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Rebuild old Mercury in-line 6

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  • Rebuild old Mercury in-line 6

    Hi to all. I am looking for some opinions on what to do with my siezed motor. It is an old mecury in-line 6 that started making a rapping noise while out on the water. Before I made it to the boat ramp, it siezed.I have not even taken the cover off to see if it destroyed the block. If it did, am I done?If it didn't get destroyed, has anyone had any luck rebuilding these thing's. The local opinion around here is that rebuilding is a waste and the engine will just give me more trouble.Any opinions would be great. I have one more parts motor that still has a good block.Thanks.


  • #2
    Re: Rebuild old Mercury in-line 6

    Sure it can be rebuilt.... First, you may want to tear it down to see how bad your cylinder walls are.... You may have to resleeve or bore out.... If you rebuild, you probably could save money by getting all your pistons and rings from WiseCo. Anyway,,, see how bad that block is first.

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    • #3
      Re: Rebuild old Mercury in-line 6

      Brian,I can't be worth anything less if you take it apart. As a matter of fact, it may be worth more if you decide to part it out.Once you see how bad things are, you'll have to make your decision.If you are just looking at cylinder boring, pistons, rings, gaskets, etc. You can make a very rough estimate of about $2 to $300.00 per cylinder. That's a lot less than a new one.If you decide to rebuild, make absolutely sure you find out what caused the failure. Probably a clogged carb.

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      • #4
        Re: Rebuild old Mercury in-line 6

        briannh1234 - I owned a 1977 Mercury 150 Inline 6 a couple of boats ago on a Baja ski boat. It was a sweet running engine. Made the mistake of pricing it to a friend one day and he bought it. I wouldn't mind having it back. If you could rebuild it without spending a fortune why not?

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        • #5
          Re: Rebuild old Mercury in-line 6

          Thanks for the Opinions.I worked some more on the siezed engine last night. The good news is that there are no holes in the block. It didn't throw a rod through the side like so many of these engines before.The #2 plug was covered in Aluminum. The rest of the spark plugs were clean. You can see the piston through the #2 spark plug hole and it does not look good. We could only spin the flywheel a little bit and then it binds. Me and my friends yanked the block (starter motor, distributor, 3 carb's and all) brought it inside. I think I will have some more time to tear it down this weekend.When I continue the teardown, I was going to leave everything I can mounted to the block and just take it apart at the crankshaft. From there I should be able to see if there are any other cylinders + pistons that are damaged. Is this a good plan?I still have several options open to me: rebuild this engine, buy a rebuilt head, buy another one of these heads used, buy a completely different motor. But I need to determine what went wrong with this one.I spend some time reading many of the other threads on this board and other peoples problems and solutions. It seems several things could have gone wrongThe engine is a 1979 140hp. Thats 24 years old!When we were testing the motor out of the water, we noticed gasoline coming out the front of the bottom carb. My normal solution to carb problems is to add carb cleaner to the gas and run the engine. According to some of the other threads carb cleaner is very bad for these motors! I was testing a new prop. I have no tachometer or speedometer. I may have over-reved the engine!When the engine started making the rapping sound I found the vent on the gas tank was closed!Anyway, thanks again for the opinions. I will check back here often and will update this thread after I take the block apart.

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          • #6
            Re: Rebuild old Mercury in-line 6

            I took the transfer port covers off this weekend. Through the intake hole you can see the body of piston #2, and it has several groves in it running parallel to the direction the piston travels. I think I lost some rings on #2.The #1 piston does not look well either. You can see the top of the piston, and it is missing some pieces. Does this mean the problem was probably with the number 1 (top) carb?The rest (3 through 6) look OK. And I haven't found any other damage to the block yet. Are there any common failure points I should be looking at?Anyway, I am going to take the exhaust side off next. Also, I am going to call around and get some prices on Boaring, re-sleveing, honeing, etc.Any one who has experience doing this, please post here. I would love to here other peoples stories about fixing these blocks. Thank you.

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            • #7
              Re: Rebuild old Mercury in-line 6

              I don't know much but I do know that these things overheat from the top down. Heat rises. If you have progressive damage from top to bottom, top being worst, bottom being best (least damaged) then I would suggest that it was too hot, if like you say the carb wasn't the source of the problem.Wait for an expert to confirm my statement, it's heresay. I'm not a mechanic. I'm just planning on becoming one, trial by fire to rebuild my 85.

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              • #8
                Re: Rebuild old Mercury in-line 6

                brianh1234 you might want to check out Grubb's Marine at www.oldmercs.com. they are specialists in the old inline 6 mercs. They have parts, manuals, a shop, everything you could want. Check out the site, it's loaded with info.

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                • #9
                  Re: Rebuild old Mercury in-line 6

                  brianh1234 you might want to check out Grubb's Marine at www.oldmercs.com. they are specialists in the old inline 6 mercs. They have parts, manuals, a shop, everything you could want. Check out the site, it's loaded with info.

                  Comment



                  • #10
                    Re: Rebuild old Mercury in-line 6

                    I would guess that leaving the vent closed caused the motor to lean out and the top carb would be the first to lose fuel. That may not have been the only cause. The inline six is very sensitive to octane and old gas or too much timing with low octane gas can cause problems too.If you have any intention of rebuilding yourself then take pictures before you break it down for reference. It shouldn't be to hard to find some used pistons or crank and then your just out for a gasket set, but if it seized then your block will probably have to take a trip to the machine shop for a boring or a sleeve. If you want somebody else to look at it then I'd recommend a marine store in S.C. I've dealt with that is very knowledgable with inline 6's and reasonable on price. The guy used to race'em and is who I'd send my powerhead to. Email me if you want to know more.watfor20@aol.com

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                    • #11
                      Re: Rebuild old Mercury in-line 6

                      Thanks for the opinions. Keep em coming.I took the exhaust side of the block apart. I am not sure if this is important but: What I have observed is that it looks like the #1 cylinder put out a lot of black icky exhaust, while number 2 looks like almost no exhaust has come out of for quite some time. I wonder if I lost a reed?The rest of the cylinders looked the same, some exhaust came out but not as much as cylinder #1, or as little as cylinder #2.

                      Comment



                      • #12
                        Re: Rebuild old Mercury in-line 6

                        Sorry for the delay. The crankshaft and all the pistons are out of the block. The #2 piston did not want to come out. It looks less like a piston and more like a meatball. It's missing major chunks. Parts of the rings are now embedded in the piston. All the missing chunks are now smeared all over the wall of cylinder #2. The other five holes look O.K. enough. I still wonder what caused the failure.I have been offered 6 new in the box pistons with rings and stuff, (for 86 bucks each) and 1 new gasket kit, (for 200 bucks) and a used block (free if I buy the pistons and the gasket kit.) The block is in better shape than mine in that it doesn't have chunks of former pistons smeared all over the inside. I have read the chapter of the manual on rebuilding the block and I am thinking this: If the block passes the test's in the manual, and it does not need to be boared, that I should buy the lot. The lot includes all the used head parts including complete crank with old pistons, carburators, crank cover, and more,.. but I am not sure that it would be complete.Any opinions now would be great. I have not spent any money yet, just time. Thanks.

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                        • #13
                          Re: Rebuild old Mercury in-line 6

                          bump.

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                          • #14
                            Re: Rebuild old Mercury in-line 6

                            If my calculator still works properly you are talking $716 plus some time & maybe a few more $ (for beer etc..you cant work on an outboard without refreshments)to get a rebuilt powerhead.If the gearbox is still good its a cheap engine & just think of the fun youll have & the satisfaction of fixing it yourself.Hooty will probably tell you to glue the old one back together with JB weld!!!

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                            • #15
                              Re: Rebuild old Mercury in-line 6

                              whatever you decide to do, you should get a tach.or you could end up here again.it is the most important piece of instrumentation you can have on your boat.

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