Update...Dead Bike... No, SHE LIVES..... Hurray

[Sid Squid]

Originally Posted by Ol Boc

Right-O Sir, but explain this please: why would the designer do what you say? If the pistons were perfectly opposed, one might realistically expect perfect balance. Then, to get the right port timing for scavenging or whatever, one would simply machine the ports higher/lower.......

(Do you know, this is a VERY interesting thread....aren't we lucky that Numbers smashed his box. Without that, we would never have had this discussion!!!)

The higher up the cylinder the ports are the lower the corrected compression ratio, particularly in the case of the diesel variants of these engines that would compromise performance considerably.
Balance wise it isn't a great drawback as these sort of motors are usually several banks long, therefore the various cylinders can be arranged to best counter any imbalance.
A bigger loss is that the pistons don't give exactly the same power output, one not having full stroke under combustion pressure, better that way than arranging full symmetry and the consequent loss in compression though.

Originally Posted by Sid Squid

The higher up the cylinder the ports are the lower the corrected compression ratio.......etc etc

Thank you Sid! I've been sat here for a bit, moving hands back and forth in front of my eyes to simulate what you say!!

I find it fascinating to consider how the designer figured that all out in the first place. Engines like this, Deltic, Bristol Hercules...all so interesting. I have Harry Ricardo's autobiography....that's an insight in places too.

Having rattled on like an ol' gummer, I shall now hook off!