30 BHP Blog

In the first image on the below you can see how the bottom skirt in the image impedes with the transfers on that side.
The next image shows the shape needed which needs to be cut from the skirt. I first use a small hacksaw to cut the majority of the shape away and the use the flexi drive to finish the cutting then make the edge nice and smooth.
Then I cut 2mm from the bottom of the inlet skirt, this makes the skirt 66mm long



the skirt length along with the measurement from the top of the barrel to the bottom of the inlet port (97mm), minus the measurement that the piston top edge sits below the top of the barrel at TDC (.3mm) gives an inlet duration of 163.43 degrees.

Once everything was cleaned the engine was put back together, The squish checked and the gaskets trimmed back.
While the engine was apart I changed the gear selector shaft as this had given me some problems, also the clutch steels needed filing to take the burrs off and a new set of strong springs added. The clutch is a standard basket with 5 Tino Sachi green plates and aluminium steels.


Mid March 2013 the scooter went on two different dyno’s on the same day. The dyno runs were not set up runs, they were just power runs to see if the changes had improved the engine or made it worse. The result was very pleasing, a fraction under 30BHP and 21 Ft Lbs Torque

The graph below shows the latest run in RED and the best previous run on that dyno from December 2011 in BLUE

The graph below shows the latest run in BLUE and the best previous run on that dyno from March 2010 in RED

Managed to get the time today to do the helicoil and the other bits and bobs needed to get it ready for a road test.
Four of us headed off for the petrol station close by, Mik running in his GT200 big block prototype kit, more about that later, Nige running in his new TS1, Sulla having just been for an MOT coming along just for the ride and me taking “Scion Rat” (thats its new name) out for its first road miles with the 30 BHP engine.

Scion Rat felt much quicker than before, it now accelerates much more aggressively and hits 9k RPM easily in the first 3 gears. Its a bit flatter when traveling in top gear at anything under 50mph than it used to be but it will still pull in top at those speeds.Everything was going well until only around 10 miles into the journey, while traveling at around 50mph I decided to see how well it would pick up when dropped down to 3rd and given full throttle. It picked up really well hitting 8k RPM in no time at all then all of a sudden there was a loud bang and as I felt the back wheel locking I grabbed the clutch in. to my amazement the engine was still running. I slowly let the clutch out and felt the back wheel locking again.
I pulled over and couldn’t get my head round what was wrong, the engine was running fine, i could select all gears, It would free wheel but if I let the clutch out the back wheel locked up.
I turned the engine off then tried to kick the kick-start down but it was jammed. There was nothing else I could do but get a friend (Mat) to come and recover me in his van. When I got the scooter back home I took the side case off and found the problem….

The chain had snapped in two!
This chain has been in the engine for many years and when I rebuilt the engine a few weeks ago I inspected it looking for cracked or missing shells and found non, the chain was in good order if a little stretched which is required for the 17 X 47 sprockets. I’m beginning to think that chasing 30 horses may have been a bad move.
The only sprocket chain combo I have available now is 18 X 47 which will give me a long 4.44 final drive. I intend to fit that tomorrow to see if the engine will pull top gear at lower speeds, I have no doubt it will pull it once in its power-band but ridding everywhere at 80mph+ just isn’t practical.

We will see.