Ways to Fix a Rusted Out Pipe

[cjpayne]

I started this thread due to the outrageous climbing prices of the NOS K1-later exhaust pipes. If you have a way to fix these pipes, PLEASE post here whether it's a cheap obvious fix or a time/money consuming project.
Here is a picture of the most common problem. The asbestos clamp grommet that causes these things to rust in to two pieces.

 

[cjpayne]

Well, here is my first attempt. Went to the local cycle shop and scrounged around in the scrap pile. Found this piece of exhaust off of who knows what, but it fits for what I need it for. Not tight, but not too big. Slipped over the OEM exhaust easily.



Cut off a piece and cut a line down the middle. I probably should have used a thinner cutting wheel, but I have plenty of pipe to redo if I have too.



Tried it out and clamped on with a temporary hose clamp. I know now that I should have used a thinner cutting blade, but you get the idea. Just need to disassemble, blast, get positioned, clamp down again, tacked, .....blah, blah, blah. Whoohoo!!!(homer simpson). There was still enough of this pipe left that it actually fit back into its original position. Got lucky on that one, but will later make sure on the bike before its welded up.

 

[69ST]

Unless you want to expand the discussion beyond the simple & practical, this is one of two methods. The second would require a second cut, splitting the patch collar into two hemispherical shells..to place over an intact (i.e. not broken into two pieces) headpipe.

This one looks to be about double the minimum length needed to repair the break, a consideration if an invisible, or as close to that as possible, matters to you. I'd sandblast the headpipe & the patch, before welding. The seam weld adds strength, so it could be argued that the split collar method is better. That weld can be dressed-down flush. The end weld beads can only be dressed-down flush with the patch, which leaves them visible at the very ends.

That's about all there is to this, seriously, unless one wants to consider something really elaborate...which may not be practical.

 

[motoman287]

I've bought used bikes with a piece of beer can wired around the hole/break in the pipe. I do NOT advocate that as an adequate method, lol.

 

[cjpayne]

Unless you want to expand the discussion beyond the simple & practical, this is one of two methods. The second would require a second cut, splitting the patch collar into two hemispherical shells..to place over an intact (i.e. not broken into two pieces) headpipe.

This one looks to be about double the minimum length needed to repair the break, a consideration if an invisible, or as close to that as possible, matters to you. I'd sandblast the headpipe & the patch, before welding. The seam weld adds strength, so it could be argued that the split collar method is better. That weld can be dressed-down flush. The end weld beads can only be dressed-down flush with the patch, which leaves them visible at the very ends.

That's about all there is to this, seriously, unless one wants to consider something really elaborate...which may not be practical.

Yeah, this patch could at least be half this size, but this was my first time and wanted plenty of length to work with, just in case the OEM pipe itself was too thin to take the clamp pressure. It appears now that the pipe is VERY thin in the old grommet area, but the rest is still solid.
I would, however, still like to see any other repairs done out there in CT land. Doesn't matter how simple, ugly, or beautifully elaborate.

 

[cjpayne]

I've bought used bikes with a piece of beer can wired around the hole/break in the pipe. I do NOT advocate that as an adequate method, lol.

Lol. My buddies '71K0 had a piece of rubber hose and two hose clamps that obviously didn't last very long.

 

[kirrbby]

I love brainstorming!

I have lots of ideas for different types of repairs, and at least 2 pipes that need this repair...will make for good show and tell, and hopefully spark some more ideas.

 

[hrc200x]

Here is a 78 and K0 repaired pipe using a miller wire feed welder. The K0 I used a bent ct70 handle bar (proof to never throw away anything ever) and cut a piece out. The 78 was spliced using a piece of bicycle handle bar. Remove all heat shields, Cut Honda pipe back far enough to get into good metal, chamfer the ends of the Honda pipe to get good steel to weld to. Bolt head pipe and muffler section to bike, leave both loose and try to eye ball head pipe to muffler alignment and tighten header/muffler. Measure distance of piece needed for splice in a few different spots to get the longest length. Cut piece out of pipe, test fit, if its close with no big gaps chamfer ends and tack weld into place, top, bottom, and outside. Take pipe off and weld up. K0 pipes are pretty crude because of not being able to rechrome easy, but the painted ones turn out pretty good. If I recall 7/8 inch handle bar is really close, a little bigger than the Ct pipe, when seen up close it appears to have a fat spot after repair is complete and painted but not too bad.

I refuse to spend money on a new fiber gasket just to have it rust out again, so I will run the muffler guard with no front clamp.

 

[ArcticMinibike]

Here's an example of what a 16 year old kid (me) with access to high school shop class did in the early 80's. Heavy gauge galvanized sheet metal, a roller, and a ton of pop rivets. Pop rivets and zip ties, is there anything they can't do?

It actually worked pretty well but with all those rivets, probably a little restrictive on the flow. I think I rolled it as close as I could, with some overlap, and used a hose clamp to squeeze it tight while I drilled and riveted. When I took that pipe off to replace it last fall, it was solid as a rock.

These days I think I'd just do the split thin wall tubing thing and MIG it. Not something I had access to back in 1983.

 

[69ST]

I love brainstorming!

I have lots of ideas for different types of repairs, and at least 2 pipes that need this repair...will make for good show and tell, and hopefully spark some more ideas.

In no particular sequence:

• Overlapping patch...split tubing, since it can be clamped tightly for welding. This is best for a pipe that's still in one piece, as it preserves alignment and results in virtually zero flow restriction. It's not the prettiest but, possibly the strongest.
• Internal patch...a length of tubing with the same OD as the headpipe and enough wall thickness to create spigot ends that tightly fit inside the headpipe. Make the spigot ends long enough to add structural support, weld the ends, then dress the welds down level with the headpipe OD. You'll lose 1-2mm of ID which may restrict flow a little. Tapering the end that faces upstream (toward the port) will minimize turbulence. This type of repair combines strength and outward invisibility. The biggest downside is all of the work involved, starting with sourcing the proper sized tubing and lathe work, which most will have to farm out. Best guess, a machine shop will want at least $50 to make one.
• New section of tubing with the same dimensions as the headpipe, butt-welded. Simple, inexpensive and invisible. It's also not the easiest thing to properly execute. There's a high probability of the weld bead protruding into the pipe. The amount of actual restriction is impossible to predict. I expect that there'd be less reduction in cross-sectional area than with a stepped-tube repair but, there'd be more turbulence. Flow concerns are probably more theoretical than actual, especially with a bone-stocker. However, the longterm strength of the weld joints is a real concern. This is thin-wall tubing, with lots of thermal expansion.
• New headpipe...can't beat all-new, solid, metal. And, it'd be relatively easy to hide the weld joint, at the muffler. The downsides are practical - cost (this won't come cheap) and the difficulty in exactly matching the configuration of the original.
• Modify a K0 muffler...Aside from the chrome plating, the only real difference between a K0 muffler and the K1 is the main heatshield mounting configuration.(Honda changed the rear hanger configuration with the K4, eliminating the stud/nut spacer) Adding K1-later mounts to a K0 muffler is a lot easier than the reverse. This gives you a perfect fit, and the OEM manufacturing detail, including the compliance wording. Successfully painting chrome isn't the easiest task going but it's not the most difficult, either. Best method would be having a plating shop chrome strip it and you might be able to find a shop willing to do this with an unused pipe. Sandblasting it would probably be more practical and, in some ways, as good, or better...no acid solution to worry about. Etching primer isn't really an option, since the muffler will likely exceed 300F. K1 headpipe shields will cover the headpipe, so only the muffler needs VHT. For someone with a little basic welding capability, this seems a relatively painless alternative and less than half the cost of an NOS K1-later exhaust.

Something that hasn't been mentioned in this thread...condition of the muffler. Honda used some really thin sheetmetal for these. More times than not, it seems, a rotted headpipe is accompanied by a muffler with rust holes along the bottom seam. Those are a sonofabitch to weld. Silver brazing works but, silver brazing rod has gotten pricey. There are a lot of repairable exhausts out there. However, many, if not most, of them are likely to be good enough for riders, not purist restorations. Making the repairs invisible is a usually a big project.

 

[kirrbby]

Good stuff.

With the internal patch. How about making it out of 2 separate pieces of thin walled pipe. A longer piece to fit inside and a short piece of the correct od cut to fit. Might even be able to use 2 pieces of the correct od pipe, but split the longer/inner piece so it can be made to fit inside.
Once it's all welded in, with good penetration, the inner piece wouldn't move.

 

[kirrbby]

With the new headpipe. It seems the hard part is the bottom loop. It must be tough to bend pipe to such a small radius?? But the header only has 2 bends. If they were made in 2 separate pieces of pipe, then joined in a jig, seems like it would be easier to get it right..? Rather than having to hit it right, out of one piece.?

 

[69ST]

Good stuff.

With the internal patch. How about making it out of 2 separate pieces of thin walled pipe. A longer piece to fit inside and a short piece of the correct od cut to fit. Might even be able to use 2 pieces of the correct od pipe, but split the longer/inner piece so it can be made to fit inside.
Once it's all welded in, with good penetration, the inner piece wouldn't move.

The potential Achilles Heel with multiple layers is that oxidation might occur between the inner & outer shells. Dunno if it'd be applicable here, I've seen it happen with automotive dual-wall pipes. It's certainly be less involved than machining a piece.

With the new headpipe. It seems the hard part is the bottom loop. It must be tough to bend pipe to such a small radius?? But the header only has 2 bends. If they were made in 2 separate pieces of pipe, then joined in a jig, seems like it would be easier to get it right..? Rather than having to hit it right, out of one piece.?

You'd be dealing with butt joints. Not only does that eliminate the advantage of a new headpipe, there's a big disadvantage. The closer to the port, the higher the peak temperature...and with it greater stress from heat-cycling.

 

[kirrbby]

You'd be dealing with butt joints. Not only does that eliminate the advantage of a new headpipe, there's a big disadvantage. The closer to the port, the higher the peak temperature...and with it greater stress from heat-cycling.

Aww...That's just stinky! I guess now I'm back to building a bending jig...out of wood of course. Lol

 

[69ST]

Aww...That's just stinky! I guess now I'm back to building a bending jig...out of wood of course. Lol

Stinky butt joints?! :31::19:

 

[Z50nut]

Here is a 78 and K0 repaired pipe using a miller wire feed welder. The K0 I used a bent ct70 handle bar (proof to never throw away anything ever) and cut a piece out. The 78 was spliced using a piece of bicycle handle bar. Remove all heat shields, Cut Honda pipe back far enough to get into good metal, chamfer the ends of the Honda pipe to get good steel to weld to. Bolt head pipe and muffler section to bike, leave both loose and try to eye ball head pipe to muffler alignment and tighten header/muffler. Measure distance of piece needed for splice in a few different spots to get the longest length. Cut piece out of pipe, test fit, if its close with no big gaps chamfer ends and tack weld into place, top, bottom, and outside. Take pipe off and weld up. K0 pipes are pretty crude because of not being able to rechrome easy, but the painted ones turn out pretty good. If I recall 7/8 inch handle bar is really close, a little bigger than the Ct pipe, when seen up close it appears to have a fat spot after repair is complete and painted but not too bad.

I refuse to spend money on a new fiber gasket just to have it rust out again, so I will run the muffler guard with no front clamp.

I had the same concern about adding that oem gasket to a new pipe. Old CT recommended motorcycle header heat wrap which I used instead.

 

[69ST]

I had the same concern about adding that oem gasket to a new pipe. Old CT recommended motorcycle header heat wrap which I used instead.

That has to be better than the OEM packing.

Best I've found is what's used with Chinese knockoff K1-later style mufflers. Just don't know which vendor(s) sell them...Tbolt, Trailbuddy?

 

[fatcaaat]

I recently fixed one and was very happy with the result. First, I cut the cancer completely out which left me with a pipe about 1/2" shorter than stock. I then fashioned an overlapping OD fix made with .0625 wall thickness only an inch long. I put them together, welded, and voila. Since it was only an inch long, you don't even see it with the heat shield on. Instead of the heat grommet, I just put it together without the grommet and tightened up so it wouldn't vibrate. Done.

If you are a really good welder, you can actually butt weld a piece in there and then grind them down and no one would ever know. Just make sure you give a good bevel to all four surfaces. I have fabbed my own exhaust up and use this technique when necessary

 

[b52bombardier1]

While a MIG, TIG or standard arc weld repair is perfectly suitable here for our older points equipped bikes, I would not do this on a later model bike with a CDI ignition. Arc welding generates high voltage surges all over the bike and at best, I think it would be safest to completely remove the CDI module (not merely disconnect) before welding on anything with delicate electronics.

At least this is how I've been taught though I have never had to worry about this on anything I have ever welded.

Rick

 

[cjpayne]

I went ahead and kept the length of the patch because the pipe was thin in this area. Luckily my neighbor has a wire feed welder. I ground the welds down and then used header paint. It isn't the prettiest patch, but it was my first time doing this.lol