Front Forks - Refurb. + new seals.

The side with the deep recess and visible spring faces down, the shallow recessed side faces up. The manual says to use a seal-driver tool, but I just put both the old seals on over the top and knocked them down with a wooden drift / hammer.

Oil level should be 130mm from top (5,1 inches).

I have yet to get the top caps on!

HRC stickers for the white wheels.

Power Valve Recon + Port Grinding!

Power valve was coated in nearly 2mm of carbon and jammed solid.

The wire-wheel cleaned it up pretty good.

Got a new dust-seal from BDK Engineering as it is almost impossible to remove the old one without wrecking it. Dust seal link - http://bdkraceeng.co.uk/tc/products.php?144  

I also began grinding the exhaust port in the barrel to remove the ridges left either side from the casting and knife-edge the centre-divider. I will also have a crack at the inlet port in the crankcase before it goes back together.

Inspiration - '86 Rothmans paint/decals scheme.

I made a Tamiya model of this bike last year for a laugh [this post], now it's time to get serious and build a real size running replica! 

Colour wiring diagram!

Forget struggling with the black/white hard-to-trace diagram in the back pages of the manual - this colour-coded one is much easier. Major big ups to ripzay who made this for nsr125.co.uk.

White wheels, Michelins, front disc, sprocket and bearings!

£150 the lot - from a 52-reg JC22 - both wheels, powder coated white and balanced (saving about £120), new Michelin Pilot Street semi-track tyres (saving £125), new wheel-bearings (saving ~£20), better rear sprocket with red-adonised nuts and a better front disc (saving ~£30). Not a bad haul, plus I still have my old wheels/tyres/disc to sell.

Parts wish list!

Engine:

• High-comp piston kit. (Mitaka, Vertex).
• Carbon race-reeds. (Boyeson, Clapets, Hy-Tech).
• Dell'Orto carb. up-jet kit. (Dell'Orto, maybe Sigma).
• Race exhaust / expansion tank. (Arrow, JollyMoto, custom).
• 180cc barrel / piston / head kit. ().

Bodywork:

• Complete NSR SP250 fairing-kit in Rothmans colours / decals. (It will fit).
• Lightweight single race mirror.
• Clear bubble.

New head-Stock Bearings - All Balls Racing needle-rollers.

New piston + gaskets!

With the engine stripped, I measured the piston diameter with a set of digital-calipers, as with 25k miles on the bike I figured it may have been bored out some and require a larger diameter piston, but this was not the case and it's running the normal 54mm one.

I ordered a Mitaka Racing piston kit, which includes a new top-end bearing for £35.50 delivered. No engine rebuild would be complete without gaskets so I got a Lextek set from Chinese Motorcycle Parts Online on eBay for £19.95 delivered.

Engine Strip Down and Post Mortem

Faults:

• Lack of compression.
• Power-valve limited operation.

I stripped the top-end of the engine down with it all still fixed in the bike frame, which made it a quick and easy job. I found the restrictor-plate has already been drilled out of the exhaust and the carburettor too, so that's saved me a bit of work!

The piston and rings looked ok, with a little scoring to the front and rear faces, which matches the score marks to the cylinder-wall, shown in the pic below. I can just about feel the score marks on the piston itself so for what the cost I will be replacing it, but they cannot be felt at all in the much harder cylinder-wall. The scoring, along with a distinct lack of soot leads me to believe the engine has been run with too little 2-stroke oil in, probably through error, but possibly due to the oil-pump not being able to delver enough to the de-restricted engine, particularly if the carb. has been up-jetted. I will check to see if this is the case before ordering a set from Dell'Orto.

Fault Finding 1 - Electrics

Left headlamp / main beam bulb. >>> Loose bulb terminals.

Right-hand indicator switch.    >>>    Faulty switch, works when wobbled.

Dimmer switch. >>> Does not seem to be working at all.

Main elec. power >>> 20A Main Fuse, full power when hard-wired. >>> Try different fuse holder?

Starter-Relay >>> Relay works when Green/White earthed to bypass Neutral-switch.

Starter-Wiring >>> Full power shown across starter-motor live and ground.

Neutral-Switch >>> Works fine when connected. Was perma-earthed to bypass neutral and kickstand switches, I guess to allow bump-starts.

Starter-motor >>> Does not work when removed and hard-wired to battery. Dis-assembled it shows no sign of the armature inside the motor. >>> I'm guessing the previous owner removed these parts to make the bike bump-start easier or stop it making a noise. >>> Definately need a new starter motor, not cheap at £125.

Bought the bike!

With only around 500 left on the road, NSR 125 are becoming as rare as their bigger brothers. There are never many up for sale and bikes needing a little bit of work and with no MOT are fetching £750. I didn't want to spend over £500, so went for a 'Spares or Repair' example that I picked up for quite a bit less than that!

It's a JC22 2001 (51) with the 'Foxeye' lights. There is quite a bit missing, but I am hoping it just squeezes into the 'Repair' category and I don't end up breaking it for spares as so many others are being. At least parts shouldn't be too hard to source...

The fairings are not too badly damaged and easily rescuable, but it's missing both front mirrors, indicators and, of course, the side panels. The latter two I missed the most, so to sweeten the deal the guy threw in a left-side panel from an older JC22 that has the Mick Doohan style NSR graphic. Awesome.