Stripped LU Plug

[van]

I've had trouble with the bottom plug on the Lower Unit for years, finally it stripped the gearcase this season getting it out. I took the LU off and brought it to the dealer. They gave it a good try and installed a helicoil, but it would not hold pressure. (15 psi I think they use to test). So I took it home and brought it to my work where I have a good machinist. We looked it over and discovered that the drilling for the helicoil was not perpendicular to the seat for the plastic washer that shy it would not hold pressure.

So we decided to do the following.

Remove the helicoil---DONE
Then we see there is plenty of metal in that area (over 1/2" thick/deep).
I purchased some stainless steel NPT (tapered pipe thread) plugs (1/4 NPT).
We are going to drill it out 7/16" and tap with the pipe thread tap (1/4 NPT).
Insert the NPT plug with some teflon tape and/or nevaseez and I should be good to go. Only issue is I'm not going to have the magnet there anymore, but I can put that at the top hole.

So its do this or buy a new LU case at about 1500$, and if this fails I have to buy a case anyway.

Opinions are welcome...

Here are some images (I hope)

[ProcraftMike]

Sounds like a good usable fix. The top and bottom plugs on mine have magnets. Isn't there a way to magnetize the lower plug? I thought when we were kids, we use to mess around with rubbing magnets on metal things and it would make them magnetic as well. I don't remember all the details as it was quite a few years ago.

[mikedb1972]

dont know for sure, but i think you could lay the 1/4 npt plug on top of a speaker magnet for a day or so, and then the plug should hold some magnetism. cant say how strong, but should magnetize it enough for whst your looikng for. i would give it a try, wouldnt hurt anything.

[gearcaseman]

Sounds like a good way to save your housing. Why not remove the magnet from your plug and marinetex it in a drilled hole in your new pipe plug?

[Dover]

wow --sounds like a plan........ as far as the magnet thing, just might have to change the LU oil more often to be on the safe side...

[SwatDawg]

I change my plugs every 5th time I do the lower unit oil, costs me around $10 for both plugs... Sometimes I think Im paranoid untill I read posts like this. Good luck.

[van]

Sounds like a good way to save your housing. Why not remove the magnet from your plug and marinetex it in a drilled hole in your new pipe plug?


I like the idea, but I'm afraid if that magnet popped off that would be the end my of lower unit. I'm hoping the magnet at the top and yearly changes will be enough. One guy said to me "HECK,,they never had magnets in them years ago and they worked just fine !!!!! "

I thought maybe I would drill the new plug with an undersize hole and press in the magnet, but still it worries me.

[SEAHORSE]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SwatDawg &raquo;</TD></TR><TR><TD CLASS="quote">I change my plugs every 5th time I do the lower unit oil, costs me around $10 for both plugs... Sometimes I think Im paranoid untill I read posts like this. Good luck.
</TD></TR></TABLE>

the threads on the stainless steel drain plugs do not strip or wear, only the aluminum threads in the gearcase if they are overtightened. Save your money and your sanity and only buy the sealing washers, 311598, each time you drain the oil.

[van]

Almost finished, I drilled and tapped for the pipe plug, but the tap could not go in deep enough, so I brought it back to work and cut about3/8" off the tip, that will get the threads wider so the plug goes flush or recessed in the original hole.

So once the thread is right, I will wrap the plug with teflon tape and some thread sealant, finish replacing other seals and orings, close her up and do a pressure test.

[Stut]

Can you define "overtightened" Seahorse?

I have looked and looked but can not find any torque recomendations for these plugs. I'm no Heman, but I can get quite a lot of torque into a big slotted screw drivers with both hands white knuckled, and teeth grinding.....

Talk about paranoid....I lose ~10lbs ever time I replace my lower unit oil just from stress over too tight/too loose.

[van]

Finally done, changed all the seals, prop seal, shaft seal, shifter seal and every o-ring I could get to. Changed the water pump, and put a new zinc on the carrier. Then pressure tested in both directions to check both plugs and its all good !!!!
Fill her with oil and I put it on the engine this weekend. Was not a bad fix, I hope someone else can use this info. Thanks for your input also. ~V~

http://i158.photobucket.com/al...26463

http://i158.photobucket.com/al...26493

http://i158.photobucket.com/al...26520