BSA Bantam "Stuffer Plates" Flywheel Baffle Plates

[doubleboost]

This crank is a mess loose rivets badly drilled holes .
I cut some plates on the plasma table .
After a bit of googling I went for the weld option .
I used 309 filler wire (the welds were mostly fusion welds).

 

[oldbikedavey]

Might even get a wiggle on with casting that D.7 reed valve barrel that I've been patternmaking on sporadically......

 

[Morrisman]

Are they to boost the primary compression? I remember chatting to a ‘scooter boy’ many years ago about 2 smoke tuning, he had a very ‘quick’ Lambretta.

 

[Robotstar5]

Are they to boost the primary compression? I remember chatting to a ‘scooter boy’ many years ago about 2 smoke tuning, he had a very ‘quick’ Lambretta.

They're supposed to close off the wells in the crankshaft, but sometimes come loose.

 

[doubleboost]

I don't think mine will come loose .
The rivet method has caused some damaged engines .

 

[Morrisman]

They're supposed to close off the wells in the crankshaft, but sometimes come loose.

But I think the idea is that the charge gets compressed more, as it’s squeezed into a smaller volume, before shooting up the transfer port more energetically. I seem to remember my scooter buddy making some sort of aluminium insert to do the job, pressed into place.

 

[Robotstar5]

But I think the idea is that the charge gets compressed more, as it’s squeezed into a smaller volume, before shooting up the transfer port more energetically. I seem to remember my scooter buddy making some sort of aluminium insert to do the job, pressed into place.

Yes the plates do reduce the crankcase volume, but how effective it is would be debatable as it would mean less volume for the initial charge before being compressed

 

[julianthegypsy]

When I bought my first bike. A D14/4, every time the engine stopped you could hear a spinning noise. My mate knew exactly what it was, the packing rings spinning. Took it apart and as I remember centrepunched around the edge of the crank. They never moved again. They used to make a horseshoe packer as well that went around the crankcase, but decided that with the rings in place the crankcase compression was already 13:1 and any more wouldn't make any difference. Happy days!

 

[OJCar]

Very nicely done by DoubleBoost.

But while raising the crankcase compression does work on an engine like a D7, it is not worth the effort.
Later Bantam engines have them fitted as standard but the gains are tiny.
Many more gains to be had from porting, carb size, expansion exhaust and a raised compression squish head.
However it will always be an exercise in rolling it in glitter!

 

[julianthegypsy]

Very nicely done by DoubleBoost.

But while raising the crankcase compression does work on an engine like a D7, it is not worth the effort.
Later Bantam engines have them fitted as standard but the gains are tiny.
Many more gains to be had from porting, carb size, expansion exhaust and a raised compression squish head.
However it will always be an exercise in rolling it in glitter!

Expansion chamber really helped. I wanted a Todd head but never found one. That would really help. Still, it would out accelerate a suzuki gt125, and my mates honda 250's only took it because they could brake quicker into corners and then needed a long straight to get away. Brilliant bike. I wouldn't look at any of the earlier ones though, no poke at all!

 

[oldbikedavey]

Expansion chamber really helped. I wanted a Todd head but never found one. That would really help. Still, it would out accelerate a suzuki gt125, and my mates honda 250's only took it because they could brake quicker into corners and then needed a long straight to get away. Brilliant bike. I wouldn't look at any of the earlier ones though, no poke at all!

Not a Todd head, but I can cast up BAFCO items if required......

 

[brightspark]

But I think the idea is that the charge gets compressed more, as it’s squeezed into a smaller volume, before shooting up the transfer port more energetically. I seem to remember my scooter buddy making some sort of aluminium insert to do the job, pressed into place.

yep padded big ends

 

[Melvyn Best]

Are they to boost the primary compression? I remember chatting to a ‘scooter boy’ many years ago about 2 smoke tuning, he had a very ‘quick’ Lambretta.

That brings back memories of using araldite to stick corks into the crankshaft web holes on my old LI 150 to get a bit more power when I was 16

 

[Morris]

Not a Todd head, but I can cast up BAFCO items if required......

BAFCO?