Removing screws on exhaust housing

[ward cleaver]

I removed the screws on the exhaust housing of my 1961 Johnson 40hp motor. What a struggle. I started out all 12 screws with liberal doses of WD40. Seven came loose after a couple of hits on the impact driver. Three more required quite a few stern raps but did come out ok. The last two were trouble. After banging with the impact driver failed, I ended up having to cut a wide slot in the phillips head with my dremmel so that I could use a large flat blade screw driver turned sideways. Even then it was a major struggle.

I took a close look at the screws and I see that the threads of the reluctant ones are filled with what looks like corrosion to me. I soaked them in mineral spirits overnite but they still won't allow a nut to thread all the way up to the lock washer. Are these screws ruined? What is this stuff in the threads?

 

[dazk14]

Re: Removing screws on exhaust housing

Likely mineral deposits. Wire wheel usually does the job. Without a pic, hard to be sure.

 

[boobie]

Re: Removing screws on exhaust housing

If you have a grinder, put a wire wheel on it and they will clean right up. Then take a tap of the proper size and clean up the holes where they came from. When you put it back together use OMC Gasket Sealing compound on them.

 

[Chris1956]

Re: Removing screws on exhaust housing

Those are stainless steel screws right? They can react with the aluminum exhaust housing. Sounds like you did well. Clean up or replace the screws. I like to use Permatex #2 or Permetex Aviation gasket maker on the threads, when reinstalling.

 

[ward cleaver]

Re: Removing screws on exhaust housing

I don't think a picture will help much in this case. It just looks like the threads are full of something hard. Could be whitish in color but hard to tell. A bit granular. Whatever it is does not want to come out. I've had them soaking in CLR to see if that does any good. If it is mineral deposits it should help at least a little bit. I'll put them to a wire wheel. I expect that'll clean them up. Weird that it only showed up on half the screws and not necessarily the ones lowest in the water. Good thing I got to them now. A few more years and I doubt they would have come out in one piece. Gasket sealer sounds like a good idea especially if it is a reaction between the SS and the aluminum.

As far as cleaning out the holes, can you recommend a set of taps? I have a lot of tools, but no taps.

 

[Chris1956]

Re: Removing screws on exhaust housing

Normally OMC used course thread, standard bolts on those motors. It has been a long time, but 5/16" screws seems to be the size. Standard taps should work well. You could buy a die to clean up the threads as well.

Is it possible the stuff on the threads was hardened anti seize?

 

[boobie]

Re: Removing screws on exhaust housing

1/4/20" screws I would guess. You can get a cheap tap&die set at Harbor Freight.

 

[yorab]

Re: Removing screws on exhaust housing

The '63 75hp used 1/4" X 20 fasteners for the exhaust housing and I'd imagine that it was the same for your motor. The original screws used cadmium as a corrosion inhibitor. I don't know whether this was an alloy or simply a coating, but it worked against environmental corrosion. You can readily find 50+ year old motors without any rusty fastener heads. Since cadmium is toxic, especially in industrial quantities, you won't find those fasterners easily or even at all these days.

Many fasteners that I've removed had that same whitish gunk at the threads. It could be a galvanic reaction between the dissimilar metals of the motor and fastener or it could be from oh-so-slight water intrusion over many years. When I replaced my fasteners, I went with stainless steel in order to prevent rusty bolt heads. I also used Loctite Marine Grade Anti-seize and Corrosion Inhibitor. This stuff is specifically formulated to prevent galvanic corrosion between dissimilar metals. I'm not sure how well this will work out in the long term, but I'm guessing that the fasteners will last at least a few decades before any corrosion issues arise.

 

[ward cleaver]

Re: Removing screws on exhaust housing

Interestingly enough soaking the screws in the CLR cleaned out those threads overnite. So I'm guessing its mineral deposits especially since you would think that all the screws would have been effected if it were due to dissimilar metals. So cleaning up the screws is not a problem but the screw holes is another matter. And they have a lot of that stuff in there. I've never used a tap or a die. I'm assuming its not rocket science.

 

[boobie]

Re: Removing screws on exhaust housing

They also sell "thread chasers" which will work in tighter spacers and are made for cleaning up threads. Sears and most parts houses should have them.

 

[dazk14]

Re: Removing screws on exhaust housing

Just to clarify specific uses. Loctite marine anti-seize is a grease - which is fine for non-gasket-ed surfaces. If you use a grease based product on a head bolt, you can be assured of 2 things...

The head bolt is unlikely to stick (good) and the head gasket is also unlikely to stick/seal (not good).

For seals that need to stick. Dry, or gasket sealing compound/Mercury perfect seal - is the order for the day.

For connections you do not need to stick - lower units for example - grease based products work well and every shop has it's own home grown concoction.

I think everything else has been covered.

Good Luck!

 

[ward cleaver]

Re: Removing screws on exhaust housing

I'm thinking about putting a very light coat of Permatex #2 on the threads of these screws and on the bolts to the lower unit. That should keep out any water and coat the metals. Good idea or bad idea?

I put silicone thread sealer on the screws to the cap on the lower unit and Permatex #2 on the seal. Should I have just used the Permatex on those threads too?

And lastly, is there anything I can use routinely on threads just about anywhere? I just hate it when screws and bolts and nuts refuse to come off.

 

[Chris1956]

Re: Removing screws on exhaust housing

Permetex #2 was recommended for a long time for motors used in saltwater. The only problem is that it can build up on the threads and in the tapped holes.

BTW - All the screws and bolts on my '59 Johnny were stainless steel. Everything else on the exterior was either aluminum or brass.