Mercury crank
 

How do you identify the difference between a 049-53 ford crank and a mercury 'crank? I've forgotten, its been too long.

Re: Mercury crank
 

Clean out plug on the front will be five eights inch diameter, is the best way

Re: Mercury crank
 

The counter weight width as well. I forgot the measurement, but if I recall correctly, the Merc crank counter weight is approx. .500" wider than a Ford crank. Something like 6" in total width at the widest part for a Merc crank seems to ring a bell.

Re: Mercury crank
 

A Merc crank is 12" longer than a Ford crank. REALLY?

A merc counterweight is 6" wide, a Ford counterweight is 5 3/4 wide is what I think he meant.

Bill

Re: Mercury crank
 

Haha. I meant to say the width of the counter weight is 1/2" wider. I'll correct it. It's been a long day.

Re: Mercury crank
 

Yes, thanks Bill.

Re: Mercury crank
 

I have about 10 Flathead Ford/Merc cranks here at the moment. All are 8BA style, later pieces!

They both measure about 7.000" across the front c/weights, if there is any difference it is immeasurable with a conventional ruler.

The plugs are another story, the Merc is .625" (5/8") like mentioned above. These actually lend themselves very well with this size to drill & tap fpr a 3/8" NPT pipe plug, requires no add'l drilling. We do these all the time!

Thanks, Gary in N.Y.

P.S. Here's a shot of a Merc on one of our balancers now getting balanced. On the left I wrote the dimension (7.000") in "chalk" to show the span of the c'weight, on the right that single line shows the pressed-in oil plug, it measures 5/8". I can supply a shot of the front c'weight on the 239" Ford also if necessary?

Re: Mercury crank
 

Gary: Check the width of the 2nd counter weight in from the one with the chalk line. Is there a difference between the two widths of this weight? That's the one I've always checked.

Re: Mercury crank
 

i built a simple v shaped rack, rotated the crank and measured the stroke. since the difference is a 1/4" it is not hard to tell.

Re: Mercury crank
 

That's where the difference is, the second counterweight the thick one.

Bill

Re: Mercury crank
 

Well anyone who has spent time building lots of Flathead s should know the second counterweight is wider on the Merc crank than the Ford! Heck the difference is plenty enough to see without measuring if you build enough of them. Not to mention the cranks are not the same weight just saying. Another detail to mention not all Merc crankshafts have 5/8" oil plugs I have seen 1/4" on a few also.
Ronnieroadster

Re: Mercury crank
 

Ron,

Have you found that the extra weight impacts fuel economy in any way?

Re: Mercury crank
 

Hi Tim, the "span" across the second c/weight (where I have the 7.000" number in my photo) measures 5.750" on the 239" 8BA's, the 255" Merc (on the balancer) measures 6.000". Now, the "thickness" of the c/weight is the same on both, nominally speaking it is just above 2.000", probably 2.050" or so?

Hi Ronnie, in ALL my years of building/dynoing these Flatties, I can't even really recall ever doing an OEM 239", so yes, we are very limited with our knowledge about that particular shaft. I have a bunch here now that we've taken in on "trades" (at least a 1/2 dozen or more just recently) but not sure tonight I ever built a single one, there was never a market around here for that size.

To add to that, other than that OEM Merc shaft you see on the balancer tonight in my photo, the last time I recall building an OEM 255" Merc was back probably about 15 or 20 years ago, somewhere in that time frame anyway! It was our first build using the OEM shaft but with the Eagle H-beam rods (conventional rod journals, not the 2.000" ones) and learned on that build that their rods were absolutely no good to us. Haven't used a single one since then!

Hope this clears some of the questions up??

Thanks, Gary in N.Y.

P.S. Back in the late '80's and into the early '90's were doing the ALL the machining on an average of 10/15 blocks per year. At that time I was tied in with a close friend who did nothing but Flatheads, he also did nothing but the Merc's. We did do a bunch of 4.125" stroker cranks for him, but all were on the OEM Merc shafts! Grinding the 255" cranks for this stroke was very popular back then, today we use everything new (Eagle cranks/Scat rods/Ross pistons). I just learned today Eagle supposedly only has 8 (4.250") shafts in inventory, we are considering taking all 8??

Re: Mercury crank
 

Fuel economy will be affected by the weight difference but I have found a faster speed caused by this additional weight gets you to the gas pump faster :D

Re: Mercury crank
 

Besides all of that, I discovered in the mid 50's that some Merc cranks are cast steel and most are cast iron. The steel ones were obviously the better choice for welded strokers.

Re: Mercury crank
 

I think the Canadian Nerc cranks had a 3/8 oil plug.

Re: Mercury crank
 

Where's then "like" button?

Re: Mercury crank
 

Here's a good article by Bill Boomer I came across a few years ago about the Merc crank identification.


http://myflatheadford.com/identify-4...ry-crankshaft/

Re: Mercury crank
 

Hey Gary,
Do you recommend to tap the front weight for a pipe plug instead of a press in plug?

Tommy

Re: Mercury crank
 

Hi Tom, without a doubt, have all 4 tapped. The nice part about the Merc's starting with the 5/8" plugs is they don't need drilling, they're already the correct size to just tap for the 3/8" NPT thread!

Thanks, Gary in N.Y.

P.S. In all my time doing these builds we've literally done hundreds of those crank holes, more than 90% were Merc's, we did some Ford's way back in time.