Does it happen under acceleration, then when you depress the clutch it disappears? If so I think it maybe something to do with the clutch. If not then it's not the clutch.
My Minor:
A Clarendon Grey 1953 4 Door Series II.
MMOC - 66535
I'm afraid it sounds very much like the head gasket has blown. Is the car now seriously short of power ? Of course - just check before you move the car again that it's not a wheel about to fall off due to loose wheel nuts. If still plenty of power, but just very noisy - it's maybe just a blown exhaust!
Tappets ?? I doubt it! Faint rattle at worst. Why did it need a new head gasket ? Once an engine blows the head gasket I'm afraid it's much more likely to blow another - at least until it 'proves' itself by getting a few thousand miles under it's belt.
I thought Big ends but it happened suddenly, I would expect noise build over time also no noise at idle
Have been in garage since early afternoon, and found the tapits where little off and the distributor was little warn abut have mended each then checked the vacuum and there is none (think diaphragm is busted) now that could explain the jack hammer like sound when I accelerate because timing becomes off but also found though some test I have completed that cylinders closest to fire wall are not firing (found this though pulling plug off at time and front two stop engine at idle and back to make very minimal difference) I have check plugs for good spark and there is.
You can get a head gasket from any local parts supplier - it's same as Mini 998 engine ! Should be very inexpensive - ~ £5 or £6. Make sure they don't give you the 1275 Mini gasket - unless you have a 1275 engine ??? Would suggest MOSS or Bull Motif if buying parts that are not available locally.
Its the same gasket as a 998 mini of any year, although motor factors will still list it under minor too Gasket about £6 on its own or just under £20 for a whole head set
Gasket about £6 on its own or just under £20 for a whole head set