Hi all
A very interesting thread. My A10 has long had oil leaks from the top end, but after a rebuild, copper rocker gaskets, surface preparation etc, its fairly oil tight... UNTIL you hold high speeds for long periods of time. If you hold 80mph (about 4000rpm on mine) for along distances it starts to leak from the top end - as well as out of the tacho cable connection, the inner timing case tacho cable fitting boss and even the oil tank filler cap!. Clearly seems to be a high revs only crankcase breathing problem, as described by many. I have a tube on the engine breather leading to the chain, and very little (if any?) oil comes out there since I sorted out the pistons, bore and valve guides (to which I added seals on the inlets).
As this is a higher revs problem, I was going to try the rocker cover mod, but am unclear from this thread if that badly affects the main timed breather, or just helps sort the problem out. I wondered:
1) Does anyone use the 'road draft tube' idea? This would be a pipe running from the valve cover down to an open end facing down and located in the vehicle's slipstream so that (ref Wikipedia):
"When the vehicle is moving, airflow across the open end of the tube creates a draft that pulls gases out of the crankcase. The high location of the engine end of the pipe minimises liquid oil loss. An air inlet path to the crankcase, called the breather and often incorporated into the oil filler cap, meant that when a draft was generated at the tube, fresh air swept through the crankcase to clear out the blow-by gases."
As a physicist, (but not an A10 breathing expert!) this makes a lot of sense
2) If not the above, do you need a collector, or just vent to the air/chain etc via a tube
3) A PCV valve was suggested - is this necessary, and has anyone tried this? I don't have an airbox though, so it seems this would not work correctly.
I'm happy to modify and experiment, but am only looking for rocker box mod advice as everything else is spot on.
Just for background info, my A10 is heavily modified, runs 9:1 pistons, has gas flowed head, spitfire cam etc.
Thanks
Adrian