Minimum Brake Rotor Thickness

[foreda]

Greetings all
Does anyone know what the minimum thickness is for 78E brake rotors? I would like to turn my rotors down but auto shops won't touch em. Also, does anyone have a pattern and procedure for drilling the rotors?

[DiverRay]

There is a thread just below this with the answer for the rotor thickness. The drill pattern can be had with a search, as I no longer know the exact name of it. I believe Jerry had the pattern, and it may be posted in the "Tech Tip" area. You will need to get there from the home page.

[TopCatGr58]

Hey FOREDA,

Remember, there are tech tips from the DROP DOWN menus at the top of the web site page, not just in the FORUM'S tech tips sections, and it was Ken Talbot that provided a nice PDF of the drilling pattern for the rotors, and it should also be in the tips.

You can't get an auto shop to turn the rotors because they are not plain cast iron like AUTO rotors, they are hardened stainless steel, that's why PlainDick had to come up with a special GRINDING device to flat grind them, a cutting tool would just CHATTER or break trying to cut the rotor!
T.C.

[foreda]

Rotors

Thanks TC. I tried to download the PDF for drilling the rotors but was unsucessfull. I sent Ken a PM to see if he still has the template but have not heard from him yet.

[planedick]

Minimum thickness

I'm sure that Yamaha wants you to maintain new thickness (.260"), but I have went so far as a minimum of .215" and did as best as I could a test under extreme conditions to find a failure, but nothing failed. I use a toolpost grinder setup to resurface mine and usually you don't have to remove only about .005" to get a smooth finish unless there are deep grooves. Notice that the pads don't wear to the outside so you can lay a straightedge from the center area to the outside and see how much is worn by the gap under it. Because I am aware of the liability issues involved I'm very reluctant to grind other peoples' rotors.

[foreda]

Rotors

I'm sure that Yamaha wants you to maintain new thickness (.260"), but I have went so far as a minimum of .215" and did as best as I could a test under extreme conditions to find a failure, but nothing failed. I use a toolpost grinder setup to resurface mine and usually you don't have to remove only about .005" to get a smooth finish unless there are deep grooves. Notice that the pads don't wear to the outside so you can lay a straightedge from the center area to the outside and see how much is worn by the gap under it. Because I am aware of the liability issues involved I'm very reluctant to grind other peoples' rotors.

I totally understand. My rotors really aren't that bad.The only reason I wanted to smooth and drill is totally cosmetic. I suppose I could fork out the money and buy new drilled rotors?? Anyway, thanks for all the replies.
Dale

[Ken Talbot]

Foreda - I posted a reply (at least I thought I did) in the visitor messages section. Basically, my ISP lost a server a while back which took out e-mail service, internet access, and personal web pages. Everything came back in a few days except the web pages. I have the template files here at home and can send them to you as e-mail attachments.

Drop me a note in the Private Mail section with your regular e-mail address and I'll get the files on their way.

[fredintoon]

I totally understand. My rotors really aren't that bad.The only reason I wanted to smooth and drill is totally cosmetic. I suppose I could fork out the money and buy new drilled rotors?? Anyway, thanks for all the replies.
Dale

Hi Dale,
the least hassle route is to see if Andreas has a set of used slotted rotors for you.
But if you gotta drill, here's what I found. The pattern don't matter, the pads don't care. A regular pattern is best because it won't unbalance the disk. I have seen brake disks advertised on E-Bay that had obscene pictographs picked out in drill-hole patterns but perhaps you don't want that kind of image?
So pick a likely pattern and mark it on the disk with heavy centerpunch marks.
Yamaha's brake disks are made from an alloy steel that's tougher than old boots.
You will need a drill press, a squirt can of cutting fluid that says "suitable for stainless steel" and cobalt steel drill bits.
Use high drill pressure, low drill speed and lots of cutting fluid.
First drill them all with 1/8" or 3/16" pilot holes. Then enlarge them to 3/8" or even to 1/2" If you go bigger than ~1/2" you will lose surface area.
Happy drilling.

[foreda]

Rotors

Thanks Fred
Adnreas sent me a note saying he has rotors so that is probably the route I will take. I do have a drill press and bits but will have to get some cutting fluid.
Happy Holidays and
Merry Christmas to all!!