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Old 08-05-2019, 05:28 PM   #1
philipswanson
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Default 1CM Merc Crank In A 40?

Does anybody know if the 51 Merc crank (1CM) is compatible with the stock 1940 floating rod? I know the other way around is disastrous. This set up would be one oil hole in the rod and two oil holes in rod journal. OK?

Last edited by philipswanson; 08-05-2019 at 05:33 PM.
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Old 08-05-2019, 06:02 PM   #2
42merc
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Default Re: 1CM Merc Crank In A 40?

Stock '40 Ford rod bearings will not fit. Wrong size.
Must use Mercury bearings. They are compatible.
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Old 08-05-2019, 06:12 PM   #3
rotorwrench
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Default Re: 1CM Merc Crank In A 40?

Some folks use floater rod bearings on them but the journals have to be the right diameter to start with. Fitting the later cranks in 24 stud motors isn't too bad but it takes more work to fit them in the earlier 21 stud engines. It's all been done before.

Using the floater type crankshaft with lock in bearings is the part to avoid when there is only one oil hole per journal.
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Old 08-05-2019, 06:46 PM   #4
Ol' Ron
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Default Re: 1CM Merc Crank In A 40?

The 40 engine comes in two sizes 3 1/16 and 3 3/16. The crank, rods and pistons will drop right in. The 221 block must be bored an 1/8 to fit the rods. Or the crank turned to 1.998 for the floater's. However, if you select to bore, better off using a later block and make 276. I've found that a "STOCK" 276 with EAB heads milled for .045 piston clearance, is a toque monster.
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Old 08-05-2019, 06:47 PM   #5
Bored&Stroked
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Default Re: 1CM Merc Crank In A 40?

A stock 1940 Ford has either 91A or 21A connecting rods - which use a 1.999 journal. So, you can either swap the rods over to 99A or 29A full-floaters (for the later 2.138 journal), or you can use 49-53 rods with the relatively inexpensive insert/tanged bearings, or you can go traditional "HotRod" stroker motor. Depending on the BORE SIZE, you may not be able to run the larger rods . . . they may NOT fit through your bores, which makes assembly a HUGE pain in the butt (it can be done, but it isn't fun!). The smaller 3 1/16 bore of the 221 Ford engine required the smaller rods - for exactly the reason I just stated.


Traditional Stroker - Using 91A or 21A Rods:

You can elect to have the Merc crank offset ground to a stroke of 4 1/8" - by using the smaller rod journal. Now you can use your early rods and their smaller full-floating bearings and you'll pickup a few more cubic inches. Of course you'll need to have the right pistons (for 4 1/8" stroke or 3/16 LC) . . . but you'll be buying pistons anyway (unless you already have a set for the 4" stroke Merc crank and your bore).

If your bores are large enough (like 3 3/16), then the cheapest route is to pickup a set of new 49-53 rods (SoCal has them for about $250 or so), then run the later insert bearings. I've never precisely measured the minimum bore you need for the larger rods - but it is easy to figure out (just measure a 29A or 49-53 rod).

Also, every machine shop and engine assembly guy knows how to use insert/tanged bearings . . . but most do NOT know how to setup full-floaters so they actually float. You have to hand "fit" full-floater bearings for them to correctly float (I've never had a new set that worked out of the box).

I've put a video on the process on YouTube and others have written about it in books, videos, etc.. If you have any issues or further questions, feel free to PM me.

Best of luck . . . now get that big ole' traditional 4 1/8" stroker motor going! LOL

B&S
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Old 08-05-2019, 07:02 PM   #6
frnkeore
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Default Re: 1CM Merc Crank In A 40?

Are there any clearance problems with the after market 4 1/4" cranks?

Frank
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Old 08-05-2019, 07:16 PM   #7
philipswanson
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Default Re: 1CM Merc Crank In A 40?

Thanks everybody. A real WEALTH of information for any flathead engine builder. Glad I checked with you guys!
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Old 08-06-2019, 09:50 AM   #8
frnkeore
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Default Re: 1CM Merc Crank In A 40?

So, no one has installed a 4 1/4" crank?
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Old 08-06-2019, 10:06 AM   #9
JSeery
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Default Re: 1CM Merc Crank In A 40?

Lots of them out there, I have one in a 59a, but no experience with the earlier blocks. Someone will jump in here sooner or later.
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Old 08-06-2019, 01:02 PM   #10
philipswanson
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Default Re: 1CM Merc Crank In A 40?

Is there a floating bearing rod that I can run in the '40 block and not have to bore or offset grind the crankshaft? Anotherwords a total drop in. ???
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Old 08-06-2019, 02:04 PM   #11
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Default Re: 1CM Merc Crank In A 40?

This is the one I'm talking about, it uses floaters but, Speedway has one with inserts, for $750.

https://www.ebay.com/itm/Eagle-Crank...8AAOSwjRtbNCsE

Frank
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Old 08-06-2019, 05:48 PM   #12
philipswanson
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Default Re: 1CM Merc Crank In A 40?

Quote:
Originally Posted by frnkeore View Post
This is the one I'm talking about, it uses floaters but, Speedway has one with inserts, for $750.

Frank
Do you think I could run this crank without boring? I don't want to bore because this block is NOS 3 1/6". 1940.
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Old 08-06-2019, 05:52 PM   #13
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Default Re: 1CM Merc Crank In A 40?

Quote:
Originally Posted by philipswanson View Post
Do you think I could run this crank without boring? I don't want to bore because this block is NOS 3 1/6". 1940.
Probably so if you install pistons with rings & rods up from the bottom. A pure pain.
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Old 08-06-2019, 07:14 PM   #14
Bored&Stroked
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Default Re: 1CM Merc Crank In A 40?

You have options - as long as you get to a 1.999-2.000 journal. Here is an Eagle crankshaft that has a 4.125 stroke and 2" journals. This would allow you to run rods that fit through your bores. Now - with that said, I have NOT measured the exact rod journal dimensions to see how they deliver them - and then determining the rod journals clearances I'd have with full-floater bearings and 91A or 21A rods. It is hard to really know until you actually have the crank, a set of bearings and a set of rods in your hot little hands.

https://www.cnc-motorsports.com/eagl...aft-41621.html

If you do NOT already have rods and bearings, then you might consider the 2.00" SCAT h-beam rods for the flathead - and use the Buick CB-610 insert bearings. One thing VERY NICE about the Buick bearings is that if you use the "-P" versions, you can get them in .001 undersize . . . for more clearance. I like to keep things a bit "loose" on my bearing clearances.

Here is the bearing I'm talking about:

https://www.summitracing.com/parts/cle-cb610p1

I just ordered a 4.250 stroke Eagle crankshaft, a set of SCAT 2.00 inch rods and one of the above bearings - so I can test/validate clearances for a 293 stroker motor.

Also, I have NOT measured one of the SCAT 2.00" rods to see if it will go through a 3 1/16 bore. If this approach is an option, let me know and I'll measure a rod for yah.

Best of luck!
D
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Old 08-06-2019, 07:35 PM   #15
Fordestes
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Default Re: 1CM Merc Crank In A 40?

If you use 3-1/6'' bore block with 4'' stroke 1CM crankshaft .Where do you find 3-1/6'' pistons to fit the 4'' stroke merc. crank without ordering custom pistons ?
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Old 08-06-2019, 07:58 PM   #16
Bored&Stroked
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Default Re: 1CM Merc Crank In A 40?

Quote:
Originally Posted by Fordestes View Post
If you use 3-1/6'' bore block with 4'' stroke 1CM crankshaft .Where do you find 3-1/6'' pistons to fit the 4'' stroke merc. crank without ordering custom pistons ?
Solid question . . . pretty much applies to ANY stroke over 3 3/4" with these smaller bore sizes. I'd call Ross and talk to them about what they have to offer - before I started acquiring all the other parts. Custom pistons can be made - but the price pretty much doubles over stocking items.
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Old 08-06-2019, 09:57 PM   #17
Ol' Ron
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Default Re: 1CM Merc Crank In A 40?

B&S has the crank for you and your present rods will work with it, Unfortunately I don;t think anyone makes prisons for your application and the balancing might be expensive.. hy not get the right block and have a crank assy installed, Short bolck shouldn't go for more than 4 grand, if you do your own work.
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Old 08-07-2019, 01:12 AM   #18
frnkeore
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Default Re: 1CM Merc Crank In A 40?

From what I've read, in the hay day of the FH, for racing applications, they were said to use the std piston with a 4" crank.

It puts the piston about .085 above the block and there are several ways to accommodate that. Thicker headgasket and chamfering the piston are 2 of them. You only need to keep the piston, .035 - .040, below the head.

I haven't done this, only read about it but, the above is how I would adjust for the increased piston height.

Also, I'm interested in how the 4 1/4 crank fits. I got the head off of mine, today and I'm .040 over (3.102) it has taper so, it will be .050 or .060 over, after it's bored.

Yes, I know the mains will have to go down to 2.399.

Frank

Last edited by frnkeore; 08-07-2019 at 01:20 AM.
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Old 08-07-2019, 02:57 AM   #19
Fordestes
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Default Re: 1CM Merc Crank In A 40?

frnkeore , stacking head gaskets can (in my opinion ) decrease reliability , There are head shims around to help correct an over milled block but not my first choice ,if you are using a 221 block ? where do you plan to get the 4-1/4 stroker pistons in anything smaller than 3-5/16? I have a few very nice 221 blocks I have decided to go ahead and try to use , the standard 239 and 255 bore is my only cost effective solution for using the 221 blocks. too bad someone don't produce 3-1/16 x4'' stroke pistons, I recently used up the last 5 sets of new old stock Badger 3-7/8'' stroke pistons from the early 50's. so I too am looking at alternatives , Egge wanted about $500 just to set up to produce some special flathead pistons about 5 or so years back. myself I would like a few sets of 3-3/16 .060 or .080 x 4-1/8 stroke pistons , as for me the boring bar is not always the right answer. I want to leave a little wall thickness , I believe an over bore greater than .060 is not necessary for a good street engine. thats just my opinion. mabe a few of us can see what it would cost to collectively have a few sets of custom pistons made ,I understand the major cost is in the set up .

Last edited by Fordestes; 08-07-2019 at 03:02 AM. Reason: spelling
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Old 08-07-2019, 08:02 AM   #20
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Default Re: 1CM Merc Crank In A 40?

Let me pass this along, we are in the process this week of installing a set of the 2.000" journal Scat rods in an 8BA for a member up here.

His finished bore size is 3.228" (this is .040" over on this platform) and the big ends of rods will not fit through the bores as they come from Scat. They measure 3.232" (nominally).

I had another shop in my area contact me recently with the very same issue, very same bore size!

The small difference can be overcome by simply sanding the very outer sides of the big ends, we take about .002"/.003" from each side and then renumber the rods. The "shrinking" removes the original "lasered" numbers.

Another alternative to using the 2.000" Scat's with a smaller bore would be to install the pistons with the rings mounted and 1 lock ring installed in each piston into each bore, no pins, pull each piston below the bore bottoms, push the pins in and install the other lock ring. real "pain" but I believe some motorcycles are done this way.

(Add) Thanks Dale!

Thanks, Gary in N.Y.

P.S. If you call Scat they will tell you NOT to use their the rods at that bore size, they recommend a minimum of .060" over on the OEM 3.188" bore size. If you follow my directions above I'm saying they WILL go at 3.228" with some "massaging".

Last edited by GOSFAST; 08-07-2019 at 09:28 AM. Reason: C-size
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