85 hp Force lower unit stuck

[Hydrilla]

This week I picked up a little Glasstream bass boat with a non-running 85 Force on it. I want to give this motor my best effort before I give up on it. The flywheel turns, but the prop is stuck solid. It won't move whether I put the motor in neutral or in gear. I took the drain screw out to see what the lower unit oil looked like, and uhh... no oil at all. It's been sitting a year, what's the chances the lower unit is seized beyond help? Any tips on what I should try?

Thanks, here's a pic of the motor. It's in great shape, except for the missing skeg. The wiring looks especially good for it's age.

EDIT: Let me add that the prop can easily be removed from the prop shaft, but the prop shaft will not turn. That's a better description.

 

[john from md]

Re: 85 hp Force lower unit stuck

Pull the lower off and see what it looks like. You will either have to rebuild it or buy one from ebay anyway. They go for about $200 on auction.

Regards,

John

 

[Frank Acampora]

Re: 85 hp Force lower unit stuck

The drive shaft turns all the time the flywheel turns. The pinion is directly connected to the drive shaft and the forward and reverse gears are always in mesh with the pinion. So if you can turn the flywheel, this tells me that both gears turn. That means the prop shaft is the only thing hung uo and the only thing that can stop the prop shaft from turning in neutral is the rear needle bearing.

If you remove the prop and remove the anode behind it you will see four bolts. Remove them and pull out the spool. It carries the prop shaft seal and the bearing. See if the bearing is rusted or spalled and check the prop shaft surface that it rides on. If only the bearing is bad, it is standard and can be bought at a bearing supply store or a Mercury dealer. If the shaft is spalled or scratched, you will need to replace it--but in order to get a used shaft you will probably need to buy a complete lower unit. You don't want to buy a new shaft--it will go at least a couple of hundred.

Next, since there was no oil in the unit, pull the reverse gear carrier and check the condition of the reverse gear and bearings. while these are out look into the gearcase and check the condition of the forward gear. You can not remove it without first removing the pinion, but if you see rust on the teeth, it is almost a sure bet that the bearing is rusted also and if it grumbles when you turn the driveshaft, then the bearing is going bad..

Any spalling, rust or lack of smooth movement on these parts indicates the need to replace the whole lower unit with a used one as it is cheaper to replace than to repair.

Oh, yeah! Forgot to mention--remove the water pump and the top plate (7 bolts) and check the condition of the drive shaft top bearing. Merc only sells them as a unit with the drive shaft but it is a standard bearing and can be had for about 45-50 bucks. Skeg repair will cost around 100 bucks. So--you can see, that depending on the damage, the lower unit may be fixable but it will be cheaper (and faster) to buy a good used one.

 

[Hydrilla]

Re: 85 hp Force lower unit stuck

Frank- wow, thanks for the detailed answer and good advice. I didn't add the skeg into the equation when I started thinking about the lower unit, but you're right- it would be best to go with a replacement. I think before I do any of that, I should do a compression check, because there's no guarantee that the motor is good. Assuming compression is good, what else should I do to make sure the motor is a good candidate for a new (used) lower unit?

 

[Frank Acampora]

Re: 85 hp Force lower unit stuck

Well, if the compression is good, then half the battle is won. Everything else that could cause a problem is bolt on and easily replaced without tearing down the engine. New, the compression should range between 145-155 PSI so on a used, dry engine anything above, say, 120 would be good. The only time you would be concerned would be if all cylinders showed really low, like 50 PSI or if one cylinder or more showed 0 PSI, Then that would require a rebuild. Rebuilding is not out of the question if the basic engine seems to be in decent condition with very little corrosion damage.

However, just be aware that in rebuilding, you are probably going to invest more than the engine is worth and while you now have an engine that is known good, you could probably have bought a used running one for the same or less money.

Although they are easily replaced, at a couple of hundred for a lower unit, a couple of hundred for coils and CD boxes, a hundred for a used stator-----it adds up. Before you get into a money pit situation, check to see that there is spark to all cylinders when cranked. If you have compression and spark, the engine will run with very little money invested.

 

[Hydrilla]

Re: 85 hp Force lower unit stuck

Thanks again. If I were to get one on eBay, can someone tell me what HP motors have the same lower unit as mine? like 85-115 or something like that? Just wondering if I have to get one for an 85 specifically.