'74-'75 exhaust ports are close in size to '73 12A ports on the outside. '76 and later are larger, thank goodness. It's ok to remove the sleeves in '74-'75, or so I've read. https://www.nopistons.com/forums/pub...IR#>/smile.png

i know you can spot a 74-75 motor by the 1757 number stamped into all the steels. the 76-78 ones are 3870 something, one of the things i need to look up



mike

I've seen 1757 on several front counterweights.

that would balance any 74-85 13b rotor. my r100 came with a 73 rx3 motor, thats the twin dizzy bottom mount starter motor, super wierd



mike

I've seen a pic of one of those. The rear plate is missing the upper inspection hole. Quite weird.

yeah its really wierd



mike

Kinda reminds me of a 20B. So does the waterpump pulley's distance from the main pulley.

wait til you see the 20b main pulley, its giagantic!



mike

Oh my, it is! The waterpump pulley also has a larger center hole. It tried fitting my FC waterpump pulley and it didn't go past the center thing.



I was wrong about the distance from the main pulley to the waterpump pulley. It's actually lower and pretty close on a 20B. I'll have to check out pics of some '73 12As when I get a chance.



I briefly installed my FC main pulley on the 20B and noticed the timing marks are offset by maybe 20-30 degrees. Interesting. I'll just line up each mark on the 20B pulley before I take it off and put the FC pulley on it to mark it. Then I'll have a baseline to measure 120º both directions and mark them. How did you accurately mark your larger 20B pulley for 120º and 240º?

i dont remember exactly, i think i marked every 90degrees, and then for 120 and 240 i did half of 90? i ended up making a big spray paint mark, thats different for 2 and 3, so its easy to see and tell apart. oh yeah the firing order is 1-2-3, the same code and idiot would have on thier luggage....



mike