Alpha One Gen One -- melted seal and water pocket

Ugarph1982

Cadet
Joined
Apr 8, 2017
Messages
16
I have a 1988 Mercruiser 3.7 with an Alpha One Gen One. Despite the idiosyncrasies of the engine, it's been quite reliable for me and provided a lot of fun. This post concerns a finding during my annual maintenance on the outdrive. This year, those maintenance items included gear oil change, new bellows (all 3), water hose, sea water pump, and new prop. The disassembly went fine and yielded no major issues. All rubber parts were intact, but due to be replaced.

One anecdote (before I get to the problem) ... Last winter, I found that my exhaust bellows had torn, but the others were in good shape, so I was just going to replace the exhaust. Anyone who has tried to change out an exhaust bellows without removing the bell housing hinge pins knows how big of a pain in the ass it is to get the bellows attached to the bell housing (and I have the expander tool.). Needless to say, I said "screw it" and just put an exhaust tube (used on the V8 motors) on the transom assembly that just slides over the bell housing inlet when the trim is down. That worked fine, but I didn't like how much noisier the boat was, so I knew I would switch back to a bellows this year when replacing the rest of them.

The problem .... I noticed a little bit of milkiness (water) in the oil when I drained it. The fluid was still dark blue, but had some cloudiness. After I split the cases and changed out the entire water pump assembly (including the base with the oil seals and gaskets), I went to put the halves back together. A quick look into the upper half revealed that the lower water seal (that I replaced 2 years ago) and the water pocket cover where melted and dis-formed (both on the side where the exhaust enters the drive). The damaged seal was a smoking gun for the water in the oil.

It's worth noting:
--I NEVER run the boat out of water without the water adapter and good water pressure. Even with the adapter, I only run it for a few moments and at low RPM's.
--The engine does not run hot at all ... Pegs at 160 per the thermostat.
--The impeller on the old water pump was in decent shape when I removed it (no missing rubber)
--I have, of course, ordered a new water pocket assembly and lower seal which will be easy to replace.

What I need help with ... What could be causing this? I know exhaust gases are hot, but mixed with water from the exhaust, I would not have expected this kind of damage in 2 years. Below are my theories. Please poke holes in them.

1) Water delivery issue. Perhaps the pump wasn't delivering enough water ... Hard to believe because the engine was not running hot even on the warmest of days.
2) The aforementioned exhaust tube ... Perhaps enough of the water was escaping from the tube before going into the drive, but the exhaust gases were still making their way through the drive. Ehh ... maybe.
3) Maybe the engine was running too lean and EGT's were too high ... No backfiring or performance issues though (hole shot or top end)
4) Maybe it's just par for the course for the old Alpha Ones.

Any input would be greatly appreciated. Sorry for the long-winded post!

Thanks!
 

Rick Stephens

Admiral
Joined
Aug 13, 2013
Messages
6,118
Lean is unlikely to be the cause. Plenty of water in normal operation to keep the water pocket cool.

The exhaust tube is not the problem.

My guess, sucked up something that plugged your intake or you pinched the water line between lower and gimbal housing.

Pressure test your drive, make sure you got the seals 100%. You replaced the impeller. Check flow, hook up the muffs to your hose, disconnect the inlet hose at the thermostat and fire up for a minute and see how much water flow you have flowing out at the engine end. Hook it back up to the thermostat and the see how much you have exiting the transom once the motor comes to temp. If all is normal, go boating.
 

Grub54891

Vice Admiral
Joined
Jun 17, 2012
Messages
5,908
If it has the power steering oil cooler, pull the hose from the intake side, see if there is any debris in there. You can also backflush to get it out of there.
 

Rick Stephens

Admiral
Joined
Aug 13, 2013
Messages
6,118
I have to revise my earlier post. The 470 always had closed cooling. So pulling the line off the thermostat won't fly.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,307
all it takes to burn up an impeller and melt the plastic is to pick up a piece of seaweed, run aground, pick up a plastic bag or other piece of debris (there are literally thousands of tons of plastic bags floating in the lakes, streams and oceans)
 

ImperialV184

Petty Officer 3rd Class
Joined
Aug 4, 2011
Messages
99
You are saying the water pocket cover was melted not the impeller right? Water pocket cover is in the top of the upper. The water from the pump probably does not offer much cooling for that it is directly inline with exhaust. When you run engine out of water are you seeing a good amount of water coming out of the exhaust vents in the gimbal housing? On my 3.7 at temp the water is hot but not too hot that it burns my hands.
 

Ugarph1982

Cadet
Joined
Apr 8, 2017
Messages
16
Thanks to everyone for the input! This forum is great. A few clarification points are below.

--It is a closed loop system (470), so the lake water only goes through the heat exchanger, power steering cooler, and back half of the riser once inside the boat.
--The impeller itself was not burned up and the thin aluminum race inside the pump housing did not show any real signs of wear. That tells me that the pump was probably not being starved for water and any blockage would probably be further along in the circuit.
--The water pocket cover has a few main parts (the 3-D assembly itself (42724A3), the cover (27-558101), the rubber seal (26-36557) and the copper pipe. The first part listed is what was melted. Additionally, the rubber on the lower water seal (26-965031) was also melted on the side where the exhaust enters the upper half.
--When I took the hose off between the bell housing and transom assembly, I found it rigid and beginning to crack. Perhaps it was kinking. It also could have been leaking (which would have been impossible to detect without it running out of the water).

What I'll do:
--I'll remove the clamp attaching the hose to the riser (just past the PS oil cooler) and flush water backwards to see what it looks like coming out of the transom assembly. This should reveal any blockages in the cooler, heat exchanger, or tubing.
--I'll run the motor with a garden hose attached to the water inlet on the transom assembly and check out the water and exhaust flow from pipe (without the bellows attached). If I've done the first step and things look good, this step would tell me whether or not there's an issue with the riser (replaced last year with a GLM part). I bore scoped cylinders 3 and 4 and there is no water or coolant, so I don't believe it is leaking or doing anything weird.
--I'll remove the inlet screens on the bottom half of the drive and make sure they are clear and that there's nothing blocking those passages up to the pump.


Anything else y'all can think of? I really appreciate it.
 

kenny nunez

Captain
Joined
Jun 20, 2017
Messages
3,056
You will have to replace the seal that is above the lower one in the driveshaft housing. The surface of the shaft which is the lower extension of the gear may be pitted to a point that a new seal will not hold pressure. You may have to add a Speedy Sleeve to repair the surface.
This means you will have to disassemble the drive shaft housing. Any time the lower seal comes apart water gets to the lower extension of the gear and since it is not stainless it begins to rust and pit. The repair sleeves are stainless.
 

Ugarph1982

Cadet
Joined
Apr 8, 2017
Messages
16
Thanks for the input Kenny ... I did the full re-seal a couple of years ago because I had gear oil leaking into the u-joint bellows. The carrier yoke on the horizontal shaft was worn big time so I replaced the whole yoke and carrier bearing seal assembly. The vertical shaft where the upper seal you are mentioning rides surprisingly did not have any grooving at all. I'm not sure a speedy sleeve would do the job in that location because the shaft is tapered. It would likely require replacing the entire vertical shaft.

Although it makes me sick to my stomach to think about having to get that spanner wrench back out and pull all of that crap apart, it might be worth at least taking a look.
 

ImperialV184

Petty Officer 3rd Class
Joined
Aug 4, 2011
Messages
99
You said that the engine hold steady at 160, if you are not getting water flow properly through the heat exchanger I do not think it would hold that temp and would overheat. On my alpha when running out of the water the majority of the water comes
out the two exhaust vents in the gimbal housing not through the exhaust bellows. If those are blocked it could be directing more exhaust through the lower and causing the heat damage.
 
Top