I wanted to know what were the differences between an 89 MC18 SP motor and a 91 MC21 motor. What parts are interchangable? I have both but only the MC18 runs right now. My bike is a MC21.
The main differences are the crank and the barrels/heads. The cranks ARE NOT interchangeable, the barrels are, however.
The complete motors are interchangeable in the frame, so any model NSR motor will fit any other model's frame (i.e. MC16 complete motor will fit into an MC28 frame).
To use the MC18 motor in the MC21, make sure to fit the MC21's G.P.S. (if you are using the PGM-III, that is!), and also use the either the complete MC21 carb assembly, or the at least the MC21's T.P.S. as I still can't confirm whether the T.P.S. readings differ on each model - I think they do.
The complete motors are interchangeable in the frame, so any model NSR motor will fit any other model's frame (i.e. MC16 complete motor will fit into an MC28 frame).
All NSR motors share external dimensions & mounting points. Just make sure the relevant electronic components are used for the chassis the motor is fitted to. (This isn't a "be-all and end-all" recipe, just a safe setting - there are circumstances where components are mixed such as with the MC21 F3 setup where a PGM-II is utilised.)
I did have a Japanese Book somewhere with text and cross-section diagram comparisson's between these two engines and maybe bikes . It's in Japanese , so I can't read it . I will try to find it , Digi-Photo with my Friend's Camera , the relevant pages , and download them as soon as I can. It could take a Week or 2 to do all this if can do it all , will try my best. Very busy !!!
No, the MC18 DOES NOT have a G.P.S., or even a provision for it.
Enzo, if you have a G.P.S. then I would say the bottom end has probably come from an MC21. How many wires come from the switch? If it has 6, then it's likely to be an MC21 bottom end; if it has less than 6 wires, then it may be an MC28 bottom end. (I think the MC28 has 2 wires, but I'm not 100% on that off hand.)
Please note: this is not a sure-fire way to identify the bottom end. Only the full engine number will tell you that.
Sorry guy's...At present, due to the design or capacities of this sight and mine ...I cannot download the pic's I mentioned previously in this thread...Sorry !!!
Andy in the begining you said fit the MC21 G.P.S. to a MC18 motor, but later you said MC18 motor has no provision. I don't follow, I'm planing to install a MC18 into a MC21, could you clear ?
If using an MC18 motor in the MC21, I'd suggest leaving the G.P.S. fitted to the harness and switched to position 3, then cable-tie it out of harms way.
This will effectively perform the G.P.S. wire splice as the PGM-III will think the bike is permanently in 3rd gear.
Before anyone asks; No, the G.P.S. splice alone will not delimit the PGM-III's ignition restriction. For some reason (even though the PGM "thinks" the transmission is always in 3rd) the orange/blue wire splice must still be performed.
Alternatively, if the MC21 motor is going into an MC18 frame, simply leave the G.P.S. in place and leave it disconnected. (If using the MC18 harness/PGM-II that is.)
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