ok guys went to replace bypass hose on my 850 engine only to discover the top piece that comes out the block is coroded can this be replaced and is there anyone out there done such a job that could give me some tips

they can be replaced - the head needs to be off obviously

if you're lucky, it'll unscrew with some heat and patience, but they're usually well rusted in. The way I've had the most success is to drill it (9/16 drill bit I think) and then run a tap through the thread to take the rest of it out.

The thread is 5/8 UNF

edit: by the way - http://www.minisport.com.au/prod1005.htm

I machine brass ones, $15 ea.
They never rust again...

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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.

i got me one of the good doctors... brilliant.

the other thing that is brilliant is using heater hose on here rather than any other stupid convaluted hose or silicon hose... the good doc also taught me that!

Cooper S all came with heater hose. Early Minis came with the convoluted one, it was a refugee from the Morris Minor 1000 and probably the mighty Austin A30 too.
The convoluted hose used to be OK (Mackay Rubber made them here) but now they are imported rubbish.

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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.

next time i change it on my minor, it will be fairly drastic, it's getting swapped for something 30 years newer and japanese !