new head core plug popping out

[Bob Culver]

Is it established without doubt that there was an undercut? Not straight forward to mass machine. Very hard to get circular with a Dremel. Too much flattening likely to crack something.

[Colin Reed]

HI Jon,
Why bugger around ,Stuart Giles made the most common sense, use what he suggested Brass flanged BSPP PLUGS,
The rest of the Ideas will most likely end with a leak and you will have wasted a lot of time.

Colin
NZ

[JonE]

I've bought a BSP tap, yes, but hasn't arrived and I want to get testing the engine which is newly back together. It also helps having other strategies for "fixing" things in the field...

[Denis Sweeney]

Just thinking again regarding the possibility of pressure in the water system, have you checked that the vent pipe on the radiator water inlet just under the radiator cap is not blocked?
I assume these are present on all versions of A7 radiators??
On my Ruby I kept getting water leaks from hoses and despite replacing them all, including the hose clamps then cleaning off all the metal interfaces to ensure they were clean and smooth, they continued to leak.
What I found was the vent pipe was blocked solid.
I had some old net curtain wire, I removed the plastic coating and this fitted perfectly into the pipe, I was able to attach this to a very very slow rotating drill and was able to work this all the way down the pipe till it emerged at the bottom and so cleared the pipe, result, no more hose pipe leaks.
Denis S

[JonE]

Denis - confirmed clear. I watch it flow out when filling up.
The flattened 3/4" plug lifted with water pressure.
The 20mm one was physically restrained on flattening and the temporary copper silicone (massaged around it) means it's all dry.

[John Mason]

If I can have my twopence worth on this thread. Is it possible that as the engine gets hot the hole for the core plug expands making the hole bigger an thus the plug pops out. Would the problem be cured if the hole was heated with a blow torch to heat and expand the hole then hammer your plug in whilst still hot. Make sure you flatten the dish shape to also make the plug expand . Just thinking out the box.

John Mason.

[Chris KC]

Steel and iron expand at essentially the same rate, any difference would be incredibly tiny.

[John Mason]

Chris Would it not make a difference as you would expand the plug hole to the larger heat expanded size. The plug when it goes in although small is relatively cold and if manually expanded to the hole size quickly enough before it takes heat from the head it should be reasonable tight. It then will tighten further as itself further expands with heat. You are considering to similar metals expanding together. Not one hot and the other cold.

John Mason.

[Colin Wilks]

Might be easier just to keep your core plugs in the freezer ?

PS Serious question Jon, was there no evidence of leakage prior to the plug popping out?

[JonE]

I'd just encourage people to also carry a 20mm spare and file it down so it 'just' press fits (I actually used a bit of hollow copper tubing as a drift so it pressed in without affecting the dome first) IF the 3/4" standard one waggles about in the space when you drop it in!