I split the cases of my ‘70 RT1 360 this morning and found that the part numbers cast in the crankcase half’s do not match the Parts Guide #’s.  Per the below photos, the left side case displays 214-15111 (DT1 250 case #) and the right side case displays 291-15121 (DT2 250 case#).  As the motor is a ‘70 RT1 360 can I assume that the 250 and 360 motors are based on the same castings and machined with different cylinder stud placement and deck heights ? 

 
Left Crankcase

 
Right Crankcase

 

 

How early is your bike? Did the very first RT1 models come with the large tooth gear set and gearbox?

Are the cases for the early DT1 to suit the large tooth gears with the early gearboxes?
291 prefix I think came in in 1970.

Maybe the 275 prefix came for the fine tooth later gearbox setup? 

Sorry as I have questions and no answers - but I do find these things interesting.

That's very interesting. Doesn't pay to look sometimes haha. Only real difference in castings that i can think of is the stud spacing is wider & casting bigger for the 360 cylinder. Think 360 had one screw behind the cylinder accessed via the hole the mag wires go through. 250 might've had that with no screw. Someone will correct me. Sure ya have a 360. Maybe the factory casting apprentice was on the piss the night before & didn't change the casting number blocks in time--well--more than once. I'll be looking at mine in the future. Good spotting by 'you'.

Here’s several photo’s showing the stud spacing of the ‘70 RT1 and my ‘68 DT1.  I don’t have a ‘70 DT1 to compare the cases to but the last photo below shows the RT1 case next to my DT1 motor and you can see several differences in the casting and location of the breather hole… 

 
’70 RT1 

 
’68 DT1