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

[AlphaGeek]

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.

-AG

 

[Mountainman]

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.
-AG

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

 

[AlphaGeek]

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.

-AG

 

[Happy Valley]

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 such....in 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.

 

[kerf]

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.

 

[AlphaGeek]

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.

-AG

 

[kawasaki999]

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

 

[AlphaGeek]

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

-AG

 

[kawasaki999]

No reason, both will work.

 

[heathyoung]

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