Jeff20B

'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.

j9fd3s

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

Jeff20B

I've seen 1757 on several front counterweights.

j9fd3s

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

Jeff20B

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

j9fd3s

yeah its really wierd



mike

Jeff20B

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

j9fd3s

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



mike

Jeff20B

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?

j9fd3s

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