Noisy Trials Bike----help!

[geremacheks]

Making a silencer----QUIET!

Open to any ideas on making a silencer quiet on a two stroke. It's a trials bike, a Beta Techno 99 model. Silencer and pipes are in good shape, but it's way too loud, with firecracker like pops at idle.

I pulled the silencer insert, torched the mung off of it (many of the holes were clogged) and wrapped it loosely with insulation, same stuff that was previously in it. Didn't work--still same irritating loud snaps.

Next I'll try something like Silent Sport packing and do it again--tighter. Should it be tight or loose? And do I need to go deeper into the next chamber to get it quiet?

Anyway I'm in need of some ideas to quiet this thing down.

Thanks.....

 

[geremacheks]

Anybody?

I repacked it twice now, tried both loosely and tightly, to no avail. Still sounds like the fourth of July.

On another board someone reccommended drilling out the holes in the baffle a little so it might absorb the noise better.......that seems to make sense. But what is the negative side of that?

I can stand as far as 12 feet behind the bike and feel the exhaust pulses hitting my clothing hard. Strapping on rubber inner tubes or leather work gloves to the stinger just to see if that will quiet it down, doesn't work much at all. It seems to keep having this straight pipe affect, the silencer packing not absorbing anything. There are no spark arrestors on these bikes, and it seems to need something to create some back pressure to get the silencer working. If I put a gloved thumb over 75% of the stinger opening that seems to help. So, as I said, some back pressure is needed here, I think. Maybe steel wool in the pipe/baffle itself? Or weld some kind of baffle in there?

Anybody got any ideas, or know somebody that is good in making silencers work the way they were designed to work? ----------Thanks.

 

[geremacheks]

Need some help in making a trials bike quiet.

I originally posted the problem in the Forum: Maintenace, Basic Q&A, Bike Repair. Title: Making a silencer----QUIET!

Please do a search, or find it in that forum. Thanks---geremachek

 

[geremacheks]

Thanks for moving these posts around for me--now I just need to get a reply......

 

[wayneg]

It is normal to feel the pulses from 10 to 15 feet away from the back of the bike - these motors run 13:1 compression, so the exhaust is expelled pretty quickly, and if the holes in the baffle are packed then there is a straight path through for the exhaust. Most Betas also make a fairly loud popping noise especially around idle - it also happens on my y2k 200c bike, and is even louder on the 270cc bikes.

I have used the silent sport packing, and found it difficult to get right, especially on the horrible shaped Techno muffler (its much easier on the Rev3 muffler). What I ended up using was a sheet of muffler packing wrapped around the baffle, and then used the silent sport stringy stuff wrapped around that fairly tightly to hold it in place while installing the baffle back into the muffler. Also remember to pack the very end cap of the muffler fairly tightly with packing - otherwise the rest of it will get loose and not muffle properly.

The main reason for the noise is the clogged holes, and if you have cleaned out the end muffler's baffle holes then you are halfway there. I sent you a PM, explaining how to clean out the middle muffler. If you look closely you will see that the middle muffler also has a baffle and packing, and these holes in this baffle can get blocked too. Fortunately the middle muffler uses wire wool as the packing, so you shouldn't need to try and repack it, only clean it out with a solvent.

Good luck

 

[geremacheks]

Wayne to the rescue: :thumb: Appreciate your post and your pm.

I really haven't been around trials bikes much, so when I heard this loud popping and cracking at idle, I was really surprised. I remember reading over and over that trials bikes were quiet and you could ride them just about anywhere without disturbing anyone. Not so with this bike. It's the loudesd bike I have ever had and I'm an old guy and have been riding since I was 18.

Anyway, I figured I could make it quiet with a little cleaning and packing, but so far failed. As I mentioned, the baffle is clean, and I did repack as you suggested: stuffed packing into the end cap, and even made the packing longer where it meets the middle silencer. You are sure right about the silencer's odd shape and difficulty to repack it evenly. Too bad that cap doesn't come off the baffle. That would make it easier to fill the silencer cavity up.

The middle silencer: now that seems to be the problem, alright. (Where's the expansion chamber?) I like your idea of a mineral turpentine solvent flush. That sure is worth a shot. What's the best way to apply it. Take the whole exhaust system off?

Are you pretty sure that the packing in the middle silencer is wire wool? Smart if that how Beta made it since it's so hard to get to the middle silencer.

I do feel know that there is a chance of quieting this thing down. I hate loud bikes. Thanks again for your suggestions.

 

[wayneg]

The baffle on the middle silencer is a formed mesh screen not a straight through pip like the rear one, so repacking it would be a major PITA! When I used the solvent trick, I took the whole middle silencer off and duct taped the end of a grease refill cartridge (used to refill my grease gun!) onto one end and this seemed to seal one end off quite well. I then stood the thing on that end in a small empty bucket and poured the solvent in. Apparently some of the other guys over here use petrol rather than turps, so I guess that would work too.

Another way of getting rid of the excess oil is to have a burn off in the exhaust pipe - such as suggested in the Tech Tips forum on www.trials.co.uk. You can do this by giving the bike a major clean out up a hill until the excess oil in the exhaust catches fire. If you have about 10 full throttle runs up a decent sized hill in third gear you will notice a large amount of smoke coming out the exhaust - this means that the unwanted oil in your exhaust has caught fire or is smoldering. Then if you give the bike another blast up the hill every once in a while to keep the temperature up you will eventually burn the excess oil out of the silencers. This might not be such a good idea if you are riding near any forestry, but works pretty well over here on the grass farmland that we seem to be using every other trial.

I guess the bottom line is that the person who had the bike before you either only used very little throttle on the bike when riding it (so it hasn't been thrashed and abused!), or was using far too much premix. The general rule of thumb for trials bikes is to use a ratio of at least 70:1 for the premix, unless you are riding the bike like a MX bike, and 80:1 is even better for a lower level rider like me - the top riders use 100:1, but they probably change the piston and rings quite a bit more often. Obviously if you are using too much oil then it has to go somewhere - usually straight into your exhaust pipe to goo things up.

 

[geremacheks]

Wayne---thanks, again.

Check my Trials Action post again: 99 Beta: Another noisy Exhaust!

J. L. has some thoughts on the inside of the middle silencer which are a little different than what you said, and see what you think.

If there was any packing material originally in that middle silencer, and if now it has disintegrated,, and with no way to get in there and replace it, would just cleaning the goo out of it make it any quieter?

I realize if there is a baffle or core in there, and I successfully clean the holes out with the solvent, I'll improve the situation; but if originally there was some packing material in there too, that I can't replace, I'll never be able to bring the original silence (if there was any) back.

I sometimes wonder too, if that residue and goo in there, at least on the walls of the silencer, should help to make it even quieter. An empty aluminum can seems like it may be a bit too resonant.

Whatever. I'm still planning on trying solvent to clean it out. But not sure of what expectations of sound levels I should have after the project is done.

 

[wayneg]

The thing is that the wet soggy packing won't allow the gas to flow through it, and it will block any gas from flowing forcing it out the end of the exhaust, so you won't get any noise reduction. Thats my understanding anyway :)