Pitman arm modified

[windybob]

Was working on a A602 today. The early kind without the pinion gear plugs in the case. The crank gears have the older pins, the kind that take the older one-stroke arms. It was set on the short stroke, but I needed to make new pins, so i thought i would just put them in the long-stroke holes. Well, come to find out, all I had were short-stroke arms. These older 602's are one-stroke only. If you want to alter the stroke, you need to replace the pins in different holes, (which are not tapered), and then change the arms. It is still only one stroke, no matter. The later 602's have the different crank gears, and the 702 type pitmans, which you can change the stroke like in a 702 mill.

Anyway, I really needed a couple of long-stroke arms, but didn't have any ( i was surprised) so I decided to take a couple late model 702 arms and modify them to work. They have the double hole at the top, but they will still only be single-stroke arms, due to the pin type in the crank gear.

If you ever have a need to do this, here is what I did. As always, be very careful with babbitt, and always check and re-check clearances, and fit, to make sure things are good.

Step 1. Take the 702 style pitmans, and bore a 7/8 hole where the pin hole is. Then grind and remove a SMALL amount of metal from around the bottom 3/4 of the outside of the arm bottom. The clearance in the bottom of the case is very small, which is why the metal gets removed. If your pedastal bearing for the crank gears is low, or worn, make sure the arm clears. you will assemble and take apart these items many times to check the fit.
Step 2...Grind off the 2 tabs on the inside of the lower part of the arm, where the round part is. Grind the tabs flat to the rest of the circle. Also, grind maybe 1/8 or so off the ribs on the outside of the arm, at the bottom of it. Grind off about 2 inches up the arm. The reason for this , is you will put a 7/8 washer on before the cotter pin, and you need the room. You will also put a washer on before you put the arm on the pin, between the arm, and the crank gear. You should not diminish the integrity of the arm by doing this metal removal. The forces on the area are opposite of the modification.

pitman 6 edited.jpg

pitman 2 edited.jpg

Step 3... set up your babbitt jig, and if you use a 7/8 piece of stock for your mandrel, you might use 1 wrap of paper for a little clearance. This is a pour I do not use any paper on. After you melt out the old babbitt, clean the inside of the arm good. Don't forget the putty under the arm on your jig. And before I put the arm on the jig, I spray the mandrel ( Pitman pin) with silicone. Helps it to come apart easy. I don't spray silicone after the arm is on the jig, if it gets into the pour area, babbitt won't stick. Make your pour to the level of the top of the sides on the arm. Remove from jig, file the edge smooth, and with a box knife slightly chamfer the babbitt. Check for fit. Lower part of arm should clear bottom of case, and up the inside of the case. Of course, you need to do this with the crank gears in position, and the pedestal cap on, and locked down. You might put a little grease in the bottom of the case, and see if the pitman picks it up when it comes around. A good way to check clearance.

Next post will have the remainder....Stay tuned...

[Smax]

Good stuff windy thanks

[Wayne]

The genius at work!

[JBarker]

Awesome ingenuity!

[windybob]

The rest of the story...

Pitman right after pouring.

pitman 4 edited.jpg

After pouring, cleaning, filing, and testing, the arms should go on basically like any other. I put a washer or 2 between the arm and gear, and one or 2 on the outside, then the cotter key. Now you see the reason to grind a little off the ribs on the bottom of the arm, to make way for the outer washer (s) so the key doesn't catch on the arm. After installing, rotate and check clearances.

pitman 3 edited.jpg

Be sure to use the top holes for the long stroke, or the lower holes for the short stroke. But after you make it one way or the other you cannot change it. Only the later 602 mills offer this choice.
Of course, this whole thing could be avoided by cutting and welding up longer arms. I just do everything the hard way.

[PaulV]

Fantastic work windy!

[windybob]

Thank you all.

[Todd]

That's a really ingenious fix. I'm impressed...!

[windybob]

That's what I do best.....make stuff work that's not supposed to. lol

When are you coming for your mill?