adjusting valve timing + clearance

Post by **alex_holden** » Tue Apr 17, 2007 9:57 pm

bmcecosse wrote:Which is why it generates less power than say a Ford engine of the same capacity and era.

Why does it make a difference if you never get two cylinders using a shared port at the same time?

Post by **Pascal** » Tue Apr 17, 2007 11:02 pm

All done! Surprisingly I found that several valves were too tight; I would have expected the opposite (yes, the engine was cold). I wonder if that might have had anything to do with my excessive fuel consumption (23 mpg in town, mainly small trips though).

Post by **Packedup** » Wed Apr 18, 2007 12:28 am

alex_holden wrote:Why does it make a difference if you never get two cylinders using a shared port at the same time?

The inlet side of things has the mix trying to change direction in the head in a hurry (3&4, then 2&1), which IIRC causes problems that 4 port heads don't have.

Pascal wrote:All done! Surprisingly I found that several valves were too tight; I would have expected the opposite (yes, the engine was cold).

Wouldn't have been the exhaust valves by any chance?

Post by **bmcecosse** » Wed Apr 18, 2007 7:48 am

They would be tight because of slight recession setting in. There is normally v little wear in the valve train - and so the gaps rarely open up. If they do - it's usually by a LOT - indicating severe wear of a cam lobe and it's matching follower. The remedy then is obvious.
And yes - the stop-start motion of the gases in the shared inlet (and to a lesser extent in the shared exhaust port) is the basic power limiter in the A series. Especially as it pulls twice rapidly on the first port(21) then the second port(34) - the first port flow coming to a (relative) standstill while the second port runs and then vice versa.