Pressure test alpha one. Where's the leak ? Where to start ?

[ChrisSmith290]

Hi, I'm trying to figure out where to start on a slow leak on my alpha one drive. I put 12 psi in the drive, 45 min later still at 12 psi. When I turn the yoke assembly clockwise the pressure drops to 11.5 and stays there. I had gear oil in the bellows that was coming from a groove in the small yoke, when I took the drives off for the winter ,about 4 ounces. The drive wouldn't hold pressure for 30 seconds when I took it off. Naturally I replaced the oil seal on the yoke too. No water in the oil when I drained it. I replaced all seals three years ago. My question is what might be leaking that would only only leak when the shaft it turned? Thanks in advance and looked around this forum a bit for something like this but couldn't find anything. Also I replaced the same on the other drive and it's perfect. They are twin 4.3's on a 1988 30' cruiser.

 

[HorizonblueDK]

Some time ago, I got involved in a repair job on a Campion with a mercruiser V8/Alpha One, that also would leak, but only when the outdrive was running. I found out that the two shaft seals under the waterpump, were not seated properly, they were installed at an angle. So when the vertical shaft was not rotating, the seals could hold the pressure, but the seals would apparently open just a little, when the shaft rotated, because of the angle they were installed in.

 

[ChrisSmith290]

Thanks HorizonblueDK that's exactly the type of info I was looking for. Now I have somewhere to start.

 

[ChrisSmith290]

It actually dropped 2 psi overnight so that leads me to believe I may have botched something. I've been doing this for years , could have got sloppy somewhere. I change out water pump kits every year never had a problem before. Next week I'll tear it down and start over. Change some seals maybe shift shaft bushing and o rings.

 

[FreeBeeTony]

Did you replace the yoke w/ the grove or only the seal?

 

[JustJason]

Sometimes they don't leak until they heat up. Sometimes they don't leak until the shafts are spinning a few thousand rpms. If you have a tricky one hook up your pressure tester and stick the lower unit in a kiddy pool

 

[ChrisSmith290]

I replaced the yoke and seal on the assembly. The kiddie pool is tough now due to sub zero temps. I suppose I could try something in my basement. I just ordered a lower seal kit with shift shaft bearing and o rings. I'll try it again next week. And yes I have the mercruiser service manual and all the special tools and seal drivers . I think I may have botched this somehow.

 

[Rick Stephens]

Sometimes they don't leak until they heat up. Sometimes they don't leak until the shafts are spinning a few thousand rpms. If you have a tricky one hook up your pressure tester and stick the lower unit in a kiddy pool

I needed to use a water trough to find my leak. Works great.

 

[FreeBeeTony]

I would also double check your pressure set-up to make sure it's not leaking...........

 

[ChrisSmith290]

Thanks that's the first thing I did when it started was to check the tester. Held overnight on my other drive. The water trough sounds great though thanks

 

[ChrisSmith290]

Ok its been a few days where work got in the way of having any time to work on this drive. I do have a good question I would like answered before I totally rip this drive apart. Keep in mind I've been unable to find the leak with soappy spray bottle and its a very slow leak. My question is when I pump air in the drive, the drive shaft housing shift shaft comes out of gear. Naturally when I put the shift shaft in full forward position and apply counterclockwise pressure to the prop shaft the drive will be in forward gear. As soon as air goes in the drive it comes out of gear and there is constant pressure keeping the shift shaft out of gear. My other drive that does not leak will keep the shift shaft in forward gear. Does this sound like the culprit could be the shift shaft bearing ?

 

[achris]

You need to understand where all the seals are and what exactly they are sealing. Have a read of this -> http://forums.iboats.com/forum/engin...63#post5509663 , it may help.

Rather than a water trough, which will get you yoke and unis wet too, use a mixture of water and dish-washing liquid. Put it on with a paint brush or a squeezy bottle and watch for bubbles.

 

[ChrisSmith290]

Achris thank you so much that was very helpful. I'm with you on the soappy water too. That's how I usually do it. I actually started another post because I was trying to dial in on this shift shaft dilemma. I'm really stumped on this one. The drive is not leaking and holding 12 psi for 6 hours now. I actually replaced all the uppers after reading the link you sent me on leaks on outdrives. I don't understand why the shift shaft moves counterclockwise out of gear as soon as I put air in the drive. I'm wondering if this is even a big deal. It's definately not going to leak oil.