how much can a crank be turned - Ford Truck Enthusiasts Forums



how much can a crank be turned

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Old 01-20-2005, 08:54 PM
cornfeed cornfeed is offline
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how much can a crank be turned

HI

I bought a 1978 f800 dump truck with a 477 and a bad knock. One of the rod bearings was completely gone. I measured the journal with a caliper and there is .040 difference between the greatest diameter and the shortest. My crank has already been turned down .020. Can my crank be turned down enough to fix this?

Thanks

Mark
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Old 01-20-2005, 10:16 PM
daerhldgs2 daerhldgs2 is offline
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NO but it can be built up and turned , although those jobs can have iffy results, it depends on the shop, some wont even attempt it because the weld sometimes peels off in use.
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Old 01-21-2005, 04:59 AM
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I used to grind cranks for this type of repair, usually very large diesel engine cranks.

Depending on the shops capabilities the crank can be ground down to clean it up. Then depending upon how much it took to clean it up the crank can either be hard chromed or welded to oversize. It is then ground back down again. Usually the entire crank is ground to the same dimension. Automotive cranks usually are not worth the expense involved but some of those old gas engine cranks are getting rare. Hard chromed cranks will last forever and are worth much more than a std cast or forged crank.
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Old 01-25-2005, 03:21 PM
noshoesreqd noshoesreqd is offline
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Another possibility might be to have a bearing shell custom sized with new babbit say if your journal were to clean up at .050 under. It shouldn't be too detrimental to the crank strength as these are fairly low speed engines, I wouldn't do it on a high performance race engine. I have restored several old cars from the 20's and 30's and sometimes you have to get creative where there are no parts available. Rebabbiting thin shell bearings is possible and I have had it done on several engines for which there were no available bearings and these motors are still running just fine today.
It won't matter if you have one journal a different size, If you can get a local machine shop to turn down the crank I could give you a place where you could send the rod and bearing to be set up.

Steve
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Old 01-25-2005, 05:23 PM
rusty70f100 rusty70f100 is offline
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If the rod bearing was completely gone, you'll likely need a new rod, as this will be damaged too.
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Old 01-26-2005, 09:31 AM
kotzy kotzy is offline
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Noshoes,
What you advise was done years ago before the journal welding process was perfected.
The inserts were called semi fitted, and cranks were turned to .060. While it saved the
cost of a crank if one was to be had, as I remember the engines done this way were very not very reliable. I would have the journal welded up, with all the exchange cranks out there, I'm sure a lot of them have welded journals.
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Old 01-27-2005, 08:23 AM
cornfeed cornfeed is offline
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Thanks for your help so far. I have the engine out and disassemblesd. I am currently getting a price check for a new crank and gasket set. Does anyone know what I can expect from this motor when I am done? Power? (Getting up to speed with a load) feul consumption? (Ive been told 3-4 mpg)

I bought this truck used (cheap) and have never driven it.

Thanks for your advise
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Old 01-27-2005, 10:53 AM
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I drove a Redi-Mix truck one summer while I was in school and I got 4MPG in any truck I drove, most of the drivers only got 2 MPG. Driving sensibly helps. My mileage drove the dispatcher and mechanic nuts because they could not tell any differences in dispatch times, engines, etc. The book keeper and owner liked it. Unfortunately the other drivers caught hell... -hehe! I think by the end of the summer a couple drivers were getting the hang of it.
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Old 01-29-2005, 11:05 PM
Birken Vogt Birken Vogt is offline
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Well to answer the question you can expect next to no power and acceleration and the fuel economy will be bad because there is only one way these can be driven, that is wide open.

Birken
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