drewfio

So I’ve been fixing up a 1984 Trek 500. I noticed paint scrapes with rust forming on both of the chain stays. Looking at it again it seems worse than I initially assessed. One spot behind the chainrings, and one on the inside of the left chain stay. If it is primarily cosmetic my plan was to remove the rust and touch the paint up.

But I’m wondering if this rust/damage is at risk for the chain stays failing/breaking, and if so, a safety concern. If it matters, from the old catalogs I gather the chain stays are Tange 2001 Mangaloy (I presume not butted). Pics attached.



Gouges and rust on chain stays.



Top view of chainstay, with what looks like a ding or dent. Problem?

bikingshearer 

I am no metalurgist, not did I stay at a Holiday Inn express last night. But to my eye, the rust plus the disfigurements are definite cause for concern. Especially the trough worn on the inside of the left chain stay.

it looks to me like that bike saw (1) a lot of tire rub on the left chain stay - and I mean a lot - to get that level of deformity, and (2) a lot of chainring grinding on the right chain stay. All told, that looks like more than just surface rust to me.

noobinsf 

Your second pic makes me a little concerned, and makes me think you should at minimum remove the paint to assess the steel underneath. Starting at the dark spot, it looks like the sparkles in the paint gather in a straight line directly horizontally across the width of the chainstay, and it makes me want to see what's underneath. Maybe it's the angle or lighting, but I would be concerned about that.

repechage

At some point it will fail.
will not put you to the ground but could ruin your day.
when?
no idea, don't invest in paint other than to prevent future rust,

Hobbiano 

To me, the rust doesn't look too bad, but that tire rub spot on the left chainstay is a bit concerning. I'd clean up the rust and touch it up to prevent further deteriation, and keep a clost eye on that left chainstay watching for any sign of a crack developing around that thin spot.

drewfio

My plan was just nail polish. Someone else on here identified a shade that matches in the ballpark of that pewter gray:
https://www.bikeforums.net/classic-v...-manicure.html

I'll start with that spot, and sand to assess the damage.

markk900

Curious: how does a thin rubber tire possibly generate enough friction to wear through steel? Not saying it isn’t possible but sounds wild to me.

Having said that checking out that left chainstay makes sense first. The chips on the drive side stay look ugly but not that concerning from my perspective.

oneclick 

Not friction, abrasion. Get some grit stuck to the tyre and it'll grind through the steel pretty quickly if you let it.

bark_eater 

I'm not a frame builder, but I may or not have spent the night behind a dumpster in Tacoma in the '90's.... But I have wondered if there is any structural advantage to filling diggers like that with bronze?

drewfio

Okay, sanded away some paint and here is what I found. definitely gouged and some material worn. There is a tiny dark groove/line that does not extend past the gouge, so I (would like to) think it is not cracked. My hope is it is simply a deep scratch mark. I can barely see it with my naked eye, but the closeup camera shot shows more detail than my eyes, ha. Thoughts?

Top view:



Bottom view:

Velo Mule

I think the thick paint is making this seem worse than it is. Paint it and ride it is my opinion.

It was good that you sanded it. You have a far better look at the actual depth of the grooves and the process of sanding it as cleanly as you did removed the rust and will provide a good base to apply a primer and then paint.

Trek had nice paint. It looked like Imron to me, but I don't know if it actually was since Imron was expensive. Their paint was thicker, more durable and better looking than most of their competitors in my opinion.

madpogue 

Pretty sure they did use Imron BITD.

Kabuki12

I would keep an eye on it and ride cautiously. A frame guy could probably build that area up a bit but I’m not sure that would make it stronger.

Korina

Post your photos in the Framebuilders forum and get some professional opinions. It's a nice bike, and worth saving if you can. Good luck.

PS Top view photo doesn't show for me.

polymorphself 

Definitely Imron.

79pmooney

Paint the bare spots, maybe with clear nail polish so you can watch for cracks. Ride it. Occasionally look cracks. My money's on the bike dying first of other causes. (Pre '85 or so, the seatstay cap cracking through the too deep "TREK" lettering - though that's easy for a framebuilder to repair.)

Treks are well made (except that cap on earlier ones). When I say something else will be the cause of your bike's death, I am not saying that's coming soon. Might be a crash, a theft or under the next owner or the one after. And if it does fail on you, it is unlikely to be an issue bigger than a ride shortener. My failure happened while riding. Felt odd so I looked down. Broke right behind the bridge. Chainstay was waving around. Rode the 2 miles home on it, then back to work on it a few days later to have the welder do a repair. I shortened the bike substantially a couple of years later in a hard crash and retired it.

Bad Lag

My guess -

That's damage from the rim rubbing against the inner surface of the chain stay. That they no longer line up means the wheel was farther forward in the drop out when this happened. It could also have had a different wheel size when it happened (27" vs 700 C).

It can also be intermittent abrasion, not necessarily continuous, permanent rubbing.

Another guess -

That stay looks to have been penetrated by the abrasion and subsequent corrosion. If you tap it does it "ting" or "tang"? :-)

Darkwater

I'd touch it up and enjoy a sweet bike, though I'd add another "C" to the ABC safety check. "Air, brakes, chain ... how are you doing, chainstays?" I've always heard that steel will warn you before it fails.
​​​​

drewfio

I'm not sure when the abrasion happened. My bet is the last owner. He seems to have just ridden it hard and gave it little care, until it would no longer run. The derailleur hanger was too bent to ride (I've since realigned), so I'm guessing that's what put it out of service. It came to me with mismatched 700c wheels (hard anodized, with quite awful wear patterns), but according to the old catalog, it originally came with 27" wheels with Helicomatic hubs.

drewfio

Update: I removed the rust from both spots, and made an attempt at a paint touch up with the nail polish others here recommended. Not a perfect match, and my touch up skills leave a lot to be desired, but both of these spot are fairly invisible once chainrings and tires are blocking their view.

Eager to ride, I've also started to hang some parts on it. Nothing was bought for this specific build so far (besides nail polish ), just pieced together from what I have. So we'll see how it goes, and the parts can go back in my closet if the frame gives up.

Bad Lag

It's a nice looking bike, make no mistake about that.

The outside of the drive side chain stay has been almost worn thru by a misadjusted pair of chainwheels.

zandoval 

Good job... But are you still wondering?

My plan would have been to closely inspect the inside of the chain stay via the bottom bracket. If no rust on the inside I then would have aggressively checked the out side. Do note that I think nothing of preserving original paint jobs when it comes to checking the integrity of steel. Rust is a very real BUGGER! Of course you now this. I would have chemically stripped both chain stays then done another inspection after sanding the hell out of um. Then it would have been rattle can primer and paint to finish. Most likely in Black Enamel.

I have successfully filled holes with Tig welding and Copper brazing on Rynolds 501 steel.

As to the injuries that precipitated this damage? I saw very similar almost exactly the same damage on a guy limping his mountain bike home from a ride. His chain ring was broken with its arm bent. The wheel was tacoed just enough to scrape the left chain stay at each revolution. Of course he did not have any rust... Yet...

drewfio

You are very thorough. What if you found some rust inside the chain stay?

zandoval 

Now that's a real bugger! My only experience with that type of rust was in Galveston Texas. I was going to UTMB and several students from out of state brought thier bikes over and stored them on back porches and balconies. Galveston salt water took its toll in just a few months. The finish on the outside of the bikes looked normal with just the expected rust on a few components, however, one bike I saw split at the top of the seat post and another the joint at the top of the forks during ridding. I had never seen rust like that. It was like a cancer spreading throughout the frame internally. After talking to some locals who ran a bike rental shop on the seawall they advised a simple fix for any newly arrived bike in Galveston. It was to take a 50:50 mix of Linseed oil and Denatured Alcohol and flush the bike's frame internally. They said they were able to get at least five years of sea side tourist use out of thier steel rental bikes and considered that good. I have a 70s UO-8 I found over there. The frame had been treated as described. Externally its steel is pitted and some of the braze-ons are gone. But internally the frame is solid. I was very surprised as the bike had been stored out side under a porch just five blocks from the waves. It is still going strong here in Central Texas.

As to the OP: If I found more than surface rust inside the chain stays I would take the frame to a Frame Maker for further evaluation.

Further Note: I don't think I have ever seen a sudden catastrophic failure of a chain stay except for maybe mountain bikers doing things they probably shouldn't. I am certain that if your chain stay starts to fail you will get a fair warning before hand. Bike looks great! Ride on stud...

drewfio

Just following up here. I finished building it up, and I’ve put a few hundred miles on it so far. So far, no issues detected, even riding some pretty rough unpaved roads. I’ll report back in a thousand miles or two if it’s still going.