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Does re-plating a part make it weaker?

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ballooney

I live for the CABE
Tonight I snapped my crank in half while riding. Stood up to pedal from a dead stop and half way through the intersection my legs dropped out from under me. The crank was a genuine Schwinn prewar crank that had been restored (replated) 30 years ago or so. Snapping a crank in half doesn’t seem like an easy thing to do so wondered if the process of replating weakened the crank?

What are your thoughts? Anyone else have this happen to them?

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I think the term used is hydrogen embrittlement. Some automotive racing associations will not allow chrome plating on critical suspension parts. So, the short answer to your question is yes it can cause hardening to metals. I believe there is a heat treat process to relieve the stress caused during the chrome process so if your interested contact a good chrome shop (if you could still find one open) and ask for their advice.

The long answer is, look at how many millions of steel forged cranks have been chrome plated during the past 100 years. Very few break. That failure would have been covered by your Schwinn Life Time Guaranty, if Schwinn was still in business you would have a free replacement at any dealership. Hope you did not get hurt, just replace the crank, hopefully you can find a replacement that has good enough chrome to use it without replating.

If you do have to have a replacement crank replated, ask them to tape the external BB threads before plating. The pedal threads will not build up with chrome because they are internal threads.

Sorry for the problem.
John
 
I think the term used is hydrogen embrittlement. Some automotive racing associations will not allow chrome plating on critical suspension parts. So, the short answer to your question is yes it can cause hardening to metals. I believe there is a heat treat process to relieve the stress caused during the chrome process so if your interested contact a good chrome shop (if you could still find one open) and ask for their advice.

The long answer is, look at how many millions of steel forged cranks have been chrome plated during the past 100 years. Very few break. That failure would have been covered by your Schwinn Life Time Guaranty, if Schwinn was still in business you would have a free replacement at any dealership. Hope you did not get hurt, just replace the crank, hopefully you can find a replacement that has good enough chrome to use it without replating.

If you do have to have a replacement crank replated, ask them to tape the external BB threads before plating. The pedal threads will not build up with chrome because they are internal threads.

Sorry for the problem.
John
Thanks for the info John. I agree, millions of chrome plated cranks and rare to snap them. I believe you answered my question in that the chrome plating process can harden the metal and since my crank went through the process twice it would be more prone to breaking.

I should have bought a lotto ticket last night since I hit on a low probability outcome already!! Ha ha.
 
what does the break look like? does it look like it just snapped all at once or maybe cracked years ago and finally broke
Agreed, it would be nice to see the clean end view of both broken ends. My bet is it cracked part way over time, and then finely broke all at once.

My son and I drag raced aircooled VW's for 19 years. We took the engine apart at least every year and had the crank magnafluxed to check for cracks. The new SCAT 86mm flanged cranks were $1500 but if you caught a crack before it let go you could save the rest of the motor. The long stroke crank was weak in the middle due to the overlap of the long throws. The VW cranks do not like 8000 RPM.

John
 
The last crank I busted tried to take a chunk of my leg with it. Be glad it wasn't a 3 piece spindle. That kind of steel breaks off in shards. I'd be curious to see the ends too.
First thought is factory defect. Second thought is, have you ever seen crank bearings ran so loose that it wore a groove in the spindle from rubbing chain stay protrusions inside the crank hanger? Maybe that happened, then it was replated, covering up the groove and creating an even worse stress point. Not too many frames have those protrusions into the crank hanger, the one I remember must have been a late 60s Rollfast. This crank looks like it broke just barely past the threads...?
 
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