The thing is, when you adjust the clearance in a particular valve train you need to make sure the cam follower or tappet is on the base circle of the cam, or the clearance will be excessive. You do this by checking the clearance on both valves in a cylinder when that cylinder is at TDC. The thing is, wild valve timing or quietening ramps in the cam profile means you have to be accurate when positioning the engine.
After decoking my Ariel SQ4 I had to adjust the valve clearances. And thanks to Simes "rule of nine" (
http://ariel-square-four.blogspot.com/2018/10/rule-of-nine.html ) this was more simple, more exact and the engine was much quieter. (
https://www.a7a10.net/forum/index.php?topic=13293.345)
I have now looked at this process for my BSA A7 and found this must be similar. I adopted it and so found the
"The Rule of Five"!
Have a look at this 4 Pictures at the Bottom - this camshaft it‘s a spare camshaft for my BSA A7:
Start with top Picture:
On the right hand side of the picture, you see the thread retaining the cam sprocket, and that
first cam is the inlet cam for number one cylinder - notice it is pointing straight up and the valve will be fully open.
Move to the left hand end of the camshaft and we are looking at the last or
fourth cam, the cam for the inlet valve on cylinder two . It's pointing straight down, which means the valve is fully closed and the tappet is on the base circle, so:
The rule of Five 1 + 4 = 5 and again 2 + 3= 5 and again 3 + 2= 5 and again 4 + 1= 5
Surely one or the other already knew this but for me as an older newbie it was a new experience and helped me a lot.
Cheers Rudy
