How to evaluate a lower unit?

[wengr]

Hello. I am considering the purchase of a 20ft bowrider with a 5.0 Merc/Alpha one Gen II. It's not local and so far I have only seen pictures. The skeg is damaged, and the prop has been replaced. Seller states that he has owned it for one year, and shortly after purchase a year ago, he hit rocks in shallow water. Broke skeg and chipped the prop. He claims the marina mechanic says just use it as is because the lower unit function is not impaired, so that's what he did. He claims many outings since without issue, and now wants to trade up to a bigger boat.
Now quite possibly that is accurate. He is completely open to a lake test and any inspection I require. But the possibility remains that a lower unit problem is the reason for the sale, so my question is - to what degree can I evaluate the functionality and condition of the lower unit? What if anything can I do in someone's driveway or during a lake test to evaluate? The boat is a 1996 model. Any advice appreciated.

 

[wahlejim]

BEFORE the lake test, undo drain plug in lower unit slowly until it starts to drain. If anything but clean oil comes out (water or milky oil) the seals are damaged and need to be replaced. Do this before the test and before firing the motor as water settles to the bottom.

During the lake test, if anything is out of alignment in the outdrive, you will feel it. Pay attention to how smooth the ride is at different speeds, how it shifts in and out of gear (a clunk into gear and very brief rpm drop in the engine are normal)

After the test, check outdrive oil again. There are some people out there who would change the oil prior to showing. If the seals are bad, you may find milky oil after a decent trip on the water.

As far as the skeg goes, a prop shop can repair those for cheap.

 

[wellcraft-classic210]

I suppose you could always have it pressure tested as part of part of any inspections // It can be done on the boat but the oil would need to be drained 1st.

 

[Rick Stephens]

I think a check of the oil before and after is great idea. Broken skeg is common - I broke one moving my boat with a tractor, didn't realize it had leaked down. I left it broken for half of last season and then welded it back up when I pulled the drive for winterization and servicing. By itself, the broken skeg is not a big deal.

To me, a decent long lake test is good enough for the mechanicals on the engine and drive. More important and costly consideration is transom and stringer wood. Close attention to those is much more important from a value standpoint.

 

[Scott Danforth]

there are two types of boaters.....those that have broke a skeg, those that will break a skeg.....and the third type.....those that will lie about not breaking the skeg.

As Rick mentioned, broken skegs are common.

which is also why getting a new skeg welded on is dirt cheap

 

[harringtondav]

All of the above advice is spot on. But I've had propeller whacks with an aluminum prop. that bent the propeller shaft. If you have a good feel, you can feel this with a test drive at all conditions stated above. Better is to get the boat on muffs without the propeller, engage FWD and hold a flat stick on the idling prop. shaft nut threads. This is a feel-touch thing, but if it's bent you will feel and see the stick vibrating. Then make the seller replace the prop shaft, or cut his price $500-$600 so you can have a shop do it.

 

[khe]

I would also visually evaluate the bellows - particularly the shift cable bellows. Any splits in the shift cable bellows or the U-joint bellows will leak water into the bilge. The shift cable bellows are the most vulnerable since they are the thinnest. With the boat on the trailer and the drive tilted all the way up, visually inspect them for splits.

 

[achris]

... The boat is a 1996 model. Any advice appreciated.

In 96 Merc were still putting the rubber bung in the top of the drive shaft housing. This collected water and didn't allow it to drain. The top of the housings corroded quite badly. Check for corrosion holes on the housing just under the top cap, just aft of centre on either side.

Chris. ....

 

[wengr]

Thanks for all the excellent replies. Is it possible/likely to have a slightly bent shaft, yet pass a pressure test and for the seals to still function correctly? And is it possible to know what are the correct tools for draining the lube, and then refilling?

 

[wahlejim]

A large flathead screwdriver and a rag is all you need. You won't be draining much, no need to re-fill. Push in hard and turn Some can be stubborn to break loose. Loosen just enough to let some liquid out. Since water drops to the bottom, it would be the first to exit the drive. The plug is only about 1/4 to 3/8 of an inch long so back it out slowly. 1 of 4 things is going to come out:

1) Clean oil
2) Milky oil
3) Water
4) Nothing, the drive is empty

If it is anything but clean oil, the drive needs some work.

If the owner is going to be a stickler about it being refilled, bring some gear lube and top off his reservoir inside the boat (if he has one). If he does not have one, the oil level should be high enough to top it off from the top plug of the out drive. But honestly, we are only talking about a couple of mL of oil from a full drive so it shouldn't be an issue.

As far as any bent shafts, bad gears, u-joints, etc. from the drive, a lake test will tell you all you need to know. Should be shifting smooth through the entire throttle range and not have vibrations when turning. If you can, have a fellow boat owner with a similar drive go with you to tell you if something doesn't seem right.

 

[harringtondav]

Thanks for all the excellent replies. Is it possible/likely to have a slightly bent shaft, yet pass a pressure test and for the seals to still function correctly?

Yes, assuming it's not bent too severely. I had one bent enough that I could see the propeller nut orbit just by spinning the prop, but it was sealed well. If the nut spins on center when you spin the prop, the shaft is likely good enough to use.

You will need a flat blade screwdriver with a blade wide enough to engage the entire drain plug slot. You will also need a lube bottle pump - available at your boat shop or most DIY stores. Your '96 probably has a lube monitor bottle in the engine bay. Remove the cap from this bottle, and remove the bottom drain plug and collect the old gear lube. Watch the first amount coming out per above for free water. Used lube will be dark, but should not be chocolate milky. That also means water entry.

Keep track of your drain and vent plug seals. They tend to stay in the housings. Your lube pump may have it's own seal on it's threaded fitting. Insert this with one seal into the drain plug hole, and remove the vent plug. Pump new lube into the drive from the bottom drain until it flows out of the vent plug. Replace this plug with a good seal and continue pumping until lube starts filling the reservoir bottle from the bottom. You will have to change to a second bottle of new lube before this happens. Replace the reservoir cap tightly and quickly remove the lube pump hose from the drain plug and replace the plug with a good seal. Make sure both plugs are sealed and tight. Then take your second lube bottle back up to the lube bottle and fill it to the line and replace the cap tightly. You will use close to two bottles of lube.

 

[wengr]

In 96 Merc were still putting the rubber bung in the top of the drive shaft housing. This collected water and didn't allow it to drain. The top of the housings corroded quite badly. Check for corrosion holes on the housing just under the top cap, just aft of centre on either side.

Chris. ....

This is good to know, Thank You. Is this the area of concern?

 

[harringtondav]

I don't know if this is the area archis was referring to, but it looks like that edge of the top cover is badly corroded or broken away. The four cap screws are flush with the top of the cap, set in cast counter-bore pockets, and the screw shown is half-naked. If there is enough metal under the flange of that screw, you may be OK. But that cap seals the drive, and takes a fair amount of bearing side loads from the input drive gear. The seller may not balk at the parts cost for the $190-$230 replacement kit, but it will also require re-shimming the included new bearings to get correct preload. Assuming he can find a shop that will actually do this, the labor charges will probably be triple the part costs. I'd make the seller fix this one, or drop his price another $1K. You will eventually have to fix this.

Also, the pic doesn't look quite right. The gimbal hsg., gimbal ring and bell hsg. are all very scummy and crusty, like a boat that has lived floating in a slip. But the out drive is fairly clean, including the factory s/n stickers. It looks like he may have put a replacement out drive on recently. .....just another caution flag.

 

[achris]

This is good to know, Thank You. Is this the area of concern?

Right here......

 

[wengr]

Excellent. All the help really appreciated. I now feel I can see this boat in a few days with a much better chance of satisfaction.