A while back, I noticed the two nuts holding the flange on my front exhaust pipe were missing. The flange was just dangling there. I got a couple nuts and secured it back on. For the last few hundred miles, I get a little popping noise from the exhaust (like decel pop, but my bike has never done that before). I thought maybe the gasket was compromised when the flange came loose, so I set about replacing that.
One busted knuckle and a broken 1/2" drive bit later, I got the new gasket installed. In the process, I think I figured out why I'm getting the popping noise (spoiler: it probably wasn't the exhaust gasket). However, I'm not sure if I got the flange and retaining ring installed correctly. That retaining ring was tricky for me; it looked like the remnants of the old one were rusted to the inside of the flange. I did get most of that crud out and the new ring seated into the flange. It doesn't fit over that lip on the top of the exhaust pipe too well, so I actually slid it up the pipe from the bottom, which is where my mistake may have been (I just wasn't sure how to keep it seated in the flange while I positioned the pipe and put the nuts on—definitely one of those "where is my third hand" moments). I didn't totally trash the studs of the flange bolts, but I think I stripped them slightly since those nuts don't finger-tighten well now (but did before). There is also some visible space between the cylinder head and flange (see picture below; you also may notice a missing bolt from a stabilizer bracket, which I think is allowing air flow and causing the popping noise). Is this too much space?
I have not taken it out for a test ride yet, but upon starting it sounded okay and I don't feel air coming out anywhere except the end of the pipe. There were some puffs of white smoke from near the exhaust port, which I'm hoping is normal for a new gasket and/or some moisture burn off (it was humid while I had everything apart). Any thoughts on that? I may update this later after I get it out for a ride (had to get the '88 moving: it's been too long and I just put on a new rear tire and flushed the rear brake on that).
There are two types of exhaust gaskets...Flat and tapered. Depending on what exhaust you have will determine which type you need to use. Typically stock header is a tapered gasket and aftermarket will use a flat one...not written in stone but typical. It looks like you got it about as tight as possible...
So after a short ride, everything seems okay and the popping noise is gone. My photo doesn't show the true width of the gap between flange and cylinder (it's larger), but comparing it to the rear, it looks the same.
I believe that when the flange came loose a few weeks back, the pipe likely dislodged from the gasket. This allowed air to get in or out when it's not supposed to, which caused the popping noise during deceleration with the throttle closed.
And yes, eighteight, in the course of this job I realized a bolt has gone missing from my top front stabilizer bracket (I think that's what the manual calls it). I thought that may be the source of bad airflow, but apparently not. Still need to replace it, obviously. Newer sportsters may not shake like the originals, but still enough that bolts go missing off my bike from time to time! (I'll never forget that time on a gravel road and I heard a weird rattle, only to look down and see my front caliper hanging by a single loosely connected bolt...)
09-06-2021 | 02:53 PM
Post-replacement of exhaust gasket
