Engine oil return question

[igya]

The 4 outside head studs allow oil to return to the block. The block (at the point where the head studs screw in) has oil drain channels cast in it. However, 2 of those channels are blocked off by the cylinder centering ferrules.

How can the oil get past these ferrules and back into the block? Are the 2 that's not blocked off be sufficient? Also, it seems that the 2 blocked stud holes would just fill with oil all the way to the head with no way to drain.

What am I missing here???

Thanks!

 

[retiredgentleman]

The engine oil does not return via the engine studs. The outer studs are exposed to oil pressure, just because that is how they had to drill the passageways.

Oil returns via the camchain tunnel, and by the drain passageways near each valve.

 

[igya]

Very true about the chain tunnel being the oil return. I know the oil tube in front of the cylinders supplied the rockers and cam with oil. But, you got me wondering about those outer holes so I just went to my shop and took another look. There's not a single hole anywhere in those tunnels, from the block to the head nuts, for oil to get to any parts. Which makes me wonder why oil would be pressurized in them. The rubber coated washers are for that reason, but why???

 

[retiredgentleman]

When Yamaha designed the engine, it happened that the oil passageways and the outer studs contacted each other. There was no reason or no intention to have them connected. As I said before the outer studs are not part of the oil circuit.

Rubber or copper washers prevents leakage...................end of story.

 

[igya]

Okay, I finally get it now. Some things are just not worth wondering about. Thanks for putting up with the ramblings of an old fool. I'm going to put that little unit back together tomorrow and let the oil take care of itself. Thanks again!!