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Merc 850 oil fill screw removal


duigoose's Avatar
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06-30-07, 12:00 PM   #1  
Merc 850 oil fill screw removal

Hello everyone, I am trying to remove the lower unit fill screw from my Mercury 850 outboard. The shop did all the work last time. I have a HUGE screwdriver that fills the entire slot space but the screw head is just not deep enough to get a 'bite'. Anyone have any tricks to loosening this screw? The vent screw comes out just fine.

 
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Bingo757's Avatar
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06-30-07, 05:31 PM   #2  
Try using a hand impact screwdriver. They cost under $10 and are very handy for loosening frozen screws and bolts. Harbor Freight sells them:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=37530

You can also try to heat up the aluminum casting around the screw with a torch. Donít over do it: just enough to expand the metal a bit.

 
duigoose's Avatar
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06-30-07, 06:00 PM   #3  
I was thinking of the impact screwdriver (and harbor freight tools since I don't have one), just wondering if there were any other options. I do have the torch though......

 
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07-01-07, 05:22 AM   #4  
Before you go banging that aluminum casing and heating that rubber O-ring (as I seem to recall but could be wrong) - make sure your screw driver tip is sharp/clean. If the edges are worn down, even a little, it will keep you from getting a bite on that stubborn bolt head. If you do get it off - replace the plug to make the next time a bit easier.

 
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07-01-07, 10:28 AM   #5  
Iv'e had some luck using a sharp pointed center punch. Set it on a offst in slot and tap in the direction of removal. After you get it out and it nots chewed up too much and you opt to put it back in,i would put some anti-seize compound on the threads.

 
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07-01-07, 07:42 PM   #6  
still in the hunt....

thanks so far for the ideas......my giant screwdriver looks good but isn't doing the job. Heat might work i reckon but that just scares me right now. I did try taking a small blade flathead screwdriver and 'tap it in the direction of removal' but it didn't budge. When I say tap I mean it should have moved but I have always had a shop do this. This isn't on my forefront but I will let everyone know what the deal is/was. I just don't want to 'booger' it up where it is past the point of no return.

 
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07-01-07, 08:30 PM   #7  
I agree to the punch trick, just pop it enough to get it moving.
The replacement plug screws are available and some even have
magnets on them now. good luck.

 
Ed Imeduc's Avatar
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07-03-07, 08:08 PM   #8  
Grind the big screwdriver so it fits the slot tight then use a 10" cresent wrenche on it by the blade as you push in hard on the screw driver. Works most of the time.

 
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07-15-07, 08:49 AM   #9  
Do what Ed says, make your own tool. Then put it firmly in the slot and give it a real good whack with a hammer. 90% of the time a single blow will do the trick. In extreme cases you may have to do a few hot cold cycles with a torch and a rag soaked in water before it will come out.

It took me a while to learn, but I change my drain and vent plugs every other oil change, so the get changed once a year. I buy them 5-10 at a time from BoatFix.com. Also make sure that you get the gasket out of the gear case if it gets stuck in there. The last boat I bought was getting water in the oil every time I went out. Come to find out there were three of the fiber washers on the plug! Two of them were stuck in the case and you couldn't see they were there. Water was getting past them at high speed and getting into the oil.

 
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07-17-07, 10:25 AM   #10  
Thank You! Thank You!

I found time to clear out the garage and get to the boat today. First of all, thanks everyone for your help and wisdom. I didn't even have to break out the heat. Looking closer at my screwdriver the tip was kinda 'old'. I broke out the dremel and ground it down so it fit very snug then gave it a couple of 'kinda good whacks' (Dan, a good whack with my luck would have broke something :-). Then I leaned all my body weight into it and used the crescent wrench near the blade and it broke free.
As a side note, the oil looked good, no water and I recovered pretty much the 21oz it called for. The magnetic plug had been put in sometime before and there was no grit on it. Now if I just didn't have to sell it.

 
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