Left and right front discs

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Paulrs
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Joined: Tue Sep 08, 2015 5:27 pm
Location: Royston, UK

Left and right front discs

#1 Post by Paulrs » Sun Jan 01, 2017 3:44 pm

Here goes my first noddy question of 2017. What's the difference between the front discs pn 31A-25831-51 and 31A-25831-11. Obviously I appreciate one is intended for the right side, the other the left. Could somebody tell me what the actual physical difference is between the two parts to make them left/right handed?

Looking forward to enlightenment.
Paul

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tacky1
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Re: Left and right front discs

#2 Post by tacky1 » Sun Jan 01, 2017 4:33 pm

I believe it the little vents in the middle, between the actual bolts and the actual disk. They point forward if you know what I mean, They go with the direction of the wheel, You can run two lefts or two rights on a bike, I did it once while waiting for a new disk, it just looked wrong
1985 RZv500
1984 RZ500 Hybrid
1986 RG500 Walter Wolf
1986 RG500 Skoal Bandit
1984 RZ350
1984 RZ350 Hybrid
1981 RD350LC
1981 RD350LC Hybrid
2009 CR500AF Supermoto 250X
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1988 YSR50 (2)
1989 VFR750R RC30
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silverstrom
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Re: Left and right front discs

#3 Post by silverstrom » Sun Jan 01, 2017 5:01 pm

Also the cleaning grooves/wear indicators cut into the discs. They are cut they way for a reason. The discs are unidirectional.
Last edited by silverstrom on Sun Jan 01, 2017 8:55 pm, edited 1 time in total.

Paulrs
Posts: 67
Joined: Tue Sep 08, 2015 5:27 pm
Location: Royston, UK

Re: Left and right front discs

#4 Post by Paulrs » Sun Jan 01, 2017 7:06 pm

Thanks for replies and the comments fit with my thoughts, but leave one further question; if you turn the disc over (inside face becomes outside) then the slots and groves would point in the same direction, so what stops the disc from being the opposite hand?

I had a quick look on my bike and could not see any obvious difference between the inside and outside of the disc's but it's hard to see as it's all assembled.

silverstrom
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Re: Left and right front discs

#5 Post by silverstrom » Sun Jan 01, 2017 9:07 pm

I believe it's because the inside mating surface is machined differently than the outside. Looks at the pics here and you can see it http://www.ebay.ca/itm/rz500-brake-disc ... TU&vxp=mtr" onclick="window.open(this.href);return false;

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tacky1
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Re: Left and right front discs

#6 Post by tacky1 » Sun Jan 01, 2017 10:25 pm

As Silverstrom said, The offset is different on each side of the disc.
1985 RZv500
1984 RZ500 Hybrid
1986 RG500 Walter Wolf
1986 RG500 Skoal Bandit
1984 RZ350
1984 RZ350 Hybrid
1981 RD350LC
1981 RD350LC Hybrid
2009 CR500AF Supermoto 250X
2007 CR500AF 250X
1988 YSR50 (2)
1989 VFR750R RC30
1984 GPZ750 Turbo

Paulrs
Posts: 67
Joined: Tue Sep 08, 2015 5:27 pm
Location: Royston, UK

Re: Left and right front discs

#7 Post by Paulrs » Mon Jan 02, 2017 6:13 am

Thanks Silverstrom, the pictures say it all.

The reason for the question was my discs will need replacing in the near future and frustratingly 31A-25831-51 is easy to locate and a bearable price, the other one isn't. No point in buying a single Yamaha disc, as the pattern discs don't match.

silverstrom
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Re: Left and right front discs

#8 Post by silverstrom » Mon Jan 02, 2017 10:10 pm

Talk to the guy at that eBay link and have him measure the discs. Buy them if they are good. The listing gives the seller's telephone number and says to contact if you don't like the buy-it-now price. You can probably get them cheaper than the eBay listing.

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