Need bolt tapping advice--MD7A--stripped thread on reverse gear

[esarratt]

I broke the water drain bolt on the side of my MD7A reverse gear (I realize that there is a drain on the bottom of the MD7A, but there is another one on the starboard side of the reverse gear too).

I was removing the bolt to drain any old water/rust that was still in the reverse gear before dropping her back in the water.

I put a little too much force on the bolt and it sheared. The bolt didn't look to happy inside--it was very rusty.

I soaked the piece left inside the reverse gear in rust release overnight, got a screw extractor and no go. The bolt remnants just came out in little rust pieces with larger parts clinging to the threads.

So I got the correct tap--1/8-28 BSPP and everything was going great until I over tapped the hole i.e., the bolt is loose. I worked very slow, I used plenty of cutting fluid, I washed out the rusty bits as I was going and this is just the way it is.

So...given the miserable "boat yoga" I have been doing all day, my thinking is to drop the whole reverse gear and just take it to the local machine shop and have them re-tap the hole to an ever-so-slightly larger size.

I have thought about doing it myself, but the angles are all wrong. I can't get a good fix on a right angle to the hole to trust my judgement in tapping it. And for $20-$50 bucks a professional can line it up in a machine shop and do it for me.

There is quite a bit of metal surrounding the bolt hole (see pic). The end result would be barely larger.

FYI: I don't know if this matters or not, but when water runs into the drain hole it comes in from a very small hole in the back rear of the drain plug. Everything else is solid. It does not open into the engine like an oil plug hole.

Is my thinking off? See any problems with my solution? I realize that slow, rust release and plenty of tapping/vibration is necessary to remove the reverse gear and shaft coupling bolts. I don't want any more snapped bolts.

[skipmac]

Problem is you can't tap to just a slightly larger size. The threads in the next larger will not line up so to do it right you would have to drill the hole large enough to get clean sides before cutting new threads.

If the bolt is just to seal the hole and has no force 0n it I would use epoxy.

Clean the hole of all oil, water and residue. Coat the bolt with thinly with lanollin, Lanocote or similar. Goop the bolt with Marinetex, JB Weld or similar and screw into the hole. After the epoxy cures the wax on the bolt will let it unscrew while leaving the epoxy to make the threads in the hole a perfect fit.

Sent from my SCH-I545 using Cruisers Sailing Forum mobile app

[svlamorocha]

Originally Posted by esarratt

.

Is my thinking off? See any problems with my solution? I realize that slow, rust release and plenty of tapping/vibration is necessary to remove the reverse gear and shaft coupling bolts. I don't want any more snapped bolts.

Next time you can also try heat; it has worked for me..

Originally Posted by esarratt

I have thought about doing it myself, but the angles are all wrong. I can't get a good fix on a right angle to the hole to trust my judgement in tapping it. And for $20-$50 bucks a professional can line it up in a machine shop and do it for me.
(snip)
Is my thinking off? See any problems with my solution?

+1 on taking the thing off to line up things properly if you will do it yourself.

I would only suggest you consider using a Heli Coil insert and maintain the bolt size; that is what Heli Coil inserts are made for.

If you will hire a pro be aware that a real Heli Coil pro (the sort of guy who "visits" mechanic shops and do inserts for them) may be able to put an insert without pulling out the transmission. They use 90-degree tools and the like.. I saw a guy do it in a similar location in an old FIat I was restoring..

[esarratt]

Originally Posted by skipmac

Problem is you can't tap to just a slightly larger size. The threads in the next larger will not line up so to do it right you would have to drill the hole large enough to get clean sides before cutting new threads.

Got it. I follow.

Originally Posted by skipmac

If the bolt is just to seal the hole and has no force 0n it I would use epoxy.

How would I put epoxy in the hole so it is still a drain hole? The water enters into the side of the bolt hole in the back--not in the "top" like an oil drain.

Hmmmm.....I need to measure the depth of the hole in relation to the length of the bolt and see exactly where the water comes into the drain. There may be space between the end of the bolt and the drain hole itself.

[esarratt]

Originally Posted by svlamorocha

Next time you can also try heat; it has worked for me..

Yeah. I tend to be a bit quick with putting on too much force. This has been a sweaty, but useful lesson (as long as I don't do it again).

Originally Posted by svlamorocha

+1 on taking the thing off to line up things properly if you will do it yourself.

Yeah. I think that's the cat's meow. I have the time and I work for free!

Originally Posted by svlamorocha

I would only suggest you consider using a Heli Coil insert and maintain the bolt size; that is what Heli Coil inserts are made for.

If you will hire a pro be aware that a real Heli Coil pro (the sort of guy who "visits" mechanic shops and do inserts for them) may be able to put an insert without pulling out the transmission. They use 90-degree tools and the like.. I saw a guy do it in a similar location in an old FIat I was restoring..

Yeah, I knew there was a device, but I did not know what it was called thanks. It seems there are many solutions.

Tomorrow I'm going to really examine it and see how easily the reverse gear can be removed and lifted over the engine. More will be revealed on that front.

[MBWhite]

I'd figure out a few things before doing any more work here.

Apologies, but I have some questions that do not appear to be fully answered-

The bolt that broke is just a drain plug bolt correct? You unscrew it and out comes the liquid from behind it?

If so, was there a washer underneath the bolt before it was removed?

Where did you get the specification for a 1/8-28 BSPP bolt?


I am wondering if you have the proper bolt. There is a BSPP (British Standard Pipe thread Parallel) and also a BSPT (British Standard Pipe thread Tapered)

Here is a pic:


A parallel thread has to seal between the head of the bolt and the tapped item, the tapered thread seals between the threads.

I suspect a BSPT plug bolt will fit the hole and seal it without any further work. I would also recommend a teflon tape or paste to not only help seal but also to make future removal easier.

BSPP:


BSPT:


Good luck!

[esarratt]

Originally Posted by MBWhite

The bolt that broke is just a drain plug bolt correct?

Yes. It drains the water which runs through the reverse gear.

Originally Posted by MBWhite

You unscrew it and out comes the liquid from behind it?

Correct.

Originally Posted by MBWhite

If so, was there a washer underneath the bolt before it was removed?

No. Or if there was one it was corroded and gone. I saw no evidence of a washer although I realize that BSPP bolts usually have a washer of some sort (crush or neoprene)

Originally Posted by MBWhite

Where did you get the specification for a 1/8-28 BSPP bolt?

From the local hydraulic services shop who measured the other bolt (it is an oil drain) on the reverse gear. They got out their calipers, feeler gauges and sized it into a fitting. That is how they came up with 1/8-28 BSPP.

I bought a oil drain cock setup from the hydraulic services company which is why they measured the other bolt in the first place.

The two bolts are right next to each other on the same piece of metal (see pic).

After I broke the water drain bolt--I got about 2-3 threads on the broken bolt, I placed it next to the known sized bolt. They looked identical.

I then took both bolts back to the hydraulic services company to get a second opinion. They could not tell precisely if they were the same since their were not enough threads to measure, but they thought they were the same sized bolt.

Then before doing any tapping I took the known-sized bolt and threaded it in as far as possible into the water drain hole. It went in perfectly (then stopped when it hit rust). I wiggled it--good fit. It appeared to be the same sized bolt.

I then tapped the bolt hole to remove the rust with a 1/8-28 BSPP tap. The tap threaded in well the first few threads. It was a good fit.

Where I screwed up was in removing the tap multiple times to flush out the rust. That over cut the hole a little. Taps are sharp.

Now when I put the 1/8-28 BSPP bolt in the hole it is wiggly--it was not wiggly when I initially tried it in the hole.

Originally Posted by MBWhite

I am wondering if you have the proper bolt. There is a BSPP (British Standard Pipe thread Parallel) and also a BSPT (British Standard Pipe thread Tapered)

I actually had this discussion with the hydraulic services company. After I got the size on the initial oil drain tap from them I Googled their information to make sure they were correct. I then went back to them and picked their brain about BSPP vs BSPT. They know their stuff. They had measured the oil drain bolt with dial calipers and feeler gauges as well as sized them into fittings. I think they were right. The threads from the known-sized bolt do not have a taper.[/QUOTE]

[MBWhite]

Well if it makes you feel any better, if all you did was screw the tap in and out I do not think you were the cause of the hole being oversized. Most likely the corrosion had eaten it away and you chasing out the threads just removed the rust that was holding hands to keep the old bolt in.

As far as how to proceed forward from here, that depends on what you can personally live with. Since it sounds like this is just a plug for an area that weeps and is not under constant water pressure, I would experiment with seeing if a tapered plug would fit as I mentioned. If it screws in and snugs up, I'd be satisfied with that.

Next on the list, before I removed anything and hauled it to a machine shop, I'd go out to my lathe and turn another screw the same pitch just make it a couple thousandths larger in diameter.

If I wasn't happy with that, I'd probably re-tap the housing to fit a 10mm bolt. Verify these numbers but according to a chart I did a quick google for, the metric measurements are:


Diameter : 1/8 n=28 P=0.907 h=0.581 Major Dia.= 9.728 Pitch Dia.=9.147 Minor Dia.=8.566


And a 10mm X 1 measures at 10mm major diameter and 8.73 minor.


I suspect a 10mmX1 metric tap will just screw in and cut all clean threads for you.



Another viable option is to get a 1/8-28 nipple and epoxy it in and just screw a cap on the end.


Which reminds me of something else you mentioned, that you were concerned about sealant clogging drain holes:


That is always a concern, the approved method of applying sealant to threads is to put it on the male fastener only and make certain that you do not get any on the last 3 threads on the end of the fastener. If it is only on the male, when you screw the item in there is no way the sealant can get pushed into the system as it is all contained behind the threads.


Anyway, I hope this can help you!


Good luck again!

[esarratt]

Originally Posted by MBWhite

Well if it makes you feel any better, if all you did was screw the tap in and out I do not think you were the cause of the hole being oversized. Most likely the corrosion had eaten it away and you chasing out the threads just removed the rust that was holding hands to keep the old bolt in.

Thanks! (really!) Yeah....I've thought about this. Alot, way to much honestly.

The small oil bolt next to this one is almost pristine and came out easily and the other larger water clean-out is in fair condition--nothing like the rusty broken bolt and pieces I removed.

And... I did put too much force on it; it just felt like it was hard to turn--a bit harder than twisting a piece of liquorice in half. I do think the saltwater had gotten it over the years. I have wondered if rust remover and tapping and heat would have helped. No way to know now. Time to move on to the solution.

Originally Posted by MBWhite

As far as how to proceed forward from here, that depends on what you can personally live with. Since it sounds like this is just a plug for an area that weeps and is not under constant water pressure, I would experiment with seeing if a tapered plug would fit as I mentioned.

Yep. I have thought about about doing this alot! That is a good idea.

Actually it is under constant water pressure, but not bad. I could actually just shut off the seacock to the engine so the water stopped coming in when the engine was not running. The water that comes out of the plug does so at about 1 coffee can every 5 minutes, but it would be higher when the boat is in the water. All these parts are below the waterline when the boat is in the water, but nothing (to my knowledge) pumps water to this drain.

Originally Posted by MBWhite

Next on the list, before I removed anything and hauled it to a machine shop, I'd go out to my lathe and turn another screw the same pitch just make it a couple thousandths larger in diameter.

Good idea. And, I don't have a lathe. But I do have access to massive amounts of various sized bolts in the area as a temporary measure.

Originally Posted by MBWhite

If I wasn't happy with that, I'd probably re-tap the housing to fit a 10mm bolt. Verify these numbers but according to a chart I did a quick google for, the metric measurements are:

Diameter : 1/8 n=28 P=0.907 h=0.581 Major Dia.= 9.728 Pitch Dia.=9.147 Minor Dia.=8.566

And a 10mm X 1 measures at 10mm major diameter and 8.73 minor.

I suspect a 10mmX1 metric tap will just screw in and cut all clean threads for you.

Thanks!

Originally Posted by MBWhite

Another viable option is to get a 1/8-28 nipple and epoxy it in and just screw a cap on the end.

Yep. I actually have one of these--the drain I bought to go in this hole.

Originally Posted by MBWhite

Which reminds me of something else you mentioned, that you were concerned about sealant clogging drain holes:

That is always a concern, the approved method of applying sealant to threads is to put it on the male fastener only and make certain that you do not get any on the last 3 threads on the end of the fastener. If it is only on the male, when you screw the item in there is no way the sealant can get pushed into the system as it is all contained behind the threads.

Ah thank you. That solves that problem. I didn't know there was a good way to do that.

[esarratt]

Originally Posted by skipmac

If the bolt is just to seal the hole and has no force 0n it I would use epoxy.

Clean the hole of all oil, water and residue. Coat the bolt with thinly with lanollin, Lanocote or similar. Goop the bolt with Marinetex, JB Weld or similar and screw into the hole. After the epoxy cures the wax on the bolt will let it unscrew while leaving the epoxy to make the threads in the hole a perfect fit.

Thanks again! Combined with MBWhites information on not putting sealant on the last three threads that may solve it.

[tinkrman69]

from the pic and your statement that the sheared bolt is not the only one but is on the side/top and the other is on the bottom, and only having a small hole in the threaded side of the hole. that plug is not a drain, but a vent to assist in draining the water passages completely. which obviously hadn't been used, leaving trapped water there to rust.

if that is the case then tap it with a tapered thread of similar size and if still loose cut the threads short and epoxy in a reducer and insert a petcock to vent the water passages during drainage. Or just just close the hole and use forced air to drain the system.

[Terra Nova]

Don't Mickey Mouse it with epoxy. Remove it to have a machine shop repair it properly.

[hellosailor]

If it IS just an air vent, not a water drain, and there is no pressure on it...


Ace hardware still sells those nice hard black rubber corks for test tubes and other purposes. The right size, screwed in hard by hand, just might do the trick for the next ten years without any machining.


You know. Good enough for gummint work. Sometimes, a cork really is all it needs.

[esarratt]

Originally Posted by tinkrman69

from the pic and your statement that the sheared bolt is not the only one but is on the side/top and the other is on the bottom, and only having a small hole in the threaded side of the hole. that plug is not a drain, but a vent to assist in draining the water passages completely.

That has a ring of truth to it. Thanks!

[Sailshabby]

Heli coil and never give it a second thought,