Bye Pass


Repair or Doing away with.

1275cc Mg Midget Head

Drill Size 14.5 mm.

Tap:Bottom 5/8 -18 UNF.

Available here:Engineering Supplies

The 14.5mm drill was to big to fit in my drill chuck, managed to drill out the remains of the outlet by gripping it with a small pair of stilsons and turning by hand, then ran the tap down to clean up the threads. Try and get a drill with a narrower shank if you can as most chucks are 13mm.

(left) New By-Pass adapter available from EMS

or this longer version from Mini Spares

There are some interesting articles on the Mini Spares website covering By-Pass or non by-pass heads, non By-pass heads still have water flow through a thermostat sandwich plate during warm up.

Blanking off the By-Pass
It is said that the By-Pass can be blanked off and a small hole drilled into the rim of the thermostat to allow a bit of water flow through the engine. I tried the hole drilling and found the engine running too cool, fitted an un drilled thermostat now to get the engine up to running temperature. For highly tuned engines best to leave by-pass in place as hot spots can develope.

5/16 allen key. 5/8 Plug from Mini Spares

Pumbers PTFE tape

Blanking Plug from the water temp sensor
I used the plug after cleaning up the the mating surface with a gringer, water flow on the head will go from- water pump through the OPEN heater valve -through heater-through heated manifold and back to the pump.