merc or ford flathead crank??

I know this sounds dumb but I was wondering if you can tell whether or not a flathead has the stock crank or a mercury 4.00 crank. When the pistons are all the way down, the measurement to the top of the block is dead nuts at 4.00 inches. Is this a mercury crank or the stock ford 3.75. Thanks.

 

your piston will travel 4" with the merc crank, and 3.75" with the Ford crank. Can you turn it over to check the actual travel?

 

It is a Merc crank. The piston would have to be 1/4 down in the hole at TDC for it to be otherwize. Congrats!

 

do you know what block you have? sounds like you have an 8BA? were you told it had a merc crank?
i guess you could measure what distance the piston is traveling in its bore, ive never heard of that being a reliable way to measure stroke, not saying it wouldnt work though.

 

This motor is turning out to be something crazy. I bouth it from a guy that new nothing about it. I thought it was just an old stocker but after inspection I have found these: It is bored 60 over, It has weiand cheater heads on it, adjustable lifters, I imagine it has a decent cam, an old weiand 2 pot intake, aluminum shiefer flywheel and now a merc crank. Clean as a whistle inside and is ready to run. It was painted dark blue when I got it. I wonder if this motor has history?? It is a 48 59A motor. With the piston all the way down, the measurement is 4 inches to top of block. Not bad for $600.00!!

 

No offense meant, but you suck...

Great find, good luck with the new engine.

 

"i guess you could measure what distance the piston is traveling in its bore, ive never heard of that being a reliable way to measure stroke, not saying it wouldnt work though..." Uh...isn't that pretty much the actual definition of stroke?? What else WOULD you measure??

 

I always tear down the block and measure the stroke from the centerline of the con-rod journal to the centerline of the crank, then I double that measurement.

Or I will check the numbers on the block and look up/find out who the most recent owner was. Then I can ask him/her what the displacement was. Then I can use the pythagorean theorem to find out the stroke since I pulled the head and measured the bore diameter.

but thats just me.

 

I give them a Polygraph test, people lie.

 

Congratulation.
I picked up a 59AB for free last year. It turned out to have adjustable lifters, late style valves and retainers, 3 5/16 bore, domed pistons and a Merc crank. It came out of a '37 four door. The only problem is it has a scored cylinder were the wrist pin retainer appears to have come loose. I'm about ready to take it to the machine shop to be tanked and magnafluxed and see what options there are for sleeving that cylinder.

It just goes to show you there are great deals to be had.

For your refererence the counter weights on a Merc crank are approx. 7" in diameter and a Fords are approx. 6".

Good luck with our project.

 

cat got your tongue?

 

I know it was a good deal but dammit I really needed something to start going my way. If the piston travels 4 inches on the crank, isn't that a merc crank? I know taking the pan off would surely tell me but I thought I could tell from the top too.

 

sounds like junk to me I will even take it off your hands.. and will even pay shipping.

Dawg

 

You sound flustered. Yes, if the motor turns and youre looking into the cylinder bore, rotate the crank until the piston stops moving down. Measure to the top of the deck. That is your stroke. All the other methods were horseplay.

You have a 4" stroke crank according to your measurements. Congrats.

 

LOL!

 

Actual correct way to check stroke is to place a barometer on top of piston and note highest and lowest reading! You do need a calculator with 25 decimal places for this, however.

 

Aren't you going to take the pan off anyway? I believe that measuring the stroke on piston is correct. but pull your pan and measure at the crank itself to be sure.

I can't imagine buying a used motor and not pulling the pan for an inspection, but I live by Murphy's law anyway...

 

Sounds like it's a good engine, so turn it over & verify the top of the piston moves 4" - I think you've got a 4" crank though...

I'd also pull the pan - it'll be easy then (and you ought to pull the pan anyway!)

 

Bruce I think the correct tool for the job would be an altimeter . pat

 

That's assuming that the piston dome actually comes up even with the deck surface ("zero deck").
Measure where the piston is in the bore at TDC, then measure again at BDC. Subtract the distance you measured at TDC from the BDC distance and you have stroke. Easy.

 

Just in case there is any confusion about this, measuring the depth of the edge of the piston in the bore at bottom dead center is the easiest and most reliable method of telling if you have a 4" stroke. It is extremely easy to tell 3 3/4" from 4". While I suppose it is possible that someone would put Merc pistons on a Ford crank, you could probably see with your naked eyeball whether or not the piston edges were an eight of an inch from the deck at TDC.

What may not be so evident is whether or not the crank is offset ground for that other 1/8". I would guess not, but if you do pull the pan you can easily spot those 21A or 91A rods with the big ends not centered on the offset ground throw. It really only matters if you are planning to rebuild it or put new bearings in it and then you would be the fool's fool if you didn't tear it down before ordering parts. You lucky dog.

 

C'mon Bruce, are you still using those things? They can only "predict" your stroke at best!

 

Actually, it's like Schrodinger's cat...stroke is always at an exact but unknown point between zero and five...our chances of guessing it correctly depend on the number of barometric readings we take and average. Find a Goodyear franchise with a good quantum mechanic if you have difficulties...

 

Measuring the stroke is always the best method of identifying crankshafts but if you are looking at a flathead crank out of the engine or have the oil pan off a quick method for identifying them is to look at the oil galley cleanout plug on the front throw. The Ford cranks have a small plug- about the size of a pencil eraser. The Mercs have a larger plug- big enough to fit your pinky finger inside the plug. I've been told there are a few exceptions to this rule but it works 95% of the time and has always worked for me. Quick and easy............ Brad

 

All cats are mammals, but not all mammals are cats.

So it is with the 5/8" cleanout plugs in the Merc cranks - all cranks with the large cleanouts are 4", but not all 4" cranks have the large cleanouts.

Same with the kidney bean casting "dimple".

Short of actually measuring the stroke, the most reliable method of determining whether a crank is 4" or 3-3/4" stroke is to measure the width of the large counterweight - under 6" = 3-3/4" right at 6" = 4"

 

Well - guess you need to tell us whether you measured at the edge of the piston of the center/crown of the dome?

If you measured at the crown, then may actually be 4 1/8 stroke- as the crown/dome sticks up approximately 1/8 above the edge of the piston. So -- it would stick up about 1/8 above the deck at TDC. Therefore, if would need to be approximately 3 7/8 down in the bore if it was a 4" crank or 4" down if it was stroked the additional 1/8 by offset grinding the crank and using 21A or 91A rods.

Hope this makes sense. Do the piston tops have markings on them? Like 1/8 LC? (Stands for 1/8 long crank -- which means a 1/4" more stroke).

Let us know . . .

Dale

 

Seems we run into this subject every once and a while; eh Ernie!!

Yep, if it's a CANADIAN manufactured Merc crank, it CAN have SMALL clean outs. (and they were usually threaded plugs rather than "push in" Welch plugs)

ANOTHER Canadian Merc 4" crank identifying mark. (found on the front counter weight; sometimes "rectangular")

This I.D. trick Ernie and I learned from Mike Davidson; the Aussi flathead "guru."