Thanks for all your ideas because I really dont want to strip this engine down if I can avoid it, I will now try to answer those ideas.
One thing I probably did not emphasis is the way the engine runs. It runs wonderfully, it ticks over perfectly and is instantly responsive when blipped. Obviously its running in so I have not revved it to death but a quick blip and its great. I have done about 250 miles on it (and about 25 gallons of oil
and it starts and runs perfectly with no smoking and the plugs are a lovely colour.
Just a very brief observation, you mentioned a fibre washer under the forward fixing on the oil pump. You probably meant to say gasket, but just in case ( and I'm sure you are aware ) the forward circular gasket is the same thickness as the main pump gasket.
Yes its actually a very thin washer which I assume is fibre and it is fitted.
I’ve just read the whole thread and you already observed the return but i still think it worth doing as it will show up any crankcase pressure build up, and also whether too much oil is going to the rockers, on that, the swing arm bikes have a “special” banjo at the oil tank that “bleeds” a small proportion of the return oil to the rockers. RDFella mentioned this a few posts ago. Given the return side only has in the region of 30% more capacity than the flow side its important that the “bleed” to the rockers is considerably less than 30% if the return volumn, for this reason a simple “TEE” to the rockers (as you mentioned early on) may not restrict the flow to the rockers enough, which would lead to a crankcase full of oil some minutes (maybe many minutes) later. Just a thought......
I agree so I removed the Tee piece and refitted the standard plunger rocker feed which has not helped at all.
As you have experience with these motors, I suggest forgetting the rocker feed for a short test, a direct connection to the feed and return plain pipes should do. Start with a drained sump, correct oil volume and see what happens. May save a load of work if the fault is simply the oiltank.
Good idea one I will try when I can but I am fairly sure the oil tank is ok it was my first thought a blocked return but I have cleaned them again quite vigorously.
In my opinion the return side is acquiring additional pressure from the crankcase pressure. Even though the crankcase breather seems to be working I suspect something wrong in this department so that crankcase pressure is pumping through the return side via the pickup pipe or via the gasket at the back of the pump. I would put an extra breather on a tappet cover. If you have a spare timing cover put a breather on that. I would also make absolutely certain the oil pump is seating properly. Sorry if this is repeating what you've already heard. Fundamentally, I think the crankcase pressure is finding its way into the oil return...somehow! The only other possibility I can think of is the oil return hole in the return pipe in the tank blocked or too small for another reason. Where else could such excess pressure be coming from? Good Luck!
Firstly dont worry about repeating anything if it helps I will love you forever :). I had a rocker box breather on which did not seem to leak oil or improve things nor did there seem any pressure coming from it but I do find the idea of the crankcase pressure actually boosting the oil pressure a very sensible train of thought. I will definitely check the seating of the oil pump because that would possibly explain a few things.
Excess pressure in the crankcase can come from a head gasket leaking into the pushrod tunnel.
Now thats a good thought as I had that many years ago on another engine and it actually ended up with the pushrods being bent from the heat. I dont think thats my problem this time as a compression test was fine but the engine was not at running temperature when I did that test. That would also explain why the plugs are still a relatively good colour.
Time for a leak down test before pulling the top end part ?
Without going back to the start what type / make rings are fitted ?
A bad bore or cocked piston from a misaligned small end will cause lots of blow by
Another top idea particularly as I actually have a leakdown tester that I have only ever used once and that was not even on one of my engines.
The pistons and rings are heppolite but they are the old heppolite from many years ago, not the newer ones. I have quite a multitude of spares some of them I have had for 40 years and altho they looked ok and all measured ok thats a damed good shout. The problem is I cannot remember if I put new rings on them or they are original rings. They were obviously measured and gapped etc before fitting and the compression seems good but again those tests were done before it was at full working temperature.
A huge thanks for all your ideas I will investigate all in turn before I rip the engine out and set fire to it :)
It might take a few weeks before I get around to it because I do have other projects on the go but I really do appreciate everybodies input.
