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Old 05-24-2020, 08:18 PM   #1
leon bee
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Default Eagle 4" 8BA Crank?

Since we been discussing Asian parts and tools: I saw these cranks for sale, less money than I would have figured. By the time you bought a decent Mercury crankshaft and had it ground, might be about the same money. These have been discussed here before, I haven't found the relevant posts yet, though. For example, GaryGosfast, I remember he liked the Eagle or the Scat one or the other, but not both of em. Any thoughts from anyone?

Also, do these go okay with original 8BA rods? Just wondering, not spending any money yet. Thanks!
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Old 05-24-2020, 08:34 PM   #2
Tim Ayers
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Default Re: Eagle 4" 8BA Crank?

Curious, what's the price of one of these? Grinding a good. old crank ain't that much.
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Old 05-24-2020, 08:54 PM   #3
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Default Re: Eagle 4" 8BA Crank?

$581 on Ebay
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Old 05-24-2020, 08:58 PM   #4
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Default Re: Eagle 4" 8BA Crank?

Original crankshafts made by Ford are superior in quality to any scat or eagle crankshaft made in china. Typical job shops that use off shore chinese parts are not a place I would spend my money or use there choice of parts as guide to what quality truly is. A good merc crankshaft including grinding would cost at the most what a cheap quality import crankshaft is going to cost.
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Old 05-24-2020, 09:04 PM   #5
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Default Re: Eagle 4" 8BA Crank?

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Last edited by Black Fifty; 05-24-2020 at 09:05 PM. Reason: Redundant post
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Old 05-25-2020, 07:06 AM   #6
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Default Re: Eagle 4" 8BA Crank?

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Originally Posted by Ronnieroadster View Post
Original crankshafts made by Ford are superior in quality to any scat or eagle crankshaft made in china. Typical job shops that use off shore chinese parts are not a place I would spend my money or use there choice of parts as guide to what quality truly is. A good merc crankshaft including grinding would cost at the most what a cheap quality import crankshaft is going to cost.
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Hi Ron, the problem using only OEM Merc cranks is there aren't enough "decent" ones around to meet the demand and the work (labor) to make certain a shaft is usable normally outweighs the price of an aftermarket piece.

I'll give you an example of the general procedure here for "prepping" an OEM 4.000" crank. First it gets magged, then the 4 clean-out holes get drilled and tapped (3/8" NPT), and next (generally) gets turned to an undersize.

By the time you purchase a used Merc crank (we get an average $300.00 for a "mint" Merc shaft) and then do all the above labor it's a no-brainer to go with a new off-shore piece! Plus you have the option of using the 2.000" rod journals w/o any add'l machining!

In short, you pay $200.00/$300.00 for the OEM piece, you mag it, drill/tap the plugs, machine it to whatever u/s and usually find it'll cost more than new! We get $525.00/$550.00 for the Eagles (depending on any shipping we see) and also now have the choice of the strokes!

We are able to balance most Eagle Flathead cranks with a bob-weight between 1500 & 1550 grams in under 1 hour! Also never had to "fill" a single one so far to get it balanced!

Thanks, Gary in N.Y.

P.S. The above info is looking at it from a business standpoint, we move enough Eagle shafts to keep a good inventory on hand, and we save the incoming frgt by buying in numbers! We now avoid ALL Scat shafts here any longer, had too many issues getting them balanced w/o adding some heavy-metal. This is based not only on the Flathead ones but on the Chev's as well!
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Old 05-25-2020, 09:34 AM   #7
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Default Re: Eagle 4" 8BA Crank?

It kind of comes down to stroke and rod-choices for me. If you're just going with a 4.00" stroke and running standard 49-53 rods, I'd rather have a performance regrind on a stock Merc crank than an aftermarket one. I would find one that is STD or .010 - then have it checked out and performance reground from there. I'm not inclined to buy a crank that is already .020 and worn . . . then have to go to .030 or more on the regrind.

Now, if you're going to a 4 1/8" stroker, then things start to change - depending on what rods you're wanting to run. To get to that stroke on a Merc crank, we have of offset grind it and either run the early 221 cubic inch 91A or 21A rods and full-floater rod bearings. Or, you buy a new set of SCAT H-beam rods with the 2" journals. You start investing quite a bit of money on rod work, floater bearings or new H-Beam rods - it starts adding up quick.

Also, one has to make sure that the Merc crankshaft you start with will actually give you a 4.125 stroke after offset grinding . . . I try to start with a STD stroke crank to ensure I reach the 4.125 stroke - such that I have the correct resulting compression height for standard off-the-shelf Ross pistons. Otherwise, if the stroke comes up a bit "short", I have to order custom pistons with the compression height (pin location) to match my newly offset ground crankshaft.

In the end, I'd still rather have a 4 1/8" stroked Merc crankshaft at this stroke level - and I'd probably run H-Beam rods as they really don't end up costing any more than reworked 21A rods and cadmium silver full-floater bearings (if you can find them).

One you get over 4 1/8" stroke - say 4.250" and you're not building a Bonneville or true race motor, then you pretty much are reliant upon SCAT or EAGLE to supply you a cast stroker at a price you can afford.

If you're building real race motors with 4.250 strokes or more - with high horsepower levels, then you're stepping up to a true billet custom crank, lower end girdles, etc. - and you're talking $3000 or more (these days) just for the crank - and God only knows how long it will take to get one . . .
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Old 05-25-2020, 02:23 PM   #8
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Default Re: Eagle 4" 8BA Crank?

B&S, I have to agree with you on all of the above, However I was told by a crank grinder that he could make a 4 1/8 stroke cranl out of one that was .020 under and even more if you wanted a 4 1/8 that was .010/.020 under. Then you'd have yo find floaters that were undersize or "H" beam wit undersize bearings. I never did the Math here but i suppose it possible to save a good Merc crank for something useful. I have one that;s .030 under that i was thinking of turning to 1.998 to save. BUT??
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Old 05-25-2020, 06:20 PM   #9
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Default Re: Eagle 4" 8BA Crank?

Quote[Once you get over 4 1/8" stroke - say 4.250" and you're not building a Bonneville or true race motor, then you pretty much are reliant upon SCAT or EAGLE to supply you a cast stroker at a price you can afford.]Quote

Not necessarily. People seem to forget about the welded strokers. You can still get one made. People also seem to have forgotten that Ford made quite a few CAST STEEL Merc cranks. (prefered for welding)
A welded crank will last as long as a billet in a street engine.
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Old 05-25-2020, 06:48 PM   #10
Tim Ayers
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Default Re: Eagle 4" 8BA Crank?

A tad off topic, but has anyone ever worked with a French 4" crank? I have an NOS one that I've been saving for my next motor.
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Old 05-25-2020, 07:08 PM   #11
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Default Re: Eagle 4" 8BA Crank?

Quote:
Originally Posted by Pete View Post
Quote[Once you get over 4 1/8" stroke - say 4.250" and you're not building a Bonneville or true race motor, then you pretty much are reliant upon SCAT or EAGLE to supply you a cast stroker at a price you can afford.]Quote

Not necessarily. People seem to forget about the welded strokers. You can still get one made. People also seem to have forgotten that Ford made quite a few CAST STEEL Merc cranks. (prefered for welding)
A welded crank will last as long as a billet in a street engine.



Hi Pete, I have a question: I have a couple Merc 4" cranks. How do I tell if they are cast steel or not?


Thanks, Allan
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Old 05-25-2020, 07:15 PM   #12
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Default Re: Eagle 4" 8BA Crank?

I don't have any desire to build an engine like you all have been describing, but I love to read about it. Amazing.
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Old 05-25-2020, 07:50 PM   #13
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Default Re: Eagle 4" 8BA Crank?

I was of the opinion that only some '32 cranks were steel. I will be interested in where this iron/steel discussion goes,
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Old 05-25-2020, 07:54 PM   #14
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Default Re: Eagle 4" 8BA Crank?

Quote:
Originally Posted by Pete View Post
Quote[Once you get over 4 1/8" stroke - say 4.250" and you're not building a Bonneville or true race motor, then you pretty much are reliant upon SCAT or EAGLE to supply you a cast stroker at a price you can afford.]Quote

Not necessarily. People seem to forget about the welded strokers. You can still get one made. People also seem to have forgotten that Ford made quite a few CAST STEEL Merc cranks. (prefered for welding)
A welded crank will last as long as a billet in a street engine.
I agree Pete . . . with one caveat - "price you can afford".

Having a crankshaft shop create a welded stroker will be a lot more money than a $600 Eagle 4.250 stroker. This is a semi-educated guess

I'm sure the prices vary all over the board, but I think the last price I heard (20 years ago) was over $100 per journal. Just for shits and giggles, I will ask Fowler what they charge these days - they have one of those cool journal welding machines (they use it a lot on big Diesel cranks with spun bearings).

I've never had a 'Cast Steel' Merc crank (that I know of) - what is the best way to positively identify one???
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Old 05-25-2020, 07:58 PM   #15
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Default Re: Eagle 4" 8BA Crank?

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Originally Posted by Ol' Ron View Post
B&S, I have to agree with you on all of the above, However I was told by a crank grinder that he could make a 4 1/8 stroke cranl out of one that was .020 under and even more if you wanted a 4 1/8 that was .010/.020 under. Then you'd have yo find floaters that were undersize or "H" beam wit undersize bearings. I never did the Math here but i suppose it possible to save a good Merc crank for something useful. I have one that;s .030 under that i was thinking of turning to 1.998 to save. BUT??
Given the stock rod-journal size of the Merc Crank is 2.138, in theory you can just make it with a .020 undersize crank - if it has no wear. In my experience it always seemed like that was pushing it - that anything under .010 was kind of a crap shoot.
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Old 05-25-2020, 08:24 PM   #16
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Default Re: Eagle 4" 8BA Crank?

had a Ford 3 3/4 crank that broke inspected at he bullard foundry lab abd it had a catavation errosion brake, from excessive oil pressure. It was also made fron perlitic iron. Not a merc crank but they spark the same??
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Old 05-25-2020, 08:26 PM   #17
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Default Re: Eagle 4" 8BA Crank?

Quote:
Originally Posted by Bored&Stroked View Post
I agree Pete . . . with one caveat - "price you can afford".

Having a crankshaft shop create a welded stroker will be a lot more money than a $600 Eagle 4.250 stroker. This is a semi-educated guess

I'm sure the prices vary all over the board, but I think the last price I heard (20 years ago) was over $100 per journal. Just for shits and giggles, I will ask Fowler what they charge these days - they have one of those cool journal welding machines (they use it a lot on big Diesel cranks with spun bearings).

I've never had a 'Cast Steel' Merc crank (that I know of) - what is the best way to positively identify one???
The cost for a welded 4.5 stroke crank would vary quite a bit due to who you knew, whether they were interested and bunch of other stuff.
It would end up somewhere between a SCAT/Eagle and a billet.
One thing for SURE. It would last a whole lot longer than a SCAT/Eagle.
4.5" welded cranks lasted for at least 20 runs in the old days of top fuel.
Scat cranks would only last 100 feet on the first run.

The easiest way to identify a steel crank is the spark test. There are very subtle differences in looks also, so unless you have compared the 2 examples side by side, it is difficult. ONE THING FOR SURE IS, ALL OF THE STEEL CRANKS I HAVE HAD, HAD "1CM" cast in one of the big counterweights.
I have seen plenty of cast iron ones with "1CM" also, so that is not a positive identifier.
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Old 05-25-2020, 08:36 PM   #18
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Default Re: Eagle 4" 8BA Crank?

Quote:
Originally Posted by Ol' Ron View Post
had a Ford 3 3/4 crank that broke inspected at he bullard foundry lab abd it had a catavation errosion brake, from excessive oil pressure. It was also made fron perlitic iron. Not a merc crank but they spark the same??
No, Ron, the sparks are quite different from cast iron to steel.
Iron is dark red with no sparkles.
Steel is yellow with sparkles.
This is for the flathead cranks only. Sparks will vary widely with different steel alloys.
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Old 05-25-2020, 09:05 PM   #19
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Default Re: Eagle 4" 8BA Crank?

"Pete" - Would it be possible to post a couple of side by side pictures of a steel vs. an iron crank? I have a pristine 1CM crankshaft and would hate to "waste" it on a street engine if it is something special.
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Old 05-25-2020, 09:22 PM   #20
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Default Re: Eagle 4" 8BA Crank?

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"Pete" - Would it be possible to post a couple of side by side pictures of a steel vs. an iron crank? I have a pristine 1CM crankshaft and would hate to "waste" it on a street engine if it is something special.
I don't have any pics of that.
I haven't used OEM cranks for many years.

The spark test is more reliable.
Take a die grinder with a 1 inch diameter stone in it and see what the sparks look like. Bear down so the sparks are bright. A cut off wheel might produce brighter sparks. Try that also.
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