Hi, trying to help out a customer with a MC21 (dry clutch model?)

He is using it on the track in Bermuda and keeps lunching gearboxes.

Am i right in thinking there is a "kit" gearbox available for these and if so does anyone know:

1) Where to get one!
2) What ratio's they are
3) Are they more hard wearing than standard items (undercut dogs etc?)

Cheers,

Sam

Hi Sam

I've had 7 NSR's all SP/SE's and only one (an MC28) had a dodgy gearbox - in that it jumped out of 4th. So generally they are very good. If a bike is breaking several gearboxes, then it might be more to do with his riding or how he puts the motor together.

I don't think there is a kit gearbox for the NSR - it's just a myth (see Tyga website for their Q&As and ratios), the MC21 and MC28 have slightly different ratios in 4/5/6, but the 'kit' mod was to use a 21 gear box in the 28. You can I believe get a different gearbox for the F3 model, but that requires F3 crankcases - rocking horse do do and mega £££s.

Cheers

Dan

The "kit" HRC transmission will fit stock cases, but as Dan says is rare. I have 3 (two dry & one wet clutch), one for each bike, and a spare with full options that will probably go in the F250 at some point once it can be justified. It's taken over 5 years to source them, and even then the full kit with options needed a new primary shaft to be sourced as it was missing. (Couldn't believe my luck when a new one came up on Yahoo! for £40!)

The HRC transmission is undercut. The HRC MC28 transmission upgrade is an MC21 selector cam and spring, which helps prevent the jumping out of gear. Generally the NSR transmission is very good, based heavily on the RS250 but obviously with cheaper mass manufacturing processes, so of course not as strong/tight.

Matt@TYGA says he busted a few, but he was winning championships -- I've never heard of people breaking them without being overly unsympathetic otherwise. Steve ran 70+hp through his wet clutch R transmission on his 300 and never had a problem.

I never used the clutch on upshifts with my standard MC21SE 'box, and that was still 100% when I replaced it with the HRC transmission last year.
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Andy.
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been doing a bit of searching and need a bit of help.

well the bikes up and running again and testing it has highlighted another problem

bike keeps jumping out of 3rd gear, (and it is only 3rd gear) only under hard acceleration at high revs, jumps into a false neutral and sometimes back in, and seems to be getting worse, literally just crapped myself out on the road, even more disapointing as i have a trackday booked on friday at mallory and was sharing sessions with a guy on an rs125 which would of been fun.

Dont know much about gearboxes and from what i've read it dosn't seem a common problem on the NSR's. THe oils only done about 500miles, light gear oil, transmission looked ok when i rebuilt the engine over winter.

Any ideas chaps?

Brendan

Funny as it sounds, gearbox problems are often caused by the most mundane of faults. Start by checking the splines on your gear linkage or shaft first, its amazing how worn linkage spines make for bad gear changes. If it's not that, next ask yourself if you have new boots or have changed the position on the gear lever - you might just need to be more positive/assertive when selecting the gear. If it's not the simple stuff, then move on to the gear box. Selector forks (make sure they are not bent), selector spring (make sure it isn't broken or stretched), dogs (make sure they are not damaged). If all of these come up negative, give me a call, I have a spare SP cassette gearbox you can borrow to try.

Dan 07974 132739

hi Dan

yeah thats what i thought when i was riding it, i tried it even with my feet of the pegs just in case i was accidently leaning on it but no differance, even ran out of petrol 2 miles from home as i lost concentation, no funny pushing it back !

linkage is fine, so i've just took the gearbox out, first thing i notice is that theres a crack in the gearbox plate at about the 3 o'clock position when installed not far off the selector. looks good hey!

the actual box itself looks ok, i looking at it as an engineer, not someone really familiar with gearboxes, the gears dogs on all the gears look good selector forks look ok and the shift drum ok, and it seems to work.

The crack is perhaps allowing one of the shatfs or selector forks to move slighty under big load and its half cahnging gear. its one thing after another with this bloody thing!!

I've found all my NSR's have had issues with clutchless upchanges, jumping out of gear sometimes etc. but never had an issue if I use the clutch.
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Never ever had a prob with one. To get the best from them they do need to be shimmed up though as required which can sometimes go astray if the gear boxes have been changed from other crank cases during their lives.

Its also very important to make sure you get the shift preload spring back in the crank cases correctly as this can cause no end of trouble and is often missed.
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I would imagine a few transmission plates have been stressed or even fractured by people trying to tighten them down without the spring held back in the correct position.

Like I said in my first post, I rarely use the clutch on up-shifts; only between 1st and 2nd, or when cruising. No problem with the SE box or (naturally) the HRC box, although the HRC transmission has a very different feel that I had to get used to. It's a lot more precise, but you have to noticeably more positive when shifting.

I've missed a few with the HRC transmission, but I know that's more my sloppiness than anything else... when the HRC box engages, it's really in there!! I've never missed a gear with the HRC box when using the clutch though, and it's never jumped out of gear.
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i think thats whats happend to this box, i was carefull to relocate the spring when i assembled the box, but when i took it to bits originally there were only two bolts securing the gearbox, no locating dowel and a couple of stray washers in the bottom, not exactly confidence inspiring i know. there are some gouge marks on the back of the plate where the shift spring has been sandwiched between the plate and case. i bet a pound that that why the bolts were missing on that side as the person could not figure out why it would not all fit properly

i 've been checking out the transmission tonight and cant find anything other then the crack in the plate that would affect the operation of it, so maybe a new plate would sort it.

are the dry and wet gearboxes essentially the same apart from the differant input shaft?

ok so comparing the part numbers in the maunuals it looks like all 21/28 gearboxes are the same apart from the imput shafts, so logic says i could get any gearbox and swap over my input shaft and i'd be back in business.

Yes you can get an R box and swap the transmission plate over onto your SP. They are all the same apart from the HRC ones.
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