How to Patch Engine Block Crack on Merc 120 I/O?


Old 07-08-04, 09:19 PM
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Question How to Patch Engine Block Crack on Merc 120 I/O?

My 120hp Merc engine has cracked in a small area underneath the manifold. It still runs and keeps compression but I leak a little water and have to use the bilge pump about every hour or so. I have heard you can patch them. I would appreciate any advice at how I can go about patching and what type of materials to use. Thanks alot.
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Old 07-09-04, 05:11 AM
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Hello wakebum. Welcome to our Boats, Sailing, Pwc's & Navaigations topic and the Do-It-Yourself Web Site.

I personally have never heard of nor know of any process to make such type of repairs. Which does not mean there isn't any nor imply such. However, if there is any type of repair, the process will be expensive and specialized.

Likleyhood, only boat repair shops would know if the repair can be made and how it can be done. Do not be surprised if any boat repair shop says no or does not know of any place doing such type work.

Most likely no one would attempt such a repair. Or a repair can be done but the likely hood is it would always have to be considered a short term stop gap measure and not a long term solution.

Much may depend upon exactly where the crack is located and the difficulty required to access it. Most likely too, much prep work will need to be done just to insure whatever repair is attempted is done as best as it can be.

Once you know first hand from the pros in your area what is required, chances are very high you will just have to use the engine as is for a short term and than replace it. Only you can make such determinations and choices to continue to use it or replace the engine asap.

The diy boat service & repair professionals and other members will have additional helpful information, suggestions and advice. Check back on your question several times for additional replies.

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Old 07-09-04, 05:24 AM
Join Date: Sep 2003
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the above poster is correct, it depends on how big the crack is etc. if u have to run the bilge pump every hr. or so it sounds like a fairly big crack. that being said, i have heard of others having some success with a product called jbweld. it's a 2 part adhesive that is mixed & applied to the crack. make sure the area is dry, & let the product set for 24 hours after u apply it. it's fairly inexpensive & worth a shot. u can find it at any auto supply store. let us know how u make out.
Old 07-09-04, 12:49 PM
Join Date: Jun 2004
Posts: 34
J-B Weld user

I have used that stuff before.Never for what your trying but why not give it a go.Its only like five bucks.However do make sure you mix it correctly or it wont be at its full strength.I think if it does do the job you might want to find a welder to redo it permanently.If J-B does ok than a weld job will definatly do good.
Old 07-15-04, 06:11 PM
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JB Weld Working

I used JB weld as you suggested. The crack was about a six inch hairline crack. I took the boat out for about six hours and it work great. Thanks for the help. JB weld is good stuff.
Old 07-16-04, 07:13 AM
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Thumbs up

Might also try Marine-Tex works real good for things like that.

Old 07-21-04, 04:55 AM
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You could follow up with a product called "Block Seal". They sell it at any of the discount auto parts stores. I used it for a corroded freeze plug that was impossible to get to. Worked great lasted 2 yrs until I sold it.
Just my amatuer input

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