Wrong head gaskets on a 40 Merc?
 

When I tore down my 40 Merc motor for a valve job, I discovered that the PO had installed head gaskets with small round holes for the center water passages instead of the style with the "keystone" shaped passages like the block has. Does anyone know what affect this has? The engine was prone to overheating but it also has a load of rust and scale in the water jackets. My intent is to clean it all out and install the proper head gaskets. I'm just wondering how much improvement I can expect to see from the gasket change.
Thanks,
Dan

Re: Wrong head gaskets on a 40 Merc?
 

Probably none, A lot of head gaskets will have holes that are smaller then the holes in the block or heads. This is a way of controlling the water flow.

Just be sure to install the new gaskets correctly. There is one end that goes to the front and one end that goes to the rear of the engine. There should be a notch in the end of thegasket that goes to the front. Some of the front water holes in the gasket are a little smaller then the rear. This is to promote flow thru the rear of the block and help cooling.

Chris.

Re: Wrong head gaskets on a 40 Merc?
 

There's an issue here...
Prewar 24 stud engines with the huge keystone water holes left the factory with keystone gaskets; postwar engines got the round-hole only gasket.
Ford overhaul instructions call for the elimination of the keystone gaskets at rebuild time, presumably to tune water distribution better. The early heads get a simple redrilling, 2 of the round holes get slightly enlarged, and then are to be used with the late gasket. The change is labeled as "for better cooling"...can easily find the specifics of the drilling if you are interested.

The early gasket is to be used only with unaltered early heads, but alteration is recommended by Ford.
Early block and late heads also gets the late gasket...this would apply to hotrod heads generally, too,
Late engine of course gets the 59A type gasket for all purposes.

So, Ford considered actual use of the trapezoid gasket to be obsolete whenever the heads came off engine to allow the drilling.

Re: Wrong head gaskets on a 40 Merc?
 

Late gaskets too have the front and back for same reason, by the way.

Re: Wrong head gaskets on a 40 Merc?
 

Bruce,
Thanks for the excellent information. It's interesting that some suppliers still sell both style head gaskets. I located the head drilling information on line but can not read the dimensions that the holes are to be drilled to. If you have a better copy, could you give me the sizes? I will see if my heads were ever drilled to the new size and then continue to run the new style gasket. My engine is so limed up that the holes are all very small so just cleaning it all out is going to make the biggest difference. I really appreciate your help!
Dan

Re: Wrong head gaskets on a 40 Merc?
 

Got it...Ford V8 overhaul manual, '37--48:

Look at central vertical row: Topmost hole gets drilled to 3/4", skip one, third from top goes to 5/8", next two nada. All done!

Re: Wrong head gaskets on a 40 Merc?
 

Thanks Bruce,
I'm looking at the same picture but could not read the numbers. I will go home and check them tonight.
Dan

Re: Wrong head gaskets on a 40 Merc?
 

Good old Henry sourced paper is nice to have.

Re: Wrong head gaskets on a 40 Merc?
 

Checked my heads last night and they were not drilled to the new, larger size. Worse than that, they were all limed up so that they were only about 1/4" in diameter. I cleaned them all out and will drill to the new, larger size. Should make a big difference. I've also managed to scrape and vacuum about 1 lb coffee can full of rust, sand and scale out of the block water passages. I'm thinking this thing will run nice and cool now. Any recommendations on what brand/type of head gasket to buy?

Re: Wrong head gaskets on a 40 Merc?
 

I recommend the Best brand of gaskets. Part # 511G for Graphtite or 511C for copper.

Jim