Warp speed?

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2wheelover51
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Warp speed?

Post by 2wheelover51 »

Well today I took off the front calipers and gave the pistons a good clean, coating them with red rubber grease. The pistons actually looked brand new, like most of the bike.
A few months ago before I was familiar with the Burgmans' hand brake I took it for a short ride and managed to leave it on for a while. I thought I had gotten away with it but for the last month or so I had begun to notice a slight vibration on using the front brake. While doing the brakes today I noticed the swept area on the offside disc was uneven :( so used my screwdriver as a dial gauge and spun the wheel. Sure enough it's quite badly warped. When I replace the disc I'll remove the front wheel and regrease the bearings.

Red Dog
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Re: Warp speed?

Post by Red Dog »

2wheelover51 wrote: Sat May 29, 2021 1:12 pm Well today I took off the front calipers and gave the pistons a good clean, coating them with red rubber grease. The pistons actually looked brand new, like most of the bike.
A few months ago before I was familiar with the Burgmans' hand brake I took it for a short ride and managed to leave it on for a while. I thought I had gotten away with it but for the last month or so I had begun to notice a slight vibration on using the front brake. While doing the brakes today I noticed the swept area on the offside disc was uneven :( so used my screwdriver as a dial gauge and spun the wheel. Sure enough it's quite badly warped. When I replace the disc I'll remove the front wheel and regrease the bearings.


Excuse my ignorance, but how can you warp the front disk by leaving the handbrake on?

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2wheelover51
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Re: Warp speed?

Post by 2wheelover51 »

Red dog you are of course correct. Handbrake being on rear disc. Doh! :oops:
So I wonder what made it warp. When I was riding it home, and for the month or two I have owned it the brakes have been fine, then a few weeks ago I noticed
the offside discs "wear pattern" was off kilter, the disc outer pad is not contacting the disc across all it's circumference. I wondered if someone has tried to
have it away while the disc lock has been on, outside a shop perhaps.. :?

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Data
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Re: Warp speed?

Post by Data »

That's a possibility 2wheelover51, about the disc lock being on when someone tried to wheel it away. I've seen damage caused in that way. But it may just be a lazy piston on one side due to debris /dirt in the caliper around the pistons before you cleaned it. Cannot remember if those calipers 'float' or not, I think they do. In which case just make sure everything is spotlessly clean so the calipers move about ok. That should do it. Calipers that stop floating will wear the pads unevenly.

Warped front discs are usually caused by owners braking either in a prolonged way down a hill or from speed, and then holding the front brake lever on whilst stationary. This creates a huge 'hot spot' on the disc as the pads transfer their heat to the disc causing it to warp. This normally is only very slight to start with, but the disc gradually warps more and more over times as the warped section of the disc get increasingly hot during stops until the owner realises there's a problem.

Regarding re-greasing the front wheel bearings, that won't be possible as you have to destroy the bearings to get them out to re-grease...which kinda defeats the object. The factory bearing are sealed on one side only and the sealed side is outwards facing and is all you can see. So nothing to re-grease. If the bearings are dodgy or getting dodgy just renew, they are cheap enough.

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2wheelover51
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Re: Warp speed?

Post by 2wheelover51 »

Thanks Data.
They're floating 2 pot calipers each side. Re: the bearings I usually just dig out the seal and refill with a mixture of gear oil and grease and I've never had a bearing go on me. Can the bearings not be removed and reinserted with the seal to the outside?
Re: the discs, when I got the bike I didn't notice any vibration from the front, it's developed gradually over the last few weeks so maybe you're right although I don't recollect any long hill braking I tend to pull on then let off on long hills but who knows, maybe that's what I did.
I've managed to get a couple of new EBC discs (and pads) off ebay for £30 plus P&P. Of course they maybe cheap Chinese discs along with EBC pads, but still a bargain I think.

steve campbell
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Re: Warp speed?

Post by steve campbell »

Warped discs often coincide with a tyre change..ham fisted tyre monkies often damage bike discs

the can be straighetend with a large ajustable and some bending force

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Data
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Re: Warp speed?

Post by Data »

2wheelover51 wrote: Wed Jun 02, 2021 5:50 am Thanks Data.
They're floating 2 pot calipers each side. Re: the bearings I usually just dig out the seal and refill with a mixture of gear oil and grease and I've never had a bearing go on me. Can the bearings not be removed and reinserted with the seal to the outside?
Re: the discs, when I got the bike I didn't notice any vibration from the front, it's developed gradually over the last few weeks so maybe you're right although I don't recollect any long hill braking I tend to pull on then let off on long hills but who knows, maybe that's what I did.
I've managed to get a couple of new EBC discs (and pads) off ebay for £30 plus P&P. Of course they maybe cheap Chinese discs along with EBC pads, but still a bargain I think.
Yes you can fit the bearings the "wrong way round" so the sealed side is pointing inwards but then the bearing will take in quite a bit of dirt and grit and the grease starts to dry out over time, kinda defeating the object. I tend to fit double side sealed bearings these days as they last even longer and they are the same price usually. Regarding the warped disc, it's probably due to a caliper not floating properly. It's pretty hard to get one of the Burgman discs to warp in normal use unless something is wrong, but repeated stops with the front brake held on after stopping will contribute to it. Let us all know what you think of your ebay discs and pads once fitted.

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2wheelover51
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Re: Warp speed?

Post by 2wheelover51 »

Data, you might be right, although I've paid particular attention to the pistons being free & clean I have to admit to being less particular with the slide pins, although they did seem to be sliding ok I might take them off again and regrease them.
Steve Campbell, I've never tried to straighten a disc, thinking it was a job for dial gauges and milling machines, etc. I do have a nice big adjustable spanner though which might do the job. I assume the disc is taken off and clamped in a big heavy vice. Do you heat your discs?

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Data
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Re: Warp speed?

Post by Data »

Usually the disc 'run out' is tiny and barely visible to the naked eye. Straightening is usually not possible at home, although you maybe able to improve it slightly as Steve says but it would need to be very bad to consider that. In the workshop we used to just change them out for new ones as you cannot afford to mess about. Best method for straightening is turning it in a lathe to take down any minor high spots, but they must be very minor or it won't work. Any disc run out increases wear on the pads and hydraulics and replacement is far easier and usually cheaper depending on the bike concerned.

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2wheelover51
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Re: Warp speed?

Post by 2wheelover51 »

Well I finally got around to replacing the dodgy offside disc with the (EBC?) ebay replacement. Braking nice and smooth again now. Just for interest I put the one i'd taken off against my window but couldn't see any distortion or warping, so as you say Data, the distortion must be pretty small.
I only replaced one side so have a spare in the cupboard now. 8-) Oh, and the wheel bearings both sides have seals which face outside and can be refilled. I didn't bother because they both seemed pretty smooth and well lubed.

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