Stripped threads on VP stern drive drain.
 

So I finally did it last October. When winterizing, I stripped the lower unit threads with the drain plug. I'm always careful with this as I know about galling in certain materials but this time I'm not sure how it happened. Probably a small piece of grit that I didn't get out before installing. Its a DP series unit.
So, I'm left with the following options:
1) Chase threads to original size. Risk of getting proper thread reforming.
2) Re-tap to larger thread size. Enough wall thickness??
3) Install stainless insert with original plug threads. Enough wall thickness??
4) Use an expandable rubber plug. Don't trust.
5) New lower housing. $$$

1, 2 & 3 run the risk of aluminum chips getting into the unit so I wouldn't feel comfortable doing it without disassembling the housing first. I'm leaning towards 2 or 3 but not sure how much metal I have to work with.
Anyone else faced this and what did you do?
Anyone have a good #6?
TIA
Edit. #5 would actually be new bearing carrier, not the whole housing.

Try re-tapping it with the tap covered in axle grease to collect the chips

Agree. I'd retap with same size. Nothing to lose.

I guess I'll just pull the housing off next month and evaluate. I think the threads are boogered to the point where they might not re-tap properly. That's why I was thinking of a helicoil insert or a larger tap. I think helicoil is the safest and wouldn't have the galling issue in the future but not sure how much room I have for it.

That would work well also.

If you are committed to pulling the stern drive apart and need to do a thread replacement, I would HIGHLY recommend you pass on the helicoil and spring for a stainless steel TIME-SERT solid inserts. A little more expensive but a world of difference in how good a fix they are comparatively speaking. When I used to be a car mechanic this is all we used and they never failed. Helicoils do. This is not a repair you want to take a chance on. Do make sure if you opt for this solution to use ample locktite on the insert's outer threads. You won't regret it. ;)


https://www.threadkits.com/time-sert...steel-inserts/


Good luck!

Time-sert
 

Thanks Maxum. I like the insert over the helicoil. Just one thing though. The insert has a flange stop to limit the thread engagement. The o-ring seal on the plug is a face seal so it would compress on the flange.

It seems the counterbore tool in the kit creates a counterbore that the flange sits in so if you control the bore depth you can get the flange to sit flush with the housing. Sound right?

I would use the timesert too. You can easily adjust the depth of the hole to get the flange flush, but I don't think you need to over-think it. O-rings can seal all kinds of ways. In my experience, grease on the tap will be more than adequate enough to catch the aluminum chips, especially since gravity is on your side. If you are truly worried, drill and tap while it's full of oil. It will be messy, but the oil will flow the chips out, not in. That said, aluminum chips are not going to damage steel gears and hardened bearing surfaces. The steel will just squishing and chop it to dust.

Been here done this, had close to the same problem, here is how the scenario played out....

1. One fall the plug didn't come out cooperatively for my mechanic.
2. We discussed the issue and several remedies.
3. My mechanic spent the winter asking around, because neither of us where excited about the cost of VP lower gear case housing....
4. Heli-coils where ruled out, the fail no one would recommend that fix.
5. In the spring we decided to roll the dice, re-tapped the threads, and filled her up and put the plug in.... it sat in the yard, and a little drip was noted.
6. Pulled the plug, and put some "goop", this is all my mechnic would refer to it as, and a new o-ring.... filled her with oil...
7. the ice was out and there where no more signs of oil leaking... in she went.
8. Ran like that for 5 or 6 years no problems... Still could get a definition of the "goop"......
9. then one day the plug came out, and didn't look so good, threads in the case seemed fine.... so a new plug was put in, sealed up nice and tight, a pressure test was done, and passed, with no "goop", ran all of last year just fine.....

So my thought would be to chase the threads, get a new plug, and if you have the ability pressure test it do it... if not fill her up with lube, and let her sit for a few days, and see what you see.

Just watch this - goes through the entire process to install.

https://www.youtube.com/watch?v=anjDQJtWFc8

There is a special tool used to create the countersink the flange sits in. These are really easy to install.

Good video. I can see that the counterbore tool has a shoulder stop to control the depth. Soon as I get some cooperating weather I'll take a look at everything. The kit for 3/8-16 Time-serts is about $80 at Amazon with inserts that are 1/2" long. Not sure if I need a shorter one but I'm pretty sure I can measure the housing to determine that.
Thanks everyone, great advice.

In the Time-Sert installation video the insertion tool looks like it may extend well into the gear case.

Will there be enough clearance inside for it to do the job or will the case need to be emptied of its internal parts first?

Dam I hope not but I think you only need to run the insertion tool just far enough to expand the threads on the end of the insert so the tool would only need to go slightly past the insert. Soon as I get decent weather I'll give an update.

wow great insight and video

Feast your eyes on this!

http://timesert.com/html/drainplug2.html

https://www.amazon.com/Time-Sert-M14.../dp/B00I3N39MC

They have shorties specifically for drain plug repairs. The key thing for this to work is the bottom part of the insert has to have material to expand and lock into.

Of course you are now obligated to provide pics so everyone can see the final product if you do this.

Not knowing your drive is it safe to assume you have a separate fill plug above?

The best plan would be to not get anything in there if possible, metal shaving are sometimes really tough to flush out.

That said, if there is a separate fill plug you could use it to apply VERY low pressure air flow to the drive while you are drilling and tapping it to blow the shavings out and keep them out.

You would need to be very careful to not use much pressure and damage the seals.

Good stuff evryone
 

I really appreciate the input from everyone.

As far as the insert length, I'll determine that when I finally get out to work on it (have to do truck brakes first).
The drain plug is 3/8-16 and although 1/2" long inserts come with the kit, they have inserts as short as 5/16" for that thread and the length from under the plug head to end of threads is 5/16". A little longer on the insert should be okay.

There is a dipstick port on the top so I could pressurize it while drilling/tapping as well as testing. I will definitely pressure test after install but I think using grease on the drill bit and tap will be okay. I can also get a Q-tip in there with grease to pickup chips.

As far as re-tapping without using an insert, I did that initially but I don't like the way the plug feels threading in so pretty sure the insert is needed as well as a new plug. I'll re-evaluate when I start.

Maxum, I'll try to remember pics also.

Unfortunately that happens alot with the drain plugs of Volvo Penta outdrive. The lower drain plug gets corrosion around it being stainless steel and aluminum. The proper way is to replace the bearing carrier and a new plug. Upon doing that the rolling torque has to be reset for proper gear lash & new seals for the carrier.

New direction
 

So, after over-thinking this (sorry Dave), I decided on the following plan.
The threads in the housing are about 3/4" long.
The threads on the plug are about 3/16" long (3 threads on a 3/8-16 thread). A little skimpy in aluminum. I believe that lead to the problem in the first place.
I was going to go with the Time-sert but was worried about drilling a straight hole with the drive installed. If the housing had been removed it would have been a different story. Also, the Time-sert kit is $80 plus additional cost for stainless inserts.
What I've done is modify a 3/8 bolt with about 1/2" thread length and machine a neck and counterbore under the head similar to the original, then drill the end and shrink fit the magnet in. I was lucky enough to re-connect with an old machinist friend that did it for a nice dinner that I didn't even have to cook.
Attached are pics. You can see the old plug with magnet removed, a new plug that I bought and the new screw with the o-ring installed.
I'll be trying it out soon.

That's a nice compromise and nicely done. I would however consider putting a very small dab of BLUE locktite on that thread.

Can't beat the price either ;)

Nicely done!

You may be able to find a replacement bearing carrier on ebay for cheap. I have seen them listed there in the past.


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