Mercury 1977 850 bleeder line

[hereto]

Hi everyone,
I have a 1977 Mercury 850 Serial #4719943. The bleeder line which runs from the bottom of the crankcase to top of the crankcase has a check valve at each end. The upper valve is one way in, the lower valve is a one way out. This bleeder line supplies the upper main bearing with oil puddled in the bottom of the crankcase.
I intend to replace the upper check valve with a standard straight thru fitting,and keep the lower check valve the same (one way out ).
Have tried this with a straight thru fitting and clear fuel line so I could see what was happening. I actually observed a better volumn of fuel,oil thru the line when I had the straight thru fitting at the top. Have been told that
this was the way it should be set up. ( top- straight thru fitting lower- one way check valve out. )
Am I getting ready to do something I will wish I hadn't ? Better oil flow to that bearing seems a win, win to me.

Thanks ahead of time for your thoughts and help. And yes, I have had upper main bearing issues in the past.

hereto

 

[Chris1956]

IMO, a straight thru fitting is fine. The bleed system on my '77 Merc 1500 had the one way at the bottom and a straight thru on the top.

 

[CharlieB]

It will work fine.

I think the theory fro the factory was to prevent crankcase pressure from the upper cylimpeding oil flow in the hose.

I wouldn't sweat it a bit. Run it.