Exhaust mount bolts keep shearing off

Xsolusx · Post by **Xsolusx** » Mon Dec 21, 2015 11:16 pm

5 so far. All shearing off inside the mount then I have to tap those bolts out and redo it. Over the course if 500 miles I have broken 5 of them off. That can't be right.

Any ideas?

avescoots1134 · Post by **avescoots1134** » Tue Dec 22, 2015 1:13 am

Are you using medium strength loctite and a lockwasher?

sc00ter · Post by **sc00ter** » Tue Dec 22, 2015 4:08 am

What exhaust are you running? I have had nothing but problems with Prima exhaust. NCY exhaust are bullet proof, and if its the stock exhaust look for rust breakage. Other things can cause bolts shearing, but lets start at the exhaust.

Xsolusx · Post by **Xsolusx** » Tue Dec 22, 2015 4:42 am

sc00ter wrote:What exhaust are you running? I have had nothing but problems with Prima exhaust. NCY exhaust are bullet proof, and if its the stock exhaust look for rust breakage. Other things can cause bolts shearing, but lets start at the exhaust.

I have an ncy. My prima broke on the mounts themselves, on the NCY the bolts are coming in half lol. I can't even understand why they would? It's not a TON of vibration. I rode home 20 miles with no bolts tonight.

I have not used any loctite because that will make getting out the broken bolts that much harder.

HowHH · Post by **HowHH** » Tue Dec 22, 2015 3:06 pm

Which bolts? the exhaust pipe studs that mount into the engine case (like these: http://www.scooterworks.com/ncy-exhaust ... nlmVofUgmI)? Or do you mean the mounting hanger bolts?

avescoots1134 · Post by **avescoots1134** » Wed Dec 23, 2015 2:32 am

Your problem is that the bolts are vibrating loose then shearing off. You need blue loctite and a lockwasher.

babblefish · Post by **babblefish** » Wed Dec 23, 2015 9:32 am

It might also be helpful to enlarge the mounting holes in the exhaust so there is a bit of clearance around the bolt to allow a small amount of movement.

avescoots1134 · Post by **avescoots1134** » Wed Dec 23, 2015 2:45 pm

babblefish wrote:It might also be helpful to enlarge the mounting holes in the exhaust so there is a bit of clearance around the bolt to allow a small amount of movement.

Noo, lol!

What's happening here from a science standpoint is that the bolts aren't actually holding the exhaust up. The bolt's job is to clamp the muffler against the engine case. When a bolt loosens up it bears the muffler's weight and proceeds to shear right off.

GearsAndSuch · Post by **GearsAndSuch** » Wed Dec 23, 2015 3:56 pm

Second this. The bolts on the engine are for sealing, not support. Sounds like you are missing a rear support. The exhaust pipe should have small bolt or screw about 8 inches back from the exit that holds the weight of the pipe about at the center of mass. Look for a mounting tab on the inboard side of the pipe between the pipe and the bike.

skully93 · Post by **skully93** » Wed Dec 23, 2015 4:02 pm

I've had the same Prima pipe on for 10k miles with no problems, but I don't do it myself, so...

it does seem to me like it's not getting supported.

sc00ter · Post by **sc00ter** » Wed Dec 23, 2015 5:05 pm

Check all the bolts that hold the muffler on the rear wheel side. I have had damaged bolts on that side affect the 2 that hold the muffler to the cylinder. That bracket, if damaged, is cheap to replace. I have never had to use locktite on any of the exhaust bolts on the Buddy 125's, so I suspect you have a stripped side bolt that may not be so obvious causing excess vibration and stress on the 2 cylinder head bolts. Now, while very rare, if the problems started after a new exhaust was installed-the exhaust could not have been welded up correct/squared. Had that happen with a Tecnigas for my old Zuma, luckily it was replaced after some complaining.

scootERIK · Post by **scootERIK** » Wed Dec 23, 2015 5:21 pm

Is it the same bolt every time? And if so which one is it?

Also, is the bracket that holds the muffler on mounted correctly?

If you have time take some pictures maybe someone will see a problem.

scootERIK wrote:In the picture the red arrows point to the bolts and nuts that hold the exhaust on, the yellow is for the bolt that holds the fender down.

One last thing you could try is to loosen all the bolts and nuts up 1-2 turns then give the exhaust a little shake to help it settle into place, then starting with the two nuts that hold the pipe to the engine(head) re-tighten everything.

Xsolusx · Post by **Xsolusx** » Wed Dec 23, 2015 6:16 pm

avescoots1134 wrote:
babblefish wrote:It might also be helpful to enlarge the mounting holes in the exhaust so there is a bit of clearance around the bolt to allow a small amount of movement.
Noo, lol!

What's happening here from a science standpoint is that the bolts aren't actually holding the exhaust up. The bolt's job is to clamp the muffler against the engine case. When a bolt loosens up it bears the muffler's weight and proceeds to shear right off.

That doesn't seem to be the problem. I actually did wonder about that so the last time I out longer bolts in so I could see them come out the back. The bolt ends are still there, same amount sticking out.

Xsolusx · Post by **Xsolusx** » Wed Dec 23, 2015 6:17 pm

GearsAndSuch wrote:Second this. The bolts on the engine are for sealing, not support. Sounds like you are missing a rear support. The exhaust pipe should have small bolt or screw about 8 inches back from the exit that holds the weight of the pipe about at the center of mass. Look for a mounting tab on the inboard side of the pipe between the pipe and the bike.

Not sure what you mean?

Xsolusx · Post by **Xsolusx** » Wed Dec 23, 2015 6:22 pm

scootERIK wrote:Is it the same bolt every time? And if so which one is it?

Also, is the bracket that holds the muffler on mounted correctly?

If you have time take some pictures maybe someone will see a problem.

scootERIK wrote:In the picture the red arrows point to the bolts and nuts that hold the exhaust on, the yellow is for the bolt that holds the fender down.

One last thing you could try is to loosen all the bolts and nuts up 1-2 turns then give the exhaust a little shake to help it settle into place, then starting with the two nuts that hold the pipe to the engine(head) re-tighten everything.

It's both bolts top and bottom. Bracket is on correctly, all holes line up. That's what makes it odd to me that it even happens because it all seems to fit so clean.

GregsBuddy · Post by **GregsBuddy** » Wed Dec 23, 2015 6:37 pm

This all sounds a bit fishy. Only one scoot' is having this problem.
One way to be certain that they don't loosen is to safety wire them.
It also sounds like the threads are damaged and no longer working correctly. When bolts back out they often damage the threads. The damage can be enough to not hold again.
Helicoils...

Xsolusx · Post by **Xsolusx** » Wed Dec 23, 2015 6:51 pm

Has anyone used a traditional oval exhaust mount from a motorcycle?