How do I test my lower unit?

[b10doyle]

For starters, I don't know anything about outboards. This past weekend I just picked up a project that I'm going to start working on. I realize most of you are pretty skilled, and you know a lot about boats/outboards, I'm just hoping that I could get some pointers for the basics and to understand more about boats/outboards. Here's my situation: I bought a boat/trailer/motor for $200. The person I bought it from said that they don't know anything about outboards either, but that everything ran really well until he backed up into a rock last summer. A buddy of his looked things over and said "your lower end is shot". That's all the information I have on the incident.
The motor is a 1987 70hp Yamaha ETLH. I do have a shop manual for it, and I was able to look up the year and model by the model number on the ID tag. The lower unit is NOT attached to the motor. It's sitting in the boat. The prop is still on it, and there's a rod sticking straight up out of the unit. There is some scratches and gauges on the housing, but it's not cracked and seems to be in somewhat decent shape (no rust or cracks or obviously damaged parts).
The help that I'm looking for is how to determine that the lower unit is "bad"? Is there a way to cycle through the gears without it being hooked up to the motor? Are there any parts that I should definitely check before turning it in to a mechanic or shopping for a used lower end? Also, what should I be doing on the actual power head to get it ready for the season? It's a 2 stroke, so no oil change needed but I'm assuming spark plugs, carb clean, fuel filter, lube? I work as a mechanic in a manufacturing facility, and I've done work to some small engine stuff like lawn tractors, chainsaws and leaf blowers, so I'm not completely useless lol I just don't know anything about outboards.

Thank you in advance for any help or advice. I appreciate it!

 

[wo-rigman]

First off, drain the oil from your lower unit by loosen the screws with an impact driver and a straight screw driver bit. Hit it with a solid but not hard blow with a hammer. Inspect the bottom plug (it's magnetic) and the oil for metal shavings or gear chunks. (Remove the top plug so the oil will run out freely). If none are found, shift it in gear with a pair of pliers by turning the short splined shaft. One way for forward the other way for reverse. Roll the prop and listen/feel for any roughness that might indicate damage to the gears inside. (it will have some resistance because you are also turning the water pump when you rotate it) Inspect the area by each seal for signs of oil that may have been leaking. If any is found you may want to pressure it up with an adapter and air to 10 psi and see if anything leaks. If it leaks you will have to install a seal kit or take it to someone to have one installed. This still doesn't prove the gears are good in the lower unit without completely disassembling it but is the next best thing. Now is also a great time to replace the water pump. Then fill the lower unit with new 90 wt gear oil. be sure to shift your unit into neutral before stabbing it back into the powerhead. Line up the shift shaft and hook up the speedometer tube. Using a floor jack to hold it while you get everything lined up works great for me. Since you probably don't have a run tank you will have to take it to the lake and try it out to verify if everything is working correctly. I hope this helps.

 

[b10doyle]

Rigman-
Thank you for the tips. I will be tackling this in the next week. I appreciate the pointers!

 

[b10doyle]

Update:
I don't know if I mentioned it in my original post but the lower unit was already removed from the outboard when I bought it. Last night I took a look at it, and I was NOT able to turn the prop completely over in either direction. It would go about a 1/4 turn and then stop. Both directions, same thing. I set up the lower unit and completely drained the oil (removed both plugs). I did see some metal shavings on the bottom magnetic one, but not a whole ton and definitely no chunks. The oil itself was black, not milky at all, and there were no chunks or anything in the oil when it finished draining.
Next, I moved to the prop. I pulled the cotter pin, and found that the retaining nut was very loose (I was able to take it off by hand). It has been sitting awhile, and I don't know if the previous owner had taken it off for any reason, but there you go. Next I slid the prop off the shaft and didn't see any real problems in the housing when I pointed a flashlight in there, other than some leaves. I also took off the impeller housing and the impeller itself (it was a little worn, but no big chunks or anything missing out of it and no broken arms). Also didn't see anything jumping out at me after taking those off.
Now for the part I don't understand. Once the prop was removed... I could turn the prop shaft over by hand. It wasn't spinning free or anything but with one hand I could work it all the way around going either direction. I'm not sure what to check next. Any advice is greatly appreciated. Thank you.

 

[wo-rigman]

When you turned it over about 1/4 turn and then it stopped did it suddenly stop like a tooth was broke off and stopping it or was it just a tightening feeling? By the way you described it, it sounds like the water pump impeller was stopping it from turning over all the way but it does turn over all the way now that you have removed it. It should turn freely but it will not just spin over. There weren't any chunks in the oil so that is good and no water is also good. Black oil can be from not changing it or it can be burned, did it smell burned? I'm guessing not. Most oil that hasn't been changed regularly will have some metal shavings on the magnetic plug.

Make sure to put it in gear and rotate it both directions, it should rotate easily but not necessarily freely and not be binding up in a certain spot. If it does rotate completely then check the prop shaft to see if it is bent, it should be straight with no wobbles when looking straight at the back of it where the cotter pin holds the nut on. If it is bent, it can make a hard spot in the rotation of it and need to be replaced. If that is ok, then reassemble it.

Reassemble it with a new water pump impeller (the fins will be curled up on the old one and that is not good), apply some grease to the fins on the impeller to make it slide in easier, fill it back up with 90 weight gear oil. and it should turn over completely in either direction, it will have some resistance because of the water pump impeller but it will still turn completely around. Then reinstall it on the motor, be sure to shift it back into neutral. Good luck.

 

[b10doyle]

When I was turning the prop over by hand it was just a tightening feeling and I didn't want to force it because I wasn't really sure what I was turning over. The oil didn't smell burnt necessarily but it did smell pretty strong. I've never dealt with it before, but I was surprised at how funky it smelled. Guess I'm just used to automotive oil. I did look at the prop shaft and didn't find any damage to the splines, or any chunks or gauges in the shaft itself and it looked straight just eye-balling it. I will work more on re-assembly in the next few days the only question I have is about the shift shaft. Is there a special tool I should be using, or will pliers do the trick? Should I be pushing it in at all when I turn it?

 

[wo-rigman]

It sounds like your lower unit may be ok, just needs servicing. You should be able to shift it into gear with a pair of pliers on the shift shaft. You may have to turn the prop shaft to get it to click into gear. Just don't damage the splines on the shaft. I shift mine with a small pair of channel locks to check it each time I have it off, so it should not be a problem. No you shouldn't have to push it in to make it go into gear.

 

[99yam40]

If I did not know anything about lower units and someone sold me a motor and said the lower was shot, I would have an expert look into it and tell me what was wrong with it and how much it will cost to fix.

Me myself would probably take it apart to see what was wrong with it internally if the prop shaft will not turn.
Could be a bent shaft binding things up

 

[b10doyle]

With everything drained and the prop off I can turn the prop shaft, the shift shaft and the drive shaft over by hand. I'm still not comfortable putting it back in the power head, in case there's something wrong that I'm not seeing. Bringing it in to my local marina this weekend to have it looked over. Thanks for the advice, big help to a newbie!

 

[b10doyle]

Okay, I brought the lower end in to a reputable mechanic by me. Within 10 seconds he said it was junk. Apparently the drive shaft was turning over way harder than it was supposed to and the shift shaft wasn't operating. Not paying for a rebuild, I'm trying to hunt down a used gearcase now. I know that some years/hp's are interchangeable, but I'm not sure what else could fit my power head. It's a 1987 70hp ETLH. If anyone has info on the conversions I'd appreciate it.

 

[99yam40]

look up you part number for your lower unit and then compare to other motors around that year