15 replies to this topic

[cradley-heathen]

as mentioned in another thread i have just bought a trials bike, but its just mental loud! i mean if you have ever run your mini with no exhaust, its about like that!

 

so.... who knows anything about 2 stroke exhausts?

 

i have had the exhaust off, and re-sealed a few obvious leaks at the joins. with the silencer off i cant see right down the middle so its not a straight through (i have had a look at a couple of spare ones my mate had and they were all straight throughs) the rear silencer is roughly 20mm at the entrance and the exit.

 

i have no problem with making a silencer from scratch if i need to, but i could use some advice on the design.

 

would a smaller bore make it quieter without strangling the engine?

 

is there such a thing as a quiet road going 2 stroke bike? (not scooters, i know they can be very quiet in standard trim)

 

could i pinch a silencer from a 4 stroke?

 

help! im sure some of you on here have had experience with bikes!

[Carlos W]

Is there any wadding in it?

I've heard of people using fibreglass insulation around the pipe that runs through the end can!

[Alex_B]

Be careful making a new exhaust, the size and design is much more important on a two-stroke engine than four-stroke, I dont however know enough about them to advise im afraid

[Sheikh Pip]

I'm with Carlos, repack with new wadding, it's very cheap to buy, maybe Cradley Kawasaki will sell it! If not I've got some in the garage you can have, I'm often in Colley Gate, so not far from you...

[cradley-heathen]

i have got to take the end can apart tomorrow and have a look inside it. however (and i know this isnt very technical) but if you tap the box, it does sound like its full, it doesnt sound like an empty tin can.

 

Sheikh Pip, i dont know if they do this kind of thing or not, but there is a place called "moto mark racing" not far from me too, cradley kawasaki is just up the road from me, ill have to try them for some wadding.

[mm man]

Does your exhaust have a rear can/ muffler on it ? If it comes apart you can wrap / (pack tightly) rock wool around the centre pipe (baffle )that will help a lot .
Two stroke engines rely a lot on the exhausts for performance so just bolting anything on can have a negative affect if the back pressure and gas flow inside the exhaust is incorrect .

[cradley-heathen]

the rear can does come appart, i just need to drill the rivets out tomorrow and look whats inside it.

 

i thought the can that is on it was something the previous owner had fitted, but from pics it seems that it is infact the original one. i have never seen a trial bike so loud though, they are only meant for pottering about on!

[Mini Manannán]

We make two stroke expansion chambers occasionally.  There is a lot to it, many, many calculations for inverse and divergent cones to be figured out using all that sin, cosin and tan you thought you'd never use after school

  Check the packing first as suggested, it's probably knackered so repack it.  Being a trials bike - a relatively low state of tune - a four-stroke silencer might not affect it too much unless you're going in for some competion

Edited by Mini Manannán, 13 April 2014 - 11:34 AM.

[cradley-heathen]

only just noticed my typo in the title, dammit!

 

anyway, i took the end can apart today and it is still full of fibre. my friends have all checked it out and they advised re-packing it and trying it then. i have however had a go at making a new one from scratch.

 

its about an inch or so longer than the old one, but it has a larger outer diameter so i can get more wadding inside it. need to get some perforated tube and wadding tomorrow to finish it off.

[meathead]

Take off all the old wadding, it will be oily and horrible. Use a blow lamp to burn off all the oil and gunk from the baffle. re-wrap new wadding around the baffle as tightly as you can get it. Stick the can back together use clear silicon on the joints.

new pop rivets. job done.

The bike will be much quieter and the bottom end grunt will be stronger.

[Tamworthbay]

Title sorted for you mate. As for the exhaust, just revel in the joys of two stroke ownership!

[cradley-heathen]

cheers mate! i just hope my homemade can will knock a few decibels off! i'll get some pics up tomorrow, were off on tuesday for some much needed practice!

[cradley-heathen]

as promised (if anyone is interested?) a few pics of my trials bike, and my homemade exhaust. its a Scorpa 250cc, from '99.

 

my first go at vinyl wrapping! im not into the fake carbon fibre stuff, but there is a local place that gave me some off cuts. the bits i did were all discoloured and looked rubbish so needed something doing with them. i quite like it now. i need a new front mudguard now to replace this cracked one.

 

my homemade silencer. when you look at it from the back its a kinda eccentric D-shape. its almost twice the width of the other one, and a couple of inches longer, it holds about 5 times the amount of wadding that the old one held, and i can confirm not only is it no louder than a lawn mower, it also seems to run better too. ok it does look homemade, but for a few hours work, its sorted the bike out and didnt cost a penny!

Edited by cradley-heathen, 16 April 2014 - 09:25 PM.

[Mini Manannán]

Trials bikes are ace fun and that looks a belter Cradders!   "Take a firm grip of the handlebars" was the advice given to me!

[Stiggytoo]

As the others have stated, you should try re-packing the exhaust. However, I think you may get away with adding a second silencer. I have 2 karts with basically the same engine. The one with the additional silencer is very quiet for a 2/ and if I'm not mistaken has more bottom end power.