aluminum screws

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txneal

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Alpine, Texas
I have a 1972 Starcraft that has some 2 inch aluminum truss head machine screws going through the transom. I need to remove ten of them, but I can't get a single one to budge. They have phillips heads and they just strip out if I try to turn them. I've sprayed them with penetrating oil, but that seems to have done absolutely no good at all. Anyone know of any tricks for getting aluminum screws and nuts apart? I've tried all 10 of them and not a single one will move at all! I'm thinking that I may end up having to try to cut them off with a dremel and cutting disk.
 
yea, I had the same issue and had to cut them off with a dremel. Once I cut the backs off, I was able to punch them out with a hammer though. Minimal damage to the transom, filled it in with filler and silicone. Rust sucks!
 
I don't think there's any rust in the threads because the screws are aluminum....at least I think they are...they're not attracted to a magnet. I just ordered some more aluminum screws to replace them with, but was unable to locate any identical to them. I had to go with round head, slotted aluminum machine screws as I couldn't find any truss head aluminum screws in the proper size. I also ordered some aluminum washers to make up for the difference in head diameter. However, I'd like to re-use the original screws, if possible, so was hoping there might be some trick to getting them to come loose. They are so tight up against the transom that I'm afraid it will be difficult to cut them with the dremel without damaging the transom a bit.
 
I had the same problem with my 1974 Starcraft. I ended up cutting them off and replaced them with 10-24 stainless screws with a washer because the screw head was smaller.
 
I think your screws are actually stainless steel and not aluminum. Aluminum is a poor bolt/screw material, you should replace your screws with stainless steel.

Drill the heads out on the stripped screws, if they drill real easy it was aluminum... if they don't drill easily they're stainless steel.
 
I would drill them out and replace them with stainless steel. I think I have seen Button Head stainless machine screws at Westlake Hardware, the one by me has a nice slection of SS nuts, bolts, & screws.
 
Last summer I attempted to replace my transom bolts with the same type of aluminum bolts that was originally installed in the boat and quickly discovered that stainless would be the way to go. The material the bolts were made from was so soft that the bolt would shear long before the nut was even close to being tightened. Pure garbage. I guess it's more Chinese crap made from our empty beer cans.
 
Agreed with all the above - aluminum is a soft metal and inappropriate for the job.
 
I ran into that last month as well. I'm positive they were aluminum because I broke them just by trying to remove the nut. It was way too soft and also why I opted for SS. I ended up being able to take a smaller bolt and hammer and back most of them out. I had at least 2 of them where I had to drill them out, but it takes very little effort to drill them out.
 
Isn't stainless steel magnetic? I just assumed these were aluminum since it is an aluminum boat and the screws are not attracted to a magnet. Is is ok to have SS in contact with aluminum? I've already ordered some aluminum machine screws, but I will not use them if they aren't strong enough to be up to the job. I emailed the company that I ordered them from and asked about the strength of the screws and whether they believed the screws would hold up well to the forces exerted on the transom by a 25hp motor. A guy emailed me back and replied that he couldn't say for sure, but he thinks they'll do the job. I don't really want to take any chances, so if its ok to have SS in contact with aluminum, I may just go that route.
 
txneal said:
Isn't stainless steel magnetic? I just assumed these were aluminum since it is an aluminum boat and the screws are not attracted to a magnet. Is is ok to have SS in contact with aluminum? I've already ordered some aluminum machine screws, but I will not use them if they aren't strong enough to be up to the job. I emailed the company that I ordered them from and asked about the strength of the screws and whether they believed the screws would hold up well to the forces exerted on the transom by a 25hp motor. A guy emailed me back and replied that he couldn't say for sure, but he thinks they'll do the job. I don't really want to take any chances, so if its ok to have SS in contact with aluminum, I may just go that route.


Any difference in metals will react, but most guys on here will recommend a little bit of 3M 5200 to coat the SS hardware. I'm not familiar with aluminum screws that are new, so I can't be sure, but they snapped off with very little effort when I turned the nut by hand. That was the only reason I opted for stainless.
 
If the screws that are currently in my transom are aluminum, they must be some good stuff because they certainly won't snap off when I try turning them, I have cranked down hard on them with a socket on one side and phillips screwdriver on the other and they won't budge and show no indication of breaking off.
 
Not all stainless steel is magnetic. The higher the nickel content its non magnetic. The bolts that you buy should be magnetic because they are lower grade of SS. Aluminum bolts are probably made out of something in the 7000 series which would make them strong. The 7000 series Aluminum is what is used in aircrafts and such. The aluminum bolts in my boat most of them twisted off but not easily. They are pretty tough. I went back with SS because I wanted something that was readily available in the area and didnt want to order the aluminum bolts.

Steve
 
txneal said:
Isn't stainless steel magnetic? I just assumed these were aluminum since it is an aluminum boat and the screws are not attracted to a magnet.


Some grades of SS are magnetic, while other grades are not. Marine grade SS is typically not magnetic. However, it's my understanding that the magnetic properties of SS can be altered, by heat treating, which changes the chemical structure of martensite and austenite in the SS. The AWS welder's procedure handbook goes into all kind of technical information on SS, most of it gives me a headache trying to understand it. I don't work with a lot of SS, I tend to work more with aluminum and steel, so, I'm definitely not an expert in the metallurgy of stainless.


Is is ok to have SS in contact with aluminum?

While putting 2 dis-similar metals together in contact with water is setting up a situation for electrolysis, manufacturers do it all the time. The trick is that the aluminum part they are putting the SS fastener into, is thick enough that it can afford to lose a little bit of material to electrolysis. A thick aluminum engine block is one thing. But problems can arise when the aluminum is a piece of thin sheet, like a transom. If it loses ANY amount of material, there's going to be an issue. Having anodes reduces this galvanic action. One thing I will say, though, is that in salt water, you can pretty much ignore the service manual when it tells you to put loctite on a fastener....trust me, galvanic action will **** near weld the fastener together soon enough.


I've already ordered some aluminum machine screws, but I will not use them if they aren't strong enough to be up to the job. I emailed the company that I ordered them from and asked about the strength of the screws and whether they believed the screws would hold up well to the forces exerted on the transom by a 25hp motor. A guy emailed me back and replied that he couldn't say for sure, but he thinks they'll do the job. I don't really want to take any chances, so if its ok to have SS in contact with aluminum, I may just go that route.

One thing to remember is that aluminum is 1/3 the strength of steel. This should answer your question about whether you think it's strong enough. If it were me, I'd use SS, and then, I'd prevent any electrolysis/galvanic action by installing an anode on my transom below the waterline. Use a Magnesium anode if you're in fresh water, use a Zinc anode for salt. For a 14 foot johnboat, you need an anode, or a combination of anodes that have at least 24 sq inches of surface.
 
txneal said:
If the screws that are currently in my transom are aluminum, they must be some good stuff because they certainly won't snap off when I try turning them, I have cranked down hard on them with a socket on one side and phillips screwdriver on the other and they won't budge and show no indication of breaking off.

That would be stainless steel!

Have you tried drilling the heads off yet? If you burn up a couple of drill bits and don't get the first head drilled out then it's stainless for sure... I'll tell you how to drill stainless after you burn up a couple of bits. :twisted: ... nah, I'll tell you now, go slow. If the bit is turning and throwing off chips you're doing good. Dip your bit in water! this will cool it off, and when you see steam coming off your bit dip it in the water again.

If it wasn't ok for stainless to come into contact with aluminum there would be a zillion aluminum boats in the recycle center. Boat manufacturers use lots of stainless on aluminum boats... from deck screws to motor mounting bolts and many in between.

I have a real nice big anode... but my wife only lets me use it once a month. :cry:
 
Jigngrub is right about trying to drill SS.....you do not want to overheat the bit, or it will quickly dull and will no longer cut.

That said, water really doesn't have the viscosity to be used as a cutting fluid, it does not properly dissipate heat, nor does it provide the lubrication required for cutting, especially a material as hard as stainless. What you really need is a water-soluble cutting fluid, but if you don't have that, then, mix some soap with the water, and use a spray bottle to continuously flood the bit as you are cutting, don't wait for it to start steaming, keep the fluid going to it. Once it starts steaming, it's bordering on getting hot enough to pull the temper from the bit, and it will get dull really quick. Motor oil also works, it's more effective than soapy water....but it makes a mess.

I don't mind welding stainless, but I absolutely HATE trying to cut, drill, or grind it! Aside from exotic metals like titanium, stainless has got to be the most difficult material to work with.
 
OK....I got the heads drilled off of all of them and it wasn't too hard. I tried using the Dremel with a cut-off wheel, but it was impossible, so I bought a cobalt drill bit and drilled them out quite easily. As per the suggestions in this thread, I decided not to use the aluminum screws and have purchased some stainless screws to use instead. Now I'm wondering how important it is to use an anode on my boat....

I'd prevent any electrolysis/galvanic action by installing an anode on my transom below the waterline. Use a Magnesium anode if you're in fresh water, use a Zinc anode for salt. For a 14 foot johnboat, you need an anode, or a combination of anodes that have at least 24 sq inches of surface.

I did some reading on anodes last night and it appears that you must not take a magnesium anode into salt water or a zinc anode into fresh.....so what do you do if the boat may be in both? My boat is in fresh water 95% of the time, but I'm planning to use it in salt water for a few days each year. What should be done in this case? Is an anode really necessary?

I have some aluminum washers....what if I were to use an aluminum washer between the stainless nut and where it comes into contact with the aluminum of the boat....sort of a sacrificial washer? Any thoughts?
 
txneal said:
OK....I got the heads drilled off of all of them and it wasn't too hard. I tried using the Dremel with a cut-off wheel, but it was impossible, so I bought a cobalt drill bit and drilled them out quite easily. As per the suggestions in this thread, I decided not to use the aluminum screws and have purchased some stainless screws to use instead. Now I'm wondering how important it is to use an anode on my boat....

I'd prevent any electrolysis/galvanic action by installing an anode on my transom below the waterline. Use a Magnesium anode if you're in fresh water, use a Zinc anode for salt. For a 14 foot johnboat, you need an anode, or a combination of anodes that have at least 24 sq inches of surface.

I did some reading on anodes last night and it appears that you must not take a magnesium anode into salt water or a zinc anode into fresh.....so what do you do if the boat may be in both? My boat is in fresh water 95% of the time, but I'm planning to use it in salt water for a few days each year. What should be done in this case? Is an anode really necessary?


In brackish water, you would use an aluminum anode. But if you're in fresh water 95% of the time, you should use a magnesium anode. If you're only operating in the salt water for short periods, and you're not leaving the boat tied up in port, magnesium anodes will be fine. The problem comes when you try to use a magnesium anode in the salt water for extended periods of time. As magnesium is the most reactive metal, it will quickly react with salt water, and will dissolve in about 1/2 the amount of time that it takes for a zinc anode to dissolve, leaving your boat with no galvanic protection.


I have some aluminum washers....what if I were to use an aluminum washer between the stainless nut and where it comes into contact with the aluminum of the boat....sort of a sacrificial washer? Any thoughts?

I've never tried this method, but in theory, it should work, the aluminum washer will be in contact with the aluminum hull, instead of having a stainless washer in contact with it. Having aluminum-to-aluminum contact should reduce the amount of electrical activity.
 

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