RD250 vs RD350 engine difference

[soonerbillz]

So I know that basically the lower ends are the same.
My question is specially about the clutch and trans.
I was wondering what the difference is between them beside the primary?
Also is there any difference in a 73 RD250 vs later bikes as far as those parts?
I want to use the parts in my other R5 buildup.
Thanks.

[m in sc]

just primary and clutch gear. maybe the idler gear & oil pump gear.. and oil pump as well. but thats it.

[SoCal250]

since I've been dealing so much with oil pumps lately...I can confirm that the plastic drive gear and the worm are different on a 250.
RD250
"280" pump drive gear (22 teeth)
"275" worm shaft, coarse-7 thread (or "522" fine 9-thread for late-1975 models)

RD350
"274" pump drive gear (21 teeth)
"278" worm shaft, coarse-6 thread (or "214" fine 9-thread for late-1975 models)

[m in sc]

yes. when i referred to oil pump, i meant all of it. Russ is, of course, correct.

[soonerbillz]

Is there any benefit to using a RD250 trans vs vs a RD350 trans in the 6 speed swap for a R5?
Also does the FZR discs swap into a RD250 clutch like a RD350 clutch?

[SoCal250]

Pretty sure the trans parts are identical between RD250 & RD350
Clutch parts are the same and interchangeable with the FZR/YZ upgrade.

The only parts I see different are:
Primary gear, 21T on the 250 and 23T on the 350
Primary driven gear (clutch basket), 68T on the 250 and 66T on the 350
Tach gear, primary

[soonerbillz]

Thanks guys.
I have 2 RD 250 motors so now with your help I've got plenty of hard parts to work with.

[m in sc]

the 250 primary/clutch will help reduce windage in the clutch. TBH, one of my favorite motors was a 250 bottom i did a 350 lc top on, it was quick as stink. you up the front sprocket 1 tooth and it puts the gearing about where a stock rd was, but the transmission effectively spins slower. EVERYTHING will work fine, including the 250 oil pump, drive, tach, etc. 

[Vintagetz]

It is not likely an issue on a street RD, the TZs have the same difference between the 250 and 350 as far as primary ratios.  If you run a 350 top end on an engine with a 250 primary you will very likely break gears. (transmissions are the same).