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Reply to "Mangusta Freeze Plug Leaking / Blown Out"

@bosswrench posted:

If you think that threaded core plugs are best, you're right. But unless you have lots of engine building skills and lots of tools, have a professional shop thread the block for you. First, DIY'ers will need TWO 1-1/2" pipe taps (last I checked, they were over $125 ea)  because the first one will only cut about 1 thread, then run into the cylinder walls inside the casting. So you take your second tap and with some sort of cutter or grinder, remove the tapered end up to the first full thread. That tap will then give about 4 full threads.  Which is enough with pipe tape.

And its remarkably difficult to hand-align the giant tap so it cuts straight. But once you've marked the core-plug hole with a single thread or more, you're committed- stock press-in plugs will not seal in that hole. So you may as well continue, or call the shop. And you have five more to go....Most shops will cut threads in a block using a milling machine with a boring head, not a pair of taps. They may be able to salvage a badly done thread and shorten the pipe plug enough to work.

Not sure about 302 Ford blocks but when threading 351-C blocks and tightening  the plugs, the pipe-plug tension distorts the cylinder walls enough that a honing deck plate is necessary to return to straight cylinder walls for good ring seal. Once done, threaded core plugs actually strengthen the block a little but its kind of overkill for street engines.

I've decided to pull and rebuild the engine (started a new thread).  There is a VERY good machine shop that I will send the engine to for the rebuild.  I'll talk to them about the threaded freeze caps, if I go that route I'll have them add that to the list.

I don't know ALL my limits, but I know SOME of them!

MH

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