8N Front Axle Question

[Papillon]

I needed to replace the center front axle's bushing and king pin. I stripped things down to the point where the kingpin could be removed. I started it out with a wood chisel from the bottom and continued it out with a claw hammer. It was a snug sliding fit in the bore of the front axle mounting bracket. I tapped out the old bush from the center axle and installed a new one. So far, so good. But the trouble started on reassembly. The new kingpin would not go into the bore of the bracket. It turned out that it was 7.5 thousanths larger than the old original kingpin where the old kingpin was unworn. I had a second new one but it was also 7.5 thousanths larger than the original. I had to have one of them machined down to the diameter of the old one. It slides into the bore now. Has anyone else experienced this problem?

The original reason for needing to address the wear in the pivot was that the axle kept breaking the front mount distributor cap at the number 2 post. Even with the new parts installed, the center axle section still almost touches the cap at the #2 post when pivoting up on the right side toward the generator. I am going to drill, tap and install a bolt in the bracket just below the center axle on the left side of the bracket to increase the clearance with the distributor cap.

Your input/comments are wanted.

Thank you.

 

[Smokeonthewater]

I suspect that you have something else going on... damaged radius arm maybe

Also, I can't say for sure but I suspect that the .0075 is for an interference fit
You want that pin to be very tight in the steel bracket to eliminate wear

This post was edited by Smokeonthewater on 08/18/2021 at 07:12 pm.

 

[Papillon]

I think you should re-read my post. The radius arms aren't even installed at this point. [b:9262dfcff0]The original Ford bushing is unworn at the point of contact with bracket bore.[/b:9262dfcff0] The new kingpins are 7.5 thou oversize compared to Ford part. 7.5 thou interference fit is impossible even with 10 lb sledge hammer. Pressing it in with hydraulic press would bend the mounting bracket. Shrinking the pin with LN2, maybe, but you would never get it out again. I think it's parts from the land of almost right. My radius arms are un-bent and in excellent shape, which means the center axle is located properly, but comes very close to the distributor cap post #2. There was actually little wear on the original kingpin and bushing. Replacing these parts bought very little additional clearance with the cap. Also, the new not quite to spec pin's bolt hole that locks it to the bracket is mislocated and will need adjustment with a round file to be able to install the bolt.

I was really wondering if anyone else has experienced this problem with aftermarket parts and if they have had a cap breakage problem and how it was resolved.

 

[Smokeonthewater]

I didn't have any trouble reading your original post and I see no reason to read it again. I offered you my opinion and specifically said "I can't say for sure"... maybe you should do some rereading lol

My pin and bushing are both heavily worn but I have no issues dizzy clearance...

 

[TheOldHokie]

(quoted from post at 22:35:36 08/18/21)
I think you should re-read my post. The radius arms aren't even installed at this point. [b:eaa88644de]The original Ford bushing is unworn at the point of contact with bracket bore.[/b:eaa88644de] The new kingpins are 7.5 thou oversize compared to Ford part.




I was really wondering if anyone else has experienced this problem with aftermarket parts and if they have had a cap breakage problem and how it was resolved.

I have literally made several hundred replacements for these pins so I have a fair amount of experience with the fit but not a lot with the retail replacements or cap breakage. Lets start with the fit. Lets also dispense with the use of tenths in the measurements. Tolerances on the original Ford prints almost never get any tighter than .002/.003 and never under .001.

The nominal diameter of the bore in the axle support is 1.750 and the pin is supposed to he a nominal .002/.003 clearance fit in the bore. I say that based on second hand information provided by someone with access the the original prints. If you have doubts you can obtain a copy of those prints for $100.

I could not lay hands on the OEM 8N pin i have somewhere here but an original wartime 9N pin measures 1.748 which is 100% consistent with my second hand information. I don't personally have those particular prints but I seriously doubt that dimension or fit ever changed. I also have an aftermarket pin for a Hundred series which used the same nominal bore and screwed in. That pin measures 1.745. Finally and FWIW when I make replacements my tolerance is 1.748/1.746.

Which brings us to your pins. What do they measure in absolute not relative numbers? If the aftermarket pins measure 1.757 they are junk and totally unusable. The absolute maximum you could even consider would be 1.750 and that is probably a real push (pun intended).

TOH

This post was edited by TheOldHokie on 08/19/2021 at 05:38 am.

 

[jimtrs]

My experience with the front axle pin and bushing is the bushing usually fits pretty good as long as the axle itself hasn't begun to wear, but the pin is usually a looser fit than I like. Never measured, but definitely more than a few thou clearance. Although definitely always better than the old ones I was replacing.
Only done about a half dozen or so.

 

[TheOldHokie]

(quoted from post at 13:42:25 08/19/21) My experience with the front axle pin and bushing is the bushing usually fits pretty good as long as the axle itself hasn't begun to wear, but the pin is usually a looser fit than I like. Never measured, but definitely more than a few thou clearance. Although definitely always better than the old ones I was replacing.
Only done about a half dozen or so.

Pin to axle support or pin to center axle bushing? Two different fits.

TOH

 

[jimtrs]

(quoted from post at 14:14:14 08/19/21)
Pin to axle support or pin to center axle bushing? Two different fits.
TOH

Pin to bushing.
Pin through the housing has always been better

 

[Jock(OR)]

Where does the axle touch the front motor mount when it is near the distributor number 2 post?
Rather than use a bolt, I would weld a piece of flat bar stock to the motor mount in that area.
Try various thicknesses of flat stock and use the one that gives you enough clearance, but not
any extra. You sometimes need the axle to pivot quite a ways.

Since you are using new parts at the pivot point, you should not get much wear in your
lifetime!

 

[Jock(OR)]

I also see in the Parts Manual that Ford replaced the 8N front axle with NAA parts later on. They used different spacers to position it on the pin. Perhaps that is part of the problem?

 

[Papillon]

(quoted from post at 16:08:19 08/21/21) I also see in the Parts Manual that Ford replaced the 8N front axle with NAA parts later on. They used different spacers to position it on the pin. Perhaps that is part of the problem?

Ah, that sounds like a possible cause for my troubles!

 

[Papillon]

Since I don't have a welder, I will proceed with a 1/4" bolt on each side of the axle bracket.

 

[Papillon]

(quoted from post at 19:22:10 08/22/21) Since I don't have a welder, I will proceed with a 1/4" bolt on each side of the axle bracket.

I did install the two bolts which improved the clearance to post #2 on the distributor cap and I improved the fit of the pin using brass shim stock. I now have a sliding fit of the pin to the bushing. I used a muffler pipe expander to push the shim stock tight against the center axle bushing after coating the bushing and shim stock with red loctite.