Front sprocket removal, etc

I am about to replace the front sprocket, and wanted info on the size of the nut, is there a lock-washer, and do I need to use some form of "Loctite" on re-assembly (sure I read about it somewhere).  

Any help much appreciated.

Seem to remember they are 27mm, to undo/torque up the nut place a block of wood across the swingarm through the wheel spokes, make sure the tyre valve is away from the wood. Don't use loctite, clean all parts and lube with oil and torque the nut up to 70Nm. There is a modified front sprocket nut with more thread in the nut worth the cost to stop damage to the gearbox shaft, the oem nut can come loose.
https://www.wemoto.com/bikes/yamaha/yzf_600_r_thundercat/98-01/picture/front_sprocket_retaining_nut_kit_oem

Thanks for the reply, most helpful. I will take on-board what you suggest. Soon be back on the road now. Thanks again

As we are all "off the road" at the moment, I decided to crack on with the sprocket replacement. I have removed the five allen bolts from the cover, and disconnected the gearchange lever, but the cover, although loose will not come off.

Have I missed a fixing, or could it be buildup of crud inside the cover that is preventing removal. As a 65 year old duffer, can someone help?

Spray the gear shaft with WD40 or such like and work the cover on and off to clear the muck out of the shaft bearing and seal.

Cheers, Past-it,

I wondered if gunge had built up behind the chain, but would not have thought of applying the oil.. I shall give it a go this afternoon.

Thanks again,

Dave

It is highly likely there will be a lot of gunge behind the cover.

I managed to get a stone lodged in there, didn't half make a noise and scared the life out of me.

Hope you managed to get the cover off.

Yeah, the cover came off really easy after the WD40. Now all I need is to buy the socket (if the shops are open).

There was a lot of muck inside the casing, both dried out, and full of chain oil. I once had a small stone in there, which was about the size of a sprocket tooth, which was a cause for concern, but it was a stone in the end.

I'm not sure what size the nut is, but can order a socket on-line at the moment. Measuring it in the confines of my garage is not easy, as there is barely room for the bike and me with all the other junk in there!!