Engine porosity

What did GM use to fix cylinder porosity. I just finished a tear down on a 5.7 truck engine. In the #3 cylinder there is a spot avout the size of a
pencil eraser. It has been filled in with something. I dug it out and it seems to be something like JB Weld. I decided it wasn't a block that I would use since it would need to go about .040 overbore to be useable. I sandblasted about 15 minuites and finally got all the filler out. It is obviously a void, not really porosity but just a casting defect. I know the engine has never been down, I personally know the man who bought the truck new and wore it out. Its clear that whatever was used works. The engine was at 187XXX miles and the filler wore just like the rest of the cyl. What do they use, where can I buy some/
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I don't know what GM uses, but Cummins uses a Devcon (brand) putty to fill porosity and voids in their cast iron blocks.
Dave
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Hairy wrote:

Many years ago when GM have a lot of problems with this on a few engines, they used a epoxy to seal the block.
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All true, but in 40 years including field trouble shooter for Cadillac right thru the " famous" HT 4100 engine I've never seen this done in a cylinder bore.

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I agree, blocks but not the cylinders. Cast iron brazes nicely but not sure how it would hold up in combustion area.
Shep wrote:

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I used to rebuild 2 cycle outbord motors, the ports are about the size of a dime and the pistons are humming along at 10000 RPM at Wide Open Throtle. I'm guessing that the holes were left at the factory and filled with carbon over time.
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