Re: 1964 Evinrude 75HP overheating help please
The thing to do would be to start over so as not to overlook anything. I've looked at this thread and my advice is as follows. However, first a note about the pixel size of your pictures which makes scrolling back and forth a must. It is best not to exceed a pixel size of 400 when inserting a graphic to avoid that problem.
The overheating problem was due to the blown head gasket. That allowed the combustion mixture to enter the water passageways. That in turn caused a stalemate, that is the combustion mixture (exhaust gases) were forced into the water passages and they were forced up against the water flow pressure. This caused the water flow to be at a standstill, and of course with the water flow standing still, the engine overheated.
My suggestions:
Remove both cylinder heads again, then raise the pistons on one bank at the same height so as to have the intake and exhaust ports covered, you might want to shove a rag in the cylinder sleeves also. Get a piece of wood, say 1"x 2" x 4", somewhere in that area and attach (wrap) a fitting piece of #80 wet or dry (black) sandpaper to it with thumb tacks. Keeping that sandpaper block somewhat wet with mineral spirits, go over the block cylinder surface area with it in a figure 8 motion. Check the surface with a metal straight edge to see if there are any un-level surfaces. When you're satisfied that the surfaces are level, repeat this procedure on the other bank and on the surfaces of the cylinder heads themselves.
Clean all of the accumulated grit and dirt out of the cylinder sleeves. heads, etc.
If there are un-level areas in either cylinder head that cannot be corrected, install a new or good used cylinder head.
Follow up by finishing up with the same procedure but with #220 wet or dry (black) sandpaper, making sure that all surfaces are level and smooth.
Install new head gaskets and torque the head bolts to 18 to 20 foot pounds in the following sequence.
9...10
5....6
1....2
4....3
8....7
Remove the lower unit. Yes, I know this is double work but you do not want to overlook anything. Dismantle the water pump. If there's any scoring of the water pump plate and/or the interior of the impeller housing, replace them.
It's best to install a complete new water pump, part number 379776 which is still available via your local Evinrude or Johnson dealership. Yes, I know it's expensive. The water pump plate is part number 305434, and the impeller is part number 377992, both of which are also available at the dealership. The impeller is also available at Sierra, part number 18-3005.
There is a gasket under the plate, use gasket sealer on both sides of that gasket, this sealer comes in a can that has a small brush attached to its screw off cap. Use Boat Armor Sealer 1000 (comes in a tube) on the impeller housing sealing surface so that the housing seals properly on the plate. This is to eliminate any air being drawn into the water pump impeller area. Both of these sealers can be purchased at any automotive parts type store.
Check around for a lower price on the thermostat as the engine must be equipped with one.
