I thought it best to pull the flywheel cover off the DT I just bought - glad I did.

The flywheel is covered in some kind of white powdery dust, which has stuck to the outside of the flywheel in places. Looking through the cutouts in the flywheel I can see the same powdery residue over everything behind the flywheel. At least the flywheel nut is not rusty so I am optimistic I can get the flywheel off. The inside of the case is also covered in it. Wonder if salt water has got in there at some time.

I take it the nut is a lefthand thread and I will need the 27mm puller to draw the flywheel off - I will take a look at the workshop manual before I attempt to do it.

Is there anything in particular I need to consider when removing and re fitting?

I am surprised the bike ran at all given the state of the flywheel and everything behind it - it was starting easily and ran absolutley fine.

Thanks in advance.

Copied from google. Photo of what I found on my DT400B.

Galvanic corrosion (dissimilar-metal corrosion) is an electrochemical process in which one metal corrodes preferentially, when in electrical contact with a different type of metal, and both metals are immersed in an electrolyte such as water.
 

Nut is a right hand thread [undoes to the left]. Puller body is a left hand thread [so screws in turning to the left]. Remove both washers [spring & thick flat] to let the puller get right in as is a fine thread. Keep the puller center bolt wound way back or can get a false impression of being right home as the bolt could contact the shaft first.

Schu - mine looks pretty similar to the picture, but much more powdery and dusty.

RT325 -Thanks for that I thought the crank nut might have been a LH thread too, better get a puller on order.

While you're waiting for your puller to arrive, if I were you I would remove the flywheel nut, and spray some Liquid Wrench or some kind of penetrating up in there. Let it start wicking up in between the shaft and flywheel to loosen up the corrosion.

Great minds Tom - already done that, glad to say there is virtually no rust on the nut or thread of the crank.

No problem removing the nut came off no problem all.

It will be a couple of days before the puller arrives so plenty of tiime to "marinate" the taper

I now have the flywheel off - no dramas.

Behind it was a lot more of the powdery corrosion which I carefully blew out with an air line.

The coils look OK but most of the screws have rust on them - I have managed to clear out the heads to be able to get a screwdriver to engage.

Despite the corrosion everything worked OK, so do I (bearing in mind I am in no hurry) try and dismantle everything so that I can clean everything up and risk shearing the screws off, or do I leave as is and wait until someting fails?

I am tempted to fit one of the Rex's speed shop conversions with ignition and 12v conversion and bin the old corroded items: www.rexs-speedshop.com/product/dt360-dt4...th-12-volt-lighting/
 

"The coils look OK but most of the screws have rust on them - I have managed to clear out the heads to be able to get a screwdriver to engage."

Apologies if you know this already, Andy, but the screws will almost certainly be JIS, not Phillips, so make sure that you use the correct size JIS screwdriver.

My default position is one of "if it ain't broke.......". However, the early Yamaha cdi pulsers weren't the most reliable, so I wouldn't dissuade you from fitting Rex's - just make sure that you read forum members' comments on these kits first. 

Any corroded or sad looking dirty points magnetos or cdi mags i just get the water blaster into it. Never had an issue & just blow it out after with compressor. Works for me.

I would not disassemble if it were mine.  I'd spray it off with proper electrical cleaner. Maybe then a coat of LPS 1 or electrics safe corrosion preventer.  Many out there.

Make sure magnets inside flywheel are clean...  damage to pulsar is reportedly caused by debris between spinning magnets and coils