Hey guys, I'm using an NSR mc28 chassis to house a dirty 4 stroke single. I'm just after a few answers that i cant find by searching this forum or by searching the net. hope you can help.

What is the weight of an NSR mc21/28 engine - have found a reference of 27kg? sounds a bit light to me or is it?

im guessing the rear hub of the mc28 swing arm will restrict the rear sprocket size? what is the smallest size available?

is it true that a 28 pro arm will fit directly to a 21 frame but needs 5mm shaved from each side of the pivot mounts anyone done it???

thanks, steve

I've seen and taken the pro arm off a 21 frame and it looked like it wasn't shaved at all.

Doesn't need shaving...straight fit.

straight fit, fantastic, the mc28 chassis i have has live reg/mot it would be a shame to cut it up. I found a nicely priced dead 21 frame so i will swap them over. it might help someone with a damaged bike get theirs back on the road without all the hassles of certification etc.

is there any other differences between 21/28 frame??

kiwisteve74 wrote:
What is the weight of an NSR mc21/28 engine - have found a reference of 27kg? sounds a bit light to me or is it?

To be fair that sounds a bit heavy to me.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

weighed the crf450x motor i have = 32.4kg with oil.

i would weigh the nsr but i only have the bottom end, can someone tell me the weight of a cylinder and head including powervalves?

Alzazorq wrote:Doesn't need shaving...straight fit.

Well its definitely not a straight fit. the swing arm pivot on the 28 is much larger. the threaded part that screws into the left hand side of the frame is bigger. The only way it would fit is by using the 21 pivot bolt and spacers and hope that they fit the proarm. I dont have the 21 pivot bolt or spacers, just the bare frame. then ya got to wonder why they made it bigger??

differences between mc21 and mc28 frame.

28 has extra lugs for the tail fairing to screw into below the subframe mount.
28 has a large cut out behind the headstock to mount the electric lock.
28 has a much bigger swing arm pivot and pivot thread.

can anyone tell me if the 21 spacers and pivot will slip straight into the pro arm?

cheers, steve