Methods of repairing crankshaft journals - pros/cons

[stownsen914]

To repair a crankshaft journal back to standard, I've heard of: 1. welding and grinding, and 2. hard chrome plating. I checked around, and there are vendors who handle each of these processes, and cost is similar (something like $600 to repair one journal, or about double that to do all the rod journals.

A couple thoughts on pros/cons:
- Welding obviously involves a lot of heat. I would imagine post treatment could address hardness. Any reason to be concerned about stresses being introduced into the crank during welding?
- I recently heard that plating can cause hydrogen embrittlement. This would be bad, since it leads to cracking. Not exactly what you want in your crankshaft! Does chrome plating cause hydrogen embrittlement? EDIT - it looks like at least some people on the internet believe that chrome plating does cause hydrogen embrittlement, and that it can be mitigated by baking at 200 degrees C for a few hours after the plating is done IF done within a few hours of the plating.

On a related topic, I recently heard about a process called metallizing, which could be another option. Anyone have any experience with it in repairing a crankshaft?

Thanks for any input.

Scott

[chris_seven]

There is so much BS written on this subject it is unbelievable.

There is no doubt that Nickel and Chrome plating does cause hydrogen embrittlement, I am sad to say that it is not a matter of belief it really does happen. The best method to eliminate the effects of hydrogen are shown in UK Defence Standard DEF STAN 03-4/2' and I imagine that there is an ASM Equivalent. I would suggest that you basically need to heat treat at around 200 degC for at least 3 hours and carry out this process within 24 hours of plating.


Also another simple fact is that the deposits produced by electroplating are also highly stressed and generally cracked. it is sometimes said that Hard Chrome is quite tough and compared to decorative chrome this is true but the layer is still in terms of fatigue resistance quite poor. A typical reduction of fatigue threshold stress would be around 50% which is fairly catastrophic when you apply this process to a component that has not been 'stressed' to deal with this issue.

Following grinding of hard chrome it is generally necessary to stress relieve to prevent cracks from propagating too quickly. This will involve heating again to 200 degC for another hour. I would then inspect the crank with magnetic particle tests and assuming all was well de-magnetise.

The stresses produced in Hard Chrome are typically tensile in nature they will always have a negative effect on fatigue life.


It is probably OK on large capacity very slow running diesel cranks which can be locally brush plated but I don't think that a high performance crank is a suitable candidate.

Many Companies also submerged arc weld cranks, again commonly applied to low speed diesel and large capacity slow engines.

IMHO the chances of introducing defects during welding is much too high to take the chance on something like a 911 crank.

You will of course produce distortion during welding and there will be residual stresses produced.

You an reduce these stresses by some basic heat treatment but without significant testing it will be difficult to be 100% confident although it is easy to say that all will be well. The inspection needed to guarantee integrity is far too demanding. There will be little or no scope to determine optimum welding parameters and no back up with any mechanical or fatigue tests to prove that the parameters used are correct.

It will also generally mean that the crank will be unlikely to respond correctly to a Tenifer treatment as applied to a standard crank and this will also mean that a reduction if fatigue life is probable.

I have to say that the number of potential problems that can occur during either of these complex process persuades me that the risk/reward benefits are not convincing.

[stownsen914]

Thanks Chris for the detailed response.

Anyone else have thoughts on this? I'm guessing some folks out there have used welding or hard chroming to bring a crank back to standard (or to offset grind for different stroke). What method did you use, and how has it worked out?

[KTL]

Scott,

Maybe give Ollie's a call and they can provide some details on how they approach the welding process? It's one of their service items listed, so they probably have done this quite a few times.

http://www.olliesmachine.com/uploads/Ollies_Price_List_0814.pdf

[Henry Schmidt]

Grind the crank undersized and have it nitrided. If you have to go more than .010" scrap the crank. My thoughts anyway.
Depending on the crank, we have undersized bearings available.

[chris_seven]

Originally Posted by Henry Schmidt

Grind the crank undersized and have it nitrided. If you have to go more than .010" scrap the crank. My thoughts anyway.
Depending on the crank, we have undersized bearings available.

I generally agree but gas nitriding could be a potential problem as the steel grade is wrong.

Plasma Nitriding or Melonite (same as Tenifer) would be OK.

[Henry Schmidt]

All of our cranks are Plasma Nitrided.
Plugs removed, cross drilled, balanced and plasma nitirded.
For racing we often trim flyweights as well.

[LM3929]

what would a ball park price to have one rod repaired?

Lorne M.

[Lapkritis]

Originally Posted by chris_seven

There is so much BS written on this subject it is unbelievable.

There is no doubt that Nickel and Chrome plating does cause hydrogen embrittlement, I am sad to say that it is not a matter of belief it really does happen. The best method to eliminate the effects of hydrogen are shown in UK Defence Standard DEF STAN 03-4/2' and I imagine that there is an ASM Equivalent. I would suggest that you basically need to heat treat at around 200 degC for at least 3 hours and carry out this process within 24 hours of plating.


Also another simple fact is that the deposits produced by electroplating are also highly stressed and generally cracked. it is sometimes said that Hard Chrome is quite tough and compared to decorative chrome this is true but the layer is still in terms of fatigue resistance quite poor. A typical reduction of fatigue threshold stress would be around 50% which is fairly catastrophic when you apply this process to a component that has not been 'stressed' to deal with this issue.

Following grinding of hard chrome it is generally necessary to stress relieve to prevent cracks from propagating too quickly. This will involve heating again to 200 degC for another hour. I would then inspect the crank with magnetic particle tests and assuming all was well de-magnetise.

The stresses produced in Hard Chrome are typically tensile in nature they will always have a negative effect on fatigue life.


It is probably OK on large capacity very slow running diesel cranks which can be locally brush plated but I don't think that a high performance crank is a suitable candidate.

Many Companies also submerged arc weld cranks, again commonly applied to low speed diesel and large capacity slow engines.

IMHO the chances of introducing defects during welding is much too high to take the chance on something like a 911 crank.

You will of course produce distortion during welding and there will be residual stresses produced.

You an reduce these stresses by some basic heat treatment but without significant testing it will be difficult to be 100% confident although it is easy to say that all will be well. The inspection needed to guarantee integrity is far too demanding. There will be little or no scope to determine optimum welding parameters and no back up with any mechanical or fatigue tests to prove that the parameters used are correct.

It will also generally mean that the crank will be unlikely to respond correctly to a Tenifer treatment as applied to a standard crank and this will also mean that a reduction if fatigue life is probable.

I have to say that the number of potential problems that can occur during either of these complex process persuades me that the risk/reward benefits are not convincing.

Great info Chris, thanks for sharing.

What are your thoughts on grinding a crank that has been damaged due to a spun bearing?

This is assuming bearings are available to support the grind. Will residual stresses from the bearing failure be problematic? Quite often when inspecting a crank with a spun bearing, bluing of metal on the crank is observed local to the failure. Sometimes the marking/heating stain is visible 1cm+ from the journal. I always scrapped such cranks on more common engines.

[chris_seven]

I don't think that the small amount of localised heat from a spun bearing would cause me too many sleepless nights.

The temperatures needed to produce a 'blue' colour would only be around 550 to 600degF and these colours would be produced by a very low heat input which would most likely be limited to a depth of a few thou as the heat build up would be very rapid.

Contrast this to welding - melting point of steel 2700 degF typically and a huge thermal input which will result in large temperature gradients and significant shrinkage.

I am sure you would agree that the differences are vast.

[stownsen914]

Originally Posted by LM3929

what would a ball park price to have one rod repaired?

Lorne M.

I called Marine Crank and a hard chroming vendor (forgot the name at the moment), and both quoted about $600 to repair one journal. This includes polishing the entire crank and then pulling the plugs and thoroughly cleaning. I believe Marine quoted for welding and grinding back to standard. Each additional journal for both vendors was $100 additional, presumably because overhead is similar.

To the point about contacting Ollie's, I'm looking for people's experience with this kind of work in their engines and the durability. There are definitely vendors who will take my money and do the work!

Thanks again everyone for the input!

Scott

[Henry Schmidt]

What crank are we talking about?

[KTL]

How is Marine's feedback different from Ollie's? Yeah Marine does all sorts of cranks and Ollie's does only Porsche air cooled. Does that mean Ollie's is biased and Marine is not?

I have no affiliation with either and have my one good experience with Marine on my 3.0 SC crank refurb. & modification (cross drill & lighten counterweights).

[LM3929]

The crank I was looking at getting repaired was 78/79 3.0

Lorne M.

[tom1394racing]

I was under the impression from talking with several Porsche engine builders, that both Armando at CCR and Marine Crank have good history repairing rod journals by weld and regrind. I have used Armando for weld and regrind repair on the IMS drive gear journal on a couple of cranks and have had no issues.

Comments?

[chris_seven]

Whenever you weld a component such as a crank you always run the risk of introducing defects.

The more arduous the duty the more the chance of any defects creating a brittle instability and subsequent failure.

Metal Fatigue can be quite difficult to predict at the best of times and in order to make a start the stress/strain conditions of the part need to be very carefully determined.

The next question is what is the probability of introducing a defect during welding and then what is the probability of this defect being in a region of maximum stress.

Inspection plans that ensure freedom from defects are also part of the mix.

I would have the avoidance of welding as very high on my list of 'Golden Rules for the Avoidance of Fatigue' but this statement does need some qualification.

On any critical component made from a medium carbon steel with a Carbon Equivalent pf greater than 0.4 some pre or post weld heat treatment is quite important and it is quite easy to define a suitable treatment.

It is also possible to make welded structures that are relatively fatigue resistant but it isn't easy.

To be 100% confident would need a substantial body of work to determine the correct welding conditions and give some from of liability cover.
I spent the early part of my metallurgical career working in a Power Gen company on welded structures and their long term integrity and this possibly accounts for my cautious approach.

If you just weld a damaged part it may work but it may fail - its really just a simple risk/reward analysis.

The value of the rest of the engine is also part of the judgement particularity for a high performance application.

How much is a good used crank in relationship to the repair?

[AlfonsoR]

Another opinion,

Probably the most accepted form of repairing cranks is to undersize the journals. Only problem with that is that bearings might take some additional time to get, i.e. probably not stocked. Otherwise, when the right surface prep is done, it's just as good as new.

Chris already mentioned some of the risks with either metalizing/ plating and welding. One thing I would like to add is that I would be concerned with the correct surface finish being achieved on the journals. Hard materials like chrome might be more difficult to polish to the correct and consistent surface finish.

[wdfifteen]

I just looked at the price of a new crank. $7760

No wonder you are looking for an alternative to new.

[stownsen914]

Originally Posted by Henry Schmidt

What crank are we talking about?

Henry,

Not sure if you were asking me or the other gentleman who posted on this thread, but my crank is a counterweighted 2.0L S crank. Thank you in advance for any input you can give on this.

Scott

[Henry Schmidt]

Originally Posted by stownsen914

Henry,

Not sure if you were asking me or the other gentleman who posted on this thread, but my crank is a counterweighted 2.0L S crank. Thank you in advance for any input you can give on this.

Scott

I have a huge selection of under-sizes main and rod bearings in stock.
I also have good used sts/std cranks in stock.

Another pretty cool option for the 2.0/2.2 crank is to grind it under-sized for a different rod. GT3 rod configuration (3.0 journal) or two inch Chevy.