I'm prepared to get shot down in flames here because this could be a very stupid question but is there any chance the rotor/flywheel on my 1997 XT600 could be threaded? I ask because it refuses to move despite me following all the great advice on here about using heat and a hammer with a pulling rig and protecting the end of the crankshaft. But when I look at the image on the parts page on MSP (shown below) it seems to show a thread pattern inside the central hole. Is this some kind of stepped taper or could it be thread?

If not I’m guessing I need to heat it more or hit it harder – can anyone tell me which is least likely to cause serious damage to the bike? I’m concerned that too much heat might deform the rotor or cause it to blue.

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Not threaded.

A friend of mine had one that really had to take a beating with a big sledgdehammer, if flew across his worshop when it let go.

With my own, i just put some tension on the puller, gave it a few whacks, and repeated that 2-3 times, and of it went. I was really surprised at how easy it was. So its very different from bike to bike.

My guess is that a good puller, with even tension so its not pulling slightly "sideways" will help alot.

No, not threaded, it's a taper fit - basically jammed in place with a nut to stop it coming off. If the male and female halves of the tapers are a good fit (as they should be) it can sometimes be a real struggle to get them apart. That's where the heat idea comes in - if you can get the flywheel warmer so it expands it'll release its grip on the shaft slightly (until the shaft heats up). You don't need to get it glowing in the dark but hotter than touchable should be somewhere about right. Remember it gets hot every time the engine runs so it's designed to take a bit of heat.

I've rarely (read never) had much luck with the two or three legged type of puller on flywheels. For what the proper puller costs it's worth buying one and even then it's sometimes tough (or it'll fall off straight away!). Heat it up, tension the puller (protect the end of the shaft with a sacrificial nut) and if it doesn't come off tap the end of the puller with a hammer. That's tap, not breaking concrete with a sledgehammer.

If you've got to this stage and everything is under tension do whatever you have to from the side, not in the direct line of fire if the flywheel comes off. The rear wheels of one of my cars are held on by the same method except everything is twice the size and they're always tough to get off. I've had the whole hub and puller assembly fly across the garage with some force before now. If you're in the way it'll hurt.

Thank you for the advice guys. The puller being to blame is something I hadn't considered enough, but it makes sense. I'm using a home made puller (now on the third version after the thread stripped on the first one and the plate bent on the second) that fixes into the threaded holes kindly provided by Yamaha. I've tried to keep it parallel with the rotor but I guess if it is even a few mm out it could cause one side to bind on the shaft. I'll make a stronger v4 tomorrow. It's good to know I'm not fighting against some high tensile thread through.

Be carefull when you tighten the puller, I always meassure the distances on four points from magneto to puller, up to 0.5mm accuracy should be good enough.

I wasnt carefull once, and new crankshaft had to be ordered

Wow. I've been working on anything within 2mm being good enough so that could be where I'm going wrong. I'm thinking that my homemade rigs are not good enough and I should invest in a proper good quality puller, preferably one I can use for other jobs on the bike like splitting the crankcase. I'm seeing 'harmonic balancer pullers' on ebay that look like they will do the job but all seem too cheap to be any good on a job like this. Can anyone recommend a quality tool that is likely to last? The Yamaha one is stupid money at 150 euros plus, especially as it only does one job.