TOPIC: 1961 800 EL cylinder bleed check valves?

Hello all,

I have a 1961Mercury 800EL w/full shift and have had 2-failures of the cylinder bleed check valves.

Last Fall the motor would not idle and I found the cylinder #3 & 4 check valve seat loose and floating around in the tee connection. Put in a replacement from another motor and had no problems for a year.

Last weekend the same problem occured while I was out on the lake where she would start and run at high idle but dies at low idle and as soon as I put it in gear.

This time I checked them and found the cylinder #1 & 2 check valve apparently leaking through. I took one off another motor and it seems to run fine now although I have not checked it out on the water.

My understanding is the check valves allow any fuel that acummulates in the upper crankcases to drain to the bottom crankcase to burn off. I heard that they can be eliminated simply by plugging the crankcase. I am curious what others may have have experienced.

This tiny part, smaller than a pencil eraser, has twice nearly ruined my weekend. Well actually we still had fun on someone elses boat.

Thanks,
Terry D

These are the valves.

Terry

My understanding of the purpose/function of the cylinder bleed assembly was to move gas/oil mix up from the pool in the crank case to the top cylinders so that the bearings up top are lubricated effectively. If the check valves are incorrectly installed or are failing I can see that this would, over time, promote wear in the upper bearing assemblies. Am I correct in my understanding?

I also don't understand how, if the cylinder bleed assembly was bad, it would affect idle. Can some one clue me in?

I was of the opinion shared by Peter in how the system should work, but I have discovered that the 800FGS way of doing thisngs is virtually opposite most other Mercs.
How crazy is that!
Anyway,...See the attached for 800FGS details.
I stripped the pieces in question off an original 800FGS block today.
With review of all this and to bounce back to the original question of can this system simply be blocked off - I would not.
Primarily because the 800FGS does not have a separate crankcase pressure balance system and this system doubles in that assignment.
Should there be any reason for this system to affect idle quality?
I'm with Peter in that I don't see how it would.
BUT,...I am not sitting at the top of the Mercury Mountain of Knowledge either and am but a lowly Padawan in the Sacred Order of the Black Tower Knights.
Sheeesh,...Best I could do.

Thom

yeah,....i'd not block them off - I am sure Merc put them there for a reason..... But if Doc Frank is a Padawan, I am but an Ewok....

Hello Peter & Thom,

Thanks for your earlier responses.

I am revisiting this issue again after seemingly experiencing problems with these persnickety little critters.

As described in my earlier post on the Merc 800 distributor cap a couple weeks ago I am tuning up my 61 Merc 800 after experiencing some hesitation coming out of the hole.

Had a similar problem before and determined one of the cylinder bleed check valves was leaking. So I checked them again and sure enough #3-4 was leaking a bit. I had an extra new valve so I went ahead and replaced it. Got the old Merc back together but will not water test until next week.

But I’m still trying to grasp function of the great old engines and climb that “Mercury Mountain of Knowledge”. You mention here crankcase pressure balancing and that this system accomplishes that.

It seems to me that the individual crankcase pressures should and will vary depending where they are at in the stroke cycle. If the top or middle check valve is stuck open the pressures will equalize to the bottom crankcase which of course is at a different point in the cycle.

I could be answering my own question now but the orifice on the check valve is very small and pressure leakage through would probably be minimal.

As far as plugging them I would not do that and I like to keep things as original as possible. If Charlie thought this is the way to do it I will not argue. But I was told that others have taken that approach.

Thanks,
Terry