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Old 25-06-2016, 18:39   #1
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Help! How to fix crack in engine block

Hey i have noticed a pinhole crack in my engine block that leakes oil a ton. my diesel runs at about 160 degrees. its an m-18 univwersal. does anyone know what to patch this pinhole with? i was thinking some kind of 2 part epoxy, but woiuld that hold up under high temps and semi-hi oil pressure?
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Old 25-06-2016, 18:49   #2
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Re: Help! How to fix crack in engine block

A picture or description of where the hole is would help.
The easy way would be to drill to a tap size and put a bolt with sealer in the hole. The smaller the better. Possibly it could be brazed. If completely cleaned of oil you could epoxy.
Cast iron needs to be heated to about 700, then welded, then wrapped with insulating blankets and allowed to cool slowly. Just welding cold iron will cause cracks. Usually at the weld but sometimes cracks continue on the original stress line.
Long time since I welded cast iron, we used asbestos blankets.
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Old 25-06-2016, 19:01   #3
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Re: Help! How to fix crack in engine block

If you really can get the hole or crack completely clean, you might try JB Weld. Sometimes that stuff will really surprise you. Then there is always the question of what caused the problem in the first place.
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Old 25-06-2016, 19:11   #4
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Re: Help! How to fix crack in engine block

A crack has to be stop-drilled at the ends.
Grind the crack open to provide access.
Then you might be able to seal it with nickle based welding rod.
There is a chance that high temperature rated epoxy such as JB Weld could hold it the surface is very well cleaned.

If its just a pinhole casting defect then a drilled and tapped hole with a bolt works.

Fixing a crack in cast iron is problematic at best.
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Old 25-06-2016, 19:19   #5
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Re: Help! How to fix crack in engine block

This really isn't a do it yourself fix.
Turninturtle is giving the best advice.
JB weld should only be used as a temporary fix.
If it is leaking oil a "ton" as you say then it has breached an oil galley and that is a big problem.
There is no such thing as a pinhole crack. You either have a pin hole or a crack. I guess you could have a pinhole that developed into a crack.
Any way about it an experienced diesel mechanic is what you need.
Don't half ass this repair. Your life may depend on it. And don't pass it on to the next guy, because then his life may be on your conscience.
I don't have much experience with boats, but I have a ton with diesel engines.
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Old 25-06-2016, 19:32   #6
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Re: Help! How to fix crack in engine block

Note...

Just about any repair of the casting its advisable to dismantle the engine so you can clear ALL metal filings out instead of letting them pass through the engine, clogging oil passages and/or scoring cylinders and/or wiping out bearings.
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Old 25-06-2016, 19:41   #7
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Re: Help! How to fix crack in engine block

Had a cracked cast iron manifold, patched it with JB Weld to get me home. Sold that boat 15yrs later with JB Weld still intact.
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Old 25-06-2016, 19:54   #8
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Re: Help! How to fix crack in engine block

Good Night. I use to swear by JB weld until I needed to patch worm holes on the valve section of a positive displacement pump pushing 120 GPM @ 800psi. I used Marine Tex. A two part epoxy type repair putty. I swear by it now and always have some aboard. The valves held under the pressure until I was able to get a replacement fluid end 6 weeks later, and after changing out the fluid end we tried to remove the valves using a bottle jack valve remover and we're unable to get the repaired lives out.

Suggest the hole be at least 1/16, clean from oil and press some marine tex into the hole. It will hold. I also did a temporary fix on my expansion tank and it held. I'm a believer in Marine tex.
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Old 25-06-2016, 20:57   #9
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Re: Help! How to fix crack in engine block

Ok i have a little bit more time to type now .
so ive looked it over and oil is coming ouyt of a small hole in one of the cast-in oil pipelines.
it sooms to have rusted out, but i cant get a good look at it because its at an odd angle right now. could it have been a casting defect that has finally appeared over the years?

The hole in my engine is below the starter motor on this m-18, above that square with the four screw holes. the hole is just above the top right screw hole.

ill try to get some pictures of my engine first thing tomorrow

Plus, Marine tex? will that hold up in the high heat?
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Old 26-06-2016, 09:37   #10
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Re: Help! How to fix crack in engine block

Quote:
Originally Posted by Jsta_Rebel View Post
Good Night. I use to swear by JB weld until I needed to patch worm holes on the valve section of a positive displacement pump pushing 120 GPM @ 800psi. I used Marine Tex. A two part epoxy type repair putty. I swear by it now and always have some aboard. The valves held under the pressure until I was able to get a replacement fluid end 6 weeks later, and after changing out the fluid end we tried to remove the valves using a bottle jack valve remover and we're unable to get the repaired lives out.

Suggest the hole be at least 1/16, clean from oil and press some marine tex into the hole. It will hold. I also did a temporary fix on my expansion tank and it held. I'm a believer in Marine tex.
You have had better luck with Marine Tex than we have. Never could get it to stick to metals once the metals heated up and pressure was applied to the patch.
Best solution to a cracked block is a replacement block. If the cast is cracked in one place, probably ready to crack in other places. JB Weld may work if you can get 1. clean metal; 2, all the cracked surface is covered by the JBW, and 3. the crack is not likely to expand when the block is heated.
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Old 26-06-2016, 09:51   #11
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Re: Help! How to fix crack in engine block

I had a crack in a gasoline boat engine many years ago (caused by a surprise freeze). I chased the crack with a grinder, cleaning it out and then had a friend weld it (carefully). I then sealed the surface with JB Weld, and gave it several coats of heat resistant paint. It lasted for years with no problem. I eventually sold that boat.
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Old 26-06-2016, 09:54   #12
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Re: Help! How to fix crack in engine block

While JB Weld or Marine Tex might work. If you can figure out how to drill the ends of the crack and properly drill/tap in lieu of epoxy it would be nice.
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Old 26-06-2016, 09:56   #13
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Re: Help! How to fix crack in engine block

I have an old mechanics handbook that teaches welding cracks in cast iron machine cases with thermite. I've never tried it but appeals to my inner pyro. The book says to build a clay tunnel, like a termite track, and fill with thermite. At the top of the tunnel a small piece of magnesium gets the reaction going. Anyone else heard of this?
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Old 26-06-2016, 09:58   #14
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Re: Help! How to fix crack in engine block

Problem with this one is the clue in the opening post "leaks oil a ton". So there is oil under pressure on the inside leaking out rather than just a hole into the engine block.
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Old 26-06-2016, 10:06   #15
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Re: Help! How to fix crack in engine block

Never did engine blocks but lots of practice arcing on slant six manifolds Cast rods ,quick beads on crack and rapid peen , bead again, peen .Idea is that peening relieves the cooling stresses Worked for me.
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