How to retap gear case bearing carrier threads, Merc 15hp 2 stroke S/N 0T533347

I'm pretty sure the bearing carrier was never out on my 2002 2 stroke 15hp Mercury o/b. The carrier is finally out, but it looks like it left some of it's thread behind in the gearcase, likely due to either fatigue, the hear, corrosion, or all 3. Anyway the case is in good shape and there's a lot of meat in there, so I think I can just retap it carefully to accept the new carrier. The old carrier on has about 2 threads left on it.

Is there an actual mercury part you can buy, and if not, any suggestions, or known taps that are the right thread size and pitch? The motor's SN is 0T533347.

Any help, ideas, or tips are appreciated!

Thanks

Will a helicoil work?

Jeff

I don't know enough about helicoils, but my understanding is helicoils are for rebuilding missing threads, vs retapping enough existing metal to recreate the right size thread. Is that correct, or am I incorrect?

Thanks

That's an awful large "tap" that would be required. Perhaps a pipe fitter might be able to re-tap (??)

Is there any way you can just clean up the threads yourself on the housing? I'm thinking maybe a small pick (like a dental pick) to remove any (material) from the bearing carrier threads that are adhered. Clean it up enough and then install a new bearing carrier (carefully), well greased - might finish pushing the rest of the (crud) out of the housing (sorta use the carrier as the "tap").

The whole design with the "screw in" carrier was a poor idea. My 15 horse (1991 model) is "welded" in place from running in salt water. Always figured if there was an issue I would be better off replacing the entire lower unit then trying to work on it - don't know that I could get the carrier out without destroying the case.

.."
The whole design with the "screw in" carrier was a poor idea"

I always thought that was a good idea? Of course, I never owed one new enough to see they corroded all together. Thanks!

Jeff

That's my goal is to just clean them up, they are there which is good. On another thread, or site, can't remember, I found that someone suggested this too:

https://www.mcmaster.com/catalog/125/2620

It's the one on the bottom, the internal thread repairer. I bought the metric and standard size sets, as I'm not sure which I need, and the tool. McMaster Carr contacted the manufacturer and they confirmed it will work for left hand thread. It supports NPT and standard threads too. If it's long enough to reach down the throat of the case, this should do it. If not, I found a new case for $355.

That thread repair tool looks interesting and can't see why it wouldn't work just keep in mind that the case is aluminum so do "take care"- should be able to reach, you are not going that "deep" into the case.

Even if you have to go with a new case that is significantly less than a new 15 horse motor. And the top end of these motors is close to bullet proof. I have an 86 and 87 9.9 and a 1991 15 horse and all are still running great. They have collectively seen a couple of new coils, two base gaskets, one transfer cover gasket, one upper crank seal and all have had carb rebuilds. But with the "youngest" being 28 years old I can't complain too much.

If you do end up replacing the case you should either buy the special socket that goes up at the top of the drive shaft to allow you to correctly torque the pinion gear back on (used to be about 35 bucks and proper torque is essential or you can toast the gears), or take it into a shop to have that one (function) done. The rest can be done at home without much issue. At least there are no shims on these gears like the old cases and a new case is the perfect chance to replace all the seals and effectively get a brand new lower unit that should easily last 25 years or more (two of mine are in their 30's with nothing more than regular gear oil changes and an impeller every other year).

Thanks very much for your words of encouragement. This tool seems like the right thing! When you say take care, you just mean go slow because it's aluminum and will cut quickly, right? I will, with cutting oil too. I think I may be able to save the case. I'm sort of working with an old salt that does repairs, so he has many of the tools as he runs a marine service business. He was the one that was actually able to get the old carrier out. He just didn't have the dies big enough. So we are kind of working together. I told him I'd find a solution, and he said when I thought I had something to come back to him and we'd get the carrier back in and reinstall the prop shaft and everything. I'll then reinstall the shifter, water pump, all new gaskets, etc. I had already bought all that stuff.

My logic was the same as yours too, that even at $350 for a new lower case if I need it, I'm still in good shape. I actually only paid $500 for the motor last year. So with this I'm still only around $900 with parts. Used ones are at least that if not more, and likely have their own issues. If I can get this fixed, I'll be happy, but if I need a case, so be it.

Yes, just slow and easy. You will (probably) be using a carbide cutter on aluminum and the cutter can do a lot of damage quickly if you force it.

Let us know how it works out for you.

Thanks. I am curious how the part works, since there are all difference die sizes, but it's not a fixed diameter as the handles seem adjustable. Why would you need all the different dies if you can adjust the handle?

From what I can tell from measuring with a caliper, the bearing carrier is M55 with a pitch of 1.75. At least I'm guessing it's metric, as the US measurement would be like 2.13 inches or something odd. It measured slightly more than 55, but I'm thinking when you measure metric the size doesn't count the threads. Or it is an oddball size, and this tool since it's infinitely adjustable up to 6", should be just what I need. Just don't get how thread per inch and pitch comes into play with how it works. I'll find out tomorrow when it arrives.

A dremel tool with a cut off disc, at slow speed and a steady hand works great. Fixed a many duck hunter 25's this way ...and a lil ATF is your friend doing this.

faztbullet said:

A dremel tool with a cut off disc, at slow speed and a steady hand works great. Fixed a many duck hunter 25's this way ...and a lil ATF is your friend doing this.

Click to expand...

REALLY steady hand! One slip and buh bye! ha ha. I'll see how the tool works. I'm nervous about cutting too deep, but using ATF is a good idea as I have plenty of that on hand, vs actually cutting oil.

If you run it slow(variable speed type) with a light hand it will follow the valley in threads and yes I have slipped but it wont cause problems...

Thanks, I suppose as a last resort. But I got the rethreading tool today, and this thing is very cool! I see how it works now. The dies have a few threads in them, so they line up by size. Very neat design and likely self corrects. And it just reaches to the bottom of the threads in the case. This is very neat. Here's some pics. Obviously the close up of the cutters I show are not the proper ones, just the ones that came installed. I bought the full standard and metric set of dies, plus I have the ones it came with.

Now on to the next decision, are the threads metric and 1.5 pitch, or american/standard and 16 threads per inch. I believe 16tpi. Here's a close up of another bearing's threads matched up against both the american size and metric size dies. The 16tpi seems just a tad more in alignment, and the bearing I'm using is slightly worn with some flattened edges.

Opinions? You can see what size is what as it's stamped on the die. American 16 threads is the first one, and the second is metric with a 1.5mm pitch.

Here's another pic of the tool too.

Should be the 16TPI

faztbullet said:

Should be the 16TPI

Click to expand...

Thanks!

Well for the record, and for any else that might stumble upon this, the tool worked like a dream, and the new bearing screwed right in...unreal. Now the test will be torquing it down a bit and making sure the threads hold up, but sure seems like I'm on the upside of bad...