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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