Help! Sheared off lower drive

[Powell Boater]

I'm new to this forum and hoping that someone can help me identify possible causes for the apparent failure and inexplicable separation of my lower drive from the rest of the motor.

I am a part owner of a houseboat on Lake Powell (Utah). Last year we installed two brand new 60 hp Mercury Bigfoot engines. Last week one of the other owners was using the houseboat and reported that as he was starting to back away from the beach, one of the engines made a horrible noise. He shut it off and got in the water to investigate. He found that the lower drive unit on one of the engines was missing. Thankfully the water depth at the stern of the houseboat was only about 5 ft. so he was able to dive down and recover it.

Inspection by the owner (which has since been confirmed by another owner and the mechanic at a repair facility) revealed no evidence of a collision with anything. The prop, the skeg and ther rest of the lower unit appear undamaged. The drive shaft was sheared off and there is some damage to the middle unit. Four of the five bolts which connect the lower unit to the rest of the motor were completely missing and the fifth was sheared off (I don't yet know which of the five bolts was sheared and which were missing).

The engine has only had one servicing since installation, a routine replacement of the impeller back in March of this year. This was the only time the houseboat has been out of the water since the new motors were installed. I understand the impeller replacement requires removal of the lower unit. The mechanic said that he saw no evidence of any internal mechanical failure. He also said that any attempt to file a claim with Mercury under our warranty will be denied because Mercury will say the damage was the result of an impact with a submerged object even though there is no evidence of any impact.

I've never heard of any situation like this and would welcome any theories which might explain it.

 

[j_martin]

Re: Help! Sheared off lower drive

It would be my judgement, given that there is no impact sign on the lower, that the mechanic that replaced the impeller forgot to torque down the mounting bolts for the lower.

hope it helps
John

 

[emckelvy]

Re: Help! Sheared off lower drive

That mechanic is trying to cover his You-Know-What!!! A properly-bolted-together joint is as strong or maybe stronger than the rest of the motor so I'd be very suspicious of that mechanic's diagnosis.

You would have had to strike something pretty hard to shear the lower unit off, and in all likelihood it would have cracked either the lower unit housing or busted off the center section.

There's no way that 4 bolts could just be missing in a collision; you'd at least find the sheared-off ends in the center section, or the bolts would have pulled the threads out.

Check the lower unit and center section, where they mate together, for signs of rubbing or "working". You'll probably find that they have been 'scrubbing' against each other for quite some time before enough fasteners fell out to allow the lower unit to shear off. I'd expect to see worn paint and possibly worn aluminum at the "joint".

Also check the bolt holes in the lower unit and you'll probably see signs of "working".

Next thing I'd do is take it to another boat mechanic for a fair and honest appraisal of the damage and see what they say about how it could have happened.

If you have insurance, contact the adjuster and I bet they'll come to a similar conclusion.

I'd also contact the regional Mercury Service Rep to see what their thoughts are.

The mechanic is just trying to deflect blame here, obviously Merc isn't going to warrantee the mechanic's failure to tighten down the lower unit, so the dealership will have to 'eat' the charges. I'm sure they don't want Merc to know about their sub-standard work, either!

HTH & let us know what happens...........ed

 

[yb240]

Re: Help! Sheared off lower drive

Did the mechanic do the same service to both the motors? If so check the other lower unit to see if the bolts on that lower unit are properly torqued.

 

[j_martin]

Re: Help! Sheared off lower drive

Did the mechanic do the same service to both the motors? If so check the other lower unit to see if the bolts on that lower unit are properly torqued.

I wouldn't be surprized if they were fine. You put the foot on, and get everything started. Then it takes several different wrenches to tighten the bolts and nuts down. Could have put both on, then got interupted between them when tightening.

I'd get on it earnestly. This problem isn't going to solve it self or be fixed real inexpensively. Nobody is going to volunteer to pick up the tab. You may have to force feed it to them.

hope it helps
John

 

[Powell Boater]

Re: Help! Sheared off lower drive

Thank you for all the insights and useful suggestions. My original conclusion, albeit a long-distance one without seeing the broken parts for myself, was that the simplest explanation, i.e. mechanic forgot to torque down the bolts, was most likely the correct one. I have asked that the other engine be inspected to make sure a similar fate doesn't await it since both engines had the impellers replaced at the same time. I hadn't thought of contacting our insurance carrier but thanks to the suggestion from emckelvy (any relation to Rich McKelvy, Asst. U.S. Attorney for Utah?), I've contacted our insurance company. They said they would send an expert to take a look at it. I'm still waiting for photos of the damaged parts. When I get them I'll certainly look for the things everyone has suggested.

 

[emckelvy]

Re: Help! Sheared off lower drive

I hadn't thought of contacting our insurance carrier but thanks to the suggestion from emckelvy (any relation to Rich McKelvy, Asst. U.S. Attorney for Utah?),

Not that I know of but you never know, there's plenty of the McKelvy Clan out there! My Grandpa came from the Missouri McKelvy's and his ancestors came from either Ireland or Scotland.

It'll be very interesting to see the outcome of this one, eh??? Can hardly wait!!!

 

[Yepblaze]

Re: Help! Sheared off lower drive

Is this a boat that is left at the lake, on the lake, or in some area where it could be vandalized?

It would seem pretty indicative of what's leftover after the lower unit had been partially removed (the four bolts that are missing) and left to operate with only the one (hidden and unknown to an amateur thief) bolt that broke away under operation.

 

[Powell Boater]

Re: Help! Sheared off lower drive

Yepblaze, the houseboat is kept in the water all year except when its pulled out for maintenance. It is not docked, but moored in a buoy field a fair distance from shore along with several hundred other houseboats. I guess vandalism is a possability but you'd think they'd need scuba diving gear to do it.

I just spent some time at a boat dealer in Salt Lake looking at a Mercury outboard for myself so I'd know how its put together and what the odds are of it being just a freak accident or a mechanical failure inside the engine. I had assumed that the bolts holding the lower unit on went up through the lower unit plate and wer secured by nuts on top. This is not the case, the bolts come down and have the nuts underneath. This being the case, I'm beginning to doubt the report that four of the bolts were missing. They may have all sheared off. I'm still waiting for photos.

 

[Powell Boater]

Re: Help! Sheared off lower drive

If I did this correctly, here are some photos of the damage. These were taken by the mechanic who, I believe, failed to torque down the bolts properly. He didn't include any pictures of the inside of the middle unit.

 

[j_martin]

Re: Help! Sheared off lower drive

At first glance, that was unbolted mostly. The detail needed to figure out what happened to the fasteners just isn't in the picture. If all the studs are cleanly missing, and the threads in the mid aren't messed up, then the aborted theft theory seems likely. If the threads in the mid are distorted, and/or there is side wear in the holes in the lower, then the loose bolt theory seems likely.

You're way overdue for an independent expert investigator. Could be an expensive mistake.

hope it helps
John