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How To Fix a Stripped Drain/Fill Hole

Todd in NY

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When I drained my gear oil on my 1989 Evinrude 150 last week I realized that the previous owner used a rubber plug in the top drain/fill hole. The rubber plug kinda worked, but there was some water contamination in my gear oil. The bottom plug was correct. So I went to the local Evinrude dealer and bought two new drain/fill plugs. When I tried the new plugs in the top hole on my motor, the plug fell into the hole up to the head of the screw, never touched the threads.


Well crap, the top hole is stripped out and no one makes a plug bigger than the OEM 3/8" plug. I'm no mechanic, but I have to come up with something.




I searched the internet and found a stainless steel socket cap screw, 7/16"-14 x 1/2" long, so I ordered it from Fastenal. I ordered a 1" long 7/16 socket cap screw with it, just in case I needed a backup plan.


First I had to remove the bottom half of the screw head, turn it down to the same diameter as the OEM screw/plug. I don't own a lathe, it's Saturday, so I can't have a machine shop do the work. No other choice but to "turn" this down myself. So I threaded a 7/16 nut onto the screw, stuck it in my bench vice and began to file the bottom half of the head down, using the edge of a file. I kept turning the nut & screw every so often to keep the filed portion uniform.




Nearly an hour later (I think, but I lost track of time) I got the filed portion down the the right size. I then used a small needle file to remove any burrs and rough edges.






I needed the hole to be 25/64" for a 7/16-14 tap, but I didn't bother to drill it out because I could easily slide a 3/8" drill bit into the hole by hand. The tap handle was too long to use, because it kept hitting other parts of the motor.




So I had to resort to using a small adjustable wrench. I had to be extra slow and careful so the tap would go in straight.




Mission accomplished! My new plug/screw fits like it should. Now I have to find an O-ring or washer that will fit my 7/16" plug, because none of my OEM washers or O-rings fit. Found one, make that two... whew.


NOTE: Before tapping the hole, raise the motor up all the way, then turn the motor toward you. When making the new threads, turn the tap in a 1/4 turn, then back it out some, to help the shavings fall OUT of the hole. Continue this process until finished making the threads. Keep the motor in this position until the hole is tapped and all shavings are removed from the hole.




The bottom plug on top in the pic, the top plug on the bottom (not trying to confuse you), and my fabricated new plug in the middle.


I used some Q-tips to carefully remove any shavings from the hole. I then lowered the motor and added about 16 ounces of gear oil through the top hole. This is to flush out any shavings that might have fallen inside the gearcase when tapping the hole.




Now it's time to install my new plug to make sure it fits with the O-ring. It seems to fit nicely, but I didn't tighten it all the way. I still have to add 33 ounces of new gear oil.




The gear oil is filled, both plugs are in. Time to raise the motor and see if any gear oil leaks out of the top hole. If it does, I'll remove a little more metal where I filed down the lower portion of the screw head.


Thanks for reading this. I hope none of you ever have to deal with this issue, but I wanted to post this as an option for you to try. Here is the finished product :yes:



Edited by Todd in NY
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The helicoil video I just watched has you breaking off a tang that allows you to screw the threaded insert into the new hole, after you thread the insert into the hole.


Great idea if there is a helicoil that doesn't have a tang that needs to be broken off inside the gearcase. Or maybe a tang that can be pulled outward to be broken off.


Also, not sure what size hole would have to be drilled for a 3/8" drain plug.


Thanks for the idea! I would've looked into it if I knew they existed before I fixed it my way.

Edited by Todd in NY
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55 minutes ago, Dusty said:

Threaded inserts are another option as they don’t have a tab. You need a slightly larger hole, but use a solid steel insert for the repair.


How do you keep a threaded insert or helicoil from threading into the gearcase? I like the idea of keeping the same thread/plug size but there's nothing in that hole to keep a threaded insert type of thing from eventually threading deeper into the hole. I'm asking because I'm not familiar with threaded inserts of any kind, and maybe I'm missing something...?

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Nice job , but yeah I typically fix these with threaded inserts , just like spark plug holes ,,, or any drain or fill hole ..  it’s basically a thin hardened tube with threads on outside and inside .: inside threads are same as oem.. outer threads you drill and tap for .. comes with a tool you thread them in with,, cover it with some red loctite on outer threads ..  also comes with a tool you insert after it’s threaded in and hit with a hammer that flanges the edges and peens it in place ... they are a life saver ..  gotta appreciate the job you did though , definitely got it done and won’t have to do it again . 


Also when doing this I dip the tap in sticky axle grease so the filings Stick to it 


if you google timesert that’s what I use 

Edited by JTowne
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44 minutes ago, JTowne said:

BTW if you ever need a hillbilly lathe put your drill in the vice with whatever kind of clamp on the trigger .. chuck up your bolt.... and you know the rest . 


I was trying to figure out a way to hold that 7/16" nut in my drill, but it only holds a 1/2" bit. By that point I was determined to just use what I had on hand.


I appreciate the feedback from everyone. That's why I took the time to document my work and post it here.

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