How much end thrust on 8BA Crank ??

D

David Lien

Member
Today I set a reground crank into an 8BA block. I snugg the main bearings to 55 Lbs. tourque, and checked the end play on the thrust bearing. It measured .017. The book calls for .006 Max. My guestion to this board is can I run that much end play???:confused: Can I by a rear main bearing with thicker thrust flanges???:confused: I have had the crank sitting here for 5 years so it will be a little hard to return to the machine shop. Thanks for any help I can get with this issue.
David
 
I feel your pain. I've learned that shopping a used flathead is not just the visual stuff, but also the history. If it was raced, it probably had a heavy clutch used and you need to do the push/pull test on the crank before buying. You're not the first. I've read a couple threads where some after many months found this problem during assembly. Maybe look into spray welding the crank?. Gurus here will set you straight.

Lonnie
 
David - did you torque the main bearing bolts to 105 ft lbs. 55 ft lbs. is not enough (3 increments)?
The end play should be in the range of .002" to .006". The rear main bearing is
the 'thrust bearing' that controls end play. Did you measure measure the main bearing diameter with an inside micrometer? And then measure the crank. Do the measurements w/o oils on the bearings. Subtraction yields the main bearing clearance - up to .025" is OK per Ford's spec.
 
Federal Mogul used to make a .010 oversize thrust bearing. I don't know if you can still get them but it's worth checking. Walt
 
You might be able to shim the bearing flanges out using .005" shim stock on each side. Or get a another crank.
 
Yes, there was "back-in-the-day" thicker thrust flange bearings. Availability today is a big question? I would put a .005 shim at the rear, only, of the block and cap. This sounds easy but it is not. And, it is not a perfect solution because the bearing face will be at a slight angle to the crank thrust face. It will, however, work out ok. I shimmed the bearing of an engine I have put around 40,000 miles on and have not had problems.

In my case I made several different shims before I was finally satisfied that I had a proper fit and installation. To begin the operation I layed a piece of stainless steel shim-stock about 2 inches and overhanging, about an inch, both the front and rear of the block and cap housing area. I pushed and hammered, with a wooden block, the bearing halves over that shim stock. After each half was pretty well in position I removed the bearings and moved the piece of stock, or made new pieces, around to new locations and repeated the operation until I had the bearing flanges "stretched". Finally I cut pieces to closely match the half-moon of the bearing and "Super-Glued" those pieces to the rear of the block and the cap. One of those pieces developed a wrinkle and tore loose so I had to begin again, but, eventually I achieved the desired result and have been happy with it.
 
No, shim at the rear. Since presumably the crank thrust face is worn the shaft, if bearing is shimmed at the front, would assume a new, uncoordinated, center to center running position, farther forward than when shimmed at the rear. Too, when shimmed at the front and the clutch is released the shaft would be sent forward to the full extent of the thrust face wear. There is a limit to how much misalignment the assembly can withstand without self destructing. The limit is likely more than the described assembly might have depending on rod to rod side clearances and small end to pin boss clearance. However, it would not be wise, nor necessary, to test the limits.
 
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Thanks to all for the ideas on how to repair my crank. Love Machine in Salt Lake City will weld and repair the crank for under $150.00:) It is a 4" crank sooooo that is what I will do .. Thanks again for all your posts and ideas on my problem. David
 
David, Your solution is the best one. I have a 4" crank that had a bent thrust flange when I got it, apparently due to some idiot's careless removal procedure. My expert machinist just welded up a new thrust flange. Wasn't cheap, but was the only feasible solution in my case. John R.
 
This thread begs a good question. If I were to walk up to a table at a swap meet to inspect an 8BA crank and whip out my telescoping gauge and micrometer, what is the stock measurement between the forward and rear thrust surfaces? I've done the installed "push/pull no-thanks" before, but does anyone know the stock measurement?

Lonnie
 
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