Hello NSR friends,

im from Germany and over the last months this forum and the posts helped me a lot to get a MC28 with MC21 engine + electrics back on the streets.
Now I'm facing a problem and don't really know where to start, I try to describe:
I am not able to shift in gears 5 and 6 while driving. Shifting in gears 1-N-2-3-4 works perfectly. When I try to shift from fourth in fifth there's no "clicking" sound and I'm landing in a neutal.
When the bike is standing on a spot, regardless if the engine is running or not, then I can shift up in 5th and 6th gear, so then it works. For me it seems like it only doesn't work when the bike rolls.
Transmission Oil is currently 20W50, going to get it corrected to 10W30.
I filled up 0.8l after rebuild. At the rebuild itself i didn't change anything in clutch or transmission, just replaced mechanical seal and checked some other parts.
Gear shift linkage was my first thought, tried some positions but couldn't get it going.

What do you think could be the problem? Clutch, shift forks, oil?

Thank you in advance for your input.
Kind regards from Lake of Constance, Felix

Hello Felix, and welcome to NSR-WORLD.

Is your transmission "wet" or "dry"?

In case you're unaware, our Honda approved English Service Manual is available here »

Direct link to Section 9 - Transmission Troubleshooting

First thing I would suggest is to get the correct fluid in the transmission. Then check the service information regarding wear limits (both Clutch and Transmission sections), and get back to us. Bear in mind even the newest MC21 motor is over 30 years old now, and things do wear out, but believe it or not, it could be something as simple as a slightly misadjusted clutch cable.
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!

Hello Andy,

thank you for your reply.

My transmission is a wet one. I've started to disassemble the clutch and transmission, I want to check all possible sources of error.
Currently I'm waiting for the tool to remove the clutch basket, it should arrive at the end of the week.
One thing I already noticed is a missing washer under the clutch basket nut (the one with "OUT SIDE";
No 20 on https://www.cmsnl.com/honda-nsr250r7-1990-l-japan_model49620/partslist/0059.html).
I'm not wondering at all after I've alredy faced some other issues with missing washers or even bolts, I think the pre-owner was overwhelmed with reassambling the engine after tuning tries or better said overhaul.
I will take out the complete transmission when I receive the tool to check wear limits and components etc.

By the way, some guy with another Honda bike in another forum had simular shifting problems, there it was caused by a wrong sided washer, see
http://forums.sohc4.net/index.php/topic,138663.175.html

I'm going to let you know some more details when I've disassembled the transmission. Can I also use 10W40 oil?

Kind regards and thank you very much.
Felix

Hello,

i disassembled the clutch and transmission, I noticed the left shift fork is a "NF5 3(or B) L", so looks like it's from Honda RS250 NF5, wondering if the shift forks are interchangeable, does anybody know? Just asking, because standing on a spot I was able to shift.
Is the "L" shift fork responsible for power transmission of 5th and 6th gear?

Other shift forks are KV3 C + R, so this should be correct.

This was the only thing I noticed directly after disassembling the gearbox, will take another look today evening or tomorrow.
I will upload pictures later.

Thanks for your opinion after this input.

Kind regards, Felix

Hello again,
I just compared the "NF5 L" to "KV3 L" shift fork (picture KV3L available on CMSNL), they are different, so that could be the problem, see the attached picture.
As I have tried, the NF5 fork clamps sometimes when I shift up in 5th gear, sometimes it works, sometimes not, I tkink that must be the problem, cant imagine anything else.

Both of the shafts, the drum and the star selector look good, dont want to take apart the shafts with the different gears, now plan is to search and buy a "KV3 L" shift fork and the washer for under the clutch basket nut and then reassemble alle parts.

There hasn't to be a o ring on a wet clutch main shaft, correct?
Can you look at the picture and confirm it looks like a NSR (and not RS250 NF5) gearbox?

What do you think? Still cant believe someone put in a shift fork of another bike.

Kind regards, Felix

Hello, it's me again and sorry for triple posting.

The problem is solved, turned out the pre owner took a normal transmission of MC21 but with HRC shifting forks, the forks, especially L and C are different, R could be same, I actually did not measure.
After I've found out the issue I thought about buying complete transmission or only shifting forks, at that time in Japan there was a complete MC28 wet transmission I've bought at an auction. Three of the gears have a different ratio (doesn't bother me), counted the teeth of the gears when it arrived last week.
As i did not disassemble the MC21 transmission with the shafts and gears, I wanted to make sure there are no other problems than the shifting forks and so I reasselbled the engine with the complete MC28 transmission I got from Japan. It was very "mechanic friendly" to reassemble. The other thing I corrected was the missing clutch basket nut washer (OUTSIDE washer).
Now I took also 10W40 as transmission oil, had no 10W30.

End of story, the NSR now is completely assembled and shifting without any problems. Very happy now.
Will search for another set of shifting forks for the standard MC21 transmission which I want to put back as a spare part.

Thank you for your input and kind Regards, will post pictures soon.

Great job! It feels good when you find the problem and fix it.