| choupie | -- 04-15-2011 @ 7:06 PM |
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Newbie-type question: Say you're holding a piston that was in a 59AB engine. Is there some dimension on this piston that would tell you what size crank was in the engine, or may a given piston have been used with various size cranks? If a given size piston only works with a certain size crank, is what is the telling dimension on the piston, and is there a table to determine what crank was used with that piston? Thanks, Paul
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| sturgis 39 | -- 04-16-2011 @ 2:04 AM |
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I am not an engine builder. I think they change the length of the rod when the stroke is changed or they wrist pin location is changed in the piston. I hope some of the engine builders will respond.I guess I never thought about this issue. IF IT CAN NOT BE FIXED WITH BLASTING WIRE, DUCT TAPE OR JB WELD - IT CAN NOT BE FIXED
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| 51f1 | -- 04-16-2011 @ 5:47 AM |
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I'm really not sure what you are getting at. Unless there is something I don't know about a 59AB engine, generally, all pistons and cranks used in a particular new engine are the same. By "size crank," if you mean the journals have been reground, that doesn't affect piston size. The piston remains the same unless the block is rebored, and larger diameter pistons are required, but they are the same type of piston as used originally (they look like the original). Richard
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| alanwoodieman | -- 04-16-2011 @ 5:59 AM |
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the telling of the crank "stroke" is the piston pin center line to the top of the piston. A ford has a 3 3/4" stroke, in a merc the stroke is 4", uses same connecting rod but different pistons as described above, the stroke in this case comes from the crankshaft throws being machined differently, with more offset
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| ford38v8 | -- 04-16-2011 @ 9:07 AM |
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Paul, Here's an article with pictures, by Bill Boomer. It describes the differences between a Ford 3 3/4" and Merc 4" crank. Not the question you asked, bu maybe it will help you. http://www.goldengatev8.org/docs/merccrankid.pdf Alan
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| carcrazy | -- 04-16-2011 @ 10:58 AM |
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Piston pin location as measured from the top of the piston to the pin centerline will differ with the stroke of the crankshaft. This assumes that the rods have the same center to center length for both the Ford (3 3/4 in. stroke) and the Merc (4 in. stroke). The pistons for use with the 4 in stroke will have the pins 1/8 in. higher than those for use with the 3 3/4 in. stroke. This difference in pin location is required to keep the piston from poking out of the top of the block at TDC.
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| choupie | -- 04-16-2011 @ 4:13 PM |
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So, as it does seem to be the case that a given piston will fit either the Ford crank (3 3/4 in. stroke) or the Merc crank (4 in. stroke) but not both, does anyone know what the measurement between the top of the piston and the centerline of the piston pin is for a Ford crank and for a Merc crank?
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| Stroker | -- 04-16-2011 @ 5:04 PM |
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Choupie: I think you have been given what you need to know by others. Given two pistons for a 59A, the Merc will have the pin hole 1/8 inch higher than the Ford. When you ask for a measurement, our problem is the reference point. Problem is: you can measure a piston from the top of the dome, the outside edge of the cylinder dome, the top ring land, etc. The only relevant measurement is the difference between pistons designed for 3-3/4 inch stroke 59A motors, and pistons designed for 4 inch stroke 59A motors. If you are in possession of a Ford and Merc. piston, you should be able to visually observe the 1/8" inch difference.
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| choupie | -- 04-16-2011 @ 7:15 PM |
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Okay, I'm feeling sufficiently dumb now, 'cause although I agree I should be able to visually appreciate a 1/8" difference, I consider it's hard to tell a difference when you only have one to look at. I also agree that problems with providing a meaningful distance arise when the reference point is not specified. So here's what I did: I put the piston upside down on a table and measured up to the centerline of the piston pin - 1 11/16". So now I'm anticipating that this measurement, too, will be insufficient data to determine what crank is in the engine because of the variety of dome heights that pistons may have (the inside of the piston is marked 80 and 1624 in a circle - for what its worth). So how about this: although the engine is not here, the connecting rod is still attached to the piston and maybe it has enough info on it to answer the question. The connecting rod is marked on one side: Ford U.S.A., what looks like a W with a circle around it, 31-1; and it's marked on the other side 29A, A2, 1. Is this connecting rod specific to a certain size crank? Thanks, Paul
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| 37RAGTOPMAN | -- 04-17-2011 @ 9:23 AM |
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if you put the piston on top dead center, and turn the engine over till it hits bottom, and you measure the distance it traveled and it is 4 inchs you have a MERC crank,and MERC piston, I do not think you can use MERC pistons without the 4 inch crank,if you used FORD pistons they would strike the head, they are 1/8 inch longer,in being the piston pin is offset 1/8 lower then the FORD piston the make up the difference in the longer stroke of the MERC CRANK. I am almost positive the rod are the same, this is what make of this,Lets hear how you made out, this will be interesting if , I am correct, hope this helps 37RAGTOPMAN This message was edited by 37RAGTOPMAN on 4-17-11 @ 9:26 AM
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| supereal | -- 04-17-2011 @ 10:38 AM |
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Check your piston for a part number. The 3 3/4 Ford piston will be marked "49T 6108" with a suffix letter indicating diameter (standard or oversize), and will be aluminum with a domed top and split skirt. These pistons are used with a 29A crankshaft.
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| ford38v8 | -- 04-17-2011 @ 3:42 PM |
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Paul, although a 4" crank could have been installed at a later date, your 59A block originally had a 3 3/4" crank. Hopefully, the various answers you've had will all come together to make some sense to you. Don't feel dumb about this, it's a reasonable question and deserves the best answers we can muster. Alan
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| TomO | -- 04-17-2011 @ 5:42 PM |
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Paul, If you tell us what you are trying to accomplish, we may be able to give you better answers. In my experience, when a 49-53 crank shaft is installed, the engine builder usually installs the 8BA rods to use the less expensive rod bearings and reduce the machining to recondition the 29A rods with there floating bearings. Tom
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| choupie | -- 04-18-2011 @ 8:17 PM |
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What I'm trying to accomplish is ordering the right pistons to rebuild a flathead Ford with 59AB heads. The engine was delivered to a local machine shop for evaluation of the viability for rebuild. They say it's rebuildable, and I'd rather fix what was in the car than put in a more modern engine as a replacement. The only parts I have with me are one piston and its connecting rod that came out of the engine prior to delivery. The fellow I bought the car from in 1988 (who is ~80 now) has over the years been confident that this engine had a 4" stroke Mercury crank in it. The machine shop that has the engine now believes the crank to be a 3 3/4" stroke. I was hoping to be able to determine what's what from the piston/connecting rod pair I have sitting in front of me - both of which were described with all they have to offer in the earlier posts (with the exception that the piston has 4 rings and is also stamped on the top "STD"). Although I appreciate the physical ways to check the stroke by measuring the travel of the piston in the cylinder - it's a little late for that now as the engine isn't here and the whole thing is apart now anyway. Apparently all late '30s to '48 Ford and Mercury flatheads used the same length connecting rod, used floating bearings, and had 3 3/4" cranks. I also gather, perhaps incorrectly, that '49 through '53 Ford engines still used 3 3/4" stroke cranks whereas the Mercury engines for these years used 4" stroke cranks, but both still used the same length connecting rods that were used on the earlier engines although the bearings were different. Consequently, I guess you could use a pre-'49 connecting rod with a 4" Mercury crank, but you'd have to use the earlier floating bearing setup as well. Accordingly, whatever info I might gather from the connecting rod won't be conclusive as to the crank shaft in my engine (which did have floating bearings in it). So, I was thinking that the only way to conclusively tell what size crank I have is from the piston - which apparently is a correct thought process (as the 3 3/4" crank pistons are 1/8" taller between the piston top and the centerline of the pin than the pistons that go with the 4" stroke cranks are). However, I haven't been able to get any data with points of reference for the measurement to be able to tell if the piston I'm looking at is for a 3 3/4" stroke crank or for a 4" stroke crank. Although my heart tells me to go with the report of the original owner, my head tells me to go with the machine shop's report. It'd be nice to have data to make an independent informed decision, which is what I was hoping for with the original post. Perhaps I'll toss a coin - I guess the vendor I get the new 60 over pistons from will swap them out if I got it wrong. Better yet, perhaps they were both right, it's just that the original owner is a little confused on the year the crank was made - maybe it's a 3 3/4" stroke Mercury crank from a pre-'49 engine (although I'm not clear on the advantage of using a Mercury crank over a Ford crank of the same stroke).
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| supereal | -- 04-18-2011 @ 9:45 PM |
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If you have chosen a machine shop, it is too early to order pistons until the block has been disassembled and thoroughly inspected. If the shop can't tell you which crank you have, I suspect they may not be capable. At our machine shop, we don't order parts until the engine has been completely disassembled, tanked, and inspected. When we determine the necessary bore size and the condition of the crank, we draw up a list of parts. To do so before the machine work is completed, is the wrong sequence, and would likely result in problems in assembly and add extra costs. This message was edited by supereal on 4-18-11 @ 9:47 PM
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| 37RAGTOPMAN | -- 04-19-2011 @ 6:37 AM |
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coupie if that machine shop has a Crank grinder, and can not tell you which crank you have, I would get my engine back, I am assuming they are just going to rebuild the engine with out grinding the crankshaft, if they had a crank grinder they would have to know what size the throws are to set it up, or they are planning on farming the crankshaft job out,which is what most shops do, you should be able to measure the throw of the crank if it is in front of you with a ruler, to get a rough idea it is a 1/4 inch longer, cannot understand what the prolblem is with your engine rebuilder my 3 cents 37RAGTOPMAN
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| TomO | -- 04-19-2011 @ 8:05 AM |
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If the crank rod journals have 1 oil hole, you have a 29A crank shaft and it would have a 3 3/4 stroke. If it has 2 oil holes it would be a later crank shaft and you would use the reference Alan gave to determine if the crank is a 4 inch stroke crank. IMHO I would put more faith in a machine shop that has the crank than the memory of a previous owner, no matter what his age is. I would order the 3 3/4 stroke pistons or let the machine shop order them from their supplier. I also think it is a better idea to let the machine shop order all of the parts. If there is any problem with a part, they will stand behind it and you are not caught in the middle between your vendor and the machine shop. That is why it is important to select a machine shop that has flathead Ford experience. Tom
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| supereal | -- 04-19-2011 @ 9:48 AM |
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We do have a crank grinder, and it is also used to polish the bearing journals if they don't need to be resized. We open the oil passages in the crank, as well, to remove the usual deposits from years of use. There is nothing wrong with an owner doing his own engine rebuild, but there is more to it than just bolting parts together if you want an engine that will justify the time and money.
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| avrotom | -- 04-19-2011 @ 2:22 PM |
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I have a new EGGE L991 Piston that is for a 4" stroke Merc and it measures 1.045 inches from the top of the piston at the OD or outer edge to the top of the wrist pin hole. An original Ford piston measures .017 more, so 1.062. Hope this helps.
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