Forking hell

Getting the forks off the bottom yoke was the first challenge. It seemed like someone has decided to weld a lamp bracket to the top of forks….weird. Out with the grinder, but the amount of weld meant some damage to the chrome and the tube was inevitable.


Getting the bottom yoke wasn’t straight-forward and had to use the pretend-dremmel to clean off the remaining parts of weld to get the yokes off. Apart from the weld damage, the rest of the fork chrome was in pretty good shape, but decided to strip the ‘spares’ bike and look at the forks.

Getting the fork seals out of the fork bottoms needed some care as the aluminium that houses them is pretty thin and cracks easily when using the extractor (look for the Beta tool, which is excellent)

Removing the fork seals

Managed to find the fork seals from Pyramid Parts, again via ebay .

Fork internals

Though they were pretty well non-usable and badly pitted decided to get them rechromed. Sent them off to the A M Philpot Hardchrome who do a really good service which includes delivery and collection. Took about two weeks for them to return and then ready for the fork rebuild.

Ready for assembly

Laid out the fork components from both sets of fork legs and then put together a matching set (ie kept the internals together from each fork). Reassembly fairly straightforward and the new oil seals when in ok (didn’t change the dust seals).


Filled the forks with 175mm of 10/30w oil in each leg (as per the Clymer manual) and will do some further tuning once the forks are back in the yokes and the bike put back together.

Engine Strip


Though the engine in the original bike (engine #1) seemed to run ok, decided to strip it, check the pistons and change the main bearings and crankcase seals. Also, have a quick look at the head, barrel and piston on engine #2 (on the spares bike).

A complete strip it is then, and the engine is something different from the Rotax disc valve engines on the SWMs.

Head, Barrel and Piston

On engine #1 the head was easily removed and the piston and barrel looked in good condition with no scoring. The piston is 0.25mm / 1st oversize and very usable.

Piston in engine #1

Removing the barrel on engine #2 wasn’t quite so easy and a hour or more of heaving finally got the seized barrel away, but only after breaking the bottom fin (grrrr). This piston was also 0.25mm / 1st oversize.
Piston in engine #2

Based on the condition of the second piston, decided that new piston kit and rebore wasn’t a bad option.


The flywheel / rotor bolt is a normal RH thread and holding the conrod with a bar made undoing straightforward.

The flywheel on the MX250 strikes you as being rather small, and it has the CDI sensor on the outside. The main issue for me was getting the right puller, which is an M20 x 1.5mm RH external thread and is hollow to fit over the crankshaft end. Its an MP7 puller by code, but wasn’t one I had in my expanding collection of pullers (sigh).

Gavin turned a brass version of a puller on his lathe, whilst the one I ordered from the US (not available in the UK it seems) was winging its way across the Atlantic. But alas on a bit tight and the puller threads broke before releasing the flywheel.

When the right part appeared from the US, then it took < 5 minutes to remove the flywheel. Right tool and its easy.


Removing the clutch cover wasn’t straightforward and it needed some attention from the rubber mallet.

Clutch revealed

The clutch is pretty standard and relatively straightforward to remove, though some form of tool to hold it in place is very useful.

Holding the clutch in place

I used a flywheel holding tool (acquired for less than a fiver from ebay) and it worked. Took back the lock washer and removing the nut (again normal RH thread) was relatively straightforward.

Clutch removed

Need to check the plate thickness and to see how serviceable it is.


From the Clymer manual it says you reach the kickstart spring and then remove the whole assembly, though I wasn’t sure if I could leave the whole assembly in place as I split the cases. In the end went for a compromise; half took the assembly apart, removed the circlip etc, but stopped when taking off the plate holding it against the spring.

Kickstart assembly

More later.

Primary Drive

Held the conrod in place , whilst putting a 22mm socket on the primary drive nut. Its been punched to hold it in place, though came off relatively easily. My concern is over nut itself and may need replacing with a new one.

Primary Drive

Remove the sprocket, remembering also to retrieve the o-ring thats positioned on the shaft behind the sprocket, as its omission will lead to a loss of performance and lots of smoke.

Gear Selector

The Clymer manual is a bit confusing, as there are three main types of selector layouts. The instructions are also a bit brief and its worth taking a couple of photos before disassembly.

Gear selector shaft

Looking at the RH / Clutch side, removed the clip from the end of the shaft on which the gear lever is attached (on the other LH side) and then pulled the shaft through on the LH side.

Gear selector

Noting the way the selector mechanism is meshed together, then removed the clip from the front-most shaft and then removed both sides of the mechanism, including the blade from the selector drum which lies beneath. Maybe simpler than it looks (will let you know when I try to put it back together)

Splitting the Crankcases

Splitting the cases

The Clymer manual cites the official Yamaha crankcase splitting tool, but you can rig something up with a normal puller and a couple of long M8 bolts. The bolts go into the threads vacated by the clips used to hold the crankcase seal in place.

Position the engine on its LH side, with the puller attached to the RH crankcase, with the puller tip on the split end of the crankshaft from where you’ve recently removed the primary drive.

You probably need to double check that you’ve removed all the crankcase bolts, there should be 12 in total. I’d missed one of the four which sit inside the rotor housing, as it was covered in crap. Gently applying pressure to the puller, it was quickly clear that the bottom of the cases weren’t separating so I backed it off and then noticed the bolt.

We have separation !

Once the ‘hidden’ bolt was removed, the cases came apart really easily and slowly turning the puller meant the cases came apart in parallel. The only thing to remember was to tap the gear shafts so as they stayed in the LH (lower) crankcase.

LH Crancase with gearbox

You should be able to split the cases in such a way as to leave the transmission, gearbox and crankshaft all still in the left-hand case. This makes things a lot easier, especially for re-assembly.

Kickstart spring

I’d decided that I didn’t need to remove the kickstart shaft prior to splitting the crankcases, but the spring for the kickstart (and its cylindrical housing) are infact held in by the LH crankcase. It all got a bit twisted up as the case halves came apart, so then took off the plates holding in the kickstart and removed the shaft, which freed up the spring. You can’t seem to take the tension off the spring before removing the shaft, which isn’t what the manual says.

Unidentified Beta motocross bike

There are a number things wrong with the bke, but a number of things that are also right, including the fact that it runs, and runs really well.

Need to do some research, but its an early Beta twinshock and not pre-74 (too much suspension). Someone has done a Husqvarna yellow and blue paintjob on it (crazy Swedes ?)


The forks are in the wrong way round (left in RHS, right in LHS) and swingarm bushes and head bearings are worn. The electrics and lighting kit seem to be an interesting, enduro like mod, but it seems like a motocross bike. The shocks aren’t perfect but it runs. And run well it does. It has a mans four finger clutch which will need some personal training to manage. All the gears and the bike wheelies for Italy when getting stuck into the powerband. Theres no doubt its a bit of beast.

That is got a Bing carb, rather than a Del’Orto seems to suggest early rather than later and seeing Kevin’s motocross weapon, this has a different engine shape. More research on this, though google doesn’t provide any obvious matches.

Classic Off Road Show, Telford 13-14 Feb 2010

I’d missed last years show and its a better location than the agricultural sheds of Malvern. The auto-jumble outside in the carpark seemed a lot smaller than at Malvern, though there were a few people inside the halls, with the retail traders.

The auto-jumble stand

After a delayed departure from Herefordshire, still made good time to get to Telford and got into the autojumble area by 07h45 and found a good position to lay out the jumble.

I then took the Beta TR240 into the show hall to form part of the Italian section, which to be honest was pretty badly presented with David Brick’s Beta as well as a Supertrial and TR34. Ah well, I think Wrighty had hoped for more, but what was there was the very nice Beta 125 Trail bike that had been one of Classic Bike’s restorations of the year [[It didn’t win the overall event though ]]

Lots of people looking around the jumble from 08h00, even though the show didn’t start till 09h00. By 09h00 lots of people and also some snow, though we’d managed to brew up some tea by then to ward off the cold.

By 11h00 managed to sell a few Beta spares, an engine and also some SWM spares, so all good and the day was already worthwhile. Things got quiet there after so plenty of time to head indoors to the show proper.

In the Telford carpark lift

There were some good stands, plenty of vendors and some good bikes on show. Again, all seemed to well organised and it was also nice to see overseas exhibitors and visitors to the show.

Bit of fun later, as we were asked if we were interested in a Beta motocross bike (circa 70’s). A trip over to the nearby multi-storey car park and an interesting (ie rare) example was wheel from the back of a Transit. A quick fire up and some discussions saw the bike wheeled back to the autojumbe via the lifts in the carpark, with Alan as the new owner. More on the bike in another article, but it does run and pretty well too.

Took some time to find some number plate ovals for the Yamaha MX250 project as well as a Clymer manual (for 8 quid) . A late rumage in the jumble also found some used MX body armour which will allow some room for growth.

Good show from my point of view, but I did sell some stuff, talk to a few people and have a look round.

Update on progress with the MX250


Took the tyres off the two sets of wheels, something that wasn’t exactly straightforward and didn’t think to heat the tyres up to help in removing them after 30 years on the bike. Took them down to Gerard Pettit down in Caerphilly who respoked the wheels in a couple of days. He used galvanised rather than stainless spokes for strength which seems fine by me.

Wheels and Tyres

Bought some medium compound Michelin motocross tyres from Paul at LG Racing and had the usual trouble in getting these on without destroying the inner tube. Need more lessons. Managed to polish the wheels a bit using Autosol and the ersatz dremmel bought from Argos.


Rather than getting it powder coated ( and if you do, can recommend Redditch Shotblasting ), decided to paint the frame myself. Used a couple of aerosol tins of Hammerite Satin black which seems to have given some excellent results.


Started to strip the engine (from the original bike) during a weekend of being duty officer at South Wales Caving Club and managed to look at the top end and remove the clutch.

SWCC workshop

However, the flywheel wouldn’t come off, partly as I don’t have the right puller (i have 15 others than don’t fit). Its a M20, 1.5mm pitch RH hollow puller and ended up ordering one from the US. Gavin and his lathe turned one up in brass (no steel rod available) and this was unfortunately strong enough to remove it, despite lots of heat. To be revisited.


Clutch looks ok and the steel and fibre plates are greater than the wear minimum.

I also stripped the top end of the spares bike to see about the state of piston and barrel. Two hours of grunt and effort saw the ceased piston come out of the barrel, but not before I’d d broken one of the bottom fins off. Both piston/barrels seems to be at 1st oversize (0.25mm) which is good news.

I ordered some engine spares from Motolink , specifically some gaskets, bearings and crankcase seals. Also an oversize (0.5mm) piston kit, including piston, gudgeon pin, bearing and circlips.

Plastics and Decals

All the plastics and decals have arrived from the US and they were well packaged. Also shipped in such a way to avoid paying duty, which was nice. Managed to find the tank decals on ebay from Speed and Sport Yamaha . The plastics arrived via Reproduction Decals and all looked pretty good.


More on the fork rechroming and rebuild in a separate article .

Basically, the frame is ready to rebuild and start the process of getting back to a complete bike