Stripped lower unit gear case lube vent screw

[MarkS]

So when I changed the gear case oil in my lower units last year I stripped the threads on the upper vent nut. Figured I would attend to it in the spring it held tight enough that the oil wasn’t running out so I called it a spring fix. Also sort of figured this to be a fairly common occourance with aluminum gear case and a steel nut however it seems now there is much conflicting information about it. Started at the local Merc dealer he told me I needed a new gear case. I smiled and said have a nice day. Checked around for a helicoil fix but I am being told it’s an odd size and there is no such animal. Was also told there is an option to go up a size but haven’t been able to find that either. Anyone here with outboards or outdrives have this problem before? If so what’s the best fix?

[mike ohlstein]

um..... Get a proper Bertram with inboards...... You know, like a 31.

Feelin' Mean today.

[Rawleigh]

Mark: Do you know the thread size? We may be able top come up with an option if we know that. A good machinist should have a solution for you. It doesn't have to use the factory plug as long as it is SS. Aren't those O ring sealed? If you do have to replace it I have a friend who has had very good luck with the Korean lower units. I forget the company, but you see them advertised all the time.

[MarkS]

Rawaleigh,
I think their made by a company called SDI I see their adds on the back of Soundings all the time. They are inexpensive by comparison which of course gives me a little pause, plus I did just have that leg rebuilt fall of 16 so it would be double painfull to pitch it over a stripped vent screw.

I did go to see my local machine shop and I think we have the answer. He is going to build me a new plug and tap the opening a size up. Thanks for the ideas.....Mike too I like your idea. :) Of course I am fortunate enough to know just how mean you can be. Ya big softy...

[Tony Meola]

Mark

My father would always say, change the spark plugs but "Don't screw the eyeballs of it."

I guess you felt strong the day you tried to tighten it up.

[MarkS]

Tony it’s a flat screwdriver tip. I’m just not that strong. Aluminum case vs stainless steel screw. Piss poor design that continues to this day. The Merc mechanic that told me to replace the gear case was maybe 40 . He said in ALL his years he’d never seen one stripped. How do you argue with that kind of history...

[Carl]

If you can go a size up(UN or metric) keeping O-ring seal intact, thats the ticket. But you need a new custom plug...and of course drain and flush debris from the drilling and tapping unit.

Another ugly fix would be a 316SS NPT plug...but as it would go in tight to seal you need Corrosion X or something when installing. Gotta love alum and SS combo...Alum casting is an even better mix. Look at the bright side, your in fresh water...it's worse playing with Aluminum, Stainless Steel and Salt water.

LOL..mechanic never saw a stripped plug on a lower unit...huh..guess that only happens around here. My guess is he see's em and loads them up with thread seal or lock tight letting it become owners problem.

[Stephan]

He said in ALL his years he’d never seen one stripped. How do you argue with that kind of history...

This is the definition of adding insult to injury - sorry.
Drill it (blowing air in from the bottom hole will help keep the chips out of the casing), tap it and screw it. Then show the young man what he's been missing - a whole 'nuther world from remove and replace...
Good luck,
Stephan

[Rawleigh]

Put grease on you drill and tap to hold the chips. Drill slowly so it doesn't get thrown off. Use Alumtap with the tap, even if you put grease on it to keep it from galling the threads.

http://www.tapfree.com/alumtap.html

Carl may have some better suggestions though.

[Carl]

Yes, by all means use all the tricks to keep chips from going in.

Then drain, flush and refill.


Alum a tap works well as does Cool tool and tap magic.
But for alum...a dab of kerosene or diesel works pretty slick too, especially if you have some around.

[MarkS]

What do you recommend I flush with?

[Carl]

Light weight lube, I like marvels

[Pete Fallon]

Mark S,
If I remember correctly some of the Mercury outboards had 2 different sized drain screws the bottom one had a magnet attached to collect metal chips from the gear oil and the top screw was a little bigger than the bottom one. Both had O rings, the different sized plugs were back in the mid to late 90's I think. Haven't fished outboards since 2001.
Pete Fallon

[captbone]

Easy ghetto option.


Put the screw back in and after sanding to bare aluminum, put JB weld over it. You can also use epoxy as well.

Change the gearlube every two years and grind the JB/Epoxy down to remove it.

It sucks but will work with the least about of headache. Both of those are used on nosecones and will work fine.

[MarkS]

Thanks for the input guys!