2F Thrust Bearing Width (1 Viewer)

[pinkiedog64]

Reassembling my 2F and went to install freshly machined crank tonight and crank hung up on thrust bearing (#3). New crank is from a '79 2F and is .030" over. Old crank was .020" over. Block is 11/75. I bought .030" main bearings from SOR that are for 9/73-10/84. Old thrust bearings (upper and lower) both measure 1.415" wide and old crank measures 1.416-1.417" where thrust bearing goes. New crank also measures 1.416-1.417". New bearings measure 1.427".

Should the the thrust surfaces of the freshly machined crank been opened up during its machining to .030" over to the 1.427" (+.001" or so) width? It seems that since the old crank was .020" over and the new is .030" over that opening up the thrust width on the new crank by .010" over the old would be correct.

Thoughts?

 

[DougAustinTx]

The depth of the cut on the journals has nothing to do with the thrust face of the crank (unless the machinist failed to maintain the width of the journal as he made his cuts). If your thrust is insufficient, you can clearance the new bearings by lightly sanding them on the thrust face until you have adequate clearance. I have had to do that on several engines, but I attribute the tightness to slightly too large bearings.

 

[pinkiedog64]

I've rebuilt two other engines and not run into this and both had the cranks machined down undersize. So are you saying when a crank gets machined undersized for new bearings the thrust faces are not typically also machined, and thus the thrust width of a brand new crank should be the same as that of a undersized crank?


And if that’s the case, I wonder why the thrust bearing halves I received are almost exactly .010” wider than the set of bearings I took out.

 

[65swb45]

If you look at the threads on crankshaft failures, you will better understand why the thrust face is not cut if it can be avoided. I have had a few instances where replacement bearing tolerances varied from company to company. I have polished bearings as @DougAustinTx suggests.

 

[pinkiedog64]

Thanks. It does seem odd to me that the thrust faces of the crank would be machined. I am ok with polishing the bearings, but to remove .005" from each side of the thrust bearing is quite a bit. Think I'll check with SOR where I bought the bearings and see if they would be willing to measure others to compare.

 

[Tools R Us]

... I am ok with polishing the bearings, but to remove .005" from each side of the thrust bearing is quite a bit. ...

Not something that I would be concerned about. Much prefer to take a bit off the bearing and make the thrust perfect, than have it sloppy where nothing can be done about it.

 

[pinkiedog64]

Figured I'd update with the answer to this one. Turns out with the 2F (probably F, 3F/3FE, too) when you go up to .030" on the mains the thrust width increases by .010". So standard, .010" and .020" over all have standard width thrust bearings, but it jumps up .010" at .030" over. I had bought a freshly machined crank and even had my machine shop check it out after I got it in the mail to check runout and confirm rod/main bearing sizes so I could order the correct size bearings. Neither machine shop caught that the thrust bearings needed to be oversized. I confirmed this with SOR and
my machine shop once we started investigating why my .030" over main bearings didn't fit at the thrust surface. According to his bearing books/suppliers, that's just how those bearings are. He said he thought I could special order .030" mains with a standard thrust but it would be expensive and long lead time.

So, heads up to all you doing F (or any) engine rebuilds. Check thrust bearing width in addition to main and rod bearings! May save yourself some grief.

 

[65swb45]

That is good info.

 

[Bluegrass40]

@pinkiedog64 did you end up machining the crank, removing material from the bearing, or ordering new bearings? Did you run into any issues with the path you chose?

I’m dealing with a similar situation now. I have .25mm undersized bearings and crank and I’m haning on the thrust faces. I need to take measurements (on Monday) to verify what I’m dealing with.

Thx.