Broken 3.2 crank need some advice
 

I'm getting ready to rebuild my 84 3.2 again. It has about 10,000 miles since the last rebuild. First I'm looking for a good used crank if anyone has one. I was going to remove the heads with the cam housing together, what is the procedure? Since the miles are low I was just going to replace the bearings and put it back together does this sound ok.

Thanks

Tim

Depends on what caused your failure. If you have shrapnel everywhere you might have bigger problems elsewhere.

Tell us more about how/why the crank broke, and whether this is the only problem you know of.

Oh, and hi, Tim. Thanks for selling me that bar. :D I'm sorry to hear about your engine woes.:(

What happened after 10k miles to necessitate another rebuild? A broken crank sounds a little severe. Are you sure all it needs is new bearings?

Oh yeah, EBS has the 3.2 cranks :).

Good luck!

I rebuilt the motor because of a spun #6 bearing. I had the crank ground and hard chromed back to standard on that one journal. There was no metal in the case or in the filter. I heard it go and shut the motor down, although I didn’t know what the problem was at the time. I’m talking best case if everything checks out.

Thanks

Tim

I would love to see a picture. How about a description of the break?

3.2 crank woes, not too uncommon
 

Hi, sorry to here about your bearing failure. It is hard to say what failed but it's a pretty good guess that if all was well during the assembly process that your problem is/was contamination. It is critical that all parts / specs are checked completely after major crank repair and you are now learning why a std/std 3.2 crank is so valuable. We do a conversion on these cranks that can sometimes bring them back to life but in general it's best to seek out the std/std replacement.

I finally had time to tear the motor down last night. I don’t think JB weld is going to work.http://forums.pelicanparts.com/uploa...1087391713.jpg

Magnaflux, Magnaflux Magnaflux
 

Magnaflux
If this crank was installed 10k miles ago, there is little or no chance this crank was not cracked before installation. I have seen more and more cracked 3.2/3.3 cranks lately. Cracked cranks in the smaller sizes is almost unheard of. Don't get me wrong you must always magnaflux for cracks, but early cranks rarely crack.
Now why are 3.2 and 3.3 cranks cracking. Remembering that I am not an engineer, I would say that twisting loads created by horrible rod angularity is the culprit. We are also seeing cracks in cranks that have spun bearings. Often when a rod bearing losses lubrication you see great amounts of heat. this heat warps the crank. Crank shops repair the crank and during the repair process they have to straighten them. This is an interesting process. The crank grinder will locate the crank in centers and measure for the high spot, then with all the technology available to engine builders today, he takes a big hammer and a V shaped chisel and then just beat the hell out of it. The hope is the crank gets straight and does not crack. If this crank was repair because of a spun bearing, it is likely that it was pounded straight.

Tim,
Now *that* is some real fine destruction!
If I was handing out prizes for the best images of the Mechanical
Mayhem Files, this would surely be a winner.
Thanks for sharing!

Before the repair I had it magnafluxed and checked for straightness. The shop that repaired it also magnafluxed it. The crank was ground then hard chromed and ground to standard. Something in this process compromised the integrity of the crank, I think.?

Tim

Ive got no experience building engines and even less of a clue what happened to the crank, but doesn't hard chrome cause hydrogen-embrittlement in steel?

It is quite possible that in the process of grinding for hard chroming the operator removed some of the radius in the Rod Journal, hence the stress raiser forming and beach type apperance from the crank pin out.

Most likely the crank grinder missed the crack. Think horses not zebras.
People are human and mistakes happen. We could go on ad nauseam trying to analyze this failure but a damaged crank got repaired and failed shortly there after. Most likely the crank grinder missed the crack.

For those of us who insist on overanalyzing everything there's a 12 step group for you. OAA :)

PS: we have cranks

It was a response to

"Something in this process compromised the integrity of the crank"

I've heard of people checking cranks by "ringing" them. Does this test work or is it just a quick test to tell if a crank is bad (but not if it is necessarily good)?
-Chris

This question shows good insight. You answered your own question.
Ringing a crank is a good way to tell if it's bad but it doesn't tell you that it's good.

To paraphrase my favorite lawyer:
"If it doesn't ring, don't use the thing."

Re: Magnetic particle examination – crankshafts

Although common to the automotive engine rebuilding industry, the commercial engine (truck & marine diesel) rebuilding community has for many years employed a different technique to check for cracks in crankshafts and other rotating components. The most widely used process is fluorescent dye penetrant testing. The reasons for this are as follows:

1). Dye penetrant does not require that a magnetic field be introduced into the part. Do you want your crankshaft acting like a magnetic drain plug?

2). We are talking “in service cracks” and as such, are ALWAYS open to the surface. Some proponents of “Magnaflux” will tell you that dye penetrant will not locate sub-surface discontinuities. My answer to that line is that a sub-surface flaw is not likely to cause a failure. I’m sure the good Dr. Porsche & Co. subjected the cranks to non-destructive testing at many stages of the manufacturing process. Gross sub-surface flaws would have been weeded out during that process. Porsche may have employed magnetic particle examination on the final product, but also, would have subjected the crank to a proper degaussing. I suspect that most machine shops do not have the proper equipment, nor do they have the expertise to properly degauss a crank. “Pass it through the coil and call it a done deal”. Going back to surface and sub-surface; as cracks are surface breaking they will respond nicely to dye penetrant. Pay particular attention to the radius on either side of the journal, and the oil passages. I prefer the fluorescent type, but a non-fluorescent type will work just fine. One word of caution; dye penetrant will not tolerate dirt, grease or other contaminates. The part needs to be clean. Magnaflux Corp. makes a handy kit that is available from most commercial supply houses.

Right - the Engine Rebuild Book goes over the Magnaflux process, which should be performed on every crankshaft in any engine, prior to rebuilding...

-Wayne

Re: Magnaflux, Magnaflux Magnaflux
 

Every machine shop that grinds and straightens cranks that I know of uses a crank bending press.

If your crank grinder uses a chisel I suggest finding another machine shop.