No this isnt another question about oil dumping out the breather. Im hoping someone can shed some light on how oil in the EVO crankase gets back to the scavenge side of the oil pump. Is there a port or passage in the bottom of the cases that leads direclty to the pump or does the oil get sucked into the pump from another part of the engine like the cam housing / breather area (which I read somewhere).

I suppose I better come clean as to why im asking - I was drilling out the cases to fit cylinder stud inserts and i had some greased cotton wool at the bottom of the hole to catch the shavings and the pilot tool pushed the cotton wool completely through the hole inside the case. So now im wondering if it will just fly around in the main bowl of the cases or will it float in the oil and possibly block the oil scavenge (return) pickup.

Or do I split the cases just to retrieve this little bit of cotton wool?

BTW, if anyone has pulled their cylinders stud threads, the Sifton Racers stud kit is excellent. It comes with chromemolly studs, timeserts, tap and the excellent pilot drill that self centres in the hole and also counterbores for the insert shoulder. Real easy to fit even without instructions.

Thanks for any replies in advance

PS. Disregard my quote below       

Hi Wazdog,

Hope this diagrams give you an idea of the way oil flows through an Evo.

Beeza's method is easier than splitting cases and you want to get that bit

of cotton out for sure, you know it will bite you in the ass at  the worst 

possible moment if you don't.

Cheers,

Cris.

omntm 

Hey Don, thnx for taking the time to post those diagrams.

Very interesting. Now a close look at that rear sectioned view shows the return oil drawn from a pool in the cam chest below the breather gear. It doesn’t show a passage running directly from the bottom of the cases where the cotton wool will be sitting and hopefully stay. So in other words, oil is not sucked from the lowest part of the cases as ud normally expect. The only passages I see is on the primary side to feed and drain the main shaft bearing.

If that’s how it is I may risk it running it. The worst that could happen is I end up with an empty oil tank and a full crankcase which will then pump it out the breather hose (or a dry crank bearing).

And Beeza, where was the oil and petrol flush actually draining from when you had the bike layed over? The only plug on that side is the timing inspection plug.

cheers

Wazza

Part 2.

Well this pic showing the inside of the right case proves that there is no oil pickup passage. Looks like the only way oil can get out of the crankcase is through the cavity you can see at the top which is actually the casting where the motor bolts to the tranny. This cavity leads straight into the centre the screened breather gear which is probably the only place the cotton wool could end up.

 Fingers crossed im going to leave it unless someone with more knowledge can correct me b4 its too late.

no ,    i have a big sucking tool  that i can put a extended hose on the end  & put it in the case too suck out the dirty oil  if you have not turned the crank around  it wont  get  pushed into the scavenge section , i put clean oil in about a pint  give it a bit   of a shake , when you put the oil in  pour it all over the crank & case the help wash it too the bottom , you can buy the sucking tool & a cheap car shop  it's like a  big steel suringe about 60 -70 mm round - 250mm long with a pull handle  they are made for sucking excess oil out  you can pump it out on too clean newspaper to see what come's out,