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somebody in europe was reproducing them i think, or the adapters.

there are billet heads available, as well. i love my t500. the bigger issue is 5th gear, 72 and back had an issue, but 73 and up are fine. mines a 72 and 5th gear is noisy, always has been and eventually i'll have to change it im sure. NOVA in the uk makes replacements.

 

Later bikes had the oil dam below the kickstart shaft raised which was meant to keep more oil inside the gearbox, oil capacity was increased 200ml. From memory Clauss studios do a copy of the rubber insert that was available at the time but if you have the gearbox apart it's better to weld a piece in

Would think the skirt would be too thin to do that, guess you could try turning a groove to take a ring in an worn out piston to see

If it's only slightly thicker you probably wouldn't notice a difference, will slightly raise the port height & lower compression

Personally I'd have RGV250s in the list ahead of the NSR250, here they sold a heap more & dominated production racing due to it being very much a true production class unlike in some countries where all sorts of engine work was allowed

I used a 50/50 mix of brake fluid & kerosene on a bike that had sat for the best part of 40 years, came free quite easily after a few days of soaking.
1 cylinder being at the bottom of the stroke will make it harder though, you may end up needing to space that cylinder up as the other frees off if the crank isn't seized

SO... our friends at Ducati had a "trellis" steel frame for years, it worked well... but they couldn't win races any more so they TOTALLY redesigned the frame as a RIGID aluminum thing THAT NO ONE COULD RIDE.OOPS! (There was NO WAY the trellis frame was going to support a 200HP motor. They HAD to do SOMETHING)... and it's taken YEARS to figure out how to make it work (if Ducati hired a frame guy that KNEW aluminum frames BEFORE they redesigned that frame, things might have been different). If Nickey Hayden or Rossi can't make it work, you've done something wrong... then came Casey Stoner (I don't know if they got it fixed or if Stoner was just that GOOD).

Here's another secret: The trellis frame Ducatis weren't particularly FAST, they were just EXCEPTIONALLY EASY to ride. The "ride" inspired confidence. It's easy to be a HERO on a 900SS.

You might notice: I'm into frames.
I grew up drag racing and learned early that ANYONE with half a brain can make horsepower (that's the easy part)... what is HARD is getting that horse power to the ground.
Tires and suspension (and by extension: Frames) are where it's at.

... and DG swing arms... NO... anything DG made was JUNK. Still is.

You got your timelines wrong there, Stoner raced the original steel trellis chassis then swapped to Honda in frustration at not being listened to by Ducati on what needed to change on the bike(seems to be a common theme eg Lorenzo waiting 1 1/2 seasons for seat changes), Rossi came next saying that him & Jeremy Burgess would have the bike sorted in 30 seconds, basically they wanted a Yamaha with power which meant the aluminium frame that Rossi was so used to. It's taken them a long time to get the complete change in design philosophy to work

if it's not too stupid a question, what do the dividers actually do? 
cheers, gil.

Basically they make the carbs act like they're a smaller diameter than actual size until the slide gets opened above the dividers, similar to how a 2/4 barrel carb works on a car

I only had 2. this was the 1st one in 2015.

I got lucky.

No better advertisement for full face helmets than that, I shudder to think of the damage if you'd been wearing a open face helmet or none at all

Gotta love a 25% weight reduction, how it looks is a bonus

Doesn't make sense to me that if the whole ignition system is WR500 that it won't still fire in the same position with the YZ490 top end as the WR is basically a YZ in a more up to date frame
Crank goes back to the YZ465, cylinder was first used on the 87 YZ490, piston 1983 YZ490. The stator & charge coil comes from the 83 IT250K, pulser coil was used on the YZ490 from 83 as well as the IT250K
Only part in the ignition or top end that is different between the YZ490 & WR500 is the head

Forgive me for asking... But what's the reason for neutral at lights on these old bikes? Clutch wear?

Oil pumps driven off the gearbox, sitting in gear with the clutch in means no oil is being pumped

If using high temp RTV it works better if you let the flange sit for at least half an hour so a skin forms before fitting the pipes to them

Have you tried bearing sleeves?  They are thin wall shims.  You may have to grind down the shaft to clean it up, and in that case things can start to get complicated, but try that.

You may be able to get a new crank from the UK, Europe or Japan.

If it were really irreplacable you could have the crank ground down and metal sprayed and finished ground to size.

Or just try Loctite bearing fit and see how you get on.

I would never use a crank that has been metal sprayed, have seen the damage caused by it failing. Much better fix is hard chroming then ground to correct size, I have a crank in 1 of my vmx bikes that has been repaired this way which is the method everyone who deals with these particular bikes agrees is the best longterm solution

Most piston manufacturers make there pistons undersize by the clearance amount so the cylinders are bored to the nominal size, a piston marked as say 66.00 will be for a bore of exactly that size & will measure the required amount of clearance under that.
A friend bought a bike that had been bored as though the size marked on the piston was it's actual size, in his own words "it sounded like there were 2 of them trying to get out". Even thought the bore was round & parallel we had to order the next size up wossner piston & bore the cylinder to fit, runs like a dream now

Back when I was still toolmaking I did this quite a bit with through hardened tool steel, speed needs to be kept low & pressure backed off as the hole starts to break out the other side. Carbide end mills can be used to drill through hardened parts as well, good use for worn cutters