Help! MOT failure due to bent disc.

slparry · Post by **slparry** » Fri Dec 13, 2013 8:30 pm

Jon .. sorted

http://www.demon-tweeks.co.uk/motorcycl ... sc-ds-line

boxerscott · Post by **boxerscott** » Sat Dec 14, 2013 12:21 am

That sounds like a cost effective solution Steve, pity nasa did not ask you to find some booster rocket O ring seals

Corvus · Post by **Corvus** » Sat Dec 14, 2013 11:28 am

Copper wrote:Hi,

Thanks, they aren't the same mine are the later type that have the fixed washers.

I'll be gently bending metal back a few thousanths of an inch. I'd imagine that the same metal is exposed to much greater forces during braking.

I'll let you know if it works or not.

Jon

I can't argue with the fact that you've given evidence to suggest that it can be done. Although every photo so far has been of discs not typical on bmw boxers.

But one thing I would say is that you're not just moving metal a few thou. If you push onto it enough to move it a few thou it'll almost certainly just spring right back. To get it to "set" a few thou in the new position, you'd have to move it a damn sight more than a few thou, surely? That would worry me somewhat.

I'd think very carefully about applying leverage with the disc in situ, not just with consideration for damage to the disc but also the wheel turrets. They have a look about them which screams that they are designed (very well) to have the minimum amount of material to do only the job they are expected to do. Any force other than that intended could easily result in tears.

How are the discs actually warped? Is it like a wavy washer or like a Belleville washer? Or a mixture of both?

Are the discs able to be turned around so the inside face becomes outside? If so, try testing for run out both ways. If you get the same answer, in the same spot then it confirms you're dealing with a warped disc and not just varying material thickness.

I like the "who dares wins" attitude, but I think everyone is just concerned that it might end in tears, that's all.

Cheers

dave the german · Post by **dave the german** » Sat Dec 14, 2013 2:11 pm

whats disturbing is the price of the OEM discs - Would manufacturing be easier because there is no carrier? or does it mean with a carrier one disc can be used for multiple applications by changing the carrier? I would think (perhaps naievly) that a straightforward disc without carrier would be cheaper to manufacture. Given the options, I think I would bite the bullet and get the wavys off the bay

Copper · Post by **Copper** » Mon Dec 16, 2013 11:07 am

Hi,

I appreciate all the help concern and advice!

Here is the update.

Set up the bike with a dial gauge and indeed the disc is warped. It looks a lot on the dial gauge but we are talking tiny amounts in reality. I can move the needle on the dial gauge back to zero by touching the disk and applying almost no pressure.

It takes very little pressure to adjust the disc. When you think how hot the disc gets in use and the fact that the pressure from an older caliper may not be even anyway I can't really see that any damage would be caused by bending the disc by a moderate amount.

I pretty sure the disc has warped due the seized caliper piston. I think the disc gets hot due to the constant pressure from the stuck pad. When the bike is stopped the pad remains in contact pressing on the disc and as it cools it warps out of shape. If BMW fitted fully floating discs this problem may well be avoided. Apparently they have changed the disc design 3 times so that must have had some problems somewhere.

Anyway my problem is the worst of the warp is right next to one of the mounting posts and its just not possible to bend it back without worring about damaging the fixed mounting bobbin.

I have improved the warp but cannot take it out completely. And the brake still binds slightly. I could take it back to the mot station to see if they will pass it but I'm running out of time for the free re test so decided the best thing to do is order a replacement.

I've gone for a second hand one from motorworks for £100. The best price for genuine was from my local BMW dealer at £175. EBC are having problems at the moment and no longer supply a fixed bobbin version due to vibration issues.

So I think if you had the same problem it is worth attempting to sort it using the method described but its not going to work in every situation

Hopefully I'll be back on the road by the end of the week.

Jon

Corvus · Post by **Corvus** » Mon Dec 16, 2013 6:13 pm

Long shot, but you haven't had the wheel powder coated?

slparry · Post by **slparry** » Mon Dec 16, 2013 7:42 pm

dave the german wrote:whats disturbing is the price of the OEM discs - Would manufacturing be easier because there is no carrier? or does it mean with a carrier one disc can be used for multiple applications by changing the carrier? I would think (perhaps naievly) that a straightforward disc without carrier would be cheaper to manufacture. Given the options, I think I would bite the bullet and get the wavys off the bay

The pads are equally disturbing Dave.

I believe a full set of OEM pads for my K12GT is circa £160 - 180 plus fitting etc

Copper · Post by **Copper** » Tue Dec 17, 2013 7:00 am

Corvus wrote:Long shot, but you haven't had the wheel powder coated?

Yes but the posts are clear of enamel.

Jon

Corvus · Post by **Corvus** » Tue Dec 17, 2013 10:15 am

Copper wrote:
Corvus wrote:Long shot, but you haven't had the wheel powder coated?
Yes but the posts are clear of enamel.

Jon

Ok dokes.

Does your version have the wave washers?

Copper · Post by **Copper** » Tue Dec 17, 2013 11:39 am

No it has the fixed bobbins.

Disc from motorworks arrived today p***ed off to say the least, they have charged me £100 for a disc with 0.17 mm of wear left on it. Total false economy to fit it, my bike has done 25000 miles and still has around 0.5mm of wear left in it I'm going to bite the bullet and get a new one.

Jon

Corvus · Post by **Corvus** » Tue Dec 17, 2013 12:13 pm

Bummer. You'll be sending it right back!

Is the fixed bobbin version the same as wave washer version, just without the washer? Or does it trap the disc? With a little bit of lateral movement? Just curious!

McBoxer · Post by **McBoxer** » Tue Dec 17, 2013 12:19 pm

Corvus wrote:...Bummer. You'll be sending it right back!...

Or what about fitting it, taking it for retest and THEN sending it back?.....

slparry · Post by **slparry** » Tue Dec 17, 2013 1:08 pm

McBoxer wrote:
Corvus wrote:...Bummer. You'll be sending it right back!...
Or what about fitting it, taking it for retest and THEN sending it back?.....

Al you have renewed my faith in Scots

McBoxer · Post by **McBoxer** » Tue Dec 17, 2013 1:22 pm

slparry wrote:
McBoxer wrote:
Corvus wrote:...Bummer. You'll be sending it right back!...
Or what about fitting it, taking it for retest and THEN sending it back?.....
Al you have renewed my faith in Scots

Happy to help

Corvus · Post by **Corvus** » Tue Dec 17, 2013 2:54 pm

McBoxer wrote:
Corvus wrote:...Bummer. You'll be sending it right back!...
Or what about fitting it, taking it for retest and THEN sending it back?.....

Ha ha.

I'm liking it.

www.boxertrix.com

Help! MOT failure due to bent disc.

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