Ok so I have decided to take the barrel off one of my seagulls to see how they work. The first thing I notice is the difference in the size of the port allowing fuel/air into the cylinder. One being a lot more elongated. Surely these ports would be better matched to the same shape. Or are they. Has the engine got a different barrel than it should have?
Also the old base gasket covered half the port area on the barrel, presumably to match the size of the crank case port. Surely the resticting gasket and the miss match in port size cannot be good for the fuel/air flow which is creating a ledge above the base gasket and may encourage oil/fuel to hang around and maybe de-atomise before it finally goes into the cylinder.
Ian's new theroy - 'smoother delivery of fuel = Improved combustion'
So me thinks in my tiny little mind. Why not at least chamfer the edges of the crankcase port a little to elongate the opening, alter the gasket accordingly and thus make better use of the width of the port on the barrel smoothing out and chanelling the flow of fuel/air? Would that upset everything? Maybe the crank case port size is important? But in that case why make the barrel port wider?
Ha ha, as you can see I know nothing about seagulls or in fact engines whatsoever and I am sure British Seagull would have improved the design if at all possible.
What's the serial number on that crankcase the cylinder looks like an LLS or an early CP,
you could well be right, a miss matched crankcase & cylinder.
Make it idiot proof and someone will make a better idiot.
An LLS is the first of the Centuries. Very very similar to later Centuries its letter code bore no relation to reality as far as I can see.. Whereas 'C' was for Century, 'CPC' for Century Plus with Clutch' 'LLS' doesn't seem to stand for anything at all.
The other Charles will doubtless be able to offer some insight into small differences.
This business of different port sizes is interesting. I can't throw any light on it!
The cylinder is right & matches the serial number, but the crankcase is quite a bit later, so it's probable that during the Seagull repairs, the crankcase was replaced sometime post 1967.
Make it idiot proof and someone will make a better idiot.
Ok Charles so does this mean I need to look for a century or century plus pre-67 crank case to make the ports match up or would a better idea be to locate a post 67 block
Or could I just put the whole bottom half (i.e. larger gear box, 11" prop and clutch) onto my other Century WS11DD6 to create something for a 16' Yorkshire pebble type boat.
The Century plus has a little more HP is that right.
Ian there are numerous different cylinder castings, yours probably has a bridged transfer & exhaust ports & has the inlet port on the Port side, though it is the smaller inlet stubb designed for the Villiers carb.
Hugo's later cylinder has the Amal sized inlet port on the Starboard side with the transfer & exhaust unbridged.
It's a long time since I worked on any of the early classic motors like yours, but from what I can remember the transfer port notch in the crankcase was wider almost matching the cylinder in a lot of the pre 67 crankcases.
From memory from my long ago research into best component matches for racing, the SD crankcase was the best fit, though it would require some engineering work to the retaining studs to make it fit.
Use any gasket as long as it's at least 10 thou thick, & clean it up around the transfer with a scalpel.
Make it idiot proof and someone will make a better idiot.
