Do I have a mercury crank?
 

Shortly after buying my car with a frozen FlatheadI found a Flathead on Craigslist for $100 so I bought it as a back up. When I showed up to pick it up, he also gave me some other parts. Notably 3 cranks. One has 3.75” written on it, one hd 4.0” and the last has nothing. Obviously I can’t trust what someone wrote on it but I’m hopi g the one that says 4” is a mercury crank. The shop I dropped my block off this week at said the only way to tell is the merc crank will have larger oil holes. Is this true? Here’s some photos. If it is a mercury crank and I decide to machine/use it, what else do I need to change to make it work? Is it worth using? As always, thanks for all your help!

https://www.fordbarn.com/forum/attac...1&d=1670626891

https://www.fordbarn.com/forum/attac...2&d=1670626891

https://www.fordbarn.com/forum/attac...3&d=1670626891

https://www.fordbarn.com/forum/attac...4&d=1670626891

https://www.fordbarn.com/forum/attac...5&d=1670626891

https://www.fordbarn.com/forum/attac...6&d=1670626912

Re: Do I have a mercury crank?
 

Oil clean outs are certainly a great indicator. The sure fire way to tell is to measure the width of the large bob weights on the crank Merc. is just over 6" and Ford (3.75" stroke) is either 5.5" or 5.75" (I forget at the moment). Aside from actually measuring the stroke, this is the way to tell.

Re: Do I have a mercury crank?
 

Yes ^^^, and I think the merc oil cleanout plug is 5/8, ford much smaller, like 3/8 maybe

Re: Do I have a mercury crank?
 

Just to confirm, we are talking the hole in photo 2, yes? On this crank the holes are definitely much bigger than on the other crank. The third has non holes.

Re: Do I have a mercury crank?
 

You will find your answer here



https://myflatheadford.com/identify-...ry-crankshaft/




Ronnie

Re: Do I have a mercury crank?
 

Usually this is true (at least for the cranks made in the USA). I know there are some Canadian 4.00" stroke cranks that have a smaller journal oil-cleanout hole - more along the typical Ford size we see in the USA.

Re: Do I have a mercury crank?
 

This is correct. These cranks typically have the "kidney bean" dimple in the front throw. They tend to have the smaller clean out holes.

Re: Do I have a mercury crank?
 

Is there a casting mark ICM on it? CM is Mercury, it looks like a cast iron Merc crank and those usually have a casting mark.

Re: Do I have a mercury crank?
 

Sometimes I'm puzzled... If crank is loose, what's so difficult about measuring the stroke as Ronnie posted in #5? Takes at least a couple minutes. Couple of 2x6's or 1x6's to support the mains, on a bench or on the floor or where ever, and measure. Done. None of the other characteristics are needed.

Re: Do I have a mercury crank?
 

The difference would be is it virgin, or was it stroked to get to four.

Re: Do I have a mercury crank?
 

Now you guys have me wondering. I'm gonna run down to the shop after dinner and see what characteristics my merc crank has. This has been quite informative. Four years ago I was looking at a crank at the Portland swap meet. Guy wanted 100 bucks for it, claimed it was 4" mercury. While I was trying to measure it with a tape, some guy standing there watching me went up to the guy and bought it.

Re: Do I have a mercury crank?
 

So I’m pretty sure it is mercury. Is it worth using in my build? What else will I have to change to use it?

I was basically thinking of building a mostly stock engine with maybe a slightly better cam (is that a thing with flatheads?) and adjustable lifters and I’d like to run dual carbs. Will this crank be a nice upgrade if it measures out and is serviceable?

Re: Do I have a mercury crank?
 

You will need mercury pistons as the pin is set higher up. Rods are the same as 8ba. You will feel a big difference. I went total stock except for the 4" crank and in a truck I could pull all my regular hills with ease in high gear that used to require a downshift. Add the cam and dual carbs. A game changer I'm sure.

Re: Do I have a mercury crank?
 

Nice, thanks. Appreciate the real world insight! It is not an 8ba motor so maybe I’ll need new rods too. I guess at this point I likely won’t be using my old parts! Obviously I’ll measure the cranks as shown above to make sure and then take it to my machine shop to have them check it and machine it.

Re: Do I have a mercury crank?
 

Use the 4” crank. You will be glad you did.

JB

Re: Do I have a mercury crank?
 

So you see, merc cranks aren't just for hot rods, us truck guys love them too. BTW, the one I just went and checked on has 3/8" clean out holes, a kidney bean imprint on the front throw and measures 6 1/8" across the thick bob weight. It was recently turned from std to 10/20. And I'm pretty sure you can use your rods and the full floaters from your 59ab. Some prefer them.

Re: Do I have a mercury crank?
 

I don't believe that you can go from 3 3/4" stroke to 4" without welding the rod journals or having custom made rods with a smaller big end diameter. (never heard of such a rod though!)

Re: Do I have a mercury crank?
 

Re: Do I have a mercury crank?
 

Some photos. The big weight is 6.25ish inches across. There is an etching of 1CM. The oil holes are definitely 5/8”. I’m pretty stoked!

Attachment 505231

Attachment 505232

Attachment 505233

Re: Do I have a mercury crank?
 

Yup! You scored on that! Good for you!