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Join Date: Jul 2021
Posts: 689
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Crank straightening
On an initial measure, my 66mm counterweighted crank has runout of circa .035mm. Dempsey says the spec limit is .04mm. Tbh I haven't actually checked the journals for out of round yet, so it may actually be less once I invest the full time to do that. But let's assume for the purposes of this post that it's .035 and I'd like to reduce it.
Does anybody have ideally experience of or failing that knowledge of, peen straightening these early 911 crankshafts? Can it work on a force-bent crank or is it only for releasing heat distortion? This crank has not spun a bearing so unlikely to have been overheated itself. More likely it was jarred by a stuck piston, the piston rings having overheated. A video I saw on YouTube struck a (Chevy v8) with a sharp steel chisel to peen it straight. I don't think I'll be doing that. But I might consider a brass chisel if it's known to be safe. If so, where would you strike it, how risky is it, and where do these crankshafts crack, if they crack? |
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06-04-2024, 12:35 AM
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It's a 914 ...
Join Date: Jan 2008
Location: Ossining, NY
Posts: 4,696
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I spoke to Marine Crankshaft about this at one point. The guy mentioned being able to straighten cranks, and are experienced with Porsche cranks.
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06-04-2024, 04:58 AM
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Join Date: Mar 2019
Posts: 1,602
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Cranks are routinely straightened using a steel chisel with the same radius as the crank, right at the fillet. It's just how it's done. Scary to watch for the uninformed or the owner, but that's the only way that I've ever seen it done. Using a press can crack it.
I'd leave it to the professionals though. No way that I'd try this at home. |
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06-04-2024, 05:31 AM
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Join Date: Jun 2009
Posts: 1,237
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Any time you lose a rod and depending on the severity, the crank is kinked. It is straightened and then turned.
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06-04-2024, 06:29 AM
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Join Date: Jul 2021
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I heard that Porsche cranks are harder than most. That claim would appear to be supported by the fact the webs and counterweights are so thin compared with some other cranks. If true, I would have thought this could make peening straightening problematic with these cranks.
Sent from my SM-S918B using Tapatalk |
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06-04-2024, 09:26 AM
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Join Date: Jul 2021
Posts: 689
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Ok well on the basis others have done it, I went straight in and reduced the runout from .04mm to .01mm. It turns out the 911 crank responds to quite gentle taps with the chisel - at least for the small corrections I needed to make.
Thanks for your advice. Sent from my SM-S918B using Tapatalk |
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06-04-2024, 12:55 PM
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