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  1. #1
    Petty Officer 1st Class
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    Default 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. #2
    Chief Petty Officer
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    Default 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.

  3. #3
    DJ
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    Default 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.

  4. #4
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    Default 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?

  5. #5
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    Default 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.

  6. #6
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    Default 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.

  7. #7
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    Default 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.

  8. #8
    Cadet
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    Default 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.

  9. #9
    Cadet
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    Default 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.

  10. #10
    Petty Officer 2nd Class
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    Default 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

  11. #11
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    Default 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.

  12. #12
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    Default 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.

  13. #13
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    Default Re: Rebuild old Mercury in-line 6

    bump.

  14. #14
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    Default 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!!!

  15. #15
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    Default 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.

  16. #16
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    Default Re: Rebuild old Mercury in-line 6

    catfish - I am with you 100% on the tach issue. Can't break the engine in correctly without it. I am going to get a water pressure guage too - seems like cheap insurance.Sharkcat - Your calculations are good, but I am going to need 3 carb rebuild kits as well. (unless they are part of the gasket kit)I haven't heard back from the guy with the pistons + block so I am wondering if the block he is offering does need a trip to the machine shop.I have been looking through the manual some more. The biggest problem I see in putting this engine back together is that you must insert all 6 pistons with rings into the block at the same time as part of the crankshaft assembly. There seems to be no way around this so I am going to have to either buy/rent the special tools needed, or find someone with the special tools and pay them to install the crank + pistons.Has anyone ever assembled one of these? Is there another way that doesn't involve these special mecury tools?

  17. #17
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    Default Re: Rebuild old Mercury in-line 6

    I've been told it can be done with aluminum can strips and hose clamps, but I ain't tried it yet and I hear it ain't too hard to break a ring with these jokers. The merc clamps are hard to find at a reasonable price but I've seen a pic of some homemade compressors made from 3/8 square tubeing. The guy I know in S.C. offered to drop mine in for me a reasonable price.If you only want to do it once-- then I'd pay somebody to do it. My solution was to shelve the inline and get a v-6.

  18. #18
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    Default Re: Rebuild old Mercury in-line 6

    what200's got the hot ticket. I use 4"-5" hose clamps for ring compressors and they work like a champ. I use 'um on OMC's but they should be wide enough to catch both rings on your engine. If not, do like what200 suggested and wrap a piece of can around 'um.c/6Hooty

  19. #19
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    Default Re: Rebuild old Mercury in-line 6

    Hello again. Thank again for the reply's.I bought the lot of parts. I checked out all the new pistons and they are complete. The gasket kit is still sealed and is still flat. The block is a great match but ... The front cover ... I should have checked it more closely before buying the lot. It is a newer engine than mine and they must have redesigned some of it. There is no place to mount my distributor, and the block didn't come with one. The block is not as complete as I thought. I did get the crank, 4 connecting rods, some covers, 3 carbs, no old pistons, and not enough parts to rebuild it. While the front cover from my block looks like it will fit, the manual I have say's "don't do that!" I am thinking of selling the block on ebay.In the meantime ... I guess back to the original block. I can't seem to find someone local who will bore the number 2 hole. Plenty of places in Florida, etc.. but nothing near New Hampshire. (A local place named Land & Sea used to do them, but not any more.)Does anyone know a local machine shop that can handle this kind of "blind hole"? A local shop would save me shipping & handling & time.Thanks again.

  20. #20
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    Default Re: Rebuild old Mercury in-line 6

    bump

  21. #21
    Petty Officer 1st Class
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    Default Re: Rebuild old Mercury in-line 6

    Hi again. Yea I know - summers over and I still have not got my motor back together. I have had a very buzy summer and if all of them are going to be like this I will sell my boat...I called one of the local machine shop's that turned me away before - They must have heard the desparation in my voice and felt sorry for me. My block is back now and the top two cylinder's have been bored. I have new pistons for the bottom four cylinders and 2 new oversized pistons for the top two.Since there was no definitive cause for piston failure, I have decided to follow the manual and inspect all the parts before re-assembly. (probably a good idea anyway)I have been checking the reed blocks. I borrowed a feeler guage and almost all the reeds from the top 2 cylinders are out of spec. The manual say's the gap should be no more than .007, and I can fit a .008 feeler in most of them. Some of them seemed stuck shut until I forced them open.Why does the gap matter? Once the engine is running the reed's are just gunna slap back and forth. Are stuck reeds a problem? Or will the engine force those open when running? Will new reed stick anyway, since they will be mounted to the old reed cage? New reeds are kinda expensive, and I can't seem to find anyone with new reed cages.Any help would be great. Thanks.P.S. - Moderators - could we get a spell checker added to this thing?

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