I have just had my second welsh plug pop out. What is the reason for this? The car wasn't overheating, oil presure was normal, and not revving too hard. This is the second time the same plug has popped out. The block isn't damaged. What is the cause? Please help.

Are you sure you have the right cap on the radiator?

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Lillee - 1969 Morris Mini K

.. common prob, as pristic found the other day.
There are 2 common Mini radiator necks, the Oz one and the shorter UK one. However, many other cars have a longer neck still and if you use too long a cap, the valve cannot open when it hits 13psi.
Then..
1. welch plugs can pop, and or
2. radiator hoses can pop.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

When I rebuilt the motor of the MGA it didn't take long to have 2 welch plugs depart the scene, the 2nd one at night on a lonely country road (but I was carrying a spare, having learnt my lesson the 1st time, and a local farmer had some loctite - all fixed in a few minutes!), and it turned out to be the size of the welch plug - metric sizes had been used in the imperial block, and they were ever so slightly undersize and hadn't seated properly when tapped in the middle. I later found out that this was a problem others had encountered too.
Don't know if anymore popped out later - it was fine for a few more months before the car was sold.
Anyway just a thought........
Peter

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1969 Mini Cooper S MKII (1330)
1972 Honda 750/4 (his),1976 Honda 400/4 (hers)
1982 Honda CB1100RC (ours)

KC says in Mini Expert that the seats have to be completely free of rust and smooth and use a sealing compound in there as well.

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

Must be the Problem for the week it seams...they are poppin out every where

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Stop Licking the Dog...I Don't Care Who Started It

Use Stag as a sealant between the Welsh Plug and the block - It works really well but it is a bit messy.

Also everything else that has been said above

Matt

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No 2 is what happened to me, though there seemed to be some leakage around one of the welch plugs as well.Cost me a head gasket and a tow.

Thanks for all the help with welsh (welsch) plugs. I thought it was a very un-common occurance for them it pop , so thanks for the help.
Should be back on the road real soon.

When I was rebuilding engines (as a job), we always were critical of Welsh plugs.

1: Clean surface of seat (a wire brush on a die grinder works great)
2: Clean welsh plug edge (thinners)
3: Apply epoxy glue on seating surface (some glues soften with heat!)
4: a: On disc welsh plugs fit with the dome out and as it hits the seat step, use a socket (or better the end of a flat bar) 1/2 the diameter of the plug and a hammer to splay the plug out. I have seen plugs people have used a ballpean hammer to splay and they are the ones that fall out.
b: On bucket welsh plugs I would always lay them on a bench and tap the centre slightly flat. This splayed the OD slightly and made for a tight fit (dont tap to much or it wont go in). then use the biggest socket the fits into the plug to drive it in.
5: Wipe off excess glue.

PS: Do not stake the plug once in as it will be the last time you get a good seal if you do.

Problem solved

On the 1275 Cooper S are they cup or dome welch plugs? And what size? (Are all 4 the same?)
(I haven't got access to my motor at the moment to physically check, and need to order some, hence the silly question sorry).
Peter.

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1969 Mini Cooper S MKII (1330)
1972 Honda 750/4 (his),1976 Honda 400/4 (hers)
1982 Honda CB1100RC (ours)

Cooper S and 1100S are both cup type, but different sizes.
They give less trouble, IMO.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks Doc. Do you know what size they are?

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1969 Mini Cooper S MKII (1330)
1972 Honda 750/4 (his),1976 Honda 400/4 (hers)
1982 Honda CB1100RC (ours)

Cooper S 1.625", 1100S/LS1275 etc- 1.3125".

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks mate, you're a legend
Peter

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1969 Mini Cooper S MKII (1330)
1972 Honda 750/4 (his),1976 Honda 400/4 (hers)
1982 Honda CB1100RC (ours)