Lower Unit drain plugs holes not smooth

[rubilacx]

I think I figured out why my lower unit oil tends to go low. both of the drain holes on my lower unit are not smooth, it looks like the previous owner got crazy trying to take the plugs out. I'm wondering if I should JBweld or epoxy in a stainless washer that is the correct diameter to make a smooth mating surface for the gaskets. Anyone do anything like this before?

[pstephens46]

I think I figured out why my lower unit oil tends to go low. both of the drain holes on my lower unit are not smooth, it looks like the previous owner got crazy trying to take the plugs out. I'm wondering if I should JBweld or epoxy in a stainless washer that is the correct diameter to make a smooth mating surface for the gaskets. Anyone do anything like this before?

Hmm. Panasonic on this forum, is the resident metallurgical expert. He may have some tips on resurface and threading. This looks to be a good example of why over-tightening screws, bolts etc create havoc.

[panasonic]

Two things. Are the threads damaged at all? And could you possibly take a another picture with holes cleaned up...no oil running out.

What you are suggesting could work I suppose if done correctly. If it were my engine I would try and repair the counter bore seat.

Take another picture so we can see it a little better.

[Bluefish]

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[rubilacx]

The threads are still OK. Both lower unit drain plug holes are fubar on the mating surfaces though. I could only shake my head like what the heck did this previous owner do...!

I will take a few more pictures of both surfaces today. I'm also wondering if I could sand them down with a Dremel to get it flat. I am very concerned about putting it back in the water knowing it will likely leak.

[rubilacx]

Here are two more pics, one of each hole. Any ideas Panasonic or anyone else? The gaps are approximately the depth of the elevated ring around the holes.

[panasonic]

Oh boy someone really done the job on those..

I am going to say no to the dremel, that will probably make it worse.

That spotface or counterbore, what ever you want to call it, has to be flat obviously and perpendicular to the thread bore, so when the plug is screwed down it will touch all the way round.

[panasonic]

So you are going to need to counterbore those holes and clean up the sealing surfaces so the gasket can do its job. Here is an example of a counterbore with a pilot. The pilot fits snugly into the threaded hole to keep you square while machining the spotface. m5-counterbore-drill-10-0mm-pilot-5-3mm-din-373-fine-021400-146011-en-G.jpg

[DennisG01]

I agree with your sentiment, Rubilacx, about not putting it back in the water. I also agree about "what the heck!"

I agree with Panasonic - using a Dremel (other than to take off any burrs) wouldn't be good - too hard to control it to get a flat surface.

I think the "proper" way to do it would be to take it to a machine shop and have them shave it down to clean/smooth. I don't "think" you're going to have any clearance issue with the screws hitting the gears inside since not much really has to be taken off and I highly doubt the clearance tolerance is THAT tight. But it's easy enough to check/verify and/or take a little off the screw shank if needed.

I'm not sure you could use a counterbore cutter without damaging the threads (maybe with lots of oil and go very gently?) and also risking not keeping the surface 100% perpendicular to the hole. The machine shop should be able to figure out a jig.

On the other hand, if you can clean it up really well... REALLY well... then I think your idea of epoxy (like Marine Tex or PC-11, etc) and a stainless washer will most likely be just fine. You won't need (or want to use) much goop - and even though it will likely be cured in a day, I would give it at least a couple days for good measure. Use your drain screw to hold the washer gently, but snugly, in place while it dries. Apply some wax to the screw threads - just in case a little goop squeezes out on the threads, it won't stick.

[panasonic]

I dont know what your skill set is and would you be confident to try this.
If you can find a counterbore the right size diameter and pilot is the first thing... You can do this with a good cordless drill and work very slowly. If you brought it to a machine shop this how they would probably fix it, by hand with a counterbore.

Setting up a lower unit on its side in a milling machine would be quite time consuming and not particularly easy and time is money at a machine shop.

Last but not least...is there enough material there to machine away to clear all the damage?. It isn't very thick there and I am counting probably 5 or 6 threads depth.

So if you are able to do some measurements with a vernier caliper and want to try I can help you source a counterbore. I am assuming you are in the states, so lots of places to get them. Mcmaster Carr would be a good place to start.

[DennisG01]

Setting up a lower unit on its side in a milling machine would be quite time consuming and not particularly easy and time is money at a machine shop.
.

Agree. It's likely not the "normal" thing they do. Some machine shops have some very creative and talented people working there, though. At a minimum, it would likely be worth a conversation. A long piece of all thread screwed into the drive can be used get it set perpendicular to the drill press with a rotating table. Ratchet straps, clamps and shims can help hold it in place. I know that sounds a little MacGyver-ish... and there's probably a better way - that's just the first idea that popped in my head.

[panasonic]

I agree with your sentiment, Rubilacx, about not putting it back in the water. I also agree about "what the heck!"

I agree with Panasonic - using a Dremel (other than to take off any burrs) wouldn't be good - too hard to control it to get a flat surface.

I think the "proper" way to do it would be to take it to a machine shop and have them shave it down to clean/smooth. I don't "think" you're going to have any clearance issue with the screws hitting the gears inside since not much really has to be taken off and I highly doubt the clearance tolerance is THAT tight. But it's easy enough to check/verify and/or take a little off the screw shank if needed.

I'm not sure you could use a counterbore cutter without damaging the threads (maybe with lots of oil and go very gently?) and also risking not keeping the surface 100% perpendicular to the hole. The machine shop should be able to figure out a jig.

On the other hand, if you can clean it up really well... REALLY well... then I think your idea of epoxy (like Marine Tex or PC-11, etc) and a stainless washer will most likely be just fine. You won't need (or want to use) much goop - and even though it will likely be cured in a day, I would give it at least a couple days for good measure. Use your drain screw to hold the washer gently, but snugly, in place while it dries. Apply some wax to the screw threads - just in case a little goop squeezes out on the threads, it won't stick.

We hand counterbore or spotface holes on Aircraft structures all the time as most times the part cannot be removed from the aircraft or it is to difficult to mount up on milling machine, too big or multiple other reasons. It is quite doable.

The pilot on the counterbore has to be a snug fit to keep you square and its a smooth surface so it wont damage the threads.

Not saying the washer wouldn't work...

[99yam40]

keep in mind you need to keep all the shavings out of the gearbox also

[DennisG01]

We hand counterbore or spotface holes on Aircraft structures all the time as most times the part cannot be removed from the aircraft or it is to difficult to mount up on milling machine, too big or multiple other reasons. It is quite doable.

The pilot on the counterbore has to be a snug fit to keep you square and its a smooth surface so it wont damage the threads.

Thanks for that - good to hear that it can be done by (a steady) hand

[rubilacx]

I appreciate the ideas. I'm researching counterboring as that is not something I have done yet. Skill level is pretty high overall so I'm not too worried about being able to do "something"... just careful as to "what".