Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Hey all, just bought my first boat with an OMC 4.3L and an OMC Cobra outdrive. The main issue keeping her out of the water is a drive problem. I need to do some serious troubleshooting, but I wanted to go ahead and get some preliminary information, offer my introductions, and ask some questions. I started a thread for all non-engine issues here: 1988 Thompson 240 Fisherman.

The guy I bought the boat from told me the engine was running fine, and the propeller spinning, but the propeller wouldn't provide any power to move the boat. He said he took it to a mechanic who, after a brief investigation, diagnosed it with a burnt out Gimbal Bearing. When I bought it, he started up the engine for about 30sec (to prevent overheating with no water hooked up) and the engine sounded very nice. Anyway, for my first question, I was wondering if anybody can please confirm that it is indeed likely the Gimbal Bearing that burnt out.

Like I said, this is just from talking to the guy I bought it from and hearing it run for a bit. So I guess my second question would be to please point me in the right direction for troubleshooting. I've looked at several of the FAQ threads and some of the other threads, but nothing jumped out at me as being relevant to an outdrive issue.

I did pick up the OMC manual to guide me through any repairs I may need to make. The troubleshooting section does not seem to cover the issue I'm having.

So in summary:
Question 1. The engine sounds like it runs well, the propeller spins, but there is no power providing forward movement. Please confirm whether it is the Gimbal Bearing likely burnt out?
Question 2. If not the Gimbal Bearing, could you please point me in the right direction to begin troubleshooting the problem?

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

The gimbal bearing would make noise but if the propeller spins, I wouldn't think it would prevent the boat from moving. I would think the propeller hub may be a problem. If the gimbal bearing was seized the engine wouldn't start or turn over. My 2c.

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Do some searching on prop hubs/spun prop hubs like the above poster mentioned. A spun hub will still spin the prop while running out of water or even at low speeds....but when you get on the power the shaft will spin inside the prop not giving you any thrust.

A bad gimbal bearing will just make noise or completely lock up the engine and drive.

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Thanks guys. After considering this and doing a bunch of research, I'd say it definitely seems to be the most likely cause of the issue. I'm going to go ahead and pick up a new prop and prop kit. I guess I forgot to mention the prop was pretty dinged up, which makes an even better case for a spun prop hub. Anyway, I requested some advice on the prop forum here.

Again, thanks for the help, I'll update if this resolves the issue.

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

You might as well get an impeller or full kit since the PO thinks it's OK to run a motor for 30 seconds without water. #30 seconds dry eats impellers.

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

^^^^^^ do what GA_Boater said. Even running that thing for a few seconds dry screws up your impeller.

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

GA_Boater said:

You might as well get an impeller or full kit since the PO thinks it's OK to run a motor for 30 seconds without water. #30 seconds dry eats impellers.

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Ayuh,.... Ditto that,... Rebuild the raw water pump,....

Ya probably oughta pull the drive, 'n Inspect the gimbel bearin', along with everything else in there,...

'n if the Prop don't fix yer original issue, the Coupler is the 2nd most likely point of that kinda Problem,...

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

As the above two responses said... inside of the outdrive is a rubber impeller (it looks like a rubber star). It spins with the outdrive's drive shaft and sucks water into the outdrive and up into the engine. It needs water to lubricate it. If it spins without water, it will burn out the rubber fins on it and it won't work anymore. So, the prior owner did a big No No by not hooking up a hose when he started the engine. He may have fried that impellor.

Now, that said, your lack of prop spinning could be from 2 different things. 1. A spun prop hub. and if the prop is banged up, the previous owner may have hit something to cause the prop to spin the hub. The hub is a rubber packing in the prop to help save your other movable parts in the event that the prop does hit something (hub is cheaper than a drive shaft)

2. I'm a mercruiser guy, so you OMC owners can answer this.. but, at the back of the engine, is there a coupler where the drive shaft sticks into the rear of the motor? If so, can't it go bad too? A hub would normally spin before a coupler would go out, but it would be the next place to look if the hub isn't bad.

Either way, the prop will spin out of the water. It needs to be tested under a load before either would give out. I think when I spun a hub, I could still go about 10mph before it would start to give out.

Check out the link below it may help. If you have the original lower shift cable there is a good chance your gears could be gone. I have a OMC 2.3 outdrive and the same thing happened. Boat will startup great. But it wouldn't engage. This was my first boat purchase so I didn't know everything to check out before signing the deal. I ended up needing all new bellows, water pump impeller, gimbal bearing, lower shift cable, and outdrive lower unit. $1000 in just repairs. Good luck and hope the information helps.

OMC Cobra Sterndrive Tech Info

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Thanks for all the help guys. I'm definitely going to be looking into the stuff you guys mentioned as top priorities. I think I'm going to start with getting a new prop. I updated the other thread on the prop forum with what I'm planning on going with for a prop. I'll keep you guys posted when I work on the other stuff.

Ya, that shift linkage and the impeller switch sound like urgent tasks.

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Time for an update. Over the weekend, my friend and I took off the propeller. It actually looked good on the inside. I'm still glad I got the new propeller because the old one was pretty beat up. Plus, sounds like it's a really good idea to keep a spare on board.

However, the prop looking good was bad news because that meant something else was wrong.

We removed the stern drive unit from the gimbal ring and as the yoke shaft came out, we immediately saw the problem. The splines at the end of the shaft were filled with metal powder and grease. We excavated the splines gently and wiped the shaft clean. After cleaning and wiping, the yoke shaft and splines looked to be in good shape.

Looking into the boat, past the gimbal bearing, we saw what I think is the coupler. The coupler splines had all been worn away; probably turned into the dust that was in the yoke shaft splines. I felt and moved the gimbal bearing, it moved smoothly, turned freely, and was well lubricated. At this point I'm pretty sure the issue is with the coupler, which several people commented on before as a likely cause of my lack of thrust despite the propeller spinning out of water.

We also took apart the impeller and inspected it visually. It looked to be in very good shape.

So, the plan for right now is to pick up a coupler (this one) and an alignment tool (this one). We'll raise the engine and install the coupler, then lower the engine and reconnect, align the engine, and then put the outdrive back. Does anybody have any input on whether they agree this is the right course of action at this point?

Also, I was wondering if anybody in the Norfolk, VA area has any of the tools I'll need available and they'd let me use them? Specifically, I'm talking about the alignment tool and an engine hoist.

See images below.

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Anyone?

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Hard to see in the pics but all that metal came from something...must be the coupler. Probably hadn't been greased in ages. Can't help you with the tools except...Engine Drive Alignment Bar Motor Tool for Volvo SX 3851083 and OMC Cobra 18 4442 | eBay

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Andy82 said:

Anyone?

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Ayuh,.... Yer plan sounds like a Solid plan,....

Got a picture of the input shaft, Cleaned,..??
If there's Any detectable wear on the splines, Replace it, so's ya don't have to be doin' this again soon,...

'n Grease the 'ell outa the coupler,...
Lack of Grease, trollin', 'n Bad alignment are the 3 coupler Killers,...

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Sometimes repair shops will lend you their tool or rent you their tool. You can test the coupler. When everything is assembled, you can paint a line on the coupler and drive shaft (so it marks where the drive shaft is in the coupler). Then you drive the boat in the water. If it slips, then the lines done line up anymore. I think I actually painted mine with white out (the product found on your office desk) when I tested mine. You can do the same thing to test your prop. I don't think you can look at a prop and tell if the hub is spun or not (maybe you can). But, it sounds like you found your problem.

It sucks that of the problems it could be, yours was one of the harder ones to get to (having to pull the engine).

On the positive side, I think it was me that said it could've been the coupler (yippee for me guessing right! haha). Well, anyway, iboats is a great tool to help diagnose so that you can repair this kind of stuff.

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Andy82 said:

The guy I bought the boat from told me the engine was running fine, and the propeller spinning, but the propeller wouldn't provide any power to move the boat. He said he took it to a mechanic who, after a brief investigation, diagnosed it with a burnt out Gimbal Bearing. When I bought it, he started up the engine for about 30sec (to prevent overheating with no water hooked up) and the engine sounded very nice. Anyway, for my first question, I was wondering if anybody can please confirm that it is indeed likely the Gimbal Bearing that burnt out. QUOTE]

And, by the way, a worn out gimbal bearing wouldn't prevent the prop from spinning the proper amount. It would just get noisy and could've assisted in the failing of your coupler. (I'm sure you see exactly what a gimbal bearing is now that you have taken everything apart -- and you now know more than the seller did) So, while it is all apart, it may not be a bad idea to change the gimbal bearing just in case...unless you are really confident in the one that is in there now.

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Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

I know it's been a while but I wanted to go ahead and post this update.

We ended up lifting the engine about a foot or so to be able to get to the coupler. We basically put a mobile lift on the inside of the boat since I didn't have access to any kind of overhead lift. Probably not the absolute best approach, but we moved very slowly to keep an eye on everything. We disconnected everything (lots of pictures to reference back to) and began lifting. Once we got to the point where we could get to the coupler, we removed it. Oh man was that coupler beat to hell. It had melted rubber and zero splines. We changed it out with the new one and lowered the engine back in. We made sure it was well aligned and then put the outdrive back on. It was a hell of a project, but it worked!

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Great Job, now you know a whole lot more than most people do about their boats and you will be pulling that drive to check the bellows, grease the gimble, ujoints, drive shaft splines and check alignment every year right??
BTW, if you do that the coupler can easily last the life of the boat....my 25 year old Cobra still has the original one on it....
And while we're talking greasin' splines, the best grease I have found is OMC/Bombardier's Triple guard grease, it sticks on very tenaciously and will last longer than other greases.

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

If you take care of her and pull the drive and grease the coupler splines/check alignment as regular maintenance, the coupler will last forever.

Did you put in an impeller kit? Don't forget that because the PO sure abused it by starting her up with no water. That will avoid a lot of problems down the road.

Thanks for the update, it's good to know when advice or guidance works.

Re: Outdrive not putting out power - 1988 OMC 4.3L / Cobra

Lou: Ya, it is amazing just how much I learned and how much more comfortable I feel overall with that part of the boat. What seemed like this overwhelmingly daunting task at first (just removing the outdrive) turned out to be pretty straight forward and not at all super costly time-wise. Lifting the engine was quite a bit more challenging, but still doable even to an amateur like me. I'll definitely be taking the drive off yearly to perform all tasks you and GA_Boater recommended, as well as what's in the winterizing/summerizing post by that genius fella that posts about all the engine matters, as well as what's in the manual.

Thanks for the grease recommendation, I'll make sure to pick up some of that stuff. I didn't realize Bombardier now has rights to OMC stuff, very good to know. Here's what I ended up using. Do you agree that it is best to err on the side of heavily over-greasing than just moderately greasing?

GA_Boater: See the above, much of the same response. Regarding the impeller kit, I did remove all the parts and closely inspected each piece. Everything seemed to be in excellent shape so I decided not to replace it. About advice or guidance working, you are so right! I couldn't have done it without all the help from the kind people generously giving their time to assist me. I don't believe I ever said thank in my follow up post.

To everyone that helped me in this post: a HUGE thank you! No way I would've got it done without you folks's help, so thanks thanks thanks.

Now...to tackle the next few issues, figuring out why she's not planing, and getting a new shift cable and aligning it.