Mercruiser 350 Alpha One problem

[allingeneral]

Hi all. Long time no see

I have a 1989 Mercruiser 350 with an Alpha One outdrive and I'm having a problem.

Problem indications:
When using a stainless steel prop, the boat will not plane. It gets about halfway to plane at about 3500 RPM, then the engine revs and the boat loses all power as if something is letting go in the driveline. I thought that I had a spun prop, but took that in and had the hub replaced and the old one was fine. So, of course, when I tried it again, I had the same problem.

The boat doesn't do this when I use my aluminum prop. I am assuming that the stiffness of the stainless prop creates more torque, thereby breaking the driveline loose and the aluminum prop will eventually start doing it as well.

I've been told that there's a rubber coupler between the engine and the outdrive (mounted to the flywheel?) and that the engine must be removed in order to replace it. Can someone give me an idea about how difficult this is to do for a fairly experienced backyard mechanic, or have a link to a resource that would be helpful? What kind of adjustments and/or alignments are required?

Is there anything other than a spun prop or the engine coupler that could be causing this problem?

Thanks in advice for any replies.

Regards,
Rick

 

[Trent]

Re: Mercruiser 350 Alpha One problem

A slipping coupler usually causes the engine temp to go up. Look at the rear of the engine. Do you see any "rubber dust". This is the normal sign of a slipping coupler along with temps going up. How hard is it to change a coupler? Depends on the boat. You need to remove the outdrive and then pull the engine enough to get to the coupler. Sometimes you have to remove the engine from the boat to get to it.

 

[Bondo]

Re: Mercruiser 350 Alpha One problem

Is there anything other than a spun prop or the engine coupler that could be causing this problem?

Ayuh,... My guess is the SSteel prop you're playing with is the Wrong 1, or otherwise is Screwed up...

If the Coupler is slipping, It would do it with Both props.... Period, No ifs, ands, or Buts...
Ditto with any other driveline issues....
If this happens Only with That particular Prop, it's the Prop...

 

[mkast]

Re: Mercruiser 350 Alpha One problem

What pitch propellers are you using?

 

[Don S]

Re: Mercruiser 350 Alpha One problem

Try your other (aluminum?) prop again. Normally, when the rubber part of the coupler fails, you will not get even close to 3500 rpm before it starts slipping, then when it does, you will smell rubber burning.
Just an FYI, A coupler that fails by the rubber breaking loose will still turn the raw water pump in the drive. The only way a faulty coupler will cause an overheat is if the splines in the coupler are gone, at that point it won't turn the prop at all.

 

[allingeneral]

Re: Mercruiser 350 Alpha One problem

Ayuh,... My guess is the SSteel prop you're playing with is the Wrong 1, or otherwise is Screwed up...

If the Coupler is slipping, It would do it with Both props.... Period, No ifs, ands, or Buts...
Ditto with any other driveline issues....
If this happens Only with That particular Prop, it's the Prop...

I had the hub replaced in the SS prop. The guy who pressed the old one out said there was nothing wrong with it. What else can possibly be wrong with a prop other than a spun hub? If the size were incorrect, I can't imagine that it would produce the problem I'm having...maybe low power or too much RPM, but not halfway to plane and just suddenly lose all headway and rev out the engine.

 

[allingeneral]

Re: Mercruiser 350 Alpha One problem

I don't recall ever smelling a burning rubber odor of any sort.

I used the aluminum prop to pull my kids on the tube all last summer and it never exhibited this problem.

I can't recall the propeller pitch - I think the both props are the same, either 17 or 19.

I'll check for "rubber dust" near the rear of the block.

 

[Don S]

Re: Mercruiser 350 Alpha One problem

Put the aluminum prop back on and try it. If it works ok, you know you have a prop problem of some sort.

 

[TilliamWe]

Re: Mercruiser 350 Alpha One problem

Put the aluminum prop back on and try it. If it works ok, you know you have a prop problem of some sort.

Exactly

 

[sdoomaha]

Re: Mercruiser 350 Alpha One problem

If you have tried your aluminum again, and all is fine...is your stainless high performance...vented by chance? IE....are there any holes drilled in front of the leading edge of the prop blades? Are you running any kind of a hydrofoil? I've personally experienced "prop slip" from both....

Hope you isolate it....

 

[ziggy]

Re: Mercruiser 350 Alpha One problem

just a thought.

does the ss prop install proper and sit up very close to the drive? there are different thrust washers that are different thickness for various props.

 

[allingeneral]

Re: Mercruiser 350 Alpha One problem

The SS prop isn't vented and it seems to fit just right with the same thrust washer as the aluminum prop. No hydrofoil installed. Cavitation...hmm... doesn't seem like it would cavitate like that, but if everything else seems to be in order, it's certainly a possibility.

Thanks for the replies!

 

[Don S]

Re: Mercruiser 350 Alpha One problem

Did you retry your aluminum prop? or are you just going to avoid those comments?

 

[allingeneral]

Re: Mercruiser 350 Alpha One problem

Did you retry your aluminum prop? or are you just going to avoid those comments?

Oh, yes - I switched back to the aluminum prop when the SS prop didn't work out for me. I have been running the aluminum prop for 3 years and it's never caused a problem.

The SS prop was in the boat when I bough it and I just decided to try it out one day. The problem that it introduced has me scratching my head - and I haven't used it again since the last retest after replacing the hub.