195.6 OHV cylinder head, internals examined

Hot-rodding the Nash/Rambler 195.6 overhead valve six

aka Have your head examined!

Here's a crack-ridden cylinder head photographed and sliced up to show it's innards. It's proven very useful in surveying coolant flow and where one might remove metal from ports.

All of these cracks are in the same head! Someone really did it in, probably ran for an extended period without coolant.




Here it is chopped into slices. These heads are getting scarce, but this one had four cracks in four cylinders, so safe to say it was unsuitable for repair. I had it hot-tanked and media blasted before crack-checking, so it's nice and clean for photos.

My saw would take only about 9" x 9" so I could not make optimum cuts, but I got some good revealing slices. I chopped it in half crosswise (between 3 and 4, off a bit on purpose), then chopped off half of #6, then sliced the remaining 4, 5 cyls in half lengthwise, about half way through the ports.

The coolant chambers are of course rusty inside (nice photo contrast) and very rough. Three of the cracks are in or near the exhaust seat, closest to the intake seat. The water jack there is very poor, and tapered, and looks like lousy water flow -- but the cause of the crack is a leakign headgasket, this is just the first place to go. If it wasn't here, it would be somewhere else, due to the cooling problem caused by the leaking headgasket.

The exhaust ports are fairly square. Not that it matters much at these flow rates, but it would be easy to improve, and the metal is plenty thick. I may remove the big lumps and smooth and polish the exhaust ports on my "turbo" head, to minimise heat retention more than anything.

NOTE: Clicking the small photos will fetch a rather large, 8-megapixel, image. Slow! Great, pointless detail! And if that wasn't enough, there's movies:



Sections

This is how the head was sectioned; the pieces here are stacked together and labelled A, B, C, D.



Section A -- cylinders 1, 2, 3



Sections B and C

This is the longitudinal slice that reveals the port arrangement.





These show the water jacket side of two of the cracks. They don't appear to pass all the way through, and these are not indicative of head "problems", but are only a symptom of the severe overheating -- something had to go first!



Section D





This is a typical steam hole, from the water jacket between the two valves down into the block (through the headgasket).





Details of the middle exhaust port, cylinders 3 and 4 siamesed. This port is different; it has an upper chamber that protrudes under the carb to warm it up!