Main Motorcycle: T140 cafe NRE900cc
Join Date: Jan 2012
Other Motorcycle: Yes
Extra Motorcycle: Of course
There is a crankcase Drain underneath the engine, towards the left side. It is important that this area is clean before you take it out and the drain is clean before you put it back, if you get grit inside the bottom of the engine there is a chance that you stop the return side of the oil pump working.
If you remove this crankcase drain, you should only get a small cup full of oil from the bottom of the engine.
You can run the engine once it has been drained and the cleaned (no grit) and the drain plug put back. The crankshaft is lubricated from the oil tank, so you are safe.
It is easier to think of the dry sump system system as two separate items, the feed and the return.
The oil pump is in fact two oil pumps inside one pump body.
Side one is the feed, oil from the tank is fed to the smaller of the two pistons and pressurised, it passes out of a non return ball valve to the chamber where the oil pressure relief valve sits. This valve is spring loaded, once 60psi pressure is reached it opens a port to dump the excess pressure, the excess oil from this port goes into the crankcase.
Once the oil pressure is regulated, the crankshaft and exhaust cam followers are fed with oil at 60psi, the used oil drops to the bottom of the crankcases.
The excess and used oil dumped in the crankcases has the bottom of engine flywheel spinning in it, this splashes up to lubricate the cylinder walls and inlet camshaft.
Side two is the return, a pipe in the bottom of the crankcases picks up the excess and used oil, through the larger of the two pistons in the oil pump, the return has 30% more capacity than the feed, so it will always clear out more oil than can be pumped in. This is a good thing, it means the crankcases do not fill up with oil.
Then retuns the oil to the top of the oil tank. Half way along the pipe is a tee, this feeds some oil to the valve gear at the top of the engine. Because the return side is pretty much open to the tank, the return oil pressure is low.
Last edited by Rancidpegwoman; 04-02-2019 at 09:46 AM.