If you have an old rotary valve engine that deserves to be restored
contact me. I am really good at it and very particular.
100cc Air Cooled Rotary Valve
Stroke: 53.8mm
Rod length 100mm
Bores Size: 48.80mm
Piston Size: 48.71mm
Clearance: 3.6 thou
Exhaust = 165 deg
Transfer 124 deg
Boost = 124 deg
Valve close = 65 deg
Valve opens = 122 deg
RV clearance = 12 thou
End Play = 10 thou
Timing = 100 thou
Squish = 1.0 mm
Combustion chamber = 7.0cc
Compression Ratio = 14.3 : 1
RPM limit 16,500
The rule for engine size was stated as 100cc. In engineering terms thats 100 +- 1. This engine is 100.63cc. In National specs it was plus 6%. Hence 106cc to 200cc.
Stroke: 53.8mm
Rod length 100mm
Bores Size: 48.80mm
Piston Size: 48.71mm
Clearance: 3.6 thou
Exhaust = 165 deg
Transfer 124 deg
Boost = 124 deg
Valve close = 65 deg
Valve opens = 122 deg
RV clearance = 12 thou
End Play = 10 thou
Timing = 100 thou
Squish = 1.0 mm
Combustion chamber = 7.0cc
Compression Ratio = 14.3 : 1
RPM limit 16,500
The rule for engine size was stated as 100cc. In engineering terms thats 100 +- 1. This engine is 100.63cc. In National specs it was plus 6%. Hence 106cc to 200cc.
I love this engine. BM FC100 in almost perfect condition. World
Champion in 1968 with a Swede on board. This engine came from that
campaign. Built in May 1967. I aquired it from the old Swede engine
tuner who was part of that BM importer setup. It has survived in pristine condition because it was one of the fastest engines at the time.
In 1971 I started kart racing and I had 2 used BM FC100's. A factory five port (ex Peter Dell) and
a standard 3 port. I learned my engine building skills on these
engines. I raced them with great success as a junior until 1976. In
1976 the 3 port engine finished 5th
at the Nationals in 100cc International against a whole lot of new
engines and top drivers. Literally a 10 year old engine at that
time.
This engine is state of the art for the time. The inlet was widen to get the required valve timing instead of cutting the disc. The ignition side transfer port is 2mm larger than the inlet side. The liner was removed and machined to achieve the desired port timing and angles. The bell housing ring was machined off to allow more cooling. Every surface is dimensionally correct, true and square. It was bored to maximum size. I was told "it was in the fastest batch of engines. At an early round in 1968 the conrod broke. The engine was rebuilt and set aside." And that's what it looks like. Virtually new everywhere you look at it with some minor repaired damage to the crankcase casting and valve cover. I reduced the compression from 5.7cc (17.5:1) to 7.0cc to run on modern fuels. In the day it would have been run on Leaded AVGAS with 20% benzine. 108 octane.
It runs a CEV ignition. It would have been run with a Dell Orto carby and pump at the time. However the Tillotson HL227 is still correct for this era engine. The quality and strength of the castings is amazing. I have looked around at alloy castings from the 60's in cars, motorbikes, other engines etc and the BM castings are better than anything I came across. BM's are strong engines.
This engine is state of the art for the time. The inlet was widen to get the required valve timing instead of cutting the disc. The ignition side transfer port is 2mm larger than the inlet side. The liner was removed and machined to achieve the desired port timing and angles. The bell housing ring was machined off to allow more cooling. Every surface is dimensionally correct, true and square. It was bored to maximum size. I was told "it was in the fastest batch of engines. At an early round in 1968 the conrod broke. The engine was rebuilt and set aside." And that's what it looks like. Virtually new everywhere you look at it with some minor repaired damage to the crankcase casting and valve cover. I reduced the compression from 5.7cc (17.5:1) to 7.0cc to run on modern fuels. In the day it would have been run on Leaded AVGAS with 20% benzine. 108 octane.
It runs a CEV ignition. It would have been run with a Dell Orto carby and pump at the time. However the Tillotson HL227 is still correct for this era engine. The quality and strength of the castings is amazing. I have looked around at alloy castings from the 60's in cars, motorbikes, other engines etc and the BM castings are better than anything I came across. BM's are strong engines.
