Possible slipping coupler 84 3.8 OMC sterndrive

[gst95dsm]

Hello iboats! First post here after a couple hours of searching. Alright let's get to it!

I've recently bought a very well preserved 1984 Seaswirl 18" runabout. It has the 3.8 OMC combo in it. I have taken it out 3 times now. The first two times were without issue, ran great, drive worked perfect, ran cool, no issues. Well we took her out today and she started up fine, idled out fine, came up to temp fine, and then when I went to GO... she came up on plane and then seemed to slip. RPM's climbed but not speed. I immediately knew something was up, so I looped back around at just above idle speed back to the dock. Things got a little stranger on our way back to the dock. The engine temp got a little hot. It did not SHOOT up to overheating but was definitely hotter than normal. My first instinct was that the prop hub was spun. I am relatively new to boating and this is my first I/O but I am a good mechanic overall. I proceeded to take off the prop, the prop nut felt like it had about 20ft. pounds (if that) on it. The prop looked fine (no loose rubber) so I reinstalled it and tightened it down. Well guess what... battery was now dead and it would not start! So I charged the battery a bit and went to start it. This is about an hour now from when we shut it down initially.

Well she started up fine with some juice in the battery. I let it idle for a bit and watched the temp. It came up normally and stabilized. I told the wife and kid to wait at the dock and I idled her out again. Everything seemed fine. Went to GO again the same thing happened (slipping). I looped her back around, and decided to try one more time with the trim all the way to the down position, to my surprise it took right off with no slipping. Ran her up to about 35mph, and the temp was normal. Slowed down and tried again..... everything was fine, trimmed to 1/2 and things were fine, trimmed to UP........ things were fine! temp was stable, boat took off with a bunch of power just like it had the previous two times out. So I flag the wife to park the truck and I idled her back to the dock... picked them up and off we went. Temp held steady the entire time, even while basically trolling at 1500rpm for about an hour. Any time I wanted to take off, no slipping. CRAZINESS!

Now don't get me wrong... I don't "want" to have a problem and I am glad we got to have some fun after the initial drama but I know it did not slip for no reason. Upon searching on here I have been able to determine that the coupling could be at fault here. I smelt no burning rubber and see no residue on the engine. No loud whining either. Could this thing slip intermittently and then seem fine? I'm not afraid to change this thing.... but was hoping to get a summer out of this boat before I have to do any major repairs.

Some little tidbits of info from the PO and me.... New motor mounts and transom boot installed last season. Trim rams seem to leak, prop spins freely in neutral and is (locked) when in gear. Thanks guys for any help or insight you can provide. Sorry about the long post...geez.

 

[chiefalen]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

when i read your post you stated you have trim rams.a 1984 would have a half moon shaped gear on the back.if you have the half moon gear than its a stringer.

 

[MikDee]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

Mark a line across the face of your prop with magic marker, or something substantial, try the boat in the water, and see if anything moves on the prop to determine if it's the prop hub, or the coupler slipping. One more item, if your outdrive, and engine, is not aligned properly, it puts excess stress on the coupler, possibly causing it to slip. The engine has to come out to replace your coupler

 

[gst95dsm]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

It's got the half moon shaped for the tilt...... but also has trim rams on the front motor mounts for the trim.

when i read your post you stated you have trim rams.a 1984 would have a half moon shaped gear on the back.if you have the half moon gear than its a stringer.

 

[gst95dsm]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

I am pretty confident the prop is ok. I don't think they "come back" once they slip but I will mark it just to see next time I go out. How can you tell if your alignment is good? To be honest that's the one thing I am not understanding is all this talk about alignment...... can't these things just bolt up? Is this similar to aligning a clutch on a manual tranny auto?

I was thinking last night about every last detail of the trip and I left out a few things. when we were trolling back to the dock after the intial slip I tilted the drive up with the engine running..... bad idea I know. Well it came up high enough to raise the water pick up out of the water..... most likely that introduced some air into the cooling system and caused the engine to heat up like it did. What do you guys think? Also I remember that the trim gauge on my boat that worked as it should before was going from full down to up and acting really strange. My NEW theory on this whole incident is that my trim rams are low on oil causing a "spot" in the range of motion where the engine is basically able to trim itself up due to the water resistance upon accelerating and causing the phenomenon "ventilation".... similar feeling to cavitation from what I understand. It makes sense because only after I trimmed the boat all the way down did it perform normally. What do you guys think about this?

Mark a line across the face of your prop with magic marker, or something substantial, try the boat in the water, and see if anything moves on the prop to determine if it's the prop hub, or the coupler slipping. One more item, if your outdrive, and engine, is not aligned properly, it puts excess stress on the coupler, possibly causing it to slip. The engine has to come out to replace your coupler

 

[Boatin Bob]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

Could still have a prop problem and you should mark it and check it as suggested. Should never, never, never run with the drive tilted up especially that high and if you do need to it should only be at idle speed for a short time or you will learn how to change those ball gears.

I think some of your confusion is that some of your reading has been for OMC Cobra's that have an engine coupler and drive shaft with u-joints and a gimbal bearing that needs alignment. Best thing to do is get your self a manual for yours. There is a drive shaft in your upper half of the drive that also turns the water pump, I've heard of those chewing the splines off causing the prop to slip and the engine to overheat (pump also slipping) and I hope that's not your problem.

 

[Maclin]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

I know you cannot run those type of drives at any tilt angle without risk of hurting the ball gears that make the "connection" from the engine's output to the actual drive. If the drive was tilted up at all when you had the slippage the first time then that could be the entire issue. It is my understanding that those ball gears cannot take any kind of power above idle without being all the way down and engaged.

 

[gst95dsm]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

Thanks for that info! I just have not had the time to pick up a service manual yet but it's going to be the absolute first thing I buy for this boat. To be clear.... I think I may have been just above idle speed when I tilted the drive and I realized in about 3 seconds that I was being dumb and put it back down. The ball gears are showing wear as I would believe they are the original but appear to have some life left in them. Remember also that this boat ended up running normally after I played with the trim. By normal I mean.... No slipping what-so-ever and no overheating. Can anyone shed any light on how leaking trim rams could cause the engine/drive to trim up upon acceleration enough to cause "ventilation", and if you've ever come across the issue? Thanks again everyone for your insight..... this seems to be a really knowledgeable forum.

Could still have a prop problem and you should mark it and check it as suggested. Should never, never, never run with the drive tilted up especially that high and if you do need to it should only be at idle speed for a short time or you will learn how to change those ball gears.

I think some of your confusion is that some of your reading has been for OMC Cobra's that have an engine coupler and drive shaft with u-joints and a gimbal bearing that needs alignment. Best thing to do is get your self a manual for yours. There is a drive shaft in your upper half of the drive that also turns the water pump, I've heard of those chewing the splines off causing the prop to slip and the engine to overheat (pump also slipping) and I hope that's not your problem.

 

[JCF350]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

There is a drive shaft in your upper half of the drive that also turns the water pump, I've heard of those chewing the splines off causing the prop to slip and the engine to overheat (pump also slipping) and I hope that's not your problem.

If anything is going to get them off the water this would be it.

 

[Manipulator]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

I'm with Bob on this one, I'm leaning towards the water pump splines being toasted. I replaced mine at about 800 hours and it was pretty worn out, also was rusted.

 

[gst95dsm]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

hmmm... possible for this to be an intermittent problem? When I get my manual on Friday i'll look into this area of the drive. I would think though that if this was the problem that it would over heat and slip consistently right? Well have to see the next time I take it out unless there is a way to inspect this without tearing to much of the drive apart..... oh well... .NEED my manual!

I'm with Bob on this one, I'm leaning towards the water pump splines being toasted. I replaced mine at about 800 hours and it was pretty worn out, also was rusted.

 

[JCF350]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

hmmm... possible for this to be an intermittent problem?

Nope, once those splines strip they're gone.

 

[gst95dsm]

Re: Possible slipping coupler 84 3.8 OMC sterndrive

Thanks... that's what I was thinking. So I would say that is not the issue.... YET... haha. Gotta love old boats.

Nope, once those splines strip they're gone.