Hi all,
It's great to find this forum! Ive spent the last few hours enjoying reading my way through the posts.

I have a NSR250R MC18 '88 (PGM 1), which Ive had since I was 18 and Im looking to restore/ get running again.
Excluding the motor, the bike is fairly sound with needing only cosmetic touchups. Its never been dropped. My questions relate more to the engine and the PGM unit.

I seized the original motor over 25 years ago and swapped it straight out for a Dry Clutch SP engine which I bolted straight in. The engine never performed all that well, and the mechanics I had look at it had issues getting the RC valves working correctly/at all. I NOW realise that the PGM 1 unit may not correctly drive the RC valves of the newer motor.

Fast forward ahead a few years in my youth, and I've seized the top end of the the SP engine. I have then purchased another 2nd hand low km motor which is the correct motor for the bike. And that is where I am at.

I have two chains of thought here. Feel free to offer advice or flame me, all will be taken in good humour

1. Option 1, Top end and bottom end rebuild the SP motor, maybe utilising a Big Bore kit from Tyga, and have alot of fun. The only caveat is I need to get the RC valves working correctly, with the PGM I. Is this possible? Do I need to purchase a PGM II? How good are the Tyga big bore kits? Are the motors still relatively reliable given the substantial hp increase>?

2. Rebuild the stock motor and install and bring the bike back to as close as original as possible? This is my end goal, as the bike is starting to be a bit of classic.

3. Option 3. Rebuild both, have the SP for fun and the stock motor for classic restoration of the bike when I'm to old to ride.

Sorry, if I seem to be waffling, just trying to get a grip on what to do here. As I said any feedback appreciated.

Regards,

Kris

Hello Kris, and welcome to NSR-WORLD!

Just about everything is interchangeable across the range, with enough knowledge... However, as you have found out with the RC Valves, for example, a little knowledge can be dangerous! 🤣🤣🤣 The different top-ends do indeed have different ranges of motion on the RC Valves.

Out of curiosity, is the SP motor you have 1990-1996? Are the barrels round?

If it were me, providing the original bottom-end is in good condition, I would probably look at rebuilding the 1988 top-end, and swapping the dry clutch transmission into the 1988 cases. However, the benefit of the SP motor [if it's MC21/28] is that you can still get brand new cranks for them, which you cannot do for the 1988 R2/4J models. (T2Racing do a reproduction centre seal, and the cranks can usually be rebuilt though.)

Regarding your proposed scenarios:

1. The TYGA 300 kit is very good these days... it's had 20 years of development! However, it's not "a substantial increase in power", as you put it. What you will get though, is a very noticeable increase in bottom-end and mid-range drive, which carries through to the top-end in quite a linear fashion. You can of course pay extra and have Matt put a tune on it, but really you want tailor made expansion chamber, slightly bigger carbs, and maybe even a different ignition to really make the most of it. It can get extremely expensive.
   
   
2. Stock bikes (or at least stock appearance, with easily reversible modifications) are worth considerably more than modified bikes, and are increasing in value year-on-year. You can't expect someone to pay for your 300 kit and all the associated mods should you decide to sell it... well, not in my personal experience, anyway, so you're always going to lose money if you go that route. If it's [close to] standard though, it's much more likely to fetch a premium. Of course, you may be lucky and be that one in a thousand who gets luck and is paid back for all the customisation, but it's extremely rare. Modifications are very subjective and personal. I know if I ever sold my MC21, all the HRC parts would come off it and be sold separately, because they add little value to the bike as a whole, but would sell for ££££s separately! (The forks alone sell for £2k these days!😳)

Anyway, that's what I think... I'm sure other's will have a difference of opinion and be along soon.

Please feel free to start a thread on your (re)build sometime, so we can follow along.
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Andy.
NSR-WORLD.COM

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Hello kristiani, Welcome to the forum. I suppose the question I would ask is, are you going to drive the bike on the road or are you going to track it (or both)? If its going to be a purely road bike then I would probably keep it standard enough MC18 spec. Will the few extra horsepower really mean that much to you on the road by putting so much money into it? maybe it will. However, maybe some tyga pipes and an airbox mod would be a nice subtle upgrade and easily reversible to 100% standard.

Although the only issue I would have with the standard approach would be the MC18 crank, as Andy said. It is tough to get them and sometimes they cannot be rebuilt.

The SP engine would be nice in it as cranks are readily available, but expensive. But its just not the same imo as having the original engine for the bike, and Andy has a great idea in swapping the dry clutch over.