How to repair a crack in cylinder head? - Vintage Mustang Forums

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post #1 of 16 (permalink) Old 06-23-2011, 01:59 PM Thread Starter
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How to repair a crack in cylinder head?

Has anyone had to repair a crack in a cylinder head before with JB Weld? The crack is under the valve cover between the rockers. Just wandering if it is probable for the JB Weld to hold, and exactly how to do it properly. I bought the head from a junkyard to replace the one I have and have done a good amount of work to it before sending it to a machinist who found two small cracks. He said the two cracks are shorter than an inch long, and probably not enough leaking through for it to have shown in the oil. I would appreciate any information on how to best fix the problem from those who have had similar issues they have dealt with. Thanks, Don
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post #2 of 16 (permalink) Old 06-23-2011, 03:40 PM
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i would probably either have it welded for real or a better option is to get a new one and take it to a machinist first to see if it has any problems.

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post #3 of 16 (permalink) Old 06-23-2011, 04:32 PM
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If it's an aluminum head, it can be welded. If it's cast iron, the only way to fix it is to drop it into the nearest trash can.

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post #4 of 16 (permalink) Old 06-23-2011, 04:37 PM
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I've heard good stuff about JB on other forums. One guy had a Suburban that had a crank in valley area and was getting water in the oil. It was just a crunch repair but it lasted. Another guy ported a set of sbf heads and went through into the water jacket from the intake port. Used JB and ran the head for many years.

Not saying this is the correct way of doing it but it seems for temporary pinch repairs, it lasted like a permanent repair. Give it a try.

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post #5 of 16 (permalink) Old 06-23-2011, 05:00 PM
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JB Weld is GREAT stuff, but it WONT over come thermal expansion! So yes, epoxy up a perforated port, or a water jacket, but it won't fix a cylinder wall or a head that has overheated and cracked.

I agree with Maxum for 95%. The answer is yes a cracked iron head can sometimes be repaired. I said repaired and intentionally didn't say fixed. It must be done by a trained welder. Strip head in area of repair. Drill out both ends of crack. Bevel out the area along the crack. pre and post heat the head. And using the "proper" cast iron welding rod in a "good" stick welder your going to arc weld it back together.

chuck it and get a new head if it came from a junk yard, they may even have a 30 day exchange. If its a numbers matching 302 Cleveland head (which its not) then "maybe" its worth the effort. It will most likely fail again at some point. JHMO

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post #6 of 16 (permalink) Old 06-23-2011, 06:21 PM
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The head can be heli-arced in place.
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post #7 of 16 (permalink) Old 06-23-2011, 10:25 PM
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Quote:
Originally Posted by Don K View Post
Has anyone had to repair a crack in a cylinder head before with JB Weld? The crack is under the valve cover between the rockers. Just wandering if it is probable for the JB Weld to hold, and exactly how to do it properly. I bought the head from a junkyard to replace the one I have and have done a good amount of work to it before sending it to a machinist who found two small cracks. He said the two cracks are shorter than an inch long, and probably not enough leaking through for it to have shown in the oil. I would appreciate any information on how to best fix the problem from those who have had similar issues they have dealt with. Thanks, Don
need to have a good welder ,not jb, at a engine machine shopweld the head and remachine the head, you can fix a iron head. i have blown up many engines in my time,unless it is a total dessaster.
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post #8 of 16 (permalink) Old 06-24-2011, 01:31 AM Thread Starter
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Thanks for all that have replied. I do intend on trying the JBWeld by drilling out the ends and grinding down the crack and filling it. I have seen it work for years on the outside of a block between the cylinders, and can not think of why it wouldn't work in the valley. The guy that did this has passed away, so I can not tap his brain for more info... Sure miss him in times like this; he was a motorhead pro.
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post #9 of 16 (permalink) Old 06-24-2011, 06:47 AM
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Hope you like changing heads. Every JB Weld 'fix' I have seen that involves the water jacket has had a short life. Do yourself a favor and break with the $40 to get it welded correctly.

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post #10 of 16 (permalink) Old 06-24-2011, 09:17 AM
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When you tear it down again it will cost you more than the price of a replacement head and you WILL have to do it again! JB weld is a half arse repair at best and besides if that head is cracked there it most likely was from overheating and so it will likely be cracked in other places also, have you had it Magana fluxed? Cobbling such as that is done on old lawn mowers and farm-All tractors and has no place on a car, especially a Mustang!
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post #11 of 16 (permalink) Old 06-24-2011, 10:39 AM
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Originally Posted by Don K View Post
Thanks for all that have replied. I do intend on trying the JBWeld by drilling out the ends and grinding down the crack and filling it. I have seen it work for years on the outside of a block between the cylinders, and can not think of why it wouldn't work in the valley. The guy that did this has passed away, so I can not tap his brain for more info... Sure miss him in times like this; he was a motorhead pro.
When youre putting a crank in that motor because the antifreeze that leaked through the gooped up crack wiped your bearings, you'll wish you had fixed it right or replaced it with a good head.

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post #12 of 16 (permalink) Old 06-24-2011, 12:43 PM
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I have to agree with others. I am all for saving money and understand you have some time involved, but that is too risky.

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post #13 of 16 (permalink) Old 06-24-2011, 01:04 PM
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are we talking about an uncommon, exotic head here like a date coded original Boss 302 or Boss 429 head?

or are we talking about a fairly common one like a 289 or 302 head?

Exotic one? take it off and get it welded properly.
Common one? buy another and transfer your parts to it.
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post #14 of 16 (permalink) Old 06-24-2011, 02:00 PM
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I wouldn't spend the money rebuilding a cracked iron head.
I wouldn't waste the intake gasket or head gasket either.
Replace the head.

I am scared to ask if this car will be for sale soon.

Sense is not as common as you think.
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post #15 of 16 (permalink) Old 06-27-2011, 10:13 AM
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Originally Posted by Don K View Post
Has anyone had to repair a crack in a cylinder head before with JB Weld? The crack is under the valve cover between the rockers. Just wandering if it is probable for the JB Weld to hold, and exactly how to do it properly. I bought the head from a junkyard to replace the one I have and have done a good amount of work to it before sending it to a machinist who found two small cracks. He said the two cracks are shorter than an inch long, and probably not enough leaking through for it to have shown in the oil. I would appreciate any information on how to best fix the problem from those who have had similar issues they have dealt with. Thanks, Don
Hopefully you've fixed the problem that caused it to crack in the first place....

Unless it's some seriously special head, save your $$$ and replace the head.
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