Cross drilled discs and lightweight sprockets...

[aardvark]

I was thinking about cross-drilling the front disc on my RD250, but have heard some horror stories about discs cracking.

So, does anyone have any advice on how I can do this without totally destroying my discs at the next race meet?

And whilst I'm at it, does anyone know where I can get some really lightweight sprockets? A couple of the guys here are getting them made up for $55. They are about 1/3 the weight of the original disc, but they are reluctant to tell me where to get them from.

[mrmina]

And whilst I'm at it, does anyone know where I can get some really lightweight sprockets?

you can get the lighter (aluminuim) sprockets off ebay.

But they only seem to sell them with the 520 conversion kit

[Neka79]

Jase..have u tried "the chain gang" ?? they do the race stuff and greeny's "dinner plate" rear sprocket i think came from there...there in amcn and based in Syd i think...

couldnt u just contact pitmans or sum1 and see wot they can do for u??

[Wattie]

please dont drill your discs... we'd miss your posts...

[Gosling1]

I was thinking about cross-drilling the front disc on my RD250, but have heard some horror stories about discs cracking.

So, does anyone have any advice on how I can do this without totally destroying my discs at the next race meet?

And whilst I'm at it, does anyone know where I can get some really lightweight sprockets? A couple of the guys here are getting them made up for $55. They are about 1/3 the weight of the original disc, but they are reluctant to tell me where to get them from.

Chain Gang is the place for sprockets, and another bloke in Sydney once knocked me up a rear sprocket for the Zed in duralium (sp?) T6, it was as light as buggery, and hardly wore at all...... (but I can't recall his name, it was a few years ago now... ).

Drilling discs is fine if you follow some simple rules:

1. Use a template to centre-punch *every* hole;
2. Make sure the holes are no larger than 5mm;
3. Make sure there is at least 12mm between holes in every direction, and at least 5 mm from the edge of the disc;
4. Don't try and put in too many holes......the above restrictions will basically determine the maximum number of holes you can drill anyway;
5. Use a drill-press;
6. Most important of all, use a 8mm bit to put a slight chamfer on every hole, from both sides, when they have all been drilled out. This is the best insurance you can do yourself to prevent the discs cracking.

I have drilled several discs on various bikes over the years, not *one* disc has cracked or fractured as a result.

[Sulli]

An interesting read http://www.usa2strokers.com/forum//foru ... 14925&PN=1
may give you some ideas