why are front disc bolts so expensive

[kneedown]

is there something special about the stainless bolts used in discs, i need to buy ten bolts for my front discs on my yzf 750 and being quoted 40 odd quid.

Cant i just use normal m8 20mm hex bolts, put one on and it fitted fine. But a friend said i shouldent use them because the bolts are specially designed.
I didnt think this was the case, any insight?

[Kickstart]

Hi

Do you trust your life to put all the braking force through some random strength generic bolts?

The disk bolts are silly money but I would be dubious about using bolts of an unknown grade to replace them.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[calyx]

What I remember from the metallurgy lessons is:
There are 3 types of steel. martensit, perlit, bylit. (probably misspelled) martensit is the hard one (easy to brake/snap). perlit is semi flexible, bylit is flexible.
manufacturing martensit is very easy and cheap. heat the iron, give it some coal fire, cool it down to 400 degrees and leave it.
Probably cheap bolts are manufactured by this method. That's why you should listen Kickstart

Alternatively you can get this kind of stuff:

https://www.rimmerbros.co.uk/Item--i-FTC1368?utm_source=froogle&utm_medium=feed
____________________
Boris - London

[pinkyfloyd]

[kneedown]

im not syaing i will use them i am just asking are they actually a special grade steel etc or is it just another case of yamaha saying "buy this from us
its the same product but because we recommend it its three times as much", as this seems to be the case for many bike specific spares

[tatters]

I,ve got a spare box of over 100 "12.9" rated disc bolts for Yamahas they are a straight swap for All YZF models l,ve used them on my YZF750 and YZF1000,

were abouts are you located as you can have as many as you need.
____________________
Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650,KZ750 Present:G650XC,C12,CRF450X,1190ADV

[kneedown]

hi mate im in south london, that would be really appreciated, how much for 12 of them
cheers

[tatters]

Thats good l,m near south london in west molesey, surrey

You can have 12 for free, say £2 for postage or you can pick them up.

Send me a PM and let me know whats good for you.


There black high tensile steel so you might want to coat or paint the heads once there fitted as they will corrode over time being made of steel something l,ve never bothered to do on my bikes.
____________________
Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650,KZ750 Present:G650XC,C12,CRF450X,1190ADV

[colin1]

I'm a bit concerned that I might one day buy a secondhand bike, where someone didnt think it was worth fitting proper strong bolts to hold the brake disc on.

Probably the most critical part of the bike subjected to some of the highest forces.

I'm a cheapskate, and will use brake pads until they are practically metal on metal, but there is no way, I'd use anything other than proper brake disc bolts to secure the brake disc.

Different metals have very different properties. Not all shiny things are the same.
____________________
colin1 is officially faster than god

[Pete.]

[colin1]

[Pete.]

Yes friction is what stops bolts coming loose which is how all bolts stay tight, but I'm talking about the friction between the disc and the wheel, not the bolt and the wheel, or the bolt and the disc.

Strictly speaking the bolts are in both shear and tensional forces combined. The bolt clamps the disc with tensile forces and the disc is held by frictional forces against the hub. If those frictional forces are overcome, shear forces will take up the remainder of the load. Copper bolts wouldn't have anything like the tensile or shear strength for either job.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[colin1]

OK got ya and I agree about the tension. I still think that the shear strength will be doing more than the friction you speak of though.

Taking a step back from the element analysis though, another way to look at it would be that the forces needed to decelerate a bike quickly are going to be huge, and the bolts are an important link in the chain in that process. It makes sense to me that they need to be a lot stronger than the usual bolt of similar diameter, thread pitch etc, as most bolts arent going to be subjected to such high forces.
____________________
colin1 is officially faster than god

[The Tot]

[MaybeGuy]

i wouldnt feel that unsafe using standard 8.8 grade plated steel bolts or something.
If theres 12 of them per disc then i doubt theyd ever shear.
All i would do is maybe use countersunk bolts to properly centralise the disc. Not that it matters too much.
____________________
Blue_SV650S wrote: it was a sh1te wheelie, but it proves that he can get it up in 3rd and can do angles. In summery, mattsprattuk is a gobby little sh1tebag, dopehead tw4t, but sadly for all of us, he probably isn't THAT full of sh1te!!
Kickstart wrote: Hi I tend to agree with Matt. All the best Keith

[Pete.]

Actually, having given it some thought on most discs runout is controlled by locating the ID of the carrier on the hub.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Kickstart]

[calyx]

[hamed]

I have a 94 model zx9r which am looking for the front disc bolts. I have looked around but only managed to find bolts for newer models. Will these bolts work on my old bike?
Thanks