Exhaust Pipe on 1974 140 Mercruiser

[bbook83]

I'm getting ready to put the engine back in and am putting on a used exhaust pipe to replace the one shown in the picture, which had been gouged badly by the armoring on the lower shift cable. I have a new seal that is an oval o-ring that goes around the opening of the receiving surface on the gimbal housing. I see seals and pipes in some of the manuals that go around the two holes on either side of the center hole through which the black and grey hydraulic hoses pass. Those two holes go back into the gimbal housing to a dead end and seem to have no function. Does anyone know the function of those holes, as it appears that they are left uncovered when the pipe is installed?

Also, I don't see mention in the manuals about a sealant on the o-ring. Do any of you use a sealant here?

 

[thumpar]

Those 2 holes should go to the idle relief ports on the other side of the transom.

 

[bbook83]

If the idle relief ports are the smaller openings from which I see exhaust and water spitting when running on the muffs, these exit from a point inside the main oval exhaust opening in the gimbal housing to which the exhaust pipe attaches. The holes to which I am referring do not exit on the other side of the transom.

Any thoughts on just using bellows cement on the o-ring to hold it into the gimbal housing and call that good without further sealant?

 

[Bondo]

Any thoughts on just using bellows cement on the o-ring to hold it into the gimbal housing and call that good without further sealant?

Ayuh,.... Some down-pipes use a single funny lookin' o-ring to surround all 3 holes, 'n some, like in yer pictire use 3 o-rings,......

The o-rings is all the sealin' needed,.....
You can glue 'em in-place, or I use grease to hold 'em, til the pipe goes on,....

As noted, the 2 smaller lower ports are the idle relief ports,...

 

[bbook83]

There is only one large o-ring that sets into a groove on the circumference of the exhaust opening. The face of the pipe is the same, so when the pipe is installed, the openings below remain exposed and no exhaust runs through them. It is of no consequence, because they dead end a few inches back into the gimbal housing and nothing gets connected to them, even though there are grooves around them to accept o-rings. I have seen pictures of units where the o-ring goes around the lower holes and the pipe is configured so as to cover them, but that is not what mine looks like. A bit of a mystery.

The Mercury parts lookup shows PN 53272A5 for the pipe for the 120 and PN 53113A7 for the 140 and 160. They both mate up the same, but the 120 has a deeper bolt receiving area. Unfortunately, I didn't note the difference and got a used 120 pipe. The gouge in the old one is not deep enough to create a leak, so I will fill it with JB weld and try to route the shift cable so it isn't in contact with the pipe.

 

[Bondo]

but that is not what mine looks like

Ayuh,.... I don't doubt ya, just never seen one like that,....

 

[thumpar]

I know there were some different configurations. It looks like you may have a combination of a couple.

 

[bbook83]

I do believe Thumpar is correct. There are two different gimbal housing gaskets for these models, depending upon the gimbal housing serial number. The one that fits my gimbal housing is cut out deeper at the bottom to accommodate the "dummy" exhaust relief ports. The other gasket blocks that area and won't seat properly. Both probably use the same lower exhaust pipe, which mates only to the large exhaust port. The functioning exhaust relief ports are on both sides, inside the large exhaust port and are simply holes angled down and through the gimbal housing. The "dummy" exhaust relief ports apparently became the real thing in later versions and the mating of the pipe was modified to include the exhaust relief ports and used the funny looking o-ring that Bondo described. If I am correct, this was probably common knowledge amongst Mercury technicians 42 years ago, but may have been lost in time since.

It is strange completely ignoring a specifically machined component of the assembly, but that is how it was set up when I took it apart, so it should work going forward.