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Crankshaft Construction


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#1 JacnGille

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Posted 20 March 2024 - 21:34

Something that popped into my little pea-brain the other day. Would the folding and forging like Japanese swords and knives make crankshafts more durable?



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#2 Bob Riebe

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Posted 20 March 2024 - 23:49

Not likely due to metal separtion.



#3 Magoo

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Posted 21 March 2024 - 11:22

Well, a crankshaft forging is "folded" a number of times, in a manner of speaking, to achieve the grain structure desired. 

 

I am absolutely no authority on swordmaking, needless to say, but I believe all that folding was to drive the impurities out of the metal (relatively basic smelting process) and to distribute the carbon regions so the cutting edge is hard while the shank is tough. 

 

 



#4 JacnGille

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Posted 21 March 2024 - 15:54

Thanks!



#5 Bob Riebe

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Posted 21 March 2024 - 18:53

They combine High Carbon and Low Carbon steel in the sword steel making processk, low Carbon steel would not really make a crank shaft better.



#6 Greg Locock

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Posted 21 March 2024 - 21:09

The horrible old LandRover I6 engine used the same block for both gasoline and diesel versions, but the diesel got a forged crank, and the gas engine got a cast crank. 



#7 Magoo

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Posted 21 March 2024 - 21:29

Detroit loves cast crankshafts. After running hideously high scrap rates trying to forge two-plane cranks for the 1932 Ford V8 (double strike), Charles Sorensen figured out how to cast them, and they work fine within limits. They called him Cast Iron Charlie. 

 

GM's name for its pearlitic malleable cast iron for crankshafts and connecting rods was Armasteel. Reportedly, it was developed during WWII for machine gun receivers to save time and $$$ on machining. 



#8 desmo

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Posted 22 March 2024 - 14:02

Anything that creates discontinuities in the structural properties of a metal piece potentially stop crack propogation. Bi-phase alloys are a good example.



#9 Lee Nicolle

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Posted 09 April 2024 - 12:45

Having been watching videos about the OHC GAA Ford engine for tanks they used cast cranks. And they lived pushing Sherman tanks around.

As did the original V12 aircraft engine.

We are lead to believe forged cranks are stronger,, but a cast crank does a very good job.

I used one for quite a while in my Sports Sedan with no issues. 12-1 Chev running [normally] to 7200. 

Then bought a engine 4 bolt and steel crank [truck engine] that after 2200 racing km was full of cracks. 

A bloke I know sponsored by a importer his spare Sprintcar engine was both 2 bolt [using studs] and cast crank. And it lived at 7500 plus. He always said it was very good, as good as the 'good' engine for power but he did baby it a bit. This in the late 80s. And yes it did win at a local level at least.



#10 Canuck

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Posted 16 April 2024 - 02:27

How the Katana is (still) made.https://www.youtube....h?v=Tt6WQYtefXA

 

(I can not for the life of me figure out how to embed a YT video consistently)

 

 



#11 GregThomas

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Posted 17 April 2024 - 07:52

I was idly looking at some video of the current pro stock drag bikes. The Suzuki is based on the Hyabusa - a 16V IL4 - which is a pretty stout engine.

It has a forged plain bearing crank and in that form is robust enough to happily accept turbocharging to quite high pressures.

It's also used in that form in a number of car applications.  With an enviable reliability record.

I've built a couple for roadrace sidecar use and have been happy with the results.

 

But much to my surprise the drag guys are building roller cranks for their application.

To my mind this makes little sense. It's effectively turning the Hyabusa into a water cooled copy of the old GS1100 aircooled from the 80's

The RPM being used would make big end life difficult too. Visually, It looks like a heavier crank too - with full circle wheels.

 

Any comments from better qualified people ?



#12 djr900

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Posted 17 April 2024 - 08:37

I vaguely remember watching a documentary where an engine type that had been used in WW2 , in aircraft & boats with a cast crank, was fitted to some tanks and suffered some broken crankshafts when used in the tanks , but not in aircraft & boats.

It was believed that dropping the clutch suddenly in a tank ( as can be required on a battlefield) was the problem that caused them to break, and of course this didn't happen on a boat or aircraft with no clutch.
( I can't remember if the tank engine crankshaft was changed later ?)

#13 desmo

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Posted 21 April 2024 - 14:56

How the Katana is (still) made.https://www.youtube....h?v=Tt6WQYtefXA

 

(I can not for the life of me figure out how to embed a YT video consistently)

You have to copy the actual URL of the video rather than the "link URL" that YT copies to your clipboard. Why are they different? Money, somehow.



#14 Lee Nicolle

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Posted 06 May 2024 - 12:23

Recently watching a video about making forged items in Pakistan. It got machine hammered and squashed smaller so I presume denser. But the material was scrap metal,, old engine blocks, brake drums, tin cans, old pieces of rusty ship. Sheet metal offcuts, etc etc.Lovely material for forging,things like trick stub axles for carrying double the manufacturers load!

Their cast alloy is no better, again cans, blocks, heads any scrap alloy the can find and melt it all together



#15 Greg Locock

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Posted 06 May 2024 - 22:30

Contamination of steel is a big deal, there is a tiny bit of truth in the claim that steel was better in the old days. It would be more accurate to say that in the old days the stuff you made from rocks and coal was better than the generic stuff you get from recycled steel, on the other hand what we get now is more consistent and better characterised.



#16 mariner

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Posted 07 May 2024 - 08:51

Great subject, here is another forged crank process YT vid. 

Big cranks, not a home lathe job.

 

 

I wonder if the move to five bearing cranks for four cylinders ( seven for sixes ) helped the swich to cast cranks as the bending moments were sort of cut in half. 

 

Also Uk Ford cast cranks at least were hollow so lighter but no great loss of bending strength



#17 Magoo

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Posted 08 May 2024 - 21:55

Winona Van Norman marketed a portable crankshaft grinder that could grind rod journals with the crankshaft and engine still in the vehicle. The kit included a set of rollers and an electric motor to rotate the rear wheels and thus the crankshaft at around 12 rpm so the grinding head, also powered by an electric motor, could resurface the journal in a centerless-grinder sort of way. 

 

They were sold under both the Winona and Van Norman brands. I've seen a number of them tucked away in the back of toolrooms but only saw them used once or twice. 

 

 

 

https://www.oldclass...k/intheblok.htm



#18 Lee Nicolle

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Posted 17 May 2024 - 08:01

Great subject, here is another forged crank process YT vid. 

Big cranks, not a home lathe job.

 

 

I wonder if the move to five bearing cranks for four cylinders ( seven for sixes ) helped the swich to cast cranks as the bending moments were sort of cut in half. 

 

Also Uk Ford cast cranks at least were hollow so lighter but no great loss of bending strength

Actually cast cranks handle flex better than steel but are weaker torsionally.

Small journal Chevs, pre 68 or so defenitly flexed. The 3 centre mains required about 4 thou clearance with oils of the day to allow for flex.

3 main 4 and 4 main 6s were at best dumb yet both Ford and Chrysler persisted with them early 60s. 144-170 Falcons were 4 main as were slant 6s until their demise. I have seen plenty of broken slant 6 cranks, both steel [for trucks] and cast break. Like many engines they break between 5 and 6000 rpm

Since I have never been around racing 144s I dont know much. I do know they break though at high rpm.

Things like 3 main MGB engines break cranks as well. English Fords as well. I have never seen a hollow pin Ford crank. 

The only factory hollow pins I have seen was first generation Camrys, And they do break. Once bought one that would not go. .

The Forged True Chev crank I bought was hollow pin and weighed near 10lbs lighter than a Chevy steel crank.