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Old 04-24-2016, 08:48 PM   #1
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Talking stock 4.3 crankshaft vs marine 4.3 crankshaft

Got my hands on a lightly used marine crankshaft last week. finally got it over to my secret laboratory where I'm building my new motor to compare it to a stock crankshaft. Right from the get go you can tell the difference. The marine crank looks much beefier and cut better. There's hardly any cast marks on the marine crank where the ones on the stock crank are painfully sticking out.

Anyone also on the FB group have seen these pictures already. But wanted to share with the site as well.

Marine on left, stock on the right.


from the other end


Front of the marine crank


Front of the stock crank. Just look at that cast line.



This is where you can really start to see the difference in beefiness and material.

Stock crank. Notice the web and how small it is.


Same web on the marine crank. Much more there and its thicker.



Rear main seal of the stock crank.


And the marine crank.


Close up of one of the counter weights of the stock.


Same counter weight on the marine crank and notice its much thicker despite being cut and machined down so much already.


speaking of that, even how the weights are cut vary. Stock...


and the marine...




So there you have it. Stock vs marine crankshafts side by side. Both used and from stock motors. I haven't had either treated, shot, or worked on yet. And I'm inclined to agree with the statement made that getting the marine crankshaft cyrod and shot would most likely yield the strongest crankshaft possible before custom billet or forged.

but will it get me my 700 at the wheels? Get me into the mid 10's? Will it do it more than a handful of times?

Thoughts? Comments?
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Old 04-24-2016, 11:13 PM   #2
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

Someone with way more smarts than me can chime in here but I went out and looked at my crank. It doesn't look like either of these in that it does not have the little nubbin on the front throw. Other than that mine "looks" much more like the marine crank. Primarily because the OD of the weights is machined. My is that your "stock" crank is cast and the marine is forged based on the parting marks. What I can do tomorrow is look at my spare crank which I know came out of an unmolested Sy.

I believe more than one crank went into these motors. I suspect Dave, among others, has that exact info.
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Old 04-25-2016, 09:08 AM   #3
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

OK with me. I was going by the shape of the lines. What about the different weights and machining? I'll dig out my other crank later this AM. Probably take a pc if it's different than the ones shown. And why doesn't my crank have a nubbin on the front of the first journal? All very interesting.
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Old 04-25-2016, 11:13 AM   #4
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

Thanks Dave. You had mentioned the two different crank sources before and that the rods had to "match" or at least should I guess. I really didn't see a casting number on mine (can't imagine it's not there) but will look again when I dig out my other.
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Old 04-25-2016, 11:14 AM   #5
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

I'm 99% sure that the 'stock' crankshaft is out of the same motor that I have on the stand right now which came from a typhoon. I might be able to score an L35 crank in the coming weeks for next to nothing and can add it to the comparison. The marine crank is definitely a marine engine crank based on the part numbers. Speaking of which, sorry I didn't include those in the first post. I've added them below. Oh, and Dave is right, these are both cast cranks. The marine one is just more machined so a lot of the pinch has been ground away.

Stock crankshaft. Part number: 10055480




Marine crankshaft. Part number: 8640

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Old 04-25-2016, 11:26 AM   #6
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

Oh, and if y'all are curious, they both weigh 41lbs. I thought the marine would be heavier.
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Old 04-25-2016, 11:29 AM   #7
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

i got the marine crankshaft because my understanding was that it would be a little tougher than what came out of the old motor. And considering it seems to be an OEM marine crank from the early 90's its not a cheap Chinese knock off. Or that's what I'm hoping. It looks and feels like it was made better. The stock crank looks like it was done quick as possible while the marine one looks like the made the mold better and used a better mixture of metal. Hence the smoother machined faces vs the stock one.
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Old 04-25-2016, 11:53 AM   #8
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

Quote:
Originally Posted by DaveP View Post
Now everybody's gonna be searching C/L for old Bayliners to harvest the cranks out of.



Gonna be funnier when I get my hands on a crank out of an L35 motor and it looks like the marine one. Even I'm going to chuckle at that if it happens.


I still find it interesting how the marine crank is molded so much better. and machined a lot to fit the engine. if they are both indeed cast iron crank shaft (vs the marine being cast steel) than logic would say the stock one is actually stronger. If they weigh the same now but there is less surface to the stock, then its denser. Less surface area, same weight. Means higher mass. Normally that mean's heavier material, or stronger material. Or am I thinking backwards?
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Old 04-25-2016, 12:03 PM   #9
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

Quote:
Originally Posted by DaveP View Post
Is the entire 8 digit number on it somewhere else? I'd like to research it. 8640 is not the Tonawanda crank. But I'm still skeptical that 8640 is a "marine only" part. There should be a date code on it somewhere too. Similar to the pad next to the casting number in the pic. I'm not sure what the pad is in the pic. Perhaps the core-mold number, or shift info. Not sure.
Sadly, all I got was the crankshaft. No idea what happened to the block and doubt the boat store has any record as to which block this came out of when they were breaking everything down for sale.

Those were, oddly, the only numbers on the crankshaft. Where there are markings on the stock crankshaft else where the marine one is blank, or has an orange dot.

Shop claims its from an 1987-1992 4.3 motor. I have no way of knowing if thats true or not.
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Old 04-25-2016, 12:35 PM   #10
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

Well....it's no longer a secret laboratory now is it? Silly rabbit...
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Old 04-25-2016, 01:17 PM   #11
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

Here ya go:

http://www.ebay.com/itm/MerCruiser-C...dWKqSb&vxp=mtr

14088840
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Old 04-25-2016, 01:28 PM   #12
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

That looks like mine but different. Also... the way the cast numbers are placed and done... looks more like the stock crank. for starters, that ebay one is missing the prominent "GM 1" mark that is on the last counter weight. They might be the same marine engine cranks, but that one looks more like an aftermarket one vs an OEM GM one like I have.
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Old 04-25-2016, 02:22 PM   #13
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Quote:
Originally Posted by DaveP View Post

Is the entire 8 digit number on it somewhere else? I'd like to research it. 8640 is not the Tonawanda crank. But I'm still skeptical that 8640 is a "marine only" part. There should be a date code on it somewhere too. Similar to the pad next to the casting number in the pic. I'm not sure what the pad is in the pic. Perhaps the core-mold number, or shift info. Not sure.
Try 14088640
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Old 04-25-2016, 03:48 PM   #14
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

Just FYI

Double checked my crank in the engine and the only number I could find was 0821 ??

Dug out my spare and it's just like the one on the left in the first set of pictures except that it has a lightening hole drilled into the last throw. Presumably this is why those protrusions are there so the factory has a place to drill if they need to? Same part number: 10055480.
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Old 04-26-2016, 10:33 AM   #15
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Re: stock 4.3 crankshaft vs marine 4.3 crankshaft

Marine stuff is generally always better and stronger. I have been around MANY performance offshore boat engines including turbines and they build them for very hard and harsh conditions. When I built the motor that's in my truck now I replaced mine with a Mercruiser 4.3 crank. I will see if I wrote any more details down in my notes.
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