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Rebuilding NSR engine

Guest tohtoh

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My bikes coming up for about 16k miles now, I know its supposed to be about every 20k that you rebuild them, but I do cain it about, so its probably best to do it a bit sooner.

I understand the engine has to be stripped down and rebuilt, but do I need to replace piston and head and such things, or will just cleaning them up and reusing them all be okay? I'm slightly worried about stripping it down because I know the piston barrel is Chromium plated or something and i dont want to cock it up.

Any little tips on what to do and what not to do would be awesome!

cheers guys!

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if you strip it down you will be well advised to fit complete new piston kit,..piston piston ring s small end bearing gegeoun.(spelt wrong i know) pin and circlips new cylinder base gasket,head gasket and any others that you have to take off.get full top end gasket set

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Plated bores last much longer than old fashioned non-plated ones.

Why do you think it needs a rebuild? Loss of performance? Piston slap? Does the owners handbook state that you must replace the piston or rings every so many thousand miles?

If not, leave it alone. Just service the bike as per the handbook - oil, air filter, spark plug etc.

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Suggested *preventitive mainintance* on the NSR if you ride hard is rings every 7k and piston kit evey 14'ish...

Sounds a lot but keeps the bikes reliable if your thrashing it...

Mine has just broken 10k, got it at 7k (with new rings allegedly) but I plan to rebuild the engine in jan (pistion kit (piston and rings, gudgen, small bearing, gaskets etc etc).

With it being a 2 stroke dont worry to much about breaking it... Mighty simple engines to be fair, just pick up a manual (online :wink: ) and work through it.

Much cheaper than waiting for it to go and having the rings weld themselves to your nice bore :P

Ps, with all that being said, generally speaking the compression falls <125 psi before the engine fails so i would give it a compression check and see how its doing. Chances are you dont thrash the nuts off it and it may be just fine ;)

Best regards


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Just service the bike as per the handbook - oil, air filter, spark plug etc.

Nsr's are two stroke, top end rebuilds are part of the service schedule.


I have owned many a 2 stroke and the service schedule did not call for a top end rebuiild, hence my question.

If it's part of the schedule then the manual will list what's needed eh? ie rings or rings and piston.

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Clearly very strange ones if the manual didnt indicate when to do a top end rebuild.

Standard 2-stroke engines should have the piston and rings replaced every 10-15k miles depending on the bike and setup. Most manuals should say this for the bikes. My RS certainly did.

My top tips is, do it in a clean space. Have a desk and towel laid out. Keep an eye on where you put the parts and make sure you rub a layer of oil around the cylinder if you leave it off for a couple of hours. Otherwise you should be alright. Its pretty self-explanatory.

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RD LCs, TDR 250s, 350 YPVSs. Yes all very strange and uncommon. No mention of a top end rebuild in the manuals.

Even stranger would be a manual stating "top end rebuild" but not stating what is required.


Quite right, which is why I said they state when to the replace piston and rings. Not "top end rebuild" :wink:

All 4 of my previous 2-strokes had in the servicing section when to change the piston and rings. Same way most now have times when to change the oil. My RS had a section purely on what to replace and when, the piston and rings were included in this.

Your 2-stroke history is of older bikes and larger capacity ones which are now rare so I havent come across them. The larger ones wont have this info anyway as they require rebuilding far more infrequently than the 125's do.

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