Mercruiser 5.7 Alpha One seems to "slip"

[ildoc]

I have very little experience in boating, so this may be basic: On occasion, when attempting to accelerate out of the hole, my 22ft deckboat with a 1996 Mercruiser 5.7 Alpha One will rev up but the boat actually slows. Backing off the throttle will cause it to "engage" again at around 2,000 RPM, but attempting to go over that will cause the same symptoms. It has almost the same feeling as a car's wheels slipping on ice. There are no unusual noises and the engine runs smoothly, and it doesn't happen on every outing. Is this a prop problem?

 

[tommays]

Re: Mercruiser 5.7 Alpha One seems to "slip"

if the motor was trimed up for running at speed and you slowed down or stoped and did not trim it down again it could do that<br /><br />tommays

 

[zzzzz]

Re: Mercruiser 5.7 Alpha One seems to "slip"

prop hub is the first thing to check...then the engine coupler

 

[ildoc]

Re: Mercruiser 5.7 Alpha One seems to "slip"

Originally posted by tommays:<br /> if the motor was trimed up for running at speed and you slowed down or stoped and did not trim it down again it could do that<br /><br />tommays

I thought of that, trimmed all the way down, and got the same results.

 

[ildoc]

Re: Mercruiser 5.7 Alpha One seems to "slip"

Originally posted by zzzzz:<br /> prop hub is the first thing to check...then the engine coupler

Took the prop off and didn't see anything obvious. What should I look for?

 

[Haut Medoc]

Re: Mercruiser 5.7 Alpha One seems to "slip"

There is nothing obvious with a spun hub. Suggest you try a different prop. & see what happens.........

 

[milkyway]

Re: Mercruiser 5.7 Alpha One seems to "slip"

It is hard to tell a spun hub by just looking at it. My experience - compare it with a new one that is identical to what you have now. That's what I did. My prop was off the hub for just a tiny 1/4" when compared with the new, but that 1/4" difference meant that the prop slid the hub. Good to hear that your engine's doing ok.

 

[wvit100]

Re: Mercruiser 5.7 Alpha One seems to "slip"

Make a mark with something, waterproof paint or scratch a line, across the rubber doughnut and the prop. Then take it out and run it around for awhile and give it the throttle a couple of times. If you then look at it and the lines aren't still together you'll know the prop is slipping.

 

[MrBill]

Re: Mercruiser 5.7 Alpha One seems to "slip"

Intermitent "prop slip" tends to be leaky or faulty trim cylinders. Under acceleration the outdrive begins to lift, then settles back down under less stress. When they (or one) first starts to go bad its baffling, you think the prop is spinning, etc. Obviously, check the prop first, the coupler seldom goes bad like that, head for the trim cyclinders. It baffled me last year for a week.

 

[ildoc]

Re: Mercruiser 5.7 Alpha One seems to "slip"

Originally posted by MrBill:<br /> Intermitent "prop slip" tends to be leaky or faulty trim cylinders. Under acceleration the outdrive begins to lift, then settles back down under less stress. When they (or one) first starts to go bad its baffling, you think the prop is spinning, etc. Obviously, check the prop first, the coupler seldom goes bad like that, head for the trim cyclinders. It baffled me last year for a week.

What do I look for in the trim cylinders?

 

[Don S]

Re: Mercruiser 5.7 Alpha One seems to "slip"

Wait a minute here. Leaky cylinders is not your problem. If you had leaky cylinders that caused the drive to come up, you would have to be in reverse to cause the problem of the drive lifting. When going forward the drive is pushed all the way down.<br />Check your prop. <br />If you have smelled burned rubber when it happens, it's probably the coupler on the flywheel.

 

[Richard Petersen]

Re: Mercruiser 5.7 Alpha One seems to "slip"

If it is none of the above, look underwater for slime and weed growth in front of the prop. The blowouts come more often and at lower speeds as the weeds grow.

 

[ildoc]

Re: Mercruiser 5.7 Alpha One seems to "slip"

Thanks for the help, guys!

 

[MrBill]

Re: Mercruiser 5.7 Alpha One seems to "slip"

Don: Trim cyclinders are 'pressurized' in both directions, drive can lift if faulty when under load, it baffled me last year for quite some time. eclymer...is your problem solved??

 

[ildoc]

Re: Mercruiser 5.7 Alpha One seems to "slip"

Originally posted by MrBill:<br /> Don: Trim cyclinders are 'pressurized' in both directions, drive can lift if faulty when under load, it baffled me last year for quite some time. eclymer...is your problem solved??

Just got a new prop and hub, but won't be able to try it until 6/25. I'll update interested parties here about the results. Thanks again, and I'll keep you posted!