Hi,

I've got an NSR250 MC28SE but I'm new to this model and was hoping someone could advise on a final drive problem I have. On a constant throttle between 5k-6k rpm the drive becomes really snatchy, it also does it when you roll off the throttle in the same rpm range. The chain tension seems fine. Any ideas?

Thanks, Ian

Check your chain for stiff links .

The MC28 has no cush drive (they needed all the power they could muster) so on/off throttle snatch will be more than the other NSR's.
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If I have to take the carbs off once more...

The rubber swingarm's its cushdrive, isn't it?
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Andy.
NSR-WORLD.COM

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Now now boys......let's answer the guy's question.

There should be no snatchiness (is that a word?), even on the direct drive MC28.

I'm presuming that your chain is reasonable condition.

Check the torque arm between the singarm axle/engine for wear. If those bushes are worn then this causes the snatching, and also usually makes for clunky gearchanges.

Also true if the engine mount bushes are worn.

Also look at the front sprocket. Is the countershaft worn? I've seen some where the sprocket/mainshaft combo was so buggered you could practically remove the sprocket without undoing anything. To be honest Honda took a bit of a wrong turn on this one I think. Why not bolt the sprocket on like the RS?

Thanks for the suggestions. The chain is nearly new and it did it before I replaced it too. I'll take a look at the other parts for signs of wear. The bike only has 16,000km and doesn't seem to have been taken apart before. Is this the kind of mileage that the parts would wear to the point that causes the snatchiness?

Ian_B wrote:The bike only has 16,000km and doesn't seem to have been taken apart before. Is this the kind of mileage that the parts would wear to the point that causes the snatchiness?

Depends who owned it.

If it was mine then I'd be surprised it lasted that long

Check the torque arm Ian. This little thing will make the bike's drive train seem rough as hell if not connected or damaged. Trust me, I had the bolt missing from mine for a few months and it was terrible - I even had the chain come off once.

Ian_B wrote:On a constant throttle between 5k-6k rpm the drive becomes really snatchy, it also does it when you roll off the throttle in the same rpm range.

To be honest, that's a crap part of the rev range to be using, as it's about where the powervalves are opening. A constant throttle at this point can have the valves chuntering back and forth, so power climbs and falls accordingly.

Use another gear and different part of the rev range...
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Ok, so forgive the newbie question, but can someone give me a reference from the workshop manual for the torque arm and bushings that are the usual suspects for the snatchy gear change and drive?

Thanks again,

Ian

This part:



Workshop Manual reference 13-14.
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Andy.
NSR-WORLD.COM

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Thanks Andy, much appreciated.

I am a good friend of Ian (we actually originally bought the bike between the two of us) and am now looking at this issue again now I have sole custody of the wondrous machine.

As a bit more background and some more symptoms:

The snatching is most obvious to me now when off the throttle when slowing for a junction or the like and all but goes away when you pull the clutch in.

Chain tension has a big impact on the extent of the problem, the tighter the chain (keeping within the limits of course) the less noticeable the snatching and incidentally gives much cleaner gear changes as well.

If while coasting down you can keep some tension on the drive-line with a little bit of throttle the issue is less noticeable.

So far we have had a good look at the linkage previously mentioned (though not disassembled yet) and have removed all the rear suspension linkages and bushings for a clean and re-grease but to no avail. I'm about to free up some workshop space to have a good solid go at sorting this out as it is spoiling what is otherwise a very comfortable and smooth bike to ride.

Given the issue seems to be related to the amount and direction of tension in the drive-line I'm thinking a gearbox issue of some sort. It seems odd that it is fine under normal drive tension (i.e the force through the gearbox to the chain and wheel) but snatches with the tension in the opposite direction (i.e the rear wheel 'driving' the gearbox).

Thoughts and further advice much appreciated.
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Cheers.

Mark Bree

Hosewa wrote:So far we have had a good look at the linkage previously mentioned (though not disassembled yet)

Well, take it apart and I reckon you'll find the problem. Just about every clunky NSR I've dealt with has been because of this torque arm or worn out engine mount rubbers.

I had an engine pack up.....I looked at it for days.....even gave it a threatening stare, but in the end still had to disassemble it to fix the problem.

So, have the swingarm out. Suspension off to get re-built this week so that will be back ready to re-fit in about 3 weeks.

Had a look at the aforementioned torque arm and bushings. Doesn't look too bad apart from being really dry, the larger of the two has a tiny amount of play but does not appear to have any damage.

Is there a wear limit on these things or would I be better off just throwing some new bushings in (items 8 and 9 on the drawing) and making sure they are well lubed up just to be sure to be sure? Seeing as it's such a pain to pull it all apart I kind of would like to avoid having to do it too often and I also need to get one of the other bikes up on the bench to work on it as well.

Cheers.
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Cheers.

Mark Bree