Hello everyone,

It's been 22 years since I owned a 2 stroke, my first ever bike was an NS125F in classic RW&B. I've now gone full circle and
just obtained an MC21SE. It's a wee bit scruffy but they seem to come up so rarely (especially here in Oz) that I grabbed it
regardless. It's definitely been a track bike: drilled caliper bolts, millage too low, not been road registered for years, no service history etc,
So with that in mind and not knowing that much about strokers I have a question.

It starts easy and seems to run ok, but assuming the worst (it's been thrashed and not been serviced) what are the main things I should check/replace (in order of priority) to get it running sweetly/reliably? (it will only be used on the track)
e.g. new rings/pistons/bearings


Extra bonus question:
How can one tell if the cylinder linings are ok, or if they need re-plated? What are the tell tale signs of problems in this area.
And, is there anyone in Sydney that does this?


Thanks in advance.

Al.

Cylinder liners - check to see if there is any damage to the electroplating/Nikasil. If there is, then you'll need them replated. You'll save money if you send them to the USA to get done. Only two places in Australia that I know of, one is up North Queensland and nobody recommends them as they have a terrible reputation, and Electosil. Electrosil is expensive. Once you've paid postage to and from the US, you'll still be at least $150 better off (estimated) than with getting it done locally. You can save $40 removing the powervalve and studs yourself.

Aluminium deposits can be carefully removed by muritic acid (it dissolves the aluminium). Muritic acid is hydrochloric acid that has been diluted.

Look for a lip, if there is a lip then it will probably need to be replated too. You can test to see if it's within its service limits with an internal micrometer. Check the piston is within the tolerances with a micrometer too. Not sure off hand what the tolerances are.

Look for cracks around the exhaust bridge, they will NEED to be repaired.

Replace the rings, if you've got the engine down already, rings are cheap to replace so you may as well do it along with the circlips and small end bearing.

As for the service, I always change all the fluids as soon as I get a vehicle if it's used. Basically you need to go over the entire bike, checking everything. I don't think I'd be able to list everything comprehensively. If you have TYGA pipes, getting a good seal on them when putting it back together is important, you should do a search for my thread on sealing leaking tyga pipes. Do NOT use the orange crap, use the higher temperature RTV stuff, it's usually grey. I've never had an exhaust not blow with the orange goo. (Please, no flaming me on this, I know some people love that gunk, but keep it to yourselves so we don't get off topic.)

Make sure the powervalves are adjusted according to the HRC method while the pipes are off, it's much better than doing it the quick and easy way. Give your carburettor a good cleaning out and if you're tempted to jet it, understand what you're doing first by reading up a lot, and always start rich. Make sure you're running a good well oiled filter. I like No-Toil as it's nice and light but sticks well.

If you've stumbled across my seized thread, you'll have realised that it's a bad idea to have the oil lines fall off. Don't let this happen to you, I suggest getting some better spring type hose clamps (the ones you can EASILY put on and off with pliers and are thicker than the crap wire ones that come on the bike). While you're doing that, make sure that the seal that seals the pump drive hasn't fallen down or gone hard, if it has you'll have two-stroke oil in the gearbox and experience the effects of it overfilling!

If it's raced, it will have been de-restricted, so don't need to worry about that, but do check the powervalves aren't gummed up and they can be moved EASILY by hand or they'll burn out the PGM.

Do a quick check of your crank seals, filling the top cylinder with petrol to see if it flows out the bottom one is a quick and nasty way to see if it is not sealing between the cylinders. Of course, check for play in your crank while you are at it too!

Remove all carbon deposits from the head, exhaust and powervalves and give it a good polish for better efficiency.

I've covered as much as I can think of, I'll leave it to someone else to fill you in with anything I've forgot.

anonymous.shyster wrote:
Do a quick check of your crank seals, filling the top cylinder with petrol to see if it flows out the bottom one is a quick and nasty way to see if it is not sealing between the cylinders. Of course, check for play in your crank while you are at it too!

After you've done this remember to stick some oil down through the crank...you've just washed away all the lubrication for the crank!

If you're going to do that (very crude) test, you should do it with 2-stroke mix anyway, negating the need to "oil" the crank! Doing so could foul the plugs on startup.

The centre seal really needs (running) pressure to seal properly, so filling one side with fuel will only really tell you if it's really knackered.
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Andy.
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Sounds like a lot of work to me, if it's new to you doing the top end (pistons and rings) won't hurt. Obviously you can check out the condition of the cylinders while they're off, clean the RC valves and set them up etc.

As for the bottom end? If the bike starts and runs well, leave it - it's fine
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How many buggered cranks have you got now Fontyyy?!
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Andy.
NSR-WORLD.COM

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Right now?

In my care?

Erm....four I think.....(how scary does that sound to someone who has one crank in one bike and is praying it's OK?)

But TBF that's a harsh question;

1 a gift from Hermit's dad (in the loft)
2 from a NF5 bottom end, swap with Dan long ago for a full flower VJ23 CDI (3' from my right foot as I type)
3 the wet bike (motor is in the back of the van, needs stripping), dates from christ nows when, the bike was under £2k a couple of race seasons ago so it's hard to moan.
4 the dry bike (Dave R has the crank), well - that bottom end is from the top end that had a squish of over 2mm when I got it and was in an engine that when it was last dyno'd made peak power over 12000rpm on stock Honda pistons....I fear no further comment is needed.

and a couple of other "should be good" ones lying around

Tch...cranks...let's be fair here who rebuilds them if they've not failed?
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I'd definitely do a service, as 'anonymous.shyster' suggested - To see a run down on what needs to be replaced or/and repaired. It's really pointless in saying you should do this just in case, etc... if maybe all it needs is something so small (which we all hope). But of course checks on the bike is a must! Then again maybe all it needs is a service??

What mods are on the bike? Maybe even some photos?

And Welcome to the Forum!

Check also all bearings in steering, wheels, swingarm, ... i cheked them in my 21 and i have replaced them all.

Many thanks for the replies, invaluable info.

Attached a couple of pictures, you can see the bodywork is falling off in places and the front mudguard is missing.

I don't know of any mods, but that may become more apparent as I strip it down.

I'll definitely do a top end rebuild. I know Tyga do the kits, is that the best place to source them? I also notice they list cylinder A B and C and they are different prices. Which ones do I need?

I'll inspect the cylinders and maybe post photos to see what you all think?

Depending on how adventurous I feel once I get that far will determine if I touch the crank or not, but I'll check the wheel bearings when I get new tyres fitted.

Oh, and the power valves.

Hopefully that will see it fit for some track action.
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Cheers....

Al

Bikes:
GPZ900
NC30
NSR250SE
RGV250 vj22

Yes, the best place to source the Tyga parts is from Tyga. They are very good to deal with. I don't know anything about which piston to use, as I've always ran a 300 Tyga kit. Something to do with the stamping. If you do a search on this site, you'll find something on that easily enough, if not, ask Matt or Paul from Tyga. Remember to mention you're a NSR-World supporter for a wee discount

On the rear of the barrel on the lower edge there will be an A, B, or C stamped into the barrel. Check in the parts manual for whitch piston matches which barrel, I think it's the same for all models, but A barrel use B piston, B barrel use no mark piston and C barrel use D mark piston.