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Hi!!
I’m rebuilding my super deluxe 850cc engine and fitted new 2k8169 core plugs. My mechanic fit them correctly but when testing the engine they are pull out. It happened two times. The first time was the front middle plug and the second time the right front one.
Does anyone have any suggestion about what could be happening? Maybe bad quality plugs?

Thanks in advance
Antonio

If they're coming out (rather than just leaking) then I would say either the recess wasn't cleaned of rust enough or they need a harder hit to get them to expand and seat properly

Hi!
This is one of the cores fitted. Maybe this pic helps

Like Graeme says here and what many others have said in the past. Clean the holes out to a perfect clean finish, put some sealant in and then, if possible slightly spread the top of the cupped surface. Then knock them in with a hardwood punch, machined to the correct diameter. A good square-on whack into the base of the hole and they ain't coming out or leaking.

Some have said that the proper way is NOT to whack them in but to slowly press them in. I just whacked mine in in the 80's and they're still good.

While the subject is still fresh, interested to hear if anyone's got any other ideas for Tonio?

Mini 1275 and A+ type core plugs are cup shaped with a tapered side, and can just be pressed into the block directly. Whereas the A series small bore engines use Welch plugs which are domed discs; they need to be expanded into the groove evenly around the circumference, else they can leak or pop out under water pressure.

This page might be helpful: https://mgaguru.com/mgtech/cooling/cool_105.htm

when mine kept bursting out it turned out to be a cracked block