with their standards'.  If you set your mics in a nice warm space and move to a colder work area or vice versa you need to give some time let your mics acclimate to the area where you are going to be measuring, even sitting them on the job itself to ensure they are both the same temp.   

[64PI]

Everything is the same, other than the new bearings.  Even the time of year I'm assembling. My bore mic, 2-3" mic, crank, etc are all at the same temperature. The temp this time of year in my shop runs between 75-80 degrees. I ordered a set of 146MX bearings and I will see what I come up with.

[64PI]

Well with a combo of the 125M and 146MX bearings I got what I was looking for. They're all .0028-003". Everything is torqued and the crank spins nice. As nice as its going to spin with BradPenn assembly oil, that stuff is sticky.