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accounting for moisture drainage-- what's a frame builder's take?

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accounting for moisture drainage-- what's a frame builder's take?

Old 11-12-14, 09:24 AM
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accounting for moisture drainage-- what's a frame builder's take?

There seems to be two schools of thought when building frames-- seal the tubes after brazing so no moisture can ever enter, or vent all the tubes to allow moisture to drain and vent. What I have found to be the majority approach, at least with manufactured frames, seems to be the worst compromise of the two-- the main tubes and stays remain vented, but the bottom bracket acts as a trap. Why do manufacturers do this? If there is any chance of water getting into the frame tubes (from numerous places-- seat post, headset, or vent holes in the stays/dropouts), the #1 place it's all going to eventually end up is the lowest point, being the bottom bracket. From there, if it's not vented by means of a hole at the bottom, or a fancy filed cutout, it's just going to accumulate, cause rust, and potentially destroy the BB. The vast majority of bike frames I work on have vented tubes, but nowhere on the BB for moisture to drain.

I just removed the BB from a bike I built up new less than two years ago, and only ridden for events-- it lives indoors when not ridden, but it has been ridden in rain, and I've washed it several times. When I recently pulled the BB, there was a TON of rust already, and it was clear the BB bearings had taken on water. I'm totally aggravated that my less than two year old (and expensive) Phil titanium BB took on water this way.

Yes I am aware of framesaver, but that's not the point. The point is that water needs to be able to exit if it's going to have entry. Would you want to have a puddle of water trapped perpetually in your BB even if it were frame-savered? It may delay rusting, but it won't prevent damage to the BB and cups. I wish frame builders (I'm referring more to manufacturers than individual builders) would think about this when designing frames and build them accordingly.

From now on, if I ever get a bike that doesn't have a weep hole at the bottom of the BB shell, I'm drilling one!

On closer thought, every hand-built bike in my collection has a weep hole in the BB, but none of the manufactured ones do.

So is there a legitimate reason for NOT venting the BB? Am I missing something? (And I won't buy the argument that water and debris can get in-- I'd rather water be freely able to get in as long as it can get out just as quickly!).
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Old 11-12-14, 09:36 AM
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I suspect you'll get a variety of methods/thoughts.

I now use two vets in every tube/blade while building. After the final cleaning I'll go back and plug the blades and seat stays completely and plug the chain stay small end vents (the BB ends are open into the shell). Each main frame tube has both ends open. I have played with closed bottle bosses with no real effect.

But I build for me and my wife only and don't live in a high water area. As my bikes get broken down every off season, and have been done so for decades, I have a real good idea to what MY needs are WRT moisture control. I do Frame Save before the initial build up and every few years later.

Too bad about your pricy BB bearings. I assume you know of Phil's service for rebuilding their products. Andy.
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Old 11-12-14, 10:15 AM
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Originally Posted by Andrew R Stewart View Post
I suspect you'll get a variety of methods/thoughts.

I now use two vets in every tube/blade while building. After the final cleaning I'll go back and plug the blades and seat stays completely and plug the chain stay small end vents (the BB ends are open into the shell). Each main frame tube has both ends open. I have played with closed bottle bosses with no real effect.

But I build for me and my wife only and don't live in a high water area. As my bikes get broken down every off season, and have been done so for decades, I have a real good idea to what MY needs are WRT moisture control. I do Frame Save before the initial build up and every few years later.

Too bad about your pricy BB bearings. I assume you know of Phil's service for rebuilding their products. Andy.
Thanks Andy. Yes, I know I can have it serviced, but what irks me is that the problem was caused more by bad design than by use/misuse-- it has less than 1000 miles on it and was never submerged in water. By contrast, the last rebuild of my commuter, which is ridden daily and lives outside and has an old Deore XT cartridge unit from the 90s (but has a drain hole in the BB shell that I specified years ago when having frame mods done), showed no signs of wear or damage to the BB.

Very curious to hear other opinions...
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Old 11-12-14, 12:19 PM
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If you use Frame Saver on the inside of the tubes, you should expect a very long life from the frame. Frame Saver is linseed oil. AMSOil also make Heavy Duty Metal Protector (I am not sure that is exactly what it is c alled, but if you talk to an AMSOil rep, hew will know what you are talking about.) The AMS stuff is far cheaper, but even the expensive stuff is peanuts compared to the peace of mind you get. Most framebuilders frame save their work as a matter of course but it is worth checking on.

My Peter Mooney was ridden through a ridiculous rain it's first winter, then again 7 years later, with many wet rides between and since. It has a little rust, but nothing to worry about. (1979 build and 46,000 miles, many wet.)

Ben
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Old 11-12-14, 02:15 PM
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Originally Posted by 79pmooney View Post
If you use Frame Saver on the inside of the tubes, you should expect a very long life from the frame. Frame Saver is linseed oil. AMSOil also make Heavy Duty Metal Protector (I am not sure that is exactly what it is c alled, but if you talk to an AMSOil rep, hew will know what you are talking about.) The AMS stuff is far cheaper, but even the expensive stuff is peanuts compared to the peace of mind you get. Most framebuilders frame save their work as a matter of course but it is worth checking on.

My Peter Mooney was ridden through a ridiculous rain it's first winter, then again 7 years later, with many wet rides between and since. It has a little rust, but nothing to worry about. (1979 build and 46,000 miles, many wet.)

Ben
Ben, I agree framesaver is a good idea, but you miss the point-- the point being, framesaver won't prevent water accumulation, nor will it preserve components that might take on water as a result of water accumulation in the frame. Notably, my $200 Phil BB.

PS-- I live near Peter Mooney's shop, and have dealt with him a few times. He straightened my Mercian fork after shipping damage. I was amazed at his ability to correct it without scratching or flaking the paint. A truly talented old-school builder.
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Old 11-12-14, 10:30 PM
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southpaw, I realized that after I sent the post. Funny, I don't think my Mooney has a drain hole. One thing that helps minimize water in the frame is a rear fender. Without, you have a steady stream aimed at the seat tube slot at the seat post. I finished my wettest ever race with on grease in my BB; it was completely clean. But my BBs have done nicely on my fendered bikes with no attention at all.

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Old 11-13-14, 11:28 AM
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Originally Posted by 79pmooney View Post
southpaw, I realized that after I sent the post. Funny, I don't think my Mooney has a drain hole. One thing that helps minimize water in the frame is a rear fender. Without, you have a steady stream aimed at the seat tube slot at the seat post. I finished my wettest ever race with on grease in my BB; it was completely clean. But my BBs have done nicely on my fendered bikes with no attention at all.

Ben
Agreed, and all of my bikes are fendered. The thing is, this bike only got caught being ridden in two-three rainstorms, but I'm guessing the real culprit was washing the bike and/or getting it doused by rain on the car roof while transporting it somewhere. More water gets on the bike this way than from riding it.
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Old 11-13-14, 04:19 PM
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I do a mix of sealed and open tubes on my bikes. I seal the seat stays and fork blades and do so during the brazing process so the air inside is very hot and therefore very dry.....this means that they will not corrode from the inside for longer than any of us will be alive.

The other tubes are all open to allow air exchange.........but for this to work there needs to be a hole in the bottom bracket to allow liquid water to run out and for air exchange. This alone has proven to keep corrosion on the inside of the frame at bay and when you combine it with a spray in corrosion inhibitor the frames can be passed down to your grandkids. But like I said if there is no hole in the BB all bets are off.

One thing to watch for is frames where the seat tube is supposedly sealed at the top and bottom. There is no practical way to seal the top of a seat tube and therefore moisture, even if only condensation, will get in the tube and not be able to get into the BB and then out the bottom of the BB through a vent hole. Way back in the day Fat City insisted that all the frame tubes should be sealed - even the seat tube to the BB shell - and I can't tell you how many of those frames had the bottom of the seat tube rust clean through and break. It was extremely common and Fat had to repair or replace a HUGE number of them. They employed a 'sealed' clamp up top but they all leaked just a little bit even if perfect and that water ran into the bottom of the BB and sat there 24/7 until the frame is toast.

So if you are making frames put in a way for the moisture to get out because despite your best efforts it will get in.

dave
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Old 11-13-14, 06:38 PM
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Originally Posted by Dave Kirk View Post
I do a mix of sealed and open tubes on my bikes. I seal the seat stays and fork blades and do so during the brazing process so the air inside is very hot and therefore very dry.....this means that they will not corrode from the inside for longer than any of us will be alive.
Dave, not quite true. That hot air has a very low % humidity but stills contains the same moisture as the surrounding air. You haven't changed the dew point at all. Say the dew point is 40 degrees F when you braze (nice and dry assuming your shop is say room temperature (70F). You heat the air inside the tube to 500F. Nice and dry, right? Yup, 0.2% humidity. It cools to room temperature. That little 0.2% humidity is now 33.6% humidity because the much cooler air can accept far less moisture in vapor form. Cool it below 40F, that dew point you started with and you have liquid moisture inside the tube.

If you are brazing in a much more moist environment, say Florida, there will be condensation at a much higher temperature, perhaps 70F. Good side of this is that the condensation can only do a little rusting. Since the tube is sealed, it will quickly run out of oxygen. No more rusting. (The reason you should never enter a steel enclosed anything until it has been ventilated. You will quietly die and so will the person who comes to save you.)

Ben
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Old 11-13-14, 06:58 PM
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Originally Posted by 79pmooney View Post
Dave, not quite true. That hot air has a very low % humidity but stills contains the same moisture as the surrounding air. You haven't changed the dew point at all. Say the dew point is 40 degrees F when you braze (nice and dry assuming your shop is say room temperature (70F). You heat the air inside the tube to 500F. Nice and dry, right? Yup, 0.2% humidity. It cools to room temperature. That little 0.2% humidity is now 33.6% humidity because the much cooler air can accept far less moisture in vapor form. Cool it below 40F, that dew point you started with and you have liquid moisture inside the tube.

If you are brazing in a much more moist environment, say Florida, there will be condensation at a much higher temperature, perhaps 70F. Good side of this is that the condensation can only do a little rusting. Since the tube is sealed, it will quickly run out of oxygen. No more rusting. (The reason you should never enter a steel enclosed anything until it has been ventilated. You will quietly die and so will the person who comes to save you.)

Ben
I got you - I hadn't thought of it that way.

How does the fact that there is a partial vacuum in the tube affect things? When the tube is heated the air greatly expands and comes rushing out of the small vent hole that's been drilled in the tube. The vert hole is then brazed shut while the tube is of course still very hot. That makes me think that that there is a partial vacuum in the tube.........is that right?

I've been heating up stays and blades and sealing them while hot for more than 25 years and not once have I seen any corrosion even when I've taken a 20 year old fork and cut it open. It looks the same as it did when it was brazed shut.

Cool stuff.


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Old 11-13-14, 07:28 PM
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I sincerely doubt that the moisture in a tube is going to cause any problems at all. Far worse to leave a tube unprotected after a single ride on salted roads. And living where you do means the relative humidity inside the tube is very low anyway.
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Old 11-13-14, 09:44 PM
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Originally Posted by Dave Kirk View Post
I got you - I hadn't thought of it that way.

How does the fact that there is a partial vacuum in the tube affect things? When the tube is heated the air greatly expands and comes rushing out of the small vent hole that's been drilled in the tube. The vert hole is then brazed shut while the tube is of course still very hot. That makes me think that that there is a partial vacuum in the tube.........is that right?

I've been heating up stays and blades and sealing them while hot for more than 25 years and not once have I seen any corrosion even when I've taken a 20 year old fork and cut it open. It looks the same as it did when it was brazed shut.

Cool stuff.


dave
I didn't think about the heated air expanding and leaving you with a partial vacuum. Doesn't change my argument except that the dewpoint will go down with the lower pressure. I don't have the calcs in front of me for that and am not about to look! But I will guess the dewpoint will now be well below zero F; maybe a problem if you ride in Antartica.

Ben
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Old 11-14-14, 03:09 PM
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The moisture content of one tubeful of air is never going to cause any corrosion of note - so sealed tubes will never corrode from the inside. The problem is when more water can get in, and that's with the seat tube mainly.

I usually seal all stays and fork blades, leave decent holes in the HT into the TT and DT, and a drain hole in the BB shell. That's on conventional frames - unconventional ones like recumbents usually get all sealed up.
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Old 11-14-14, 03:30 PM
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I did a top tube replacement last winter. The reason is when the 20+ year old frame was being prepped for repaint a couple of pin holes exposed themselves on the bottom of the TT. The painter refused to go further. The customer really wanted to keep the bike going so I replaced the TT. When it was cut out you could see the rust along the bottom of the tube along it's full length.

The bike likely never had the post or fork out more then once or twice over it's previous life. It was vented with small holes at each end. Andy.
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Old 11-14-14, 07:49 PM
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Originally Posted by Dave Kirk View Post
I do a mix of sealed and open tubes on my bikes. I seal the seat stays and fork blades and do so during the brazing process so the air inside is very hot and therefore very dry.....this means that they will not corrode from the inside for longer than any of us will be alive.

The other tubes are all open to allow air exchange.........but for this to work there needs to be a hole in the bottom bracket to allow liquid water to run out and for air exchange. This alone has proven to keep corrosion on the inside of the frame at bay and when you combine it with a spray in corrosion inhibitor the frames can be passed down to your grandkids. But like I said if there is no hole in the BB all bets are off.

One thing to watch for is frames where the seat tube is supposedly sealed at the top and bottom. There is no practical way to seal the top of a seat tube and therefore moisture, even if only condensation, will get in the tube and not be able to get into the BB and then out the bottom of the BB through a vent hole. Way back in the day Fat City insisted that all the frame tubes should be sealed - even the seat tube to the BB shell - and I can't tell you how many of those frames had the bottom of the seat tube rust clean through and break. It was extremely common and Fat had to repair or replace a HUGE number of them. They employed a 'sealed' clamp up top but they all leaked just a little bit even if perfect and that water ran into the bottom of the BB and sat there 24/7 until the frame is toast.

So if you are making frames put in a way for the moisture to get out because despite your best efforts it will get in.

dave
Dave, this is exactly what I'm thinking-- water WILL get in despite best efforts, so why not just provide a way for it to escape rather than to try to seal it out.

BTW, I remember hearing those stories of Fat City failures, and I'm not sure if this is coincidence or carryover methodology from Fat Ciy, but even current Indie Fab frames (company started from Fat City) have all their frame tubes sealed. They say so on their website.

I sent the BB to Phil, it's only $45 to have them replace the cartridge bearings. Still, I can't get over the stupidity of a bike manufacturer leaving vent holes in the tubes but then not making sure there's a hole in the BB. Before I reinstall the repaired one, Im going to clean out the BB with a carbon brush, frame-saver the tubes accessible from the BB, and drill a hole at the bottom.
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