Cranks part 2

[bio-diesel]

First let me answer your rhetorical question. The reason that every

[CleviteKid]

Hey Bio-Diesel,

We are agreeing more than disagreeing. However, strong does not necessarily mean brittle. A nitrided layer on a crankshaft, properly applied and controlled, raises the strength, and the hardness, considerably, but does not embrittle the crank.

Done WRONG, it can leave a brittle "white layer" on the surface that can crack and flake off. This does not necessarily lead to crankshaft fracture, but the hard little flakes can tear up the bearings in an instant. The U.S. Navy had this problem on diesel engines in minesweepers about 5 or 6 years ago.

Dr. Lee :cool:

[CleviteKid]

And furthermore:

The harder the crank, the BETTER it is for the bearings. A soft crankshaft journal is more likely to have sand, piston ring wear debris, camshaft wear debris, etc. embed in the crankshaft and wear out the bearings. When the trimetal electroplated overlay bearing was developed as a result of WWII, engine builders soon discovered that to take advantage of the stronger, harder bearings, they had to increase the hardness of the crankshafts, but more to benefit the bearings than the crank.

As engine loads and crankshaft stresses increased, the benefits of increased fatigue resistance from nitriding, etc. became evident.

Dr. Lee :cool:

[tom.mcinerney]

Is the doctor in??
There is a crankshaft-grinding business establishment in my vicinity. They have machinery which combines a wire-feed welder and a lathe, used to resurface cranks, by 'building up' the journals with welded deposits, followed by regrinding.
Are there any general rules regarding when/what- composition cranks might be successfully remanufactured by such means??
Am i correct in thinking that good cranks are made of forged steel; 6.2/6.5 are cast(nodular) iron; some are cast steel??
For example, welding nodular iron would probably be disastrous, leaving very hard sections in quenched areas, from high carbon? Would use of a stainless wire help significantly?
From above comments, a hard surface itself isn't detrimental, but i suppose the transition beneath it would be critical...

[CleviteKid]

Hi Tom,

The old-timers out there will remember when stroker cranks were made by welding additional steel onto the crankpins of a gasoline V-8, and then regrinding to size, but with a longer stroke. The shop in your area is doing something along those lines, but with higher productivity, and for restoration of a good journal on a damaged crank, at original stroke.

All of our cranks, at least those that came from GM for 6.2 and 6.5L engines, are nodular cast iron - and you are correct - welding on these could be disasterous. Stainless steel wire works for general welding of nodular iron, only because the stainless is so weak and ductile that is does not crack when the underlying non-stainless undergoes the austenite to pearlite + ferrite transformation.

The MCM (mine counter measures) AVENGER CLASS (http://www.chinfo.navy.mil/navpalib/factfile/ships/ship-mcm.html) and MHC (mine hunter coastal) OSPREY CLASS (http://www.chinfo.navy.mil/navpalib/factfile/ships/ship-mhc.html) ships of the US Navy have diesel engines with very low magnetic signature. The engine blocks and cylinder heads are made of cast stainless (non magnetic) steel, for example. But the crankshafts are made of alloy steel, nitrided for fatigue and wear resistance, and "de-permed" to reduce the magnetic signature as much as possible. If it were feasible to use stainless steel for crankshafts, they would be in this application, where it could keep you and your shipmates from making the ultimate sacrifice.

By the way, thanx to all the US Taxpayers on this forum for helping send me to Northern Italy for a week, where the non-magnetic engines are made by Isotta Fraschini for the US Minesweepers. I was part of a select panel assembled by the Navy to investigate teething problems with the First Article Test Engines as they were being developed.

Also note that the AVENGER CLASS (http://www.chinfo.navy.mil/navpalib/factfile/ships/ship-mcm.html) ships have Wooden Hulls - so with a copy of this web page you can win some bar bets on the fact that our US Navy has over a dozen wooden ships on active combat status.

Ciao, Dr. Lee :cool: :cool: :cool:

[Uncle Wally]

Dr. Lee,

I've even seen a few of those 'wooden' ships. The CO is usually a LT. Crew of 5 enlisted. Kinda neat.

But - back to the subject. It is my understanding that there is a form of welding that is done submersed in a type of fluid (I am not sure as to the composition of this fluid). The welding has been said to be useful for doing just as you speak above, stroking a crank. Would this type of welding be in a controlled enough environment to be suitable for other that forged steel crankshafts? I'm not sure of all the specifics, but I did read something about it within the last year or so. IIRC, it was boasting the ability to be impurity free. There's probably a lot more to it than just that, but I was wondering.

Waldo

[CleviteKid]

What you read about was "submerged arc" welding. But what it is submerged in is molten flux. The flux is applied along with the welding wire as a powder, and the heat of welding melts the flux around the wire and seals off the atmosphere. The molten flux floats on top of the weld pool and does not contaminate it. Most of the flux does NOT melt, and is vacuumed up and recycled. Submarine hulls are assembled with submerged arc welding, for example. Don't want those welds to fail at the wrong time, or anytime for that matter.

This would still be tricky to apply to a nodular iron crank. And with our engines, we would need new custom rods and pistons to keep the pistons from geting friendly with the cylinder head.

Check out the links in the prior post. I am not referring to the old plywood PT boats. The crew complement on the 224-foot, 1300+ ton MCM is more like 8 officers and 76 enlisted sailors.
http://www.navy.mil/navpalib/ships/mine/dextrous/dextrous.gif

Dr. Lee :cool: