At Woodbridge airfield 31-07-04
1 1/2 mile run up, slightly uphill, then through 10 yard section through calibrated timing beams.
In truth, I had hoped for faster, but I had had some problems at Cadwell before which needed some fixing. The old cylinder head was in such bad condition that I machined up a new one with a new combustion shape.
I then put it on a dyno, only to find that it was 5 bhp down on the 1996 figures with the old head.
Time for serious thought–
I realised that I was up against the old problem, where the plug is over the exhaust ramp and so this ignites first.
The volume over the inlet ramp is almost cut off by the fit of the piston in the head and so does not fire immediatly.
It burns when the piston has decended a little to give flame space, but the flame must now cross the area already burnt and thus fairly devoid of oxygen. Thus the burn over the inlet ramp is delayed and comparitively inefficient. Mr Scott knew all about this problem in 1911- 1914 as he had bosch make special twin spark mags to fire plugs over both exhaust and inlet ramps.
I machined in a flame tract from the plug position to the inlet ramp area, remember that my head has cast in areas to fill in the majority of these inlet and exhaust ramp volumes.
So I went with an experimental head and hope.
I have spent about three weeks in total getting the engine repaired from the damage at Cadwell when a bolt fell into the case and broke a piston, damaged the head and caused a seizure.
Ok, I had never had a problem with this item in 20 years, but I now have a design modification to prevent this happenning again. Much better it happens to me than to a customer!
I must now push on with customers work. When time and funds allow, I will have the bike on the dyno again and go further into head development.
However, Although I had hoped for better, I suppose 114.3 is a respectable figure for a Scott and one that can be quoted at scornful four stroke owners who do not realise that not only can a Scott give great pleasure by its character, but it can be quite spritely if needed.
I send sincere thanks to all who wished me good luck, to those who managed to attend and help with fettling the clutch.
This is not the end of the story–
“Only the end of the beginning”
ps I will send some pics to Ted and put some on my website, but not for a few days, as I am so busy!
Congratulations!! this must be the fastest speed ever recorded on a scott!
its certainly the fastest ive heard of!
Fantastic Roger, Well Done!
Regarding the cylinder head shape, I have always felt that the std plug position/head shape is too much of a compromise: just look at the insensitivity to ignition advance.
The later “car” engine head shape/plug position seems so much more sensible.
Colin Heath and I stopped using full squish heads, even though we had no mechanical problems at over 15:1 compression ratios(22cc head volumes). We ended up with full squish on the exhaust with a large volume on the transfer side with an “encouragement ” space for the flame path where the deflector edge bisects the combustion chamber at TDC.This drops the compression to about 12.5:1 but the bike is at least as quick. This was an attempt to get to the “car engine head shape with the std plug position; I’d love to try a different plug postion.
Anyway congratulations once again ; I can only stand back and marvel at your continuing and amazing enthusiasm for these flawed, yet fascinating motorcycles.
And I thought my 85.3mph timed by West Mercia Constabulary was the record! – S’pose I will have to try harder
Dear Al, John and Shaun
Many thanks for your congrats
John’s comments are very interesting. If I could afford it, I would just continue with a development programme. Unfortunately, earning a living is an impediment! I have six head castings here John, so if you ever decide you want one machined in a certain way, let me know.
Very interesting info!
However–for sheer laughter–
I just loved Shaun’s bit about being timed by West Mercia police!
Nearly fell off my chair!
Ok– I have worked late for about 3 weeks and Marina thinks I have left town, so, its her treat today!
Off to Ironbridge and Blists Hill on the VFR
Show her all the old display cottages and how people used to live in the old days.
She will understand it—
It is very similar to how we live now!!!!!
Kind Regards to all.
A fellow SOC member hopes that I am better at engineering than I am at spelling!
I before E except after C
I think he’s got it! — he has finally got it!