What to look for when buying a 4" Merc crank to fit a 59AB
 

What should I be looking for when sourcing a 4" stroke Merc crankshaft that will fit my 59 AB? Are there some numbers or something stamped on it that will indicate what it is? I would also think I would want to know the rod and main journal sizes? I see someone on here is advertising one, but buying one sight-unseen and having it shipped a distance scares me.

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

Read through all of these threads that have with the word
"crankshaft". It will give you lots of info. There must be at least one for sale in MA or a neighboring state. If you don't know about what to look for, bring a friend who does along with a set of micrometers.
https://www.fordbarn.com/forum/search...archid=6491456

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

https://www.google.ca/search?hl=en-C...pe=&as_rights=

R

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

Very helpful! Thank you. Now, all I need to do is find a good one!

Dave

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

I've done my last couple with the SCAT 4 inch pkg. Other than re balancing the components it worked great

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

I bet 'Ol Ron on here has one in Vermont. Walt Dupont in Maine I know has some. Not sure if they will sell. I have one but am hanging on to it. Expect to pay like $400 for a good one.

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

Yes I have one for the Loudon engine. It has bad rod journals, which will be turned down to 1.998 for 21A rods. I wouldn't recomend this to anyone unless they know how to fit floating bearings. The moral to this story is to find one that can be turned to a standard undersize. No more than .030" under, as the 40's are hard to find and expensive. Now when you find the merc crank, if you don't have the rotating assy that went with it, it will have to be balanced. I don't re balance, if I just change pistons.

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

You can also turn them down to the 21A journal size and run the new H-beam rods that use the old Buick bearings. This is another way to go if you offset grind a Merc crank to 4 1/8" stroke, but don't want to use the full-floater rods and bearings (which cost as much as the dang new H-beams anyway - by the time you get them setup). I still use 21A rods, strictly because I know how to set them up and am kind of sentimental about building non-blown engines "old school". Now on a high-output engine (blower, Ardun, etc) - I'd go the H-beam route.

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

What measurements am I looking for on the rod and main journals to ensure it's usable?

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

Here's one on Ebay that is supposed to have standard mains and rod journals.

http://www.ebay.com/itm/4-Merc-crank...RWxjQI&vxp=mtr

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

Went to Van Pelt's site and answered part of my own question. Looks like standard mains should be 2.499" and the rods 2.139". Usable (-.020) should be 2.479 and 2.119 respectively?

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

Grinding a crank true on center you have to take into the measurement that rodpins dont wear evenly.
So if the crankpin measures -0.20 in the worn part it wont clear up -0.30 being on original center.

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

Yes - you have it about right, depending on the condition of the journals. Sometimes one can have a lot of pitting, taper or other issues - that requires more material removal than .005 (.010 under).

Personally, I would not buy a .020 crank that needs a regrind - unless I got it for a fairly inexpensive price (like $200) - unless it looks really good and I'm sure it will go .030. Also, remember that you're investing in something that is going to take it's last regrind . . . limits your future options.

I'd find a STD or .010 crank if it was me.

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

Hi Dave, if you end up needing a Merc (4.000") crank I may be able to help you locate one.

It was at my shop a few months back, came in with a fresh cut (I don't recall the size but it wasn't "deep", 20/20 maybe), customer was planning on using it but decided he would be going with a stroker instead.

Not sure he wants to let it go?, he is a member up here, I will try to contact him if you like and hook you both up?

Thanks, Gary in N.Y.

P.S. If you are in Mass. he is in driving distance of both of us (I'm on Long Island)! Reasonably short trip. I don't want to give any info out until I have a chance to speak with him first?

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

The wear on a crank can tend to be at the top- the outside- The grinder can offset the center of the rod throws so as to minimize the loss of throw size. This would compromise the stroke a bit, but you'ld never notice the loss of (possibly) .005" or even .010". This would possibly leave open for another grind somewhere in the future.

Karl

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

That's intersecting Karl, most of the cranks I've seen had the majority of the wear on the inside of the throw? In fact I just checked in my pile ten cranks that are relatively easy to get at, all have the obvious wear on the inside. Also looked at a couple of Ford pinto cranks and a mk1 Cortina crank sat on the shelf, all on the inside. In my experience this is the normal in worn out engines.

Interesting yours and my observations/experience being opposite,
I say this with genuine interest, and for discussion. Not for arguing.
Martin. (hoping for further input)

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

The forces put on the crank is from the work being done from combustion driving the crank around (this is the side wear).
And then from the piston and rod being brought to a stop from the crank and turned around going up again (inside wear).
Offset grinding isnt a big issue for the stroke but if im not going to balance the crank i try and stay away from it.

Re: What to look for when buying a 4" Merc crank to fit a 59AB
 

Scooter has it nailed. Changing the direction of piston motion on the overlap(exhaust) stroke is where the crank gets abused. The normal wear then is located at what would be the bottom of the crankpin.

Offsetting for stock cleanup in the normal wear area would INCREASE stroke length rather than decrease. However, I have never moved more than .003 or so and doubt the power difference would be measurable.