Broken exhaust mount

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crcfailed
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Broken exhaust mount

Post by crcfailed »

I can't catch a break this spring, it's just one thing after another with this bike. Well this time, it's not the bike's fault, at least.

I was riding down an unfamiliar street last week and there was a... well, "pothole" is not really the right word. It was just a gigantic pit of destroyed pavement, obscured just enough by a steep decline in the street. I had no time to react and hit it going only around 15-20mph, but it really rocked the bike and I don't know how I managed to not go down, or not get a wheel stuck in it or something. I stopped right away and looked over the wheels and didn't see any obvious damage so I went on my way.

This afternoon I went for a ride and a rotted tree branch fell in the road in front of me, blocking the entire right hand lane. The road was busy and it was not safe to swerve into the other lane. I couldn't stop fast enough, so I hit it doing probably something between 30-45 Buddy mph, and the whole bike went airborne. The steering column shook and wobbled when I came down and it's a miracle I didn't get thrown from the bike but I somehow managed to keep it straight and bring it to a shaky stop. For the record, three other motorists slowed down to tell me I dropped my phone, and not a single goddamned one of them stopped or asked if I was okay. I was physically fine, but absolutely shook. The phone landed on the sidewalk, totally unaffected; I keep it in a heavy duty case. A passing pedestrian asked if I was okay and then removed the branch from the road. A police officer stopped and got out of his vehicle for just long enough to see that the branch was taken care of, and then went on his way, and did not seem particularly interested in how it got there or the fact that I had hit it.

The bike seemed ridable, and I took the side streets home so I could more closely inspect whatever I could think to check. The wheels seem straight, the brake is fine... I don't really know what else to look at. After a little bit I went back out just to see if anything else was going to fall apart on me. Rode some backroads to the next town up and then looped back. Sure enough, on my way back I began to hear exhaust popping noises so I knew something was up with the pipe. When I checked, the bottom mounting knuckle had completely cracked and broken off what I believe is the engine block. The top knuckle looks intact, but the bolt is just gone. There were some broken threads on the inside of it. So basically, the entire exhaust pipe was hanging from nothing but the studs at that point. I was able to reinstall the bottom bolt in the top knuckle on the remaining threads (only hand-tight) after brushing out the debris, but I don't really think this is adequate. There is still some slight popping coming from the exhaust and I'm hoping it just needs a new crush gasket, as that one has already been reused once.

I don't really know what to make of this kind of damage though, or what to expect moving forward. At the very least I need to figure out how to better mount the exhaust so it doesn't snap off the remaining knuckle. Maybe I could install a longer bolt and thread a flange nut on the back or something, but it'd still only be hanging there by one bolt. Ideally I wish I could just have the bike looked at professionally, if only I knew of a good mechanic who worked on scooters, and I had the money to throw at this problem.
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DeeDee
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Re: Broken exhaust mount

Post by DeeDee »

Good thing you didn't end up hurt If that were mine I would 1. carefully drill out the threaded hole of the broken tab slightly bigger. 2. take a dremel tool and clean both sides of the broken tab and the adjoining case 3. use JB-Weld (the original slow cure) and glue the broken tab back in place. Be sure to mix the 2 parts thoroughly, apply just enough to put a light film on both surfaces and mate them together. Try and keep the hole and the front and back side clean from epoxy. Let it dry 24 hours, 4. get two big fender washers that are large enough to cover both the broken tab and the engine case. Drill the holes out in the fender washers to the same size you drilled the broken tab. Mix more JB-Weld and epoxy these to both sides of the repair. Get a nut and bolt the right size to fit through your new hole, snug these down to pull your repair tight. Put a fine layer of grease on the bolt, so it will release from the epoxy. Let this cure. 5. remount your exhaust using a nut and bolt going through your new hole. You're trying to spread the stress across the broken tab and the case. Let the whole thing dry 2 or 3 days before you bolt everything down.
Less chit chat, more riding, Buddy 50, 125, 170i, RH50, Yamaha C3
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crcfailed
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Re: Broken exhaust mount

Post by crcfailed »

Thanks a bunch for that, that's super useful, I'm taking notes! I figured a fix might involve JB Weld, so I'm glad you mentioned it before I did. :D
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tenders
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Re: Broken exhaust mount

Post by tenders »

Glad you weren’t hurt! Sounds like a terrible ride that day.

Deedee, assuming the broken stub can be removed, what is the benefit of drilling the hole larger?

On the Dremeling: in my opinion once you start Dremeling the broken surfaces, you lose their perfect mating alignment. I would suggest not doing that, although you absolutely want the JB Weld on both surfaces to stick them back together. Focus instead on cleaning and roughing up the surfaces around the break so the JB Weld has a better substrate to hold on to.

Another possibility is adding extending pieces of fiberglass cloth coated/soaked in additional JB Weld once the original repair gets a little tacky. This isn’t necessarily a high precision process, and the creation of a composite material (epoxy+fiberglass cloth) can be surprisingly strong and is the basis for a lot of structural design and repairs. Having the coated fiberglass overlapping the repair and contacting solid metal an inch or so around the break will strengthen the repair considerably. Note that there is a big difference in the bond strength between layers of JB Weld if the subsequent layers are applied over tacky, as opposed to completely cured, JB Weld.
sc00ter
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Re: Broken exhaust mount

Post by sc00ter »

Glad you didn't go down! That's a heck of a snap! I've dropped many a scooter (and motorcycle) and have only broken one exhaust mount like that on a Honda Helix. Anyways, what Dee Dee said is your best bet. If done correctly it should hold just fine.

If I recall the stator/exhaust mounting points side on the Helix could be replaced without splitting the motor. I recall ordering a new outer case mount and pulling everything off that side of the motor to just replace that part. I think the part you had snap off requires splitting the case to replace, that is a 50cc in your pictures? So do what Dee Dee mentioned to avoid a huge replacement job.
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DeeDee
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Re: Broken exhaust mount

Post by DeeDee »

Deedee, assuming the broken stub can be removed, what is the benefit of drilling the hole larger?
You want to remove the direct stress from that tab. I want the hole drilled larger to pass a bolt through the hole distributing the force amongst the washers, transferring part of it to the case. If you simply thread that bolt back into the glued on tab, it won't be nearly as strong.
Less chit chat, more riding, Buddy 50, 125, 170i, RH50, Yamaha C3
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crcfailed
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Re: Broken exhaust mount

Post by crcfailed »

sc00ter wrote: Mon Apr 15, 2024 1:37 pm I think the part you had snap off requires splitting the case to replace, that is a 50cc in your pictures? So do what Dee Dee mentioned to avoid a huge replacement job.
Yeah, sorry I forgot to mention it is a 50. The whole crank case is $576 on scooter lounge. :shock:

Been busy this week and haven't had time to do much yet but I did pick up some JB Weld to start the repair. As I am looking at it now, where the broken tab mates with the case, there is a fin coming out at an angle, so there's not really a flush surface to even try and mate a washer to try and distribute the weight. The front of the tab also has a protrusion that would need to be cut off and machined down I guess to make it flush with the case.

It seems like i might need to look more into the fiberglass cloth idea. Someone else pointed out to me that JB sells a wrap type of thing specifically for exhaust repair, but I think it is more for patching the exhaust line rather than structural damage such as this.

I'll have to look at it more later, in the meantime I'm just riding around like a grandma and it's killing me. :cry:
sc00ter
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Re: Broken exhaust mount

Post by sc00ter »

It's a long shot but you might want to look into a welding shop for another opinion. You "might" be able to have the broken hanger part reattached/welded BUT:

Note there will be a lot of heat in that area, so it might be easier to pull the motor for safer access. A good weld shop will guide you on the right option. I have a great machine shop in my area and the guy knows his stuff. He builds Ducati race motors for a privateer racing team, and specializes in aluminum welding as well.

The JBWeld should work just fine. If there is a brace piece just grind it off. Grind off a little as possible! Watch for wires and hoses in the grind area.

The fiberglass fix and wrap is not the best solution because of the heat. It might work but I'd personally do it the best way possible instead. You don't want the exhaust to crack next from flexing or something, costing you more money.

Either way you will have to drill the hole larger per DeeDee instructions.

I've done some of these kinds of rig repairs, and im sure ill do them again. Just take your time and don't be embarrassed to ask questions. Posting the pictures does help. "Rigging" works just fine if done right.
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tenders
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Re: Broken exhaust mount

Post by tenders »

Heat is not an issue with the fiberglass solution I mentioned. It is essentially the same as the JB Weld-only approach but with the addition of the fiberglass, making a composite material. The fiberglass cloth is used for hot exhaust wrap and can withstand far more heat. The JB Weld that sticks so well to the metal is the same stuff used to saturate the fiberglass. You use the slowest-possible-setting high temperature epoxy possible to get maximum penetration of the fiberglass.
sc00ter
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Re: Broken exhaust mount

Post by sc00ter »

Weird, never knew or heard that about fiberglass. JBWeld works well but I'd personally have it aluminum welded back on. My friend crashed a Zuma and we never found the broken exhaust tab. We had no choice but to split the case and install a new stator side. Luckily we found a new generic replacement half and it matched up really well, just had to port match the cylinder base back up and make sure the mating surfaces were flat. I recall ScooterTuning.CA had them in stock at one time. The real Yamaha stator side was on a long back-order so we went generic. It was kinda like that Blue Line replacement parts that Scooter Works sells. Good stuff for the money.
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Re: Broken exhaust mount

Post by ohiomoto »

Have it welded or relace the case. Everything else is a band-aid at best.
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tenders
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Re: Broken exhaust mount

Post by tenders »

sc00ter wrote: Sun Apr 21, 2024 4:01 am Weird, never knew or heard that about fiberglass. JBWeld works well but I'd personally have it aluminum welded back on.
Welding > fiberglass/epoxy repair on metal…but composite construction involving a woven material (straw, fiberglass, carbon, etc) and a liquid binder that absorbs into the material and turns solid (mud, polyester, epoxy, etc) is both ancient and cutting-edge.
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