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removing corrosion in water passages

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  • removing corrosion in water passages

    1997Yamaha 70HP 2 stroke. I recently purchased this motor and the overheating alarm goes off. Replaced the impeller and thermostat and cleaned the water passages under the exhaust cover which were corroded. It worked ok for a few trips but started overheating again. Figured the water passages in the head were corroded so opened the head. There is corrosion everywhere.

    I've scrapped it out the best I can but I'm wondering if I should put a weak acid like vinegar on it. Also, the metal inside the head cover is a bit pitted and flaky, would it be advisable to just buy a new head cover and maybe head.

    I haven't actually seen inside the head yet as I broke some head bolts and I'm still working on getting them out but read another thread a got some advice for that so I'll give it a go. I could be back with more questions soon.

  • #2
    It sounds like you have some pretty serious corrosion now, but there is a product called Saltaway that can be circulated through your motor that could help remove some of these corrosion deposits. The idea is to circulate this chemical through your motor to slowly dissolve the deposits and not break off chunks that could plug up cooling passages. Also, while removing deposits, pin-hole leaks can possibly be uncovered or created. Good Luck!


    • #3
      Thanks Robert

      I've got the head off now and the corrision inside was nowhere near as bad as the crusty build up under the head cover. I've decided to just buy a new head and cover and avoid the risk of any pin holes. Unfortuntely I still have broken bolts to remove. Some broke at the top of the thread. I've been reading about ways to tackle this. The ezy-out option or welding a washer and nut onto the end of the bolt. I'm afraid of breaking off an ezy-out or not drilling down the centre (although I can make up a jig). Would heating the bolt with an oxy help? Have you any experience with the welding method? Is there a chance I can damage the cylinder block with heat?


      • #4
        I only know what I've read regarding removal of rusted/broken bolts, some apply heat, penetrating oil, welded nuts, drilling and re-tapping,etc.,.... hopefully some folks here with actual hands-on experience will offer their thoughts. Good Luck and let us know how you do on this!


        • #5
          It is not normally rust that caused the bolts to break but rather the seepage of salt water through the gasket material and then down the threads. This is the whitish substance you see on the bolt. Usually the integrity of the bolt is not compromised as the heat from the engine helps to evaporate the water and leaves the salt behind. This salt acts as a very good threadlocker. To remove the bolts you need to soften this white substance. Heat can help, but too much especially from oxy/acetelene,can melt the surrounding metal. A propane torch is fine. THIS IS CRITICAL--If you have to drill the bolt, make certain you drill centre line of the broken bolt. If the bolt goes in a blind hole, drill right through the bolt into the space between where the bolt ends and the threads continue into the head, you should be able to feel the difference in resistance as you drill. Do not drill into the head, judge how far to go by the length of a good bolt. Fill the cavity beneath the broken bolt with a good penetrating oil. heat the area gently to promote penetration of the oil into the caked salt. Don't be impatient, do this several times over a few days. I've never used it but from what robert graham says this "salt away" might be a good alternative to penetrating oil-don't know though Drill the hole a little larger until you can get an easy-out in. If worst comes to worst, you may end up having to drill out the bolt completly including part of the threaded area. You then need to go to a larger size or thread insert.


          • #6
            Thanks Bumperfood for those detailed instructions. It sounds like all is not lost. Iíve been reading a lot trying to work out what to do next rather than launch in and stuff things up even more. At the moment I am happy to keep soaking the broken off ends with WD40 and give them a tap a few times a day for a week while I think about it. I donít know if there is a better oil I can use or not, I donít think I can get salt-away locally.
            Two other things:
            1. If I heated the bolt with a propane torch until it was red and let it cool naturally, would that soften the metal and make it easier to drill and lessen the likelihood of breaking off a drill bit in the bolt? It won't make the bolt harder to drill will it?
            2. I have two types of ezy-out. The left-hand threaded cylindrical cone type and a square type. Would one be better than the other? Something I read said the left hand threaded type could expand the bolt and make it tighter as you screw it in. My experience with the square type is when it didnít come out first time it made the hole slightly odd and I couldnít re-drill it straight. Perhaps the solution there was to get the hole wide and deep enough in the first place. Just thought you might have some experience and think one was better.
            I'm very much a novice and grateful for any advice.


            • #7
              The castings are made of aluminium alloys, while the bolts are made of steel. If you heat the bolt to red, there is a good chance that you will melt some of the surrounding metal. If you can get a pair of vicegrips on any of the broken bolts, these are the ones to start on, as your chances of success are good. Use the propane torch to heat the casting, the object here is not to soften the metal, but rather loosen up the thread-locker(salt), heating the metal will cause it to expand a little and allow the penetrating fluid to soften the salt even more. Don't try to simply unthread the bolt all at once, rather apply turning pressure one way and then the other. as soon as you see the bolt start to move, apply more penetrating oil and continue with the turning back and forth. I would us something other then WD40 though. Wd 40 is a great product, but not a great penetrating oil. Try something like PB blaster or Kroil (not sure of the spelling). Make sure not to get them near an open flame when you are applying them as they will catch fire.
              Easy-outs are really misnamed, and you are right about the problems they can create. I have found that they work best if you don't drill out more than half of the thread diameter, either one works, but I prefer the cylindrical style, as I have never broken one off inside (maybe just lucky).
              Welding a nut to the broken bolt that is just slightly proud of the casting. Yes it works and it works great; but takes a lot more skill. briefly, you need a shielded gas mig welder, with an automatically darkening helmet. The nut you choose to use must have a slightly smaller id then the bolt od you are welding it to, the broken bolt must be contaminate free--no oil residue. You centre the nut over the bolt, pack plasticine around it so it doesn't move around and weld through the centre of the nut onto the bolt. Takes a good deal of skill and I usually break the weld a few times before being successful, and you have to be successful as the constant heating hardens the bolt, making it very difficult to drill out.


              • #8
                Hi, An update on where I am up to. I soaked the broken head bolts for a week with Penetrine and gently heated around them with a propane torch. I tried extracting them with an ezy-out but they were stuck solid and I had no luck. I ended up drilling them out until I could just see the edge of the thread then picked out the remainder of the bolt with a fine dentist like tool and a dremmel. Painstaking work but I've removed seven that way.

                Now I have the bottom two left and I can't get to them with the drill because of the cowling. I figure I have two choices:

                1. Get a right angled drill extension and see it that will fit in the space. I think it will be difficult to get a good cut down the center of the bolt, plus I won't be able to see in the hole very well to clean it up with the dremmel and picks. It could end up messy.

                2. Lift the motor up so I can get onto it with the straight drill, after all I'm very practiced at this now However, I'm worried about a couple of things. a) How hard are the 8 large bolts that hold the motor on likely to be to get out? They shouldn't really be locked on with salt like the head bolts are, should they? I'm afraid I'll break something else and don't want to cause myself more work.
                b) The electronics seem to be attached to the cowling, but there only seems to be two things (relays) on the right hand side with 3 small bolts (plus the tilt switch on the left side) that would need to be undone then everything should lift just a couple of inches. Would that be correct? Will all those cables going out the back of the cowling be all right if I just lift it a couple of inches? I have a block and tackle to lift it straight up and can hold it there while I get the bolt out then lower it back into place. Also, should I expect it to come off easily or will it be stuck because of the gasket and/or dowel pins.

                I am open to all suggestions on what is the best way to tackle these last two head bolts.


                • #9
                  Update: Drilled and tapped all nine broken bolts. Got into the last two bottom ones with a Dewalt right angle dril using short sawn off drill bits. Had to insert a couple of helicoils to holes that lost too much thread. Now it has a new head and gaskets and goes an absolute treat. Went 10kms out last weekend and it didn't miss a beat. I also got a bag of garfish so I'm a very happy fisher once again.

                  Thank you for your helpful suggestions on this post and through reading many others. This may have taken me some time but the toal expense was under $400 and I had a couple of mechanics not want to even look at, their sugestion was to buy a new motor! I had never done anything like this before and I have learnt a lot


                  • #10
                    Good on you-- glad you are back out on the water. Sounds like you are in the same area as Troy, Liz, Tom and the rest of those gator hunters.