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Old 11-23-2014, 08:53 AM   #1
Farmer j
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Default Cracked block repair

my model A block has a crack in the front and left side water jacket at the bottom of the jacket. Is the material there thick enough to repair it using stich screws. I bought this kit to use on a model T block, but the casting wasn't thick enough so I resorted to JB weld. I would like a more permanent repair than JB weld offers.
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Old 11-23-2014, 04:02 PM   #2
rocket1
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Default Re: Cracked block repair

I would say if the block had no machine work or new babbitt I would look for a better block
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Old 11-23-2014, 06:46 PM   #3
Dave in MN
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Default Re: Cracked block repair

The area you describe is pretty thin. A shop experienced in metal stitching can repair it. It is pretty easy for the "first timer" to fail when stitching these areas. JMO.
I often do metal stitching on blocks...but the first time in this thin area...I made a bit of a mess that took a lot of work to repair.
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Old 11-23-2014, 06:59 PM   #4
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Default Re: Cracked block repair

Is there a minimum thickness recommended for stitching? Why not drill a small hole and find out how thick it is, it's already broke?
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Old 11-23-2014, 07:17 PM   #5
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Default Re: Cracked block repair

I have a crank in the same place I used this:


http://www.jbweld.com/product/j-b-highheat/



Like true welding, the prep work is 98% of the task... clean to bare metal... So far so good...

This JB weld is a putty so you have to really work in with your fingers.. I did it for 15mins...
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Old 11-23-2014, 07:28 PM   #6
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Default Re: Cracked block repair

I think a lot may depend on what size machine screw you use for your pinning. For this I might go REAL small with a No. 6. Possibly a No. 8-32. If you have 1/4 inch thickness you have 8 threads on that bolt. Sealing is usually accomplished with a minimum 4.

It certainly would be a labor of love to drill, tap, screw in, grind off, pein a little, finish grinding, drill, rinse and repeat for the entire length of the crack.

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Old 11-23-2014, 08:14 PM   #7
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Default Re: Cracked block repair

A 6,8 or 10 would all have 8 threads in 1/4 as all have 32 tpi. In that case would a 10 be easier? Take less screws per crack? There is also a 1/4 X 32. I'd like to try this sometime, that's why I ask.
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Old 11-23-2014, 08:47 PM   #8
Joe K
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Default Re: Cracked block repair

Its obviously a game of how much endurance do you have.

Larger diameter would mean getting the job done quicker - but I can see that you might easier upset a larger diameter threaded plug if you do peining. (I'm comfortable with light peining to distort the upper line of threads and add backing to a sealant.

Smaller diameter would mean more work to install, but more protection to upsetting the plug.

My thought is to have "criss-crossing" of the lines of seal. More plugs, more seals, more overlap. (think to an example where one HUGE plug seals your crack - only one line of sealant. And think to the pressure to tilt out that plug should you try to pein the edge.)

But, work is work. And this, like many aspect of mechanical restoration, is one of compromise.

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Old 11-24-2014, 08:49 AM   #9
Farmer j
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Default Re: Cracked block repair

My stich screws are 3/16 diameter. The model T jacket was less than 1/8 inch thick. Would the jacket be thicker on a model A? The engine was rebuilt several years ago, has very few miles and runs great. I didn't notice the old JB weld repairs until after I bought it. Both have failed and I was hoping to do a more permanent repair than JB weld.
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Old 11-24-2014, 09:14 AM   #10
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Default Re: Cracked block repair

Maybe examine your screws by comparing with a known screw/screw thread? I have the micrometers and thread gauges to do this but you can do as well by comparing with 8-32, 8-40, 10-24, 10-32, 12-24, 12-28 (No. 12 is not so commonly found these days but might be the 3/16" diameter you refer.)

I have stitched a block before in the valve seat area - but this area is thick by comparison. My screw of choice for that job was 8-32 - but only because it was handy.

Another option you might consider would be to "MIG" the crack and weld it shut. A lot of hobbiest/weldors are doing this now. I confess I was surprised to claims this works well as those that do it say. But this would be work I would only trust to someone with experience and some track record of success.

Braze is out there too - but now you're getting into the "preheat" issue.

Cracks are a heartbreaker - that I do know.

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Last edited by Joe K; 11-24-2014 at 12:03 PM. Reason: Common No. 8
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Old 11-24-2014, 09:33 AM   #11
Tom Wesenberg
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Default Re: Cracked block repair

I wonder if the original JB Weld wasn't properly cleaned? I've read of many success stories using JB Weld. I have a cut open block side and will take a picture of it this morning and post it later.
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Old 11-24-2014, 10:53 AM   #12
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Default Re: Cracked block repair

Farmer J, do a search "crack repair" posted last March . I found it informative.
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Old 11-24-2014, 11:42 AM   #13
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Default Re: Cracked block repair

Farmer J: What you're seeing are typical cracks on Model A's.
Depending on your block but generally speaking they are approx 3/16-1/4" thk.

I would recommend cleaning the block and looking it over thoroughly, there may be other cracks than ones you've already noticed which are common.

We repair cracks through "metal stitching'' and speak from experience to say check block thoroughly for other cracks.

The cracks you mention are from freezing.

Enclosed two photos of the areas you have described and recommended permanent repair "NOT Jb weld."
http://www.jandm-machine.com/metalStitching.html
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File Type: jpg IMG_7919.JPG (43.3 KB, 64 views)
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Old 11-24-2014, 12:18 PM   #14
Tom Wesenberg
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Default Re: Cracked block repair

J and M sure does nice work.

Here are two pictures of a junk block I cut up to use as a jig when I make engine holders for the engine stand. This is cut through the right side of number one cylinder, and is 1/8" or a hair over.
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File Type: jpg Model A Block Cut2.jpg (80.5 KB, 56 views)
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Old 11-24-2014, 01:21 PM   #15
Joe K
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Default Re: Cracked block repair

Quote:
Originally Posted by Tom Wesenberg View Post
J and M sure does nice work.

Here are two pictures of a junk block I cut up to use as a jig when I make engine holders for the engine stand. This is cut through the right side of number one cylinder, and is 1/8" or a hair over.
1/8" and 32tpi would give you the four threads. Or go with 8-40 screws?

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