4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

[misterme21960]

Ha, I was fishing the other day boat was running fine...decided to float and fish so I turned the engine off with NO problems...fished for 30 minutes started the motor back up and it wouldn't go anywhere forward or backwards...and it does make a NON motor noise when the engine is running...not real bad but I can hear it...

With boat out of the water engine OFF, I put the boat in gear and can only turn prop one direction in either forward or reverse which I assume is right...and in neutral it spins freely...shift linkages seem to work properly never had a problem with this boat EVER and I take care of it...

Inside the Engine compartment you could eat off it, clean, and the boat is a 1988 Larson with a 4.3L Mercruiser and Alpha One Outdrive...This boat has never been beat on or misused and NO one has ever drove it but me...all the fluids are clean and fresh...all the cables that run the throttle and linkage were new 4 years ago...and until this year the boat has only been out maybe 10 times since 2008...

Funny thing is there was never even a sign of any problems until I started it up that last time...Engine would rev but wouldn't move in the water...Thinking it could be that coupler in the bell housing, but wouldn't the prop turn freely even if it was in gear, Engine off...if it was that coupler?...

Another idea of my own is where the cable attaches to the outdrive from the throttle, since the from what I see the linkage moves when I operate the throttle...Also thought the prop, so I took it off and gonna put on my spare in the morning...but I'm thinkin' if it was the prop it would still move just alittle bit in gear if the center was spinning...Any ideas so I don't have to take it to a shop, not only do I not trust any shops...But I don't believe in what they charge to work on anything for the quality of work, I can do it myself with online and book knowledge...It isn't that difficult...and I can do about anything...And these boat forums are awesome, I would love to hear any ideas and if I'm heading in the right direction with this before I put the boat up this winter

 

[RandyJ]

Re: 4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

When I had a spun hub in a prop my boat would at least move as long as I didn't throttle up...just kind of idle. In my old fishing boat I spun a coupler. The boat wouldn't move at all when in the water. If I tried to turn prop by hand it acted normally. I don't know what your coupler looks like but mine was the type shaped somewhat like a wine glass. It should be dry on the end. If it has some greasy black stuff that smells like burned rubber then it's toast. Also, did you smell anything when it happened... like burned rubber? Too, if it is the coupler then it's going to get very hot when running and spinning inside the coupler. A normal/good coupler will be cool enough to hold your hand on after it has been run.

 

[misterme21960]

Re: 4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

Didn't smell a thing...I'm getting ready to check the coupler if I can by stinking my hand in there...I might have to fix it in spring if it's the coupler...Thanks, for your comment

 

[Maclin]

Re: 4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

Another symptom of the coupler giving out is engine overheat. The impeller is in the leg, so when the coupler goes out the impeller will not spin, thus no raw water gets up to the cooling system.

 

[misterme21960]

Re: 4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

Guess I don't quite get why the prop will only turn one way in gear even though the coupler were out...I thought that if the coupler were out the prop would free spin in or out of gear...Haven't went out to the boat yet, just got some other things done then I'll work on the boat again...Thanks for the input

 

[mr 88]

Re: 4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

The gears in the lower unit engage your drive system,in one direction or the other.The drive shaft is always moving when the engine is running.You can take the out drive off the boat and it will react the same way.That shaft moves the impeller which brings the water into the engines cooling system The prop will lock up in opposite directions and ratchet in the other,so yours is working fine.Does your engine overheat when at a high idle? That is the easiest way to tell if your coupler is bad.The odds are if it is shot so is your bellows and gimbal bearing along with your U joints.There is a very small chance that your internal drive shaft,the one that goes to the impeller is broken.So check the prop hub or put spare on,check for engine temp then report back.

Guess I don't quite get why the prop will only turn one way in gear even though the coupler were out...I thought that if the coupler were out the prop would free spin in or out of gear...Haven't went out to the boat yet, just got some other things done then I'll work on the boat again...Thanks for the input

 

[misterme21960]

Re: 4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

I've posted here 2 times and it didn't show up so I'll post again tomorrow....sorry...so far everything looks new that I've looked at on my boat...Drive coupler looks as new as the day they replaced it 4 years ago, same with the bellows...everything real clean with no rust...I'll get back tomorrow after I see if this posts

 

[eatonr]

Re: 4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

I've posted here 2 times and it didn't show up so I'll post again tomorrow....sorry...so far everything looks new that I've looked at on my boat...Drive coupler looks as new as the day they replaced it 4 years ago, same with the bellows...everything real clean with no rust...I'll get back tomorrow after I see if this posts

What did you end up finding i have simalar problem?

 

[misterme21960]

Re: 4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

What did you end up finding i have simalar problem?

It was the drive coupler, everything else was fine but I freshened up the Gimbal bearing,
Impeller, carb rebuild...all a result I think from sitting in storage...It's never ran better now...

I have a new bellows kit/U-joint ect... and some other new parts but didn't need to use them everything
looked great other than the coupler...Had the Coupler replaced in 4 hours by myself, started
it up and the bolts that were supplied with the new coupler rub the housing...so in another 2
hours I replaced the bolts on the coupler and had it ready to hit the lake...All I did was pic up
an engine hoist and unbolted the mounts, then lifted the engine and spun it to the side to access
the Coupler...with a few 2x6 under it in case of a malfunction...used air tools and like I said above
doing this procedure the second time because of the coupler bolts mistake it only took me 2 hours

The replacement Coupler had a grease zerk on it to make it easier to grease without having
to pull the outdrive during the season...Make sure that you grease the coupler twice as often
if you run your boat more at low rpms...every 50 hours on a Merc instead of every 100...

Amazing how easy these 4.3L Alpha Ones are to service especially if it's taken care of and is clean...
mine you could eat off it and it's always that way...I picked up a new High FIve Prop as an extra
and it really changed the dynamics of the boat even though it's mostly used for fishing...

 

[misterme21960]

Re: 4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

What did you end up finding i have simalar problem?

It was the drive coupler, everything else was fine but I freshened up the Gimbal bearing,
Impeller, carb rebuild...all a result I think from sitting in storage...It's never ran better now...

I have a new bellows kit/U-joint ect... and some other new parts but didn't need to use them everything
looked great other than the coupler...Had the Coupler replaced in 4 hours by myself, started
it up and the bolts that were supplied with the new coupler rub the housing...so in another 2
hours I replaced the bolts on the coupler and had it ready to hit the lake...All I did was pic up
an engine hoist and unbolted the mounts, then lifted the engine and spun it to the side to access
the Coupler...with a few 2x6 under it in case of a malfunction...used air tools and like I said above
doing this procedure the second time because of the coupler bolts mistake it only took me 2 hours

The replacement Coupler had a grease zerk on it to make it easier to grease without having
to pull the outdrive during the season...Make sure that you grease the coupler twice as often
if you run your boat more at low rpms...every 50 hours on a Merc instead of every 100...

Amazing how easy these 4.3L Alpha Ones are to service especially if it's taken care of and is clean...
mine you could eat off it and it's always that way...I picked up a new High FIve Prop as an extra
and it really changed the dynamics of the boat even though it's mostly used for fishing...

 

[misterme21960]

Re: 4.3L Mercruiser runs perfect, but prop won't move boat forwards or backwards

Do yourself a favor invest in an aligment tool to check engine alignment and to align the gimbal bearing...10 minutes the outdrive can be off so you can do some preventitive maintenance...if your mechanically inclined and have computer access it's all a piece of cake when you have forums like this...I bought everything on ebay myself...and more...Good luck on your mission