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What are people’s thoughts on this?

I am being told the thrust flange on my 910 crank, once ground smooth again, will be too thin to be serviceable.  It can be sent to a specialist to have material added then ground back to spec. The crack is ‘pinned’ during the process to avoid warping. Good idea or not?.

Thanks in advance.


Cheers, Gavin

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I'd say that if the specialists can confirm it will be true after the procedure then go ahead, after all if it doesn't work they'll not be charging you (will they?).

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I agree. It’s an acceptable and common method of repair. I’ve had it done before on large diesel engine cranks, and it works a treat.

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Margate Exotics.

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I'd be very pleased to know whether this is a viable option as I have a 910 crank in the same condition, with all journals otherwise perfect. It was tried here decades ago when a mate's 907 crank went undersize on at least one rod journal owing to starvation damage incurred on track. Unfortunately there were minute surface cracks apparent after the journals were welded and re-ground so it went into the bin. We'd be fortunate if technology/methodology  in this has come good. I have an engineering brief penned by Tony Rudd filed somewhere in which the 907 crank material specification is provided, from memory SG or spherical graphite iron. I believe this would be equivalent to what in America is known as nodular iron. FWIW.

Glad to read Ian 's remarks as I was writing this. 

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It can be done by laser cladding. 
With this technology the heat input is only 10% of conventionel welding. Hence no cracks. 
The crank is steel forged. Not casted.

What kind of welding have you been offered?

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Appreciate the replies gents.

The shop that is going to repair my block was on the ones that suggested repairing the crank rather than sourcing a replacement. A used crank in the U.S. is like mega $$$ and shipping from LotusBits is equivalent mega $$$. I need to talk to the crank people on Monday so don’t have a full grasp on the process.

will post updates once I am in the know.

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Cheers, Gavin

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The Service Notes state the crankshaft is cast iron. I would also expect the crankshaft to require straightening after welding, possibly heat treating too.

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Regularly done to repair cranks on large diesel trucks, so I don't see why not.

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I pulled the crank out of my 910 for an unrelated rebuild and it was evident that one of the rod journals had been welded and reground in the past.

But when I took it to be ground for undersized bearings the machine shop said it was cracked and suggested a new one. The fact that I could tell that it had been repaired (a few tiny cracks and pits showing the weld bead)  leads me to believe the repair was not done to the best standard. But- it functioned!

IMHO, I would not be as concerned about the loads on a thrust face repair, as I would be for a rod or main bearing journal, and would go ahead with welding.

In my case, given US prices, I ended up ordering a used crank from Garry Kemp in the UK. The exchange rate is pretty good right now, worth a look at UK suppliers, but shipping costs were doubled for my last UK item due to Covid-19 which may offset any rate savings

I've read somewhere the cranks were derived from a Bedford truck engine, but never saw any follow-up on a possible interchange.

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I believe Thomas to be correct in all points stated, though would be cautious in approaching welding of a crank in the present case. I'd like to think that the technology/methodology employed these days is up to the task but there is risk if this is not the case. To the modest extent of my own comprehension a crack which emerges as consequence of stress concentration may rightly be regarded as likely point of failure, in this engine being the crankshaft main #5 where gyroscopic influence of the flywheel will work against whip of the shaft. I want to have confidence in taking my engine to 7000+ revs from time to time so will be wary of how reliable such a repair can be.

I do believe the crank to be of Bedford van origin and stand by my earlier posting in terms of material. Nodular, or spherical graphite, iron is very widely used in manufacture of stressed components like crankshafts. Back in the '70's professional drag racers were turning 9500 RPM on factory nodular cranks in the Ford Cleveland 351, for one example. Readily available literature details the physical qualities of this material as nearer steel than cast iron.

Cheers  

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Informed consensus I've so far been able to gather is that truly large cranks are likely to be made of steel. Therefore any anecdotes suggesting repair methods known to work with those are questionable in use on our cranks. How to determine whether adequate strength remains in a flange reduced by wear and grinding? I fear that the thing was designed with little more mass than needed for its intended load.

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Hey Gavin, anything new to add? I've been digging through any channels found for feedback on the crank, so far not finding much confidence in welding iron. Has your machinist spoken in dimensional terms regarding the thrust flange?

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