aparentliy    ther wer     over  81 , 400   YD1   engiens  alone     made   so thats  about   so thats  about  162, 800  plates  wich  cost  B S A mouny   if  thay  didnot   think  thay  were   werth it   i  dont   think   thay   would  have    

Gonna have to get a dyno test set up to determine once and for all.As said previously though it would have to be the same engine with and without.From my own experience the crank I repaired and had plates on felt a little torquier??? Low down compared to the one in the bike at the moment only thing is the one at the moment has a lighter conrod and piston by about 3 ounces plus the crank itself is considerably lighter.It does like to rev quite a bit more than the other make of that what you will.

It is my understanding that there comes a point, reasonably high in the rev range when crankcase pressure drops to zero - at this point the power drops away.  The side plates on the crankshaft serve to maintain crankcase pressure a little further up the rev range and thus enable higher revs to be sustained and thus power to be available to pull higher revs.  This was explained to me by a 2T racer (Yamaha) a long time ago. 

I, therefore, think that these side plates do little for performance until you start to crack on the revs - if you like to ride with your hair on fire then you will no doubt appreciate the extra revs giving you about 5 mph more in each gear possibly 6 mph in top.  Obviously this might make all the difference to a racer. 

I have also heard a plausible theory - backed up by BSA literature, that the crank side plates offer less resistance to the airflow ( read fuel and oil mixture/mist flow) through the bottom end of the engine and thus more oil gets to the top end via the transfer ports.   The theory gives us to understand that without the side plates more of the oil is deposited on the crankshaft webs - especially whilst the engine is warming up - and less gets upstairs where it is needed to cool and lubricate the bore.   As evidence for this please note that the D7 had no crank side plates as standard but it did have an extra piston ring to give it 3 rings - one of the jobs of a piston ring is to transfer heat from the piston to the bore.  

I have certainly noticed that my engines that do not enjoy side plates anymore (mainly because they are items unavailablum nowadays - otherwise I would fit them) tend to run a bit hotter than they should and as for the rev range - well I don't ride like a mainiac anymore so I don't rightly know.  Given the choice, and if I could get my hands on some, I would fit them - then there can be no argument can there ? However somebody with access to a laser cutter needs to start manufacturing them - I bet they would fly off the shelves.  I would certainly place an order for some B175 side plates. 

Sponge     

If Spacedmarine is going to do a dyno test with his D14/4 it would be very interesting to test the above assertion with some science.  Bring it on because it is a question that has been haunting me for years.     

Youd only need a couple of holesaws and some sheet steel easy peasy..I've got 4 hanging around 2 aren't so bad 2 are a bit chewed up.looking at them they're slightly different makes me wonder what vintage my crank is?

One set is slightly thicker with a recess.They were the originals,the others off the second hand crank I got

I'm guessing just mild steel would do it.They do rust if you leave them long enough.

Can do Les if you can hang on a day or 2 unless someone beats me to it 👍🏼