Kegra Racer &Taffspeed Disc Valve 1991

[silversurfer]

Scootering #73 October 1991

Probably need to save and zoom in to read it

[vince]

Kegra produced a two of these one for group five one for group six the five Graham still has, the group six motor was further developed with a TSI based top end and was sold a couple of years ago to a sprinter if he gets that right up the strip that some piece of power Looking at the pictures it appears that Taffs has no flywheel ,we managed to work a small unit on to ours to take some of the peaky motor effect away.

[red devil]

Vince, this is interesting!
As you probably know I built one in 1981 using Rotax parts, the contruction was almost exactly like yours except for a few minor changes like the disc cover plate which I machined from 6mm aluminium sheet and then made the mounting for the points. I noticed that the recess in the magneto housing was probably filled with some sort of liquid metal and then machined flat, it's what I used to seal this area.
If my memory serves me well I'm sure the Taffspeed version was built around the same time as mine but used RG500 parts, am I correct?
I too ran without a flywheel, and suffered all the usual disadvantages......like the motor running backwards!
I have no idea what the power output was but it produced roughly about the same amount of torque as my reed valve motor did, however it would peak out at 9500rpm and so did not produce the speed that my other motor would. I felt this was a result of the disc timing and I am still sure some further tweaking would have produced a powerful compact motor.
When I retired in 1983 I gave the lot to Richard Baker but he gave it back to me in 2008 still in it's original tin!!!
Maybe there's a basis for a new sprinter there!

Frank.

[teamwoodspeed]

Frank that tin mite be worth something. Hee hee
From what i know the Taff set up was based on the Suzuki RG500 inlet.

[red devil]

I recall seeing a photo of the Frankland boys testing the disc motor in a sprint frame many years ago.
They claimed it did some low 15 sec runs, with a best of 15.1. Not bad for a new engine 30 years ago! After that I heard no further news about it so I guess it went back on the shelf.
I believe the Kegra version was a lot more successful so Vince's posting was very interesting.

[ralph95]

Kegra produced a two of these one for group five one for group six the five Graham still has, the group six motor was further developed with a TSI based top end and was sold a couple of years ago to a sprinter if he gets that right up the strip that some piece of power Looking at the pictures it appears that Taffs has no flywheel ,we managed to work a small unit on to ours to take some of the peaky motor effect away.

it had a trick crank

[tony]

no not really.. keith will expand but I stripped grahams group 6 motor so I saw it all .. from memory it had another key way cut into a standard crank for the disc. It had an offset pin too but that was it.

[vince]

no not really.. keith will expand but I stripped grahams group 6 motor so I saw it all .. from memory it had another key way cut into a standard crank for the disc. It had an offset pin too but that was it.

To much detail Tony Our disc was sort of secured into position using the flywheel a manufatured spacer pushing against the main bearing track if I remember correctly. the Kegra units were one offs except there were two We didnt adapt an existing unit from another machine apart from the disc itself .I would have to check the times and details with Graham but I think both Graham and Dave Dawson ran our 150 disc at the Santa pod scooter meetings/rallys with respectable times.

[red devil]

The Rotax disc had teeth cut into the centre hole, these engaged onto a drive gear mounted onto the crank. I think the gear was a press fit onto the Rotax crank but having removed it I attempted to machine it to fit the Lambretta however, this proved very difficult as the gear was hardened. After much trouble I opted to drill a hole through the gear and fix it onto the crank using a locking grub screw.
The inlet timing on the Rotax had obviously been arrived at after much testing and one of the problems I came across was the small number of teeth on the gear meant a big change of timing degrees for a disc movement of one tooth.
As I mentioned earlier the motor abruptly peaked out at 9500rpm when I felt it should have been higher. Some more testing would have sorted this out I'm sure, but as with every noisy race bike finding somewhere to do this was always very difficult.

[antonyrudd]

I recall seeing a photo of the Frankland boys testing the disc motor in a sprint frame many years ago.
They claimed it did some low 15 sec runs, with a best of 15.1. Not bad for a new engine 30 years ago! After that I heard no further news about it so I guess it went back on the shelf.
I believe the Kegra version was a lot more successful so Vince's posting was very interesting.

taffspeeds was featured in motorcycle mechanics i believe in one of three scooter articles i will try and dig it out