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Bosch 05-15-2013 10:14 PM

Crankshaft Cracking?
 
3 Attachment(s)
Are these cracks in the crankshaft rod journal? I am not a machinist, I don't really have much experience or expertise with this sort of thing. I will try to get this to a machine shop when I get a chance, but any insight would be appreciated. This is a cast crank from a Chevy 350. I had planned to put together a decent little 350 to run for a couple of seasons in a Chevelle. It is not going to be used for racing. Just a nice strong little engine to run until I can get a big block put together. I was thinking something like a 325 to 350 h.p. 350.

The pictures are not that good, but hopefully you can see the little marks on the journals that I think might be cracks. There are also lots of paper fibers on the journals, I used a paper towel to wipe the crank off.

Thanks.

techinspector1 05-16-2013 12:05 AM

That's where the edges of the rod bearings rode on the crankshaft rod journal, not cracks. Cracks normally form at an intersection, like at the corner of the journal where the journal turns into the counterweight.

BOBCRMAN@aol.com 05-16-2013 03:45 AM

I dont see cracking. As tech said. Cracks usually form where angles meet. Especially in cast cranks.

Now, if this was a steel crank. That had been run hard. I have seen them with cracks radiating out from the oilholes. Usually not a danger factor untill they go across the journal or get into the fillets on the side of the journal.

cobalt327 05-16-2013 09:16 AM

http://www.hotrodders.com/gallery/da...ium/crank1.jpgI don't think those are actual cracks, but you can have the journal magnafluxed if there's any question.

I'd also recommend you have a better job of chamfering the oil holes. Something more like shown below:

http://www.precisionenginetech.com/w...13-500x333.jpg

oldbogie 05-16-2013 11:42 AM

Quote:

Originally Posted by Bosch (Post 1676002)
Are these cracks in the crankshaft rod journal? I am not a machinist, I don't really have much experience or expertise with this sort of thing. I will try to get this to a machine shop when I get a chance, but any insight would be appreciated. This is a cast crank from a Chevy 350. I had planned to put together a decent little 350 to run for a couple of seasons in a Chevelle. It is not going to be used for racing. Just a nice strong little engine to run until I can get a big block put together. I was thinking something like a 325 to 350 h.p. 350.

The pictures are not that good, but hopefully you can see the little marks on the journals that I think might be cracks. There are also lots of paper fibers on the journals, I used a paper towel to wipe the crank off.

Thanks.

I'm suspicious that your hunch is correct. This looks enough like early stages of fatigue cracking or is an inclusion. Are the marks on the journal in pictures 1 and 2 on the same journal as the marks on picture 3?

Id definitely get it checked out. Do you know if this shaft was reground? That can sometimes hide a journal that got toasted by a rod failure where subsequent turning of the journals cleared the burnt metal, but this could be remaining heat check cracks that scarred deeper into the metal beyond the burn.

Hard to tell by a picture but something's there that's worth investigating further.

Bogie

Bosch 05-16-2013 01:20 PM

Thanks for the input Cobalt, oldbogie and BOBCRMAN. The subject of question in the first two pictures is on the first rod journal, closest to the front of the engine. The little marks that are all parallel near the oil hole are on the second rod journal. I really don't know if the crank has ever been ground. I am pretty sure the engine had been opened up before though. The main and rod bearings have very little wear on them and I am pretty sure the rings have been replaced. You could be right, the crank may have been reground. Of all things I didn't measure the crank journals. The cylinder bores measured out at stock, but I didn't think to check the journals. I will do that tonight. Either way though I don't really think it's probably worth spending any money on this shaft.

This was a 350 out of a '74 Nova. It ran pretty well, had a two barrel carb and fresh dual exhaust. Sounded really nice. The car had been sitting for several years. The old timer that had it recently did a basic tune-up and put new exhaust on it before giving it to his high school age grandson. The kid wrecked the car into a ditch in the first two weeks he had it. I got the engine, transmission, radiator, accessories and some other parts off of it.

It is what it is I guess. I will still try to take it to a shop, maybe tomorrow. Will let everyone know what they have to say.

By the way, Cobalt, thanks for doctoring up that picture and making it easier to see. I was trying to do that in MS Paint and ran out of patience. Thanks.

496CHEVY3100 05-16-2013 02:43 PM

As stated above the crank looks to have been turned at some point ,and an attempt to chamfer the oil holes or to clear up sharp edges from turning crank,but either way they did not leave a radius on the crank ground flat on edge probably cause too much end play front to rear , ,replacement cranks are so cheap now you can buy one cheaper than you can have machine work done , (at least in my area) then you will have a useable crank without worry of past machine work or lack of, IMO.;)note Cobalts picture this is what it should look like.

Bosch 05-17-2013 11:56 AM

Measured all of the journals last night. It's all standard. Doesn't surprise me since the cylinder bores are all standard too.

I suppose it might have gotten too hot or run without oil. It's too bad because this little engine ran real well before I took it apart. Now I don't want to put it back together with this crankshaft. I will see if I can find a good 350 crank to replace it.

vinniekq2 05-18-2013 07:26 AM

good luck with the build. welcome to the forum,have fun


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