Wednesday, August 29, 2012

Studebaker meccanico

Knock knock. I open the shop door this evening and my nose is greeted with the smell of old car parts and grease. My neighbor Sam is holding part of the kingpin assembly of one of his ancient Studebakers up to my nose so I can look at it.. He explains the evenings challenge after I invite him in.
It seems pin number 14 in the diagram is not behaving itself and does not want to come out despite Sam's best efforts and biggest hammers. Looking it over it looks suspiciously like a tapered pin to me so direction might be important. Somebody has ground off the heads or whatever was sticking out flush with the forging number 11. So we cant tell which end is the small end so I don't have a clue which is the right direction. In the manual the pin looks to be tapered but its hard to tell in this old book. The insertion direction is not in the written instructions and the diagram only shows the pin on one side of the forging and may or may not be correct.
First attempt is just getting a good grip on it in a well mounted vise and trying to punch it in both directions. Under close examination you could not see the od of the pin on the one side because of the grinding job so determining which was the small end was not obvious. I figured that if I could move it even a little in either direction I would then be able to see the small end of the pin against the surface. So I started with the orientation shown in the diagram.This probably increases my odds a hair over fifty fifty but I'll take any advantage I can get.

OK. A few major whacks later and I'm wondering whats going on. Absolutely no movement and the hits feel like dead solid material. I like to use a bronze or copper hammer when I have to hit a pin punch or chisel with a heavy blow. The soft hammer grips the head of the punch and is less likely to slip off. Hard hammer on hard punch is a bad deal. Kind of like hitting to bars of soap together. If your alignment is not perfect then the hammer head can skate off the punch head and hit you, or worse the workpiece. How do I know that? Simple I saw somebody do it once......
After clobbering the pin for a while with heavier and heavier blows I finally managed to raise a little witness circle on the opposite side. The next odd thing was when I measured the circles on either side they were the same diameter. WTF? If the pin were tapered then one circle should be smaller than the other. Hummm. Well I wasn't making any headway trying the normal stuff like some heat, a little Kano Kroil and a good solid whack with a three pound hammer. When in doubt drill it out. After moving the pin a little I was able to spot the center of the pin accurately and drill a small hole through the center of the pin. Many times with stuck fasteners drilling a hole around a third of the stuck fasteners diameter through the center is enough to relax the offending fastener and removal goes easy at that point. This particular pin still wouldn't budge after drilling a relief hole through.
The irregular outline of this side of the pin got me to thinking that maybe the heads of the pins were mushroomed as part of the installation. This might explain why the pin refused to budge. I did manage to get a decent measurement of the pin from the hairline shadow I raised from the pin punching. Nominally the pin was 3/8 in diameter. I looked up taper pins just in case to see what standard taper pins have 3/8 on one end or the other. I found some that were close so I picked a drill that was a little smaller than the small end of the standard taper pin I found. Anything you can do to stack the deck a little in your favor is worth doing. The hard part is recognizing when you can stack the deck.
The mystery is finally solved. The pin is dead straight just like my measurements said and is .375 as best I can measure of the hamburgered remains. What is tapered, is a flat on the pin. This makes sense from a retention sense and as a way to eliminate any play in the assembly. But why didn't it show up on the end? There should have been a little flat that you could see from one end giving a person a clue what was going on. Sam looked through his parts books to see it they listed a pin as a replacement part.
While he was looking for the part in the book I was sneaking and making a couple of new ones from some cold rolled 3/8 rod I had lying around. Remember the rod bender article? So I get to mill a little flat on the pins at a small angle. I guessed at the angle since there were no references to go off and the mating surface was not tapered to match. Five degrees looked like too much by about double so I settled on three degrees. Actually a little less because I used a .250 pin under my little sine bar to set the angle.
This sine bar design is pretty nifty. I bought this off e-bay a few years ago and I really like it. It sits on the rails of a normal Kurt vise and is thin enough that it makes a variety of angle setups pretty easy. This monolithic sine bar was made entirely by wire EDM cutting. I checked it when I got it and Mr Ramos was a fine toolmaker. Its so simple and just the right size for Bridgeport size mill operations. I want to make another one without the vertical heel on it someday to add to the stable of sine bars in my box.
It took a couple of test fits to get the right amount of drive left sticking out for seating the pin. Sam reminded me he needed two pins one for each side of the car. Humm, I guess I'll be drilling another one of these out pretty soon.
So a couple of American made replacement parts for an American car. It was probably Korean steel so I don't get to claim a  hundred percent American made but I made somebody's day this evening.
Thanks for the fun job Sam. Bring something harder next time. Thanks for looking. By the way the diagram was right and now looks an awful lot like a flatted pin.