Can't replace it; repair it! Save hundreds or in some cases thousands of dollars. You can do it yourself! John Rooney did and he's got a tech tip with some additional resources to help you with your's.
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If you have a cracked block or head or even a Bell Housing, you can now repair it with "stitching pins" from Lock 'N Stitch in Turlock, California. If you are not mechanical, you can send your component to them and they will repair it for you. Otherwise, you can buy a self repair kit and they support you all along the way.
Here is what I did.
My 1953 3100 216 engine block had a crack in it at the left front. The truck was complete. The engine was rebuilt. When I drove it, there was antifreeze on the garage floor. I spent a lot of money having an engine shop cut in replaceable bearings to replace the poured Babbitt type.
You can leave the engine in the truck as long as you can get a drill at the crack straight on. I had to remove the fender and the inner fender well to get to mine and take the generator off. As long as you can get to it, you don't even have to disassemble the engine.
First, start off with calling Lock 'N Stitch (contact information is on their web site). They also have some good articles about repairs, and many examples -- from a valve seat in a Mopar head to the whole side of a block that threw a rod in a Cruise Ship. All of your knowledge about how to repair block cracks or not being able to repair block cracks will be changed once you see what can be done. To me, this was amazing and I didn't think it possible.
They had me drill three holes, one at the end, one in the middle and one at the far end. The 1/8" drill bit wouldn't do it so I went one size smaller. The drill spots are marked on the image on the left.
Then you take something like a bent paper clip to stick in the hole to measure the thickness of the block at the point of the crack. That will determine how you can proceed with the repair because they have different "pins" and use them for different thicknesses.
I put the paper clip into the block and marked it with a red magic marker thinking if it was inside the block there was no way I could get red on it so that gave me a good idea of the thickness. In my case the crack thickness was 1/4 of a inch right above the water jacket, in all three holes.
Once you determine the thickness of the block and the length of the crack, the technicians at Lock 'N Stitch will tell you what type of pins they recommend and how many.
In my case, I used the C-1 Castmaster stitching pins. I also had to buy one other type of pin because while doing the repair, one of the holes stripped. That is the beauty of their system. If you have a crack or stripped area, just use more pins or a larger pin to build up the area you want to repair.
They offer a tool (you can see on their website that will equally space each drill hole) but the tech support person that helped me through my repair said if I was just going to do this one and not go into the "crack repairing business." it wasn't necessary to spend $100+ to buy the tool. He told me to just drill the holes by eye because the product is so forgiving. You just need 30% of a pin left after you drill out the other 70% of a pin if you are trying to fill in a area or built up strength in the block, rear, or tranny, or anything cast iron for that matter.
It is okay if you are not exact because you can fill in the difference on the second pass.
Next, you counter sink the holes so at least 30% of the pin head will be into the block. Once every other hole is counter-sunk, then you tap the holes out to the thread of the pin they sold you for your job. They include the tap and the cutting fluid.
You put a pin in every other hole to build up strength and so you don't weaken the block any more by taping two holes too close together. All of this information and detail is on the instructional DVD the company sends you.
The pins break off while you are ratcheting them in once they hit the torque point of the pin and the hex head breaks off.
Grind off the head of the pin remaining down to the point of the block where it won't hit the socket for the next pin.
Do this process until all the pins are in. Insert pins and the grind them down. The remaining space between the pins will be where the next pass of drill holes will go. Then do the process all over until you have a pin all along the crack. Lock 'N Stich supplies you with a hardening fluid to put in the hole before you screw a pin in. Once it is absent oxygen, it will harden and give a seal along the threads so fluids will not work their way out the threads.
Grind down the pins -- be careful not to go too deep weakening the block. I went a little too deep in a few places during my repair but not deep enough where I would have to drill it all out and build up the strength. If I did go too deep, then the whole area could be built up if necessary.
Keep going until all the space is filled.
As I mentioned before, I either crossed the thread in one pin or counter sunk one too much. I sent a picture to LNS and explained what happened to the tech person working with me. He sent me a bigger size pin for that hole and a new tap. It cost me about another $100 for one hole because of my screw up. Yet, if that didn't happen, the whole job would have been done for a little more than $300 and the engine could stay in the truck and I didn't have to spend money on rebuilding another block since I just spent the money to rebuild mine.
I don't know if they didn't magnaflux it or if once they honed it out, the block weakened so I can't really say if they should have caught the crack or not. So like everything in life, I sucked it up, moved on and repaired it myself.
There is more info on the web site or on the DVD they send you when you make your purchase.
After some more filling in between pins and using a liquid metal to fill in the grind marks, I pressure tested my block, ran it for two hours or so and then repainted it and no more leak.
Go from the first picture above to this series below. I have a repaired, non-leaking block for a fraction of the cost of a replacement. That is if you can find one. You might have an old block and can't find a proper replacement. Repair it!
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