40 merc flathead question

Jason M.

Jason M.

Senior Member
I had the pleasure of finding a TON of cars in the bush today while I was actually working. I was happy to find a 40 Merc Fordoor in and amongst the old trucks and other non Fords. This car is complete aside from wheels and tires and I'm wondering if it may have a 99 block? I scraped at the intake deck with a knife and it is NOT raised. Thanks...
 
40 blocks were not raised on the intake surface. The first raised blocks appeared in August 1940, too late for installation into '40s. Yes, I have the documentation. We can and will put this myth to rest soon...
 
Most but not all '39-40 239's have "99" STAMPED not cast near right front of manifold surface of block, letters maybe 1/4" high. Wire brush, flashlight...
Look also at lower sides of block right above pan...you should see two bulges that make room for the core plugs in pan rail. This will mark engine as pre-1941, but 221's also had those.
Easiest first check is looking for the postwar "59" on bellhousing, as many earlier cars received 59 blocks as replacements.
 
Also, if you can remove a cylinder head, the Merc blocks had a round water passage in the very center. Ford blocks had an upside down 'keystone' shaped passage.
 
I am aware of the late Merc flatheads being special because of the 4 inch stroke. Is there something about the pre-war Merc flatheads (such as the 99 mentioned) out of the ordinary? If so, what is it? I may have a couple in my shed.
 
southfork said:
I am aware of the late Merc flatheads being special because of the 4 inch stroke. Is there something about the pre-war Merc flatheads (such as the 99 mentioned) out of the ordinary? If so, what is it? I may have a couple in my shed.
Click to expand...
Early Mercs originally had a bigger std bore (3 3/16 inch) than the Fords (3 1/16 inch) and seemed to have a lot of cyl wall material to bore them big.
 
Pre war Mercury flatheads also had a larger diameter connecting rod journal on the crank, 2.139 as opposed to the Ford 1.999. This larger journal crank could be offset ground down to the standard Ford journal size and then used with Ford connecting rods which provided a longer stroke. I believe a 3-3/8" stroke was attainable with a stroked early Merc crank.
 
All the early Mercs are allegedly super heavy bore castings...I have no way of knowing how uniformly thick those bores are, but I once was able to caliper a tiny area of one bore on my '39 where it came close to the trapezoidal hole in the deck.
I seiously doubt that the rest of it was the same, but the very top part I could reach would have supported a 3 1/2" bore. Now, do not go try that!!
Anyway, they were the preferrred block for many people building fuel dragsters and long run Bonneville cars.
The 1/8 stroke was fairly common, 239 crank/221 pin size, but was of course immediately dropped from consideration when the '49 Merc crank appeared.
 
I'm going back to check on this one also, I just remebered about it when I was looking through photos I'd taken recently. This old piece of equipment is abandoned right beside the road and it may be a Merc or "99" as it is the right year, 40/41 as judged by the crank mounted fan and it has the same long oil filler tube (46/48 type) like I'd seen on the 40 Merc I'd originally posted about. Is there anything visible on this engine to identify if it as car or truck? Ford or Mercury?

I noticed the Left cyl head is missing also making it easy to see the diffrent coolant passages or measure the bore. Wish I'd taken a photo of that side of the engine.
 

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It is my experience that not all 99 blocks are relieved, Certainly that is the case with the Canadian blocks I have seen here in New Zealand. Hope this helps.
 

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On Jason's engine...if it is a 99, you can tell on the side missing the head by the shape of the water passages in central row. Truck and Merc use different heads, 81 T versus 99T on truck, but of course those have frequently been changed.
 
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