MG Car Club of South Australia
TeChnical TopiC By .. Bob Schapel
T
DRY-DECKING an ENGINE
he coolant in car engines normally flows from block to head , via the head gasket holes . However , I have changed this system in my TC Special . Before 1995 , my old engine used to lose coolant when I drove it very hard . Gases from the combustion space would push across the gasket face and seep into the water jacket , blowing out some coolant . Because the car has a “ Laystall ”, aluminium head , extra torque on the head nuts would have risked distortion . So , when I built the “ new ” motor in 1995 , I blocked off all the holes in the head and block faces . I had some welded , and sealed the others using threaded brass plugs and “ Devcon ” epoxy . I then diverted the coolant flow externally from the back of the block to the back of the head . This modification is called “ dry-decking ”.
Now , when the gasket leaks a bit , the gas moves across the surface and vents harmlessly to the atmosphere , without affecting the coolant . I made the same modification to my brother Bill ’ s Special ( now in the hands of niece , Georgie ) when I built that motor in 2012 .
Coolant flow in most engines is fairly simple . However , the T-Type has a complex flow system which requires additional modifications in the drydecking process . The water pump pushes coolant along that familiar square passage cast into the right hand side of the T-Type block . Internally , at the back , that passage curves upwards and emerges only at the rearmost , large coolant hole . That hole ( two on TF blocks ) is not well connected to space around the bores or the other coolant holes .
To allow a clear passage for coolant , I drilled large holes behind the core plugs from the square passage to the void around the bores . Although it might be unnecessary , I also drilled a large hole half way between the two core plugs and fitted an extra ( threaded ) “ core plug ” to seal off the outer wall .
This opened the way for coolant to flow to the space outside the bores . I then rigged up an external coolant pipe from the core plug at the back of the block to the plate on the back of the head . I also fitted a small secondary tube very high in the block to prevent any air-lock .
I originally thought I had invented the idea but later found that it was well known , long before I was born ! The race team at the MG Factory used this system on the K3 based EX135 record breaker , and many years later , they cast some special “ dry-deck ” T-Type blocks .
The latter had a raised “ pad ” and stud holes high on the right hand side to take an external coolant fitting . I would like to know how many were cast , and where they were used . I have been fortunate to see one , but was unable to study it closely to learn about any other detail .
The original cooling system works perfectly well on street engines and most race engines , but if head gaskets become an issue , “ dry-decking ” is an option .
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