Are you guys talking about the <span style="font-weight: bold">engine</span> thrust washers? What is an "arm pin"?
Anway, if you are looking for some decent info on the engine thrust washers, here's two sites with some pictures and text.
https://www.teglerizer.com/triumphstuff/thrustwashers.htm
https://www.eighmy.com/spitfire/
Also, here's a decent text explaination of the process that I copied from an old website:
<span style="font-style: italic">The thrust washers are two semi-circular metal pieces that fit over the crankshaft on either side of the upper half of the rear main crankshaft bearing. They are held up into a groove in the block by the bearing cap, and cannot be seen with the rear bearing cap in place - unless of course they have fallen out due to wear and are lying in the bottom of the oil pan. While they are doing their job, they ride against flanges on the crankshaft preventing it from moving forward or backward more than the specified amount.
Remove the two 5/8" bolts of the rear crankshaft main bearing cap. Wiggle the bearing cap straight down. If it sticks, there is a threaded hole in the bottom centre where you can screw in a bolt finger-tight to act as a handle. Put the cap aside in a clean place for later inspection.
Assuming the thrust washers are still in place, pry the crankshaft fully forward, then use a small pointed tool or stiff wire to push up on one end of the front washer. It will be easier to remove the front one first because the front flange face of the crankshaft will still be flat. The washer will rotate around the crankshaft and drop out on the floor. Push or pry the crankshaft fully back, and push our the rear washer.
Check the crankshaft flanges for wear. The rear one will be likely worn most. If it is still smooth with no bits of thrust washer metal seared onto it, all is well.
Slip a new thrust washer into the rear position. Push the crankshaft forward and slip a new washer in the forward position. Washers come in standard thickness, and .005" and .015" oversize (ie thicker). Pick a combination of these to allow the crankshaft the specified endfloat. Checking this endfloat can be done in two ways. The simplest is to push the crankshaft fully forward, and use feeler guages to determine the space betwen the front washer and the crankshaft flange. Make sure the washers are up where they will be when the bearing cap is replaced. The second method involves using a dial guage clamped to the motor block. With the crankshaft pushed fully one way (back or forward) set the dial guage against a bearing journal or counterweight and zero the dial. Push the crankshaft fully the other way and read the guage - it should be between the 6 and 14 thousandths of an inch. If it is, your work is done.</span>