Things what don't work: silicone 90-deg coupler to reduce exhaust noise

Discussion in 'Rack Mounted Engines' started by AlphaGeek, Oct 16, 2008.

  1. AlphaGeek

    AlphaGeek Member

    I believe strongly that sharing failures is *at least* as useful as sharing successes. Here is the first of probably many interesting failures I expect I'll be sharing with the community.

    Equipment: GEBE kit with Tanaka 33cc on Giant MTB; at time of this experiment motor was 100% stock and mounted in standard position (lower bracket oriented perpendicular to ground, cylinder axis pointed forward)

    Having seen various suggestions regarding a reduction in perceived exhaust noise to be had by mounting a 90-degree redirector tip over the exhaust port, I decided to give it a shot. The metal-joint solutions (i.e. copper elbow joint) I read about here were either too permanent (welded) or failed to stay on (soldered) so I set that option aside for now.

    I haven't located a good high-temp silicone elbow joint online for anything approaching reasonable prices. Standard silicone is rated to 350F and can actually tolerate 400-425F, but two-stroke exhaust is considerably hotter than that. Fast forward to me in the local hobby store buying an off-the-shelf Ofna silicone elbow joint, which the clerk assured me (heh) that was suitable as an exhaust coupling.

    The joint came with two small white zip-ties, which I set aside in favor of a beefier black zip-tie. Install joint with black zip-tie, take a 1-mile test run... hmm, something smells like melting. Clipped off zip tie, pulled off elbow joint, inspected, reinstalled with galvanized wire twisted on to secure joint in place of zip tie.

    The silicone elbow joint melted and fell off around halfway through my commute the next morning. (sigh)

    Lesson learned: hobby-shop grade Ofna silicone elbow joints are NOT up to the task of redirecting the exhaust from a Tanaka two-stroke.

    I probably won't try any more experiments on the stock exhaust, as I have a performance pack including tuned pipe on order. However, if I were going to try again, I would drill and tap a hole in a 90-degree stainless steel elbow joint from McMaster-Carr and attach it with a set screw and high-temp thread-lock.

    Hope this helps someone avoid wasting $5.75 and valuable time repeating this experiment.


  2. Mountainman

    Mountainman Active Member

    now - come on - you should have already known that

    after all -- YOU ARE FROM SILICON VALLEY !!!

    just having fun -- always remember to

    ride that thing
  3. AlphaGeek

    AlphaGeek Member

    I think you're making the usual mistake of confusing siliCONE valley (down near LA, where they film all the adult movies) with siliCON valley (where we don't make that much actual silicon these days, since the chips are actually manufactured in other places, but anyway...). :)

    On the upside, geeky pursuits like buzzbikes are tolerated or even accepted as part of the local culture.

  4. Happy Valley

    Happy Valley Active Member

    Is there a high temp silicon tubing that will hold up?

    Exhaust temps are pretty hot. To add to the list of failures for exhaust: JB Weld. I know I've seen it asked if JB Weld would be good for fixing exhaust leaks and my experience, no. It's great stuff for many applications and states it's good up to 600 degrees.

    I made a silencer, a design off of a scooter site, that was mechanically made with a through bolt and stainless worm clamps all except for an internal baffle that was hard to get to where is was suggested to use JB Weld to secure it. It worked fine for about 2-3 hours of running time before the epoxy crystalized into crumbs.

    Still looking for a 2stroke silencer that won't rob too much power.
  5. kerf

    kerf Guest

    Soft solder won't work but silver solder will (1270 deg), copper phosphorus (16-1700 deg) rods work better. Mapp will do silver but you may need O2 / Mapp for the copper.
  6. AlphaGeek

    AlphaGeek Member

    Yeah, 2-stroke exhaust is pretty darn hot. My infrared thermometer reads up to ~500F degrees, and it was giving out-of-range errors every time I pointed it directly into the tailpipe while the motor was running at idle after a warm-up cruise. I've seen estimates of 2-stroke EGT (exhaust gas temp) that put peak temp at >900F.

    I have seen listings for silicone-based tubing which is rated at fairly high temps, but nothing exceeding 500F. The other problem is that the 500F stuff usually comes in 1.5-inch and larger sizes, nothing close to the small sizes you'd want for our hobby.

    Checked with a friend of mine who's a materials guru. He says that the material of choice in this case is T-304 stainless steel using welded butt joints. He did allow as how you might be able to use stainless-steel conduit as an acceptable substitute for the tubing purpose-made for building exhaust systems. The challenge there is that you'll need either a metallic gasket or a welded joint to keep things gas-tight -- "half-inch" stainless EMT conduit is actually 0.62in inside diameter.

    Hope this helps.

  7. kawasaki999

    kawasaki999 Member

    Silicon tubing from works, I use regular jb weld to secure. Dont use the 4 minute kwick jb weld.

    Attached Files:

  8. AlphaGeek

    AlphaGeek Member

    Good tip. Any reason you went with the clear tube instead of the reinforced variety?

  9. kawasaki999

    kawasaki999 Member

    No reason, both will work.
  10. heathyoung

    heathyoung Member

    You can do both silver solder and bronze brazing with a MAPP set - I do it quite often...
  11. Hive

    Hive Guest

    Search First

    If you had used the search engine, you would have found a lot on failed and functional exhaust devices that would have save some time etc.
    Last edited by a moderator: Oct 21, 2008
  12. AlphaGeek

    AlphaGeek Member

    Hey, that's a great idea. Thanks for pointing that out.


    Different online communities have different cultures. One of the things I like the least about this one is the tendency to assume that people with an obviously high clue level (ie me) don't know enough to use basic tools like search.

  13. Hive

    Hive Guest


    I did not mean to appear to be rude; if it seemed so, I offer a mea culpa.

    At the time, I thought the above comments seemed to be somewhat reflective of threads from past muffler histories.
  14. AlphaGeek

    AlphaGeek Member

    I'm also sorry that I got irritated. I probably should have stated explicitly in my opening post on this thread that I got the idea for the 90-degree silicone elbow from reading a bunch of older threads regarding exhaust hacks.

    Besides, the probability of a thread sounding like a repeat of twenty other threads on the same topic approaches 100% after you've been a member of any online community for any significant length of time. :) I've learned that it's important to keep a couple of things in mind:
    * there's value in re-raising a given topic from time to time, as many people don't read past the current page of thread topics (or use search)
    * even on topics considered discussed to death, there's value in trying a new approach and/or using a part/product no one has tried before

    I actually appreciate responses that say "This exact thing has been tried before, here's the link to the thread" because I might learn something interesting from the person who replies with "and you might try this other thing that *does* work". After all, the point of a community like this is to share knowledge and move forward the state of the art.

  15. Mountainman

    Mountainman Active Member

    yes - I have been known to do the same

    yes - I have been known to do the same
    I just do not use search as much as I should
    I also do agree with your comments made AlphaGeek
    a re-post of a similar thread -- does no harm

    as the young kids say these days -- it's all good -- when we

    ride that thing
  16. Hive

    Hive Guest

    Repeat Threads

    I agree, without reservation. (Hegel rules...thesis, antithesis, and hopefully, synthesis!

    Being one of the twice-failed and now as a pendant, as in - something secondary or supplementary being one of the muffler Muppets has left me scarred.
    Last edited by a moderator: Oct 22, 2008
  17. loquin

    loquin Active Member

    The silicone tubing from Dave's Motors lasted for about 2 weeks before it crumbled on my Mistubishi.
  18. AlphaGeek

    AlphaGeek Member


    That's consistent with all the specs I've seen for silicone tubing, of many varieties. There is no silicone tubing available as common stock which can tolerate the high exhaust gas temps (EGT) from these motors, especially the two strokes -- and that goes double for those being run at/near redline for extended periods of time.

    Single-cylinder, small-displacement motors have EGTs in the 900-1200F range when running at full speed. Two-strokes running at full speed (i.e. near their RPM limit) for extended periods under load will put out exhaust in the 1100-1200F range.

    The absolute best silicone tubing I've found, which is a aramid/silicone composite tubing for race applications, is only good to ~600F.

    That said, I'm sure that there are plenty of folks who run their bike motors at part-throttle under light workloads and have had success with using conventional silicone tubing for exhaust ducting. Unfortunately, I have difficulty grasping the concept of cruising at less than WOT :) so my motor tends to probe the upper bounds of the temperature range on every ride. In retrospect I probably should not have been surprised when that silicone elbow melted and fell off. Heh.

  19. machiasmort

    machiasmort Active Member

    First, I realize this post is for rack mount! Just my 2cents! I stuffed the inside of my ht exaust with steel wool (loosely). At least 30% quieter now. Every little bit helps.

    Can you get a die and thread the O.D. of the pipe to useable size thread?
    How about a brass compression fitting on the tube 90 degree into a thread fitting?
    Last edited: Oct 24, 2008
  20. kerf

    kerf Guest

    Mixture has a major impact on exhaust temp. As you lean out, temp increases. I run my 460 on the rich side of normal, get about 500 miles off the three inch piece of silicone connecting my primary and secondary mufflers.