90hp yam lower unit hidden lock nut

[Gramas80]

Having engine serviced and on collection shop told me the hidden lock bolt/nut that is under trim tab anode has at some point been sheared!
Can't prove they did it so need to know how important it is and will it need drilling and re-taping to correct thread? If it is just left will it be a problem ?

[robert graham]

That bolt is one of five that holds your lower unit on....I'd get it drilled/removed and replaced. An easy out bolt remover should be able to back it out O.K....whether or not they over-torqued it and broke it may be hard to prove...my guess is that the threads got corroded and the bolt just broke off at some point. Get it fixed.....

[Gramas80]

Was hoping to use rib then adders the problem once summer out the way. Would it be ok till then? Bolt remover?

[99yam40]

Do you think Yamaha put that bolt in there for some reason?

You can choose to do what ever you want with your motor

[TownsendsFJR1300]

Was hoping to use rib then adders the problem once summer out the way. Would it be ok till then? Bolt remover?

Once the LU is off, a machine shop should be able to remove it without much issue.

As posted above, its there for a reason.

IMO, I'd repair it, it's 20% of the bolts holding your lower unit on...

[robert graham]

Think about it, you've got 90HP running down that drive shaft and only 5 bolts holding it together....this should be a fairly simple and inexpensive fix...

[rodbolt17]

there were 7 fasteners holding that unit in place and 2 alignment pins when it left the factory.
if 6 fasteners wont hold it your fighting a losing battle.

however once the gearcase is off it takes about 20 min to drill and rethread that broken one.
myself I would run it.

[robert graham]

there were 7 fasteners holding that unit in place and 2 alignment pins when it left the factory.
if 6 fasteners wont hold it your fighting a losing battle.

however once the gearcase is off it takes about 20 min to drill and rethread that broken one.
myself I would run it.

Just checked my 90C and found 2 bolts on each side plus the bolt under the trim fin....are the alignment pins considered fasteners or is the OP's motor a different model from mine?.....just curious...

[boscoe99]

Alignment pins are just that. They are not considered as fasteners. Any of the alignment pins that I have seen are a slip fit. They can be grabbed and pulled from their respective hole. Not uncommon for them to be missing.

[robert graham]

Alignment pins are just that. They are not considered as fasteners. Any of the alignment pins that I have seen are a slip fit. They can be grabbed and pulled from their respective hole. Not uncommon for them to be missing.

So 5 bolts holding the lower unit on my 90C.....it would be like running my car/truck with a lug nut mixing from a wheel...

[boscoe99]

I see six bolts as holding a 90TLRC lower unit in place. Two on each side, one from up top that holds the trim tab and then one from down below in the trim tab cavity.

The dowel pins may act to prevent some rotation of the lower unit, were it inclined to do so. So, it might be prudent to have them installed. They do nothing to clamp the lower unit to the mid-section.

[ausnoelm]

An easy out bolt remover should be able to back it out O.K Get it fixed.....

Be very careful if you go this path, WHEN (not if) you break off the Easy Out, then you have real trouble.

[boscoe99]

In my experience an Easy Out is anything but easy. What an oxymoron.

[TownsendsFJR1300]

a 1992 90 HP (year and model is un-known):

1992 90TJRQ Yamaha Outboard LOWER DRIVE 2 Diagram and Parts

The above parts fisch shows 2 bolts on each side (4 total-part/bolt #6), (the trim tab bolt part #4 BUT, that doesn't secure the LU to the mid section) and of course the internal, rear clamping bolt... Five for this specific model.


Perhaps the later units has more mounting bolts..

A picture of the LU, from the Op would easily deceipher 5 or 7 bolts..

[rodbolt17]

if you think that 1 8mm bolt is going to lead to catastrophic failure, I got some land to sell.
next low tide we can go look at it.