Yamaha RD250LC Restoration Part Four
Series originally printed in Mechanics in 1995/96

Reeling at the cost of Yamaha parts compared with their often discounted Honda equivalents, I was relieved to speak to Jim Patch. Jim placed an advert in the VJMC magazine offering new Yamaha spares at discount prices. He was able to supply a complete, new, 250LC exhaust system for less than half the Mitsui price. I spent ages on the phone to the interesting and enthusiastic Jim, who has also promised to lend me some original decals so that I can match the colours. Jim used to be proprietor of Yeovil Motorcycles and once employed John Nash, winner of best in Show with his RD350A at Mechanics' October event at Stafford.

My overcrowded workshop was beginning to fill up with new and fettled bits of Yamaha that looked like they needed a home. In order to create some space, I made a start on the engine rebuild. A full set of seals cost a whopping £45 from Barrie Rodgers and gudgeon-pin circlips weighed in at 60p each. Mrs. Curtis had taken the children away for a half-term break, so I was able to pop the crankcases into the bath for rinsing out all those little glass beads. Thankfully, there are few oilways in the cases to harbour beads and blasting residue. Although the cases were originally bare, I gave them a coat of Simoniz 'Wheel Silver' to seal the surface against further grime and corrosion. All the threads were cleaned out using greased 6 and 8mm taps.

The joint surfaces looked perfect, but I like to give them a rub over with a long straight piece of hardwood covered in 1200 grit wet-or-dry paper, used wet. This will show up any burrs around bolt holes and bearing housings. A large surface plate or plate glass covered in abrasive paper would be better, but Elsie's crankcases are a little large for this.

With little regard to 'originality' I had all the rusty crankcase and cylinder studs zinc plated, and these were all inserted into oiled holes. The Japanese usually put their studs in dry, with a dab of loctite to secure them. I don't really care about them coming loose as it's much easier to fix than when they are corroded in place!

The crank, complete with new seals, plonked neatly into place, followed by the gear selectors and shafts which I had kept together. Compared with my CB400F there didn't seem to be much in there, but after checking everything, I smeared some gasket goo on the faces and lowered the top half on. The crankcase studs were treated to new stainless nuts and washers and torqued down.

The clutch and primary drive went back on without trauma, but when I picked up one of the caged-roller small end bearings, it fell apart in my hand. The other one seemed OK, as did the pistons, rods and gudgeon pins. I naively thought that this was simply a matter or ordering another bearing. The first one I ordered wouldn't fit, so, thinking that M&P had sent the wrong one, I pointed out the fact & ordered another. That wouldn't fit either!

It was time for a little detective work. The Mitsui literature details the small end needle-roller bearing dimensions as 16x21x19.5 (i.d x o.d x length ) with the RD350 version a little wider at 22.5 mm. My rods needed a 16 x 20 x 20 needle roller bearing, or I needed a new set of con-rods! Leafing through the bearing catalogues, I discovered that SKF list needle bearings especially for small ends. KBK 16x20x20 was the one I was looking for.

My local bearing stockist had none on the shelf, so I popped down the road to Mick Bull's where we found the appropriate replacement. My 250LC crank has, it seems, been rebuilt with RD250DX conrods. A pair of small ends set me back £8.50, but at least I could assemble the rest of the engine. I still have to repair or replace the several plastic engine covers. These have had their fair share of gravel rash, so some sort of drastic action is required.

While I was pondering my small end problem (size isn't everything!), I unpacked a set of shiny new taper roller bearings (ú22 from M&P) and fitted them to Elsie's steering head. Taper rollers are just so much nicer than cup and cone bearings which should have become obsolete when belt drives went out at the beginning of the century!

To add a bit of variety to the project, I have acquired a 350LC engine which has been lightly 'breathed on' (sufficient to wreck one big-end anyway!). The 250 engine will go into the frame to begin with, then the 350 engine, suitably fettled, will be dropped in to form a comparison. With another 12 bhp on tap, I'd better start looking out for a second front disk.

Now that the worst of the weather has passed, I am hoping to make a start on the paintwork and other cosmetic fettling. I have decided that this 250LC will be re-finished in original white and blue livery. As well as the paintwork, there are a lot of plastic parts that have to be cleaned up. The wheels still need sorting out, and I'm undecided about the front fork tubes. Hopefully the frame and wheels will be reunited by next time.

Graham Curtis 27 January 2001

Thanks to the following suppliers who helped with the project

Mick Bull Motorcycles
Unit 2,
36 Canal Street
Derby DE1 2RJ
Tel 01332 367470

Rafferty Newman
242, West St
Hampshire, PO16 0HD
Tel: Fareham (0329) 232424

Barrie Rodgers Motorcycles
163 London Road
Derby
Tel: (01332) 347977

Jim Patch
0935 881817

Derby Plating Services Ltd
148 Abbey Street
Derby
DE22 3SS
Tel 01332 382408

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