Alpha 1 "slipping"

[Southtowns27]

Hi all, Boat is an '86 Wellcraft 260 Aftcabin with a Chevy 350 (260 horse) and an alpha 1. Yesterday we were out cruising at about 18 mph, which is about 2900 RPM. Suddenly the sound of the engine changed and I noticed a slight vibration. Engine RPM and speed stayed the same, it just sounded different, almost like the exhaust got louder. I backed down on the throttle for a few minutes and everything seemed normal, so I accelerated back up. Under acceleration it seemed to "slip", like a slipping clutch or an auto tranny low on fluid. If I accelerated slowly it would hang on, but after a point, maybe 3600 RPM it would slip again. At low speeds it works fine and still shifts fine. I made it back to the dock and opened the engine compartment. I didn't notice the burnt rubber smell or any bits of rubber by the engine coupler. (The engine was replaced 4 years ago before I had the boat, so I would assume it was replaced at that time, but who knows). I pulled the boat out of the water this morning to check the prop. It has a 16x16 prop with the Flo-Torq hub. The first thing I noticed was that the nut was loose. Not backed way off, but loose enough that the lock plate was wiggling around. I took the prop off and the plastic liner in the prop looks fine, as do the splines on the shaft and inside the bronze collar. I'm kind of at a loss here for what's causing this... It doesn't seem to me that the loose prop nut would cause this, but could it?? If that's not the case it looks like the engine is coming out to check the coupler...ugh. Any insight would be appreciated!

 

[Southtowns27]

Re: Alpha 1 "slipping"

Well, here's an update already. I have the boat at home now and had some time to mess around with it. I took a real good look at the back of the engine coupler. Where the shaft enters the coupler there is a nice grease film. The grease doesn't smell burnt and there's no metal in it that I can see. The rubber around the shaft feels normal, not chewed up or anything. When I was poking around the outdrive I noticed the exhaust bellows was ripped. Actually, more like destroyed, it had 3 giant tears in it. That would explain why the boat suddenly got louder. I did notice it was louder just idling into the marina as well. So now what I'm thinking is that exhaust was making its way into the prop and causing it to ventilate/cavitate. That would explain the vibration and why it seems to slip at higher rpm. Especially since more RPM equals more exhaust. I looked at the prop and I can see a lot of new pitting in it. I'm going to pick up a new bellows tomorrow, throw it on, and see what it does. A $10 fix would sure beat swapping the engine coupler...

 

[alldodge]

Re: Alpha 1 "slipping"

Have you checked the engine alignment? If the coupler is slipping its over but check the alinment to make sure you don't have this issue in the future. While the damaged exhaust bellows would cause some issues it is high enough to not cause much issue if any with the prop.

 

[Another retired guy]

Re: Alpha 1 "slipping"

Many of the symptoms you describe could also be caused by weed build-up on the lower drive. It happens all the time in our weedy lake and we frequently have to stop, and reverse the prop for a few seconds to clear the weed, and then continue.

 

[thumpar]

Re: Alpha 1 "slipping"

The exhaust bellows should be above the waterline while on plane so it would not enter the water in front of the prop.

 

[Southtowns27]

Re: Alpha 1 "slipping"

Update... I talked to several marine repair shops about my issue, and the general consensus was that the engine coupler had given it up. I went ahead and pulled the outdrive so I could take a look at the coupler. The splines were perfect and the rubber was not chewed up. THe coupler looks relatively new, so I'm guessing they changed it when they rebuilt the engine 4 years ago (before I owned the boat). I had gotten repair estimates of $1000+ to replace the coupler. I had a nagging doubt that the coupler had failed so I put on a new exhaust bellows and brought the boat to the water. Before I totally launched, I backed the boat far enough in the water so I could lower the outdrive. I holeshotted the thing while it was still sitting on the trailer and it came up under full power with no slippage. Ok, time for a testdrive. It ran perfect. So yeah, the torn exhaust bellows was allowing exhaust gases to escape and it was ventilating the prop. A $40 repair sure beats $1000. And I'm really glad I tested my theory before I threw all that money at it for no reason. All of the repair places said it wasn't possible to ventilate the prop that way, apparently it is. Just wanted to put up an update as to what I found, maybe it will help someone else with a similar issue someday

 

[ethan169]

Re: Alpha 1 "slipping"

Interesting issue. I think its good that you looked into your own theory and ended up testing it as well. You went through the process right in my mind. Meaning you didnt just come up with some crazy theory and test it by just launching the boat and hammering down and hopping your issue has been fixed. You went through some precautionary steps to gain confidence and then progress to completion.

Good work and thanks for sharing your experience!

 

[Bondo]

Re: Alpha 1 "slipping"

Update... I talked to several marine repair shops about my issue, and the general consensus was that the engine coupler had given it up. I went ahead and pulled the outdrive so I could take a look at the coupler. The splines were perfect and the rubber was not chewed up. THe coupler looks relatively new, so I'm guessing they changed it when they rebuilt the engine 4 years ago (before I owned the boat). I had gotten repair estimates of $1000+ to replace the coupler. I had a nagging doubt that the coupler had failed so I put on a new exhaust bellows and brought the boat to the water. Before I totally launched, I backed the boat far enough in the water so I could lower the outdrive. I holeshotted the thing while it was still sitting on the trailer and it came up under full power with no slippage. Ok, time for a testdrive. It ran perfect. So yeah, the torn exhaust bellows was allowing exhaust gases to escape and it was ventilating the prop. A $40 repair sure beats $1000. And I'm really glad I tested my theory before I threw all that money at it for no reason. All of the repair places said it wasn't possible to ventilate the prop that way, apparently it is. Just wanted to put up an update as to what I found, maybe it will help someone else with a similar issue someday

Ayuh,.... Welcome Aboard,.... Thank you for sharin' yer story,....

Odd as it goes, I was bettin' that Another retired guy, 'n thumpar had Nailed the answer,....

 

[haulnazz15]

Re: Alpha 1 "slipping"

I wouldn't "holeshot" your boat on the trailer anymore if I were you. It's a good way to end up with a boat on top of your tow vehicle.

 

[Southtowns27]

Re: Alpha 1 "slipping"

The majority of the boat was still out of the water and it was still strapped to the trailer. I don't see how it could possibly have enough power to push itself forward, shear off the winch stand, and off the trailer onto the back of my dually flatbed. Not to mention it would shear off the outdrive before it got that far forward anyway.
I did this test since I didn't really want to be drifting around Lake Erie on a Monday night by myself with no beer if the engine coupler really was shot..

 

[Another retired guy]

Re: Alpha 1 "slipping"

I'm not convinced that the bellows were the cause of the problem. As it only happened once, and you have found no mechanical cause, I still think you picked something ( maybe weed ) up around the drive, and it finally dropped off as you made your way back to the dock. If it happens again, just try backing the prop for a few seconds.

 

[Southtowns27]

Re: Alpha 1 "slipping"

The seaweed idea is a very valid one. I know for a fact it will cause a similar result. However, at the time I was out in about 50 feet of water and the weeds really haven't had a chance to grow around here yet. I think the water temp just finally broke 60 degrees.. The one thing I think points to the exhaust bellows, is that the boat got louder right before all of this happened. Again, that's not to say I didn't pick up a plastic bag or some other piece of floating junk, it just seems like too much of a coincidence to disregard the bellows. I guess we'll never know 100% for sure, but I'm just glad I don't have to change an engine coupler...yet