[smcmillen66]

Hey all, buying new front discs for 1993 900 supersport. Older EBC catalog has part no. MD633x and newer catalog has part no. MD2003x as correct front disc.
Only difference is that md633 has countersunk mounting holes and md2003 does not.
I have the newer 5mm hex head front disc mounting bolts on my bike.
Discs I'm replacing appear original and do not have countersunk mounting holes.
Any idea whether I can use the countersunk md633 discs? Does it matter? The 5mm bolts fit perfectly within the countersunk area.
Only reason I care is because I found one md633 for a very good price, so I'm saving a couple hundred bucks if I can use md633 countersunk style.
Thanks!

 

[pittmeister]

Counterbore I'm guessing you mean?Countersinking is for flat head bolts.

As long as everything lines up and the bolt heads clear the forks it doesn't matter either one you choose

 

[SP3]

You need the counterbored version otherwise the bolt heads will make contact (and break) the speedo drive.

 

[smcmillen66]

Thanks guys. EBC calls it countersunk. Counterbore - same idea. The 5mm ducati hex key screws clear the forks no problem on the old discs that are not counterbored.
Just wondering based on strength...
No alignment issue based on comparing offset of old disc vs. the md633x I received.

 

[rennsportmotorrad]

If the disk's you get are countersunk then use countersunk bolts--likewise if the disk's you get do not call for countersunk bolts then use standard bolts--Its the disk you get that dictates which mounting bolts you use

 

[smcmillen66]

That makes sense. Sorry, but can you describe the difference between countersunk vs. standard bolts? The bolts I removed have a wide, flat head and a 5mm hex key socket.
Thanks,

 

[rennsportmotorrad]

for me countersunk bolts have a convex taper from the edge on the head toward the threads--they go into a hole that is countersunk with a concave taper going toward the smaller center hole-when installing the countersunk fastners they self center due to the opposite tapers

 

[RockAZ]

I don't think it matters as long as the bolts used clears the speedo drive, but countersunk bolts are easily found even at Ace Hardware or a local nutz n bolts shop for not much money so use them on the countersunk discs. For stainless steel you can get two dozen for under $10 on Amazon or Ebay. As I recall, since the discs are tapered on only one side, obviously, you can flip them over to use the other style of bolt,... but it seems the metal would be thinner so I've never done it because getting the right bolt new was so easy.

Most of the time I buggered at least one of the allen sockets getting the old ones off anyway.
The three types: ( the middle one is what came stock on my 91 900SS bike but I switched to tapered with the new discs on the 91)

Tapered

Standard

I call these shouldered, but counter bored might be the correct term? These are on my full floater discs on the 95 SP

 

[rennsportmotorrad]

Use the correct part in the first place--as an example if it is made to use countersunk bolts--Why the hell would anyone ever do something as stupid as turning the disk over and using a normal bolt & washer---If someone is that damn cheap they dont need to own anything mechanical. using the countersunk fastners in the countersunk hole's they are incredibly strong--turning the disk over the metal is thin as hell as RockAZ said to me this is asking for a failure, and the last thing you want is a failure of the fastners holding your brake disk on-can you say front wheel lockup at high speed??? I thought you could

 

[RockAZ]

I think OP was not considering flipping it over, but that he noticed that the edges of the bolt kinda fit inside the tapered area - not optimal imo,... mainly because it makes the contact area very small and with dissimilar metals expanding and contracting with heat under use I don't think it would hold sufficiently. But it might for a while, until it got "rounded off" leading very quickly to loosening up.

Or maybe its the standard bolt fitting into the "shouldered" or counter bored type? OMG, that is worse!

It's why he asked, glad to help point out the better solution.

 

[rennsportmotorrad]

And by the way --RockAZ in my previous post I am not inferring in any way that you were recommending turning the disks over and using standard bolts

 

[RockAZ]

Hmm, looked at OP's other posts - you don't have the SP model with the free floater discs, do you? I see when you initially joined the forum there was a few oddities with the VIN and model specs. PIC of the rotors!

 

[SP3]

Countersink and counterbore are NOT 'the same idea' because the hardware used in each case is NOT interchangeable. Further, there are different angles of countersunk holes/screws.

 

[SP3]

also - terminology related (EBC states it correctly here):

 

[SP3]

View attachment 978921
I call these shouldered, but counter bored might be the correct term? These are on my full floater discs on the 95 SP

Those are shoulder bolts. They are another thing entirely. If the shoulder is too tall, there is no clamping of the part going on. They are generally used to ALLOW (slight) movement of a piece relative to the part it's attached to. The end of the shoulder is what tightens against the threaded part (wheel in this case) leaving the attached part (rotor) 'free'. Not the right application.

 

[smcmillen66]

All, thanks very much for your responses. Story best told with pictures, included here (old disc, caliper, new disc, mounting bolts).
Also, for further info, the 2019 EBC "International" catalog lists MD633X as the correct disc for '91-'97 900 Supersport/Superlight, while the 2019 "Americas" EBC catalog lists MD2003X as the correct disc.
Called EBC and they said they are the same discs, but md633x have counterbored (countersunk not correct term, sorry for confusion) mounting holes while the md2003x do not.
So I guess my question is can use the counterbored/"International" rotors for my U.S. model '93 900 Supersport (which has an early '92 build date but the VIN decodes to a '93 model).
If so, are there different mounting bolts for counterbored discs?
Thanks again!

 

[SP3]

I'd just get the couterbored ones to be sure. I don't understand the 'euro vs usa' difference.

 

[SP3]

Ah, since my SP3's rotors are actually sitting here on my desk, it came to me. The floating rotors require thicker centers. This moves the bolt heads out and they foul the speedo drive. The semi-floating rotors are thinner, use a thinner center, and don't need the counterbore.

You'd think I'd remember this having experimented with the early ChiComm rotors years ago. They were thicker (though no floating) but arrived without having been counterbored. I did them myself in the mill.

 

[SP3]

Is that photo of the rotor taken by you/do you have them? If yes, what is the rotor thickness? It looks like 5.5mm.

 

[smcmillen66]

Thanks guys. I took the photos. The old (original) rotor is the first picture - the dirty rotor. No counterbore. Center thickness is 4.25mm.
New rotor center thickness is 5.5mm.
Good thinking.
So, I can think I can use the md633x counterbore version with the same bolts (which fit perfectly into the counterbores), unless anybody can think of a reason not to.
Thanks again.