Trials Australia Forums

Mark K wrote:Its interesting that the pretty new piston has an arrow to show you which way it will make the bike go.

Very few new parts are helpful like that piston, so any work on a bike usually needs to be followed by a "test ride"

I`m very sorry David. Test rides are classified as Practice and as you know in Twinshock Trials practice is banned and the word is also considered to be a very bad swear word! Shame on you!!!!!!

Bully fanatic wrote:I`m very sorry David. Test rides are classified as Practice and as you know in Twinshock Trials practice is banned and the word is also considered to be a very bad swear word! Shame on you!!!!!!

I think my body would seize if I didn't do that shameful "test riding" thing, so I live with the shame

Hi Everyone,

Rod wrote: I too love that whine from straight cut gears also on Fantics and Rotax motors.
I believe the quieter helical cut type transmissions spread load better but require thrust bearings to take the axial loads making these transmissions a little larger and heavier.
I like watching V8 supercar racing occasionally, you can certainly hear that straight cut gear whine when they give you cockpit audio, it's awesome.
With regards to Trials bikes, I think it was simply to reduce engine width and maybe reduce a little weight.

Rod, you got me thinking because my does have a slight whine, about the same amount as the Rotax powered SWMs that I have ridden but less than a . Anyway curiosity got the better of me as I thought helical gears were used because they ran quieter and herringbone (helical back to back mirror image) for high loads like in trucks.


As for Heavy Industries, weight and slimline don't seem to be a consideration, 12 mm wide straight cut gears @ 7mm between centre's is fairly coarse for a 250 and that I where I imagine the Whine comes from.

Hey Greg, I don't have an answer regarding whine in my Fantic 300 but I like the distinctive sound it makes and assumed straight cut, my parts manual implies straight cut also, but the manual is from 1984 and a bit vague I suppose. I'm not about to pull the cover just to prove a point, maybe there was a change between the 240 and 300 ?
Those Aprilia Trials bikes wearing Rotax engines of the '80's and '90's certainly had a distinctive whine about them, so once again I assumed straight cut.

I was racing a Bultaco MK 10 125 which was the 1977 model Pursang for a couple of years with BMCC and after every race I would have people who were watching come into the pits and ask if that Bultaco had primary gears. As some of you may know there was only a couple of the Bultaco models that had a gear primary drive in them and the late 125 Pursangs were one of them. The main other one were the El Bandito and the El Monterdero. It had a hell of a gear whine!

It was probably so loud Jeff because, if my memory serves me correctly, they had three straight-cut gears in series in the primary drive not two.

Saturday photos of some KT parts that saw progress towards being an assembled bike. I hope to do some more on the KT later today when/if I finish some essential home maintenance

Hi Everyone,

Rod wrote:Hey Greg, I don't have an answer regarding whine in my Fantic 300 but I like the distinctive sound it makes and assumed straight cut, my parts manual implies straight cut also, but the manual is from 1984 and a bit vague I suppose. I'm not about to pull the cover just to prove a point, maybe there was a change between the 240 and 300 ?
Those Aprilia Trials bikes wearing Rotax engines of the '80's and '90's certainly had a distinctive whine about them, so once again I assumed straight cut.

Rod, I agree with you as the whine is distinct in my 240, all of the gears inside the gearbox are straight cut but they spin slower. Aparently Rotax, at least in SWM have helical primary drive gears. Photo courtesy of Kurt:

Bully fanatic wrote:I was racing a Bultaco MK 10 125 which was the 1977 model Pursang for a couple of years with BMCC and after every race I would have people who were watching come into the pits and ask if that Bultaco had primary gears. As some of you may know there was only a couple of the Bultaco models that had a gear primary drive in them and the late 125 Pursangs were one of them. The main other one were the El Bandito and the El Monterdero. It had a hell of a gear whine!

Graham, If what John is saying about 3 primary drive gears on the Mark 10 125, it must have been an exhaust drowning whine?

Chippy, any chance of some more photos of your trio?

David, do you have one of these alooooominium exhaust flanges?

While you are working on your today I rode my for the first time since we painted Denman GREEN. It amazes me how much you can vary the whine by varying the load with the clutch and by loading it up on hills. Along with all of the pops, wheezes and crackles of the exhaust note.

Just for the record Graham, I was not practicing! Just rehearsing for the KTSoundtrack.

Greg Harding wrote:Hi Everyone,

David, do you have one of these alooooominium exhaust flanges?

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While you are working on your today I rode my for the first time since we painted Denman GREEN. It amazes me how much you can vary the whine by varying the load with the clutch and by loading it up on hills. Along with all of the pops, wheezes and crackles of the exhaust note.

Just for the record Graham, I was not practicing! Just rehearsing for the KTSoundtrack.

Wow that alooooominium flange is flash all right. It sure beats the standard steel part for weight reduction and it looks ridiculously shiny . If it had been made in the USA would it have been made of alooooominum instead?
As well as all those methods you mentioned, that amazing whiny gear sound can also be bent around using sudden applications of the rear brake.
I'm getting quite close to being able to ride my KT again and greatly look forward to hearing that symphonic whine. Still deciding on whether to polish the engine covers or leave them vapour blast finish. I think to start with, not polish, so I can ride it sooner!!