Hi Guys,

My friend as a bit of a moment at the track this week. His MC21 decided to lock up on him going into the fastest corner of the track and he managed to stay on it much to everyones amazement.

We got the engine apart today and it has nipped up the front cylinder but the back cylinder is fine.....any sugesstions of what may have cause this or anything that they are known for??

Any help would be great! The bike was on injection but will be converted to the far better pre-mix now this has happen.

o o


Last edited by DifferentStrokes on Mon Sep 28, 2009 8:31 pm; edited 1 time in total

Cheers Man,

I guess 2 strokes have a few weak points.........but man are they fun to ride!!!

Hopefully we won't have this happen again!

Apart from running pre-mix and the injection system is there any way you can prevent-/-reduce this???

i add a cap full of oil to my tank

It probably didn't sieze due to a lack of oil, on the way into a high speed corner on a near closed throttle is classic detonation seizure territory, over oiling will just make the petrol/air mixture even weaker and further increase the problem.
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cheers fonty, guess i wont be doing that no more

As Fontyyy notes, (in my humble opinion) it's more likely to be a fuelling than an oiling issue I'd think. The condition of the piston would probably reveal all you need to know though. Was there any detonation damage on the piston crown and/or any alloy flecks on the plug? If so, he will clearly need to go a bit richer on the main on that side when he rebuilds it - and maybe check head volumes and ignition timing are safe if it's a tuned motor. Only if the plug is a good colour and there's no sign of the piston being nibbled by detonation would I (personally) be thinking about oiling probs. Obviously it's a good idea to run good oil -especially on the track, but in my experience oil starvation will often take out a bearing before the piston will seize in plated bores. I've never experienced that kind of seizure (oil starvation) on a motor that has plated cyls in fact. And I've known quite a few seizures over the years

Even when the oil tank of my TZR 3XV (pretty similar motor to an NSR) ran completely dry (dont ask ) and took out a big end, the pistons showed no sign of nipping up at all, surprisingly.

Good luck with it in any case.

Wb

Cheers WB,

There was some signs of detonation on the spark plug side of the piston!

My friend has recently done the wire splices on his bike but no changes were made to the jetting.

So do you think going up to bigger jet would be a the way to go just to be safe??

Yes. But it will need to be done properly, with a series of plug chops to establish a safe setting. He'll be needing a selection of jets to play with to get it running as well as possible and remaining safe.

would a higher octane fuel have any influence on detonation induced seizures?

In theory higher octane fuel should make the motor less prone to detonation, but my understanding is that would only really be if the det was due to too small a head volume? (I'm certainly nmo expert on this stuff though). Even if runing higher octane reduced the det', if it's weaker than it should be I'd imagine you'd still be down on power over a more appropriate set up. My (limited) understanding is that race type high octane fuel is only really suitable when you are running pretty borderline race type head vols and tuning. Personally I'd be flinging some bigger jets in the detonted motor and keeoping it on the cheap (well not anyumore, but you know what I mean...) stuff.

Cheers

Wb