Author Topic: Anyone ever had a crank welded?  (Read 11366 times)

RJ

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Anyone ever had a crank welded?
« on: December 16, 2012, 06:34:02 PM »
Lister crank is cracked at the web. I knew this wen I purchased one as parts. Thought perhaps it could be repaired as kept as a spare. Anyone ever had crank work done?


dieselgman

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Re: Anyone ever had a crank welded?
« Reply #1 on: December 16, 2012, 09:30:37 PM »
Much cheaper and safer to replace the crankshaft if it is broken or cracked. your crankcase, on the other hand, is a hard beast to replace and if you break a crank while running... all bets are off for the bottom end.

dieselgman
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RJ

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Re: Anyone ever had a crank welded?
« Reply #2 on: December 16, 2012, 10:18:40 PM »
Much cheaper and safer to replace the crankshaft if it is broken or cracked. your crankcase, on the other hand, is a hard beast to replace and if you break a crank while running... all bets are off for the bottom end.

dieselgman

Agree, ideally I would replace it... problem is it's a needle in a haystack. Perhaps you can source a crank for lister CE?

-Randy

dieselgman

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Re: Anyone ever had a crank welded?
« Reply #3 on: December 16, 2012, 10:31:01 PM »
Ouch, on that one your best bet is to find another engine to cannibalize. What is your location??? There are a few CE twins around here and there - especially in the U.K.

dieselgman
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RJ

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Re: Anyone ever had a crank welded?
« Reply #4 on: December 16, 2012, 10:48:37 PM »
Ouch, on that one your best bet is to find another engine to cannibalize. What is your location??? There are a few CE twins around here and there - especially in the U.K.

dieselgman


It's one of those things, the engine is complete minus the crank. I'm sure not going to spend a boat load on importing another CE just for the crank. I could part it out, but I would like to bring the old girl back to life. If one of your UK contacts has one then I'm willing to look at purchasing a replacement. If I spend money having it welded, it doesn't hold I'm not really out much, since the engine is useless as it is...

-RJ

mobile_bob

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Re: Anyone ever had a crank welded?
« Reply #5 on: December 17, 2012, 12:16:26 AM »
what's the end use for the engine?

if it will only be started from time to time, mostly for show purposes, then maybe it is worth welding

if on the other hand you plan on putting the old girl back to work earning her keep, you ought to look for a replacement crank.

the trick to welding a cracked crank is getting all the crack ground out and filled back properly with weld metal, without inclusions.  not something a guy with a crackerbox stick welder in his back yard is going to be highly successful doing in my opinion.

after welding the thing will need to be straightened, and reground with particular attention paid to the fillet area's and special attention to increasing the fillet radius as much as possible where the weld was.

in any case probably a project for a professional crank repair shop.

bob g

ps. no i would not send it to that guy with the 100k hour engines for repair and regrind.
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cujet

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Re: Anyone ever had a crank welded?
« Reply #6 on: December 22, 2012, 03:09:39 AM »
I've welded cranks. But, not for crack repair, only to re-build the journal after a spun bearing. It's not hard to weld a journal up and then turn it down to the proper size. Works perfectly on forged crankshafts. No problems with strength issues either.

However, cracks are another matter. As cracks develop in stressed steel, the structure of the steel changes ahead of the crack. In other words, it's weakened. A proper repair is often impossible in forged steel, without reinforcements. That is why one cannot simply weld automotive suspension components that are prone to cracking and expect more than a month's lifespan from the repair.
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tiger

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Re: Anyone ever had a crank welded?
« Reply #7 on: December 23, 2012, 02:52:08 AM »
thermite welding?
Metro 12/2 ST 10 KW

millman56

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Re: Anyone ever had a crank welded?
« Reply #8 on: December 23, 2012, 08:42:57 AM »
Don`t think so, thermite welding is an exothermic process commonly used to join rails.  As far as I know ( C&G welding long ago ) the most popular way of rebuilding ic engine crank journals is by metal spraying, a non fusion process which keeps the surrounding metal below its critical temp ( the point at which the grain structure reforms) , also local deformation and stresses are reduced to acceptable levels by the even and relatively gentle application of heat, this means that no post heat treatment is neccessay and all the journal requires to finish is rergrinding to correct dimension.

Mark.

dieselgman

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Re: Anyone ever had a crank welded?
« Reply #9 on: December 23, 2012, 01:33:08 PM »
Yes, surface hardness is the key to longevity of your journal. I believe that the original Lister specs and technology for surface (induction hardening) is quite good and these parts (crankshafts and camshafts) tend to wear and last extremely well.
 
Alas, a breach completely through the forging - that is likely to be under great stress, no repair process known to be reliably successful.  :(

dieselgman
« Last Edit: December 23, 2012, 01:34:58 PM by dieselgman »
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sailawayrb

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Re: Anyone ever had a crank welded?
« Reply #10 on: December 23, 2012, 05:01:17 PM »
The problem with repairing a component by welding is NOT associated with the resulting material’s YIELD strength (i.e., the STATIC tensile or compressive load that can be applied before failure occurs).  A good weld will always be stronger than the original material and the repaired component will be able to handle the same static loading as previously.  

The problem with repairing a component by welding is that even a good weld still introduces a stress concentration in the component (i.e., a change in material strength within the component).  This stress concentration reduces the FATIGUE strength of the component (i.e., the CYCLIC tensile or compressive load that can be applied before failure occurs).  This means that the component will fail sooner under cyclic loading than as previously.  And for this crank shaft cyclic loading situation, failure will likely occur much sooner as this crank shaft would have been originally designed for an infinite fatigue life so as to never fail.  Designing for infinite fatigue life is possible and normally done for iron/steel/titanium components that will experience cyclic loading, but this is NOT possible for aluminum/copper components.  This is why components that will experience cyclic loading are NEVER welded, they are properly FASTENED…or should be…

Bob B.
« Last Edit: December 23, 2012, 05:28:16 PM by sailawayrb »

millman56

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Re: Anyone ever had a crank welded?
« Reply #11 on: December 23, 2012, 06:13:03 PM »
Yes I can go with all that,  having bought a large twin cyl shop compressor at a sale and thinking what a bargain, it turned over by hand and made all the right noises, when I got it back to my workshop and powered it up it did 1 revolution and stopped.    Opening the crankcase inspection door revealed a completely broken crank which had been tack welded to hold it in place, my stress concentration was off the scale, with a severely impaired ultimate tensile strength......

Mark.

BruceM

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Re: Anyone ever had a crank welded?
« Reply #12 on: December 23, 2012, 10:01:35 PM »
That's pretty low to tack weld a crank for an equipment sale. >:(

millman56

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Re: Anyone ever had a crank welded?
« Reply #13 on: December 23, 2012, 11:45:47 PM »
Its swings and roundabouts, have had plenty of machines that looked a load of crap but turned out to be great buys. :)

buickanddeere

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Re: Anyone ever had a crank welded?
« Reply #14 on: December 25, 2012, 04:37:24 PM »
  Welding the crack treats the symptom. What was the cause of the crack so the replacement or welded crank doesn't crack too.