Yamaico's new el Cheapo Project.

[vandy010]

i'm not real sure that'd work in a Trials section Freaky...

[EML]

You haven't watched freaky ride much have you Vandy-he'd just hold it flat!!

[firko]

Hey Pete....those TY triple clamps arrived today. I was going to try them on the Hindall flat tracker (much less offset) but I've since picked up as set of trick billet 35mm triples so I'll probably use them. They're wider pitch for the fatter Maxxis tyres too....so, TY clamps for Pete.

[JC]

Pete, those MX triples will give you much better trail spec - close to TY250

I also went thro Bell, Jennings, Robinson & Irving & none of them left me any the wiser for trials exhausts, tho Robinson did confirm that longer header & larger overall volume move the power down lower. One suggested that, since the sound waves depend on very fast opening of the ports, the sound waves aren't very strong (or significant?) at low engine speeds. That would be even more so on trials spec w lower exhaust ports were the piston speed at port opening is also lower

A few trials models did go the expansion chamber route - loooong & convoluted - circa early 80s (242/304 Cota, Ossa Gripper, Beta TR34), but most seem to just have a long header dumping into a 'box', often of indescriminate shape (whatever fit the body work?). I read recently in Trials Mag that most modern manufacturers have gone back to that.

I did a quick check on an IWT program & you'd need a tuned length of about 1300mm for 6000rpm & 170deg exh duration, but that was assuming 500deg C whereas trials engines probably run at lower temps where the sound waves also travel slower. By comparison, a TY175 pipe is about 950mm! ()

TY header length is about 26" & diffuser & midsection about 12" combined (sorry for mixing inches & mm). By the look of the weld marks there appears to be 2 internal baffle plates, the 1st in the diffuser section at about 20-25deg (to the horizontal) & the 2nd in the 'belly' at about 45deg. There's no real rear cone to speak of, just an 'end wall' to close it off & attach the tail-pipe.

Its almost as if those baffle plates are in there to break up what little sound wave effects are there (??) so theres no real "tuned length" for a returning +ve pulse.

The Beta one Vandy posted also appears to have almost no rear cone to speak of. Header looks slightly tapered tho for whatever reason.

Having said that, the WES aftermarket Ty exhausts do appear to have diffuser, mid-section & baffle cone, still w a short overall length. Some Fantic ones look similar, tho there's no guarantee of the internal shape cos of the perforated & packed inner 'skins'. I have seen a Fantic 'diffuser cone' sectioned (cut-away) & its plain perforated tube (parallel walled) inside

All rather confusing. Nothing is very conclusive 

[brent j]

Hey Pete....those TY triple clamps arrived today. I was going to try them on the Hindall flat tracker (much less offset) but I've since picked up as set of trick billet 35mm triples so I'll probably use them. They're wider pitch for the fatter Maxxis tyres too....so, TY clamps for Pete.

I'm not sure about TY175 triples but TY250 triples have a few degrees difference between the steering tube and forklegs. The forklegs have more rake to them than the steering tube. This effectively increases the offset from what the triples measure.
More so as the forkleg length is increased.

[vandy010]

i followed you through most of that JC and tend to agree.
it's all a bit grey...............
and given all the variations i've seen on homemade trials specials, then to talk to the owner/rider and they all seem to have not known what to do but are happy enough with thier results.
i reckon it's just comitting to an idea and see where it leads.
pipes

[vmxrider]

Here's an article on a TS 125 trials conversion from Cycle magazine 1973. Interesting looking pipe.

[Freakshow]

i'm not real sure that'd work in a Trials section Freaky...

as they say its "all about the style "

[Freakshow]

With your exhaust mods you can always put a potato canon on it for around the campfire later 

[bazza]

That Bully is the bees knees for shooting tee shirts in to the crowd

[EML]

OK, so a loong time ago I read an article in (I think) Dirt Bike Mag or Motocross Action, about how exspansion chambers work.
Now, if I remember correctly, they mentioned that to get it in your head, you have to imagine that the gasses coming out of the exhaust port are like a tribe of indians being chased by cowboys (or was it the other way about-not too sure but the result is similar) So, those guys are being chased and they are making alot of whooping and hollering, out of the port and into the chamber. The chamber is like a box canyon and after a bit the leading indians(cowboys) get near to the end and it starts to get squeezy, so some of them turn around and start back up the canyon towards their mates(and the enemy) That my friend is called back-pressure and a two-stroke wont work too well with out it.
Now on a trials bike, it's all happening alot slower so not so much whooping and no hollering, so maybe,just maybe, they aren't indians at all but rather Ninjas. This could explain why trials bikes creep over rocks and logs and sneak through the bush.
But it still explains nothing about how to build a pipe for a trails (Ninja) bike!

[Flatout]

Heres something ..Have you looked at the exhaust replacements that Sammy Miller Products have to offer for The TY series Yamahas..They are a Stainless Header pipe and Aluminium Chamber and silencer, Ive got one on my TY250..Shouldnt be to much of of a problem to copy they are a very basic design..Cheers and have fun..

[yamaico]

I'm overloaded with information here. I think, based on the general consensus, that I should either just build a pipe that fits, with a minimal amount of whooping and hollering, or as Freaky is alluding to, give up and go back to building motocross bikes. Some dimensions on the Sammy Miller pipe would be good thanks Stinger, just to see what they were thinking. Having said that, JC has unearthed a few trials pipes cut in half (courtesy of trials guru David Lahey) and they have a straight perforated pipe inside. The lawn mower muffler is looking better all the time. That little Suzuki certainly looks the goods, but it has a very strange pipe indeed.

Managed to get some other work done on the bike. Made up and fitted a sidestand and modified the back brake backing plate to allow the torque arm to tuck up further close to the swinging arm. Bit of a setback with the back brake as the brake pivot is too far below and behind the swinging arm pivot point resulting in very inconsistent brake pressure during swinging arm movement. I'll either move the pivot closer to the swinging arm pivot or fit a cable brake. Gives me something to think about to take my mind off the exhaust

Hey Pete....those TY triple clamps arrived today. I was going to try them on the Hindall flat tracker (much less offset) but I've since picked up as set of trick billet 35mm triples so I'll probably use them. They're wider pitch for the fatter Maxxis tyres too....so, TY clamps for Pete.

Thanks very much for your kind offer Mark, but as Brent says they have an odd rake offset to the steering head. Also, I think the TY250 forks are 34mm, whereas I have 30mm forks, with brand new freebie tubes. I think I'll go with John and Vandy and get the MX125 triples. Much appreciated though.

[tony27]

Be prepared to move the frontpegs after your first ride, they look a bit further back than ideal. If they're too far back the front sledges when turning

[JC]

The exhausts SM Products sells are the WES ones. Most of them have the internal perforated skin packed w f'glas but I'm not certain if they all do. May just be parallel tube inside also.

Pete, a couple of suggestions on colour scheme - perhaps the Peter Paice blue scheme in VMX #50 which looks even nicer in person than in the mag, or whatever yr own CT2/3 was back in the day if you still 'connect' w that bike. Or the yellow & black 'speed-block' scheme looks nice on trials Yams too. I'll sift thro my Ty pics saved from the net & email you some alternatives.