Cylinder Head Swap????

[drifter]

Working on a CD-12 (1955 – 5.5hp). Sometime in it’s past a previous owner swapped in a 59 power head. Problem is that 55 clamshell cover will not mate to the power head because the “ears” that support the cover are not part of the 59 cylinder head. Also, the 59 is a thermostat cooled motor and the housing is part of the 59 head..
The 55 cylinder head bolts up to the 59 case. However at least one water passage (the one that feeds water to the exhaust plate) needs to be drilled so as to supply water to the 55 head and subsequent passages around the cylinders. At least two passages would need to be plugged. Not sure yet, how water is returned to exhaust tower as I have not pulled the power head.
Has anyone done this conversion? The power head is very solid and I kinda hate to go shopping for a CD-12 block.
Thanks,
Drifter

[frankr]

Nice example of just because it bolts up Is no sign it will work, As you have already discovered there are some significant differences. Firstly, the thermostat controlled powerhead has two flow paths through it. One path flows anytime the engine is running. Second path flows only when ‘stat is open. There also is a significant difference in the base where it sits on the exhaust housing, and takes a different gasket.. Some time ago, I did a study of the ‘stat controlled water passages. I’ll see what I have left since my computer smoked and died.

My thinking though tends to be find the proper powerhead

[outbdnut2]

I was given a 1960 5-1/2 Johnson that someone had swapped a 1957 powerhead into. It has a seized piston – probably because it couldn’t cool properly. It has since donated parts to a few other motors.
Dave

[drifter]

As Frank indicated, the base gasket for the 59 was used on the 55 and they do not match. I now have a 55 power head and the 59 will go into the parts “stash” to undoubtedly be used on a future project.

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