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Greg

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sandblasting calipers
« on: May 09, 2005, 10:54:40 AM »
hey all...
I brought my calipers in to be sandblasted and powdercoated, and the guy sandblasted in the piston cylinder.  the piston seems to still fit nice and tight, but the finish is totally different now in the cylinder.  does anyone know if this will be a problem?  thanks!
greg
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Offline Hondell

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Re: sandblasting calipers
« Reply #1 on: May 09, 2005, 11:13:38 AM »
Yikes!!! I'm thinkin those bores are toast!!  You may get away with running a fine brake hone through them but I dunno. Sorry
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Offline Bob Wessner

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Re: sandblasting calipers
« Reply #2 on: May 09, 2005, 11:19:00 AM »
Perhaps even more important is what damage was done to the piston seal groove? As Martha Stewart might say, "this is not a good thing!"
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Greg

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Re: sandblasting calipers
« Reply #3 on: May 09, 2005, 11:22:18 AM »
hahaha, martha has bigger things to worry about than my calipers :-)

the seal groove **looks** ok, but I'm not sure what i am looking for.  It is still there.  the piston doesn't rattel around in the bore, still fits nice and snug.  what should i look for in terms of damage?

oh, and for those that followed my thread about the gas tank -- the powdercoater at least gave me back my money! 
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Offline Hondell

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Re: sandblasting calipers
« Reply #4 on: May 09, 2005, 11:24:03 AM »
Yes Bob's right. I was thinking of auto type brakes. The fluid may weep past the rough surface in the groove.
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Offline Bob Wessner

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Re: sandblasting calipers
« Reply #5 on: May 09, 2005, 11:30:40 AM »
Ha, you're right, like how to get that damn ankle monitor off!  ;D It might be hard to see any damage to the groove. If the depth of the groove has changed, or the 'corners' around the circumferance at the bottom have been rounded, could result in leaks.
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Offline MRieck

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Re: sandblasting calipers
« Reply #6 on: May 09, 2005, 02:54:06 PM »
Put it back together and see- not much in the way of options now. He more than likely bead blasted them which is not as abrasive as sand. I've met guys who bead blast entire pistons- grooves included. Their rings seem to seal OK. I'll continue to tape off the grooves myself.
« Last Edit: May 09, 2005, 06:12:24 PM by MRieck »
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Greg

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Re: sandblasting calipers
« Reply #7 on: May 09, 2005, 02:59:27 PM »
unfortunately, he did sanblast them.  i know because he didn't tape the tank very well and there is a bunch of sand in there.  >:(
anyways, it looks like the cylinder is still ok, now i just need to get the powdercoating out of one of the interior passages that they painted!!
thanks for feedback everyone....
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Offline Zeke

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Re: sandblasting calipers
« Reply #8 on: May 09, 2005, 08:45:27 PM »
I wouldn't bother assembling the caliper without honing the bore -- o-rings are designed to seal on a certain finished surface -- I might try if it was anything other than my life on the line....

Try a brake hone -- you can buy them anywhere for about 15 bucks.  If you can't smooth it out that way, then I'd take them to a machine shop.  You should also get the wear limits and make sure you haven't passed them.

Understand, that the only failure mode where you might find that the gamble didn't work is when you have to grab a #$%* load of brake and all the sudden you have none -- that ain't worth it.
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Offline Quail "Owner of the comfortable k8"

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Re: sandblasting calipers
« Reply #9 on: May 09, 2005, 08:59:42 PM »
Not knowing all the different brake designs out there, I have to raise this question.  Is the square lip seal mounted in the cylinder or on the piston.  If it is the cylinder it will not be a problem greg because the piston does not really ride on/in the cylinder.  The cylinder only offers support while braking.  The rest of the time the piston sits on the square lip seal.

Which by the way is the return for the piston.  The square lip seal distorts when you apply the brakes and returns itself and the piston to its resting postion when the pressure is released.
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Greg

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Re: sandblasting calipers
« Reply #10 on: May 09, 2005, 09:53:59 PM »
terry
if i understand correctly....the "square lip seal" (the piston ring seal, right?) is mounted in a groove in the cylinder.  So youa re saying that the rubber seal **distorts** to let the piston press on the pads, instead of letting the piston **slide** past? 
Also, I think the general concern is that the groove in which the seal sits might have been ground/roughened enough to let fluid slip **behind** the seal (ie: between the seal and the cylinder, NOT between the seal and the piston).

Zeke
If i hone the cylinder than i won't be getting the part on which the o-ring sits: namely, inside the groove.  or do the hones have the ability to smooth out the inner part of the groove?

thanks for all the comments guys...

greg
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Offline Terry in Australia

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Re: sandblasting calipers
« Reply #11 on: May 09, 2005, 10:31:48 PM »
I don't think it's a real problem Greg, powdercoating is usually impervious to brake fluid, so I can't see that it needs to be removed. The sandblasting will only remove a tiny amount of material, and the powdercoat has probably replaced more than the sandblasting removed anyway, so the chances of fluid leaking past the seal would be minimal once again.

If you've ever had a leaking seal you know right away, by the lack of lever pressure (spongey feel) and the pool of fluid on the ground anyway, it's not something that happens suddenly. In fact I've known guys with leaking seals to just keep topping it up, while waiting for parts to arrive (Brit bikes particularly) sure, your braking abilities are reduced, but you'll still have some brakes. I don't recommend it, I've just known it to happen.

My only concern would be that the square groove for the O ring is totally free of old sludge, sand and loose powder, as this will distort the seal and allow it to leak. Would I use the caliper myself? Yeah I would, but there's a lot less to run in to in these parts, ha ha! Cheers, Terry. 8)
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Greg

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Re: sandblasting calipers
« Reply #12 on: May 10, 2005, 06:25:05 AM »
terry
thanks for the advice....i think i'm going to give it a go this weekend.  i am also going to run it by a very competent mechanic who specializes in old honda restorations.....
i'll let you know how it goes!
greg
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Offline Geeto67

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Re: sandblasting calipers
« Reply #13 on: May 10, 2005, 06:36:25 AM »
just my .02 cents:

I had a couple of old junk calipers I sandblasted a while ago (I do my own blasting).  One had a groove in the piston bore you could feel with your finger nail so I figured what did I have to lose. I used a real light touch in the piston bore area but it still came up with a porous finish. After I got them out I took a dremel and polished the inside of the bore to a smooth shine. The piston still fit tight, but the groove was gone. When I reassembled them they did not leak at all. While blasting does not remove a lot of metal the finish is way too rough to be used as is in places where there is a machined finish. For future reference always take note of the parts of the caliper that have a machined finish and try to either protect it or recreate it.

Honda calipers are fairly cheap used so if you screwed it up you can just get anothe one and state over (expensive lesson though).     
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Greg

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Re: sandblasting calipers
« Reply #14 on: May 10, 2005, 06:56:25 AM »
Geeto
The Dremel is a great idea.  My girlfriend has one...is there a polishing bit i should use?
thanks!~!
greg
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Offline Geeto67

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Re: sandblasting calipers
« Reply #15 on: May 10, 2005, 02:16:37 PM »
it is going to take a really long time to get the steel liner up to where you want it (a ball hone will go faster and you can probably get one at the local speed shop) but some course jeweler's compund and the dremel buffing bit (you will need several as you will probably wear it out) and nothign to do for a full day will probably get you where you need to be. 
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cb750_chris

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Re: sandblasting calipers
« Reply #16 on: May 10, 2005, 04:08:21 PM »
You really have to know your blaster/powder coater before you hand over the goods.  They tell you they'll put scrap bolts in the holes and tape things off.  Then they turn around and stop the new guy from sweeping the floor to work on your stuff.

It's the same treatment we get at the dealler.  As soon as they know you have an old bike they automatically assume it's a piece of crap.  Hello!!!! If it were a piece of crap I would use arisol...... not powder coating. 
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Offline Quail "Owner of the comfortable k8"

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Re: sandblasting calipers
« Reply #17 on: May 10, 2005, 08:51:20 PM »
Quote from: Greg on May 09, 2005, 09:53:59 PM
terry
if i understand correctly....the "square lip seal" (the piston ring seal, right?) is mounted in a groove in the cylinder. So youa re saying that the rubber seal **distorts** to let the piston press on the pads, instead of letting the piston **slide** past?
Also, I think the general concern is that the groove in which the seal sits might have been ground/roughened enough to let fluid slip **behind** the seal (ie: between the seal and the cylinder, NOT between the seal and the piston).

Zeke
If i hone the cylinder than i won't be getting the part on which the o-ring sits: namely, inside the groove. or do the hones have the ability to smooth out the inner part of the groove?

thanks for all the comments guys...

greg
Supersport is correct, your hand is not a machine shop.  The square lip seal has 2 jobs, 1 to keep the fluid in the caliper.  2 to return the piston after the pressure is released.  If you think about it how could the piston return into the cylinder any other way.  The piston does not really ride on the walls of the cylinder.  The cylinder supports the piston when braking and transfers heat.  The piston does not slide on the square lip seal, (well it does in microns as the pads wear).  My point: if the piston is not binding in the cylinder and it is able to freely move in the bore, clean out the groove and replace the square lip seal.  If it dont't leak and the piston is in good shape.  Change your fluid often and you will never rebuild it again. Then go out to your car and change its brake fluid. 
  This concludes Terry's brakes 101.
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Offline kghost

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Re: sandblasting calipers
« Reply #18 on: May 10, 2005, 09:30:20 PM »
Wouldn't sweat it. Bead blast mine all the time. Put a new seal in it. If it doesn't leak good. If it does start a new post.
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