12 replies to this topic

[JacnGille]

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?

[Bob Riebe]

Not likely due to metal separtion.

[Magoo]

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. 

 

 

[JacnGille]

Thanks!

[Bob Riebe]

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.

[Greg Locock]

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. 

[Magoo]

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. 

[desmo]

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

[Lee Nicolle]

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.

[Canuck]

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)

 

 

[GregThomas]

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 ?

[djr900]

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 ?)

[desmo]

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.