Just bought a large parts collection and have something weird. Part of the deal are 2 Mercury 4" flathead 1951-up crankshafts, both of them are marked 1CM. Weird thing: one is cast and the other seems to be forged. Did they come both ways? or is one an aftermarket part marked with the 1CM for id purposes only?
I don't think so. I hope cam grinder Pete chimes in on this. Even though it may ring like a forged piece, I believe it is due to the material used not the process. I could be wrong, but I think 'Ol Ron and Pete are pretty certain on this. Fellas, help us out...
These are both marked 1CM, both have the 6" width across the thick section and both are 4".. but one looks like it is cast and one is forged
1CM denotes the 1951 and later crank, which has a new (not there '49-50) socket in the back to accomodate the fluid coupling pilot of the automatic transmission. This does not interfere with stick use. My understanding is that Ford went to a new casting technique in '52-3 that resulted in a much different, very smooth finish on the unmachined areas of the crank. I can't further describe because I have never owned one of those...that could well be why yours look different. If counter weighting is the same, note that forging those would be a SERIOUS challenge. One of the advantages of the cast process is that it allows a full set of counterweights with amount and location of the mass fully controllable. Many forged cranks lack center weights to fully distribute the balance and torsional effects.
That would explain the difference, there is a very obvious surface difference. And as always, Bruce Lancaster saves the day on any and all Flathead related questions. I'll try to clean up the cranks and take side-by-side comparison pictures so you can all see the differences.
Just went out and took some pictures, but it's hard to see unless you get closer, and I'm not strong enough to hold two of these next to each other and take a picture at the same time. Also noticed that one of them has some interesting inscriptions.. including: Stroke 4.125 That's the one with the smooth surface, so if we assume it's a different casting process then that one is a later (52/53) model.
I'd say the 4.125 stamping means it's an offset ground stroker crank. The standard late rod journal is 2.138". That 1.998" stamped in is likely the new journal diameter, which is what was used on earlier flatheads.
More stuff to fuss over...is the str0ker an actual 1CM? Or is it just punched so by the shop? A stock 1CM has the designation cast onto a weight so the parts man can get the right one for an AT car...look and see if there's a pilot depression in the back. There are lots of people who think all Merc 4" cranks are 1CM... Also, could be one that was carefully ground smooth--likely you'll be able to see indicators of that when de-rusted if that is the case.
The 1CM is cast in, not punched. There are NO grind marks on the crank, so this is probably a later casting 1CM as we first thought.
10-4 on that. I have a Canadian "bus" 4" crank. If you saw it laying there and where wise to it, you'd pass it by. 3/8th (small) clean out plugs, but the give away is the "belly button" or "kidney bean" cast into the front of the first weight. Throw it in some V blocks, measure 'er up & bingo, 4". Even bigger bonus is that it is usable at standard/standard and was FREE. Got to love it!
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