Crank shaft machine question.

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340dartley

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I have a 340 block in my garage that I would like to get running on the cheap. I don't want to cut corners per say but would like to clean up and use existing parts that I have.
My current concern is the crankshaft. It was in good shape and fresh .010 mains and rods when it was removed. It wound up sitting outside and became rusty. I glass beed blasted it and would like to repolish the journals and run it. Machine shop said if it was beed blasted it will have to be turned. Anyone ever home polished a crank or should I have if turned. I also need one 340 floating rod as one spun a bearing.
 
340dartley said:
I have a 340 block in my garage that I would like to get running on the cheap. I don't want to cut corners per say but would like to clean up and use existing parts that I have.
My current concern is the crankshaft. It was in good shape and fresh .010 mains and rods when it was removed. It wound up sitting outside and became rusty. I glass beed blasted it and would like to repolish the journals and run it. Machine shop said if it was beed blasted it will have to be turned. Anyone ever home polished a crank or should I have if turned. I also need one 340 floating rod as one spun a bearing.
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I would take the shops advice and have it turned for proper bearing clearances. You don't want to risk your time and effort to save a little money! 65'
 
that is not a hard replaceable part ...you can always use a 318 crank, they are both 3.31 stroke
 
Yup - rust is fatal on a bearing journal. It has to be removed, then the damage from the removal (and the pits from the rust) removed and the journal properly shaped and sized. You can go .020 or .030 under and you're fine with a moderate power level. Mopar cranks are very strong. Even the cast ones.
 
This is a forged steel crankshaft. If I have to turn it to .020 then I will. I was more just curious if I can polish the journal's myself after I beed blasted it. At this point there is no rust or pits on the journal surfaces. Just wrong finish because of beed blasting. I realize that I shouldn't have beed blasted it now.
 
I noticed that you glass bead blasted the crank. Now this could have been not so hard on the surface, meaning the "roughness" of the journals COULD be polished out. But then I could be totally wrong... Sure I wouldn't do any journal polishing at home.
Take the crank to a machine shop and rely on their expertise.
 
stixx said:
I noticed that you glass bead blasted the crank. Now this could have been not so hard on the surface, meaning the "roughness" of the journals COULD be polished out. But then I could be totally wrong... Sure I wouldn't do any journal polishing at home.
Take the crank to a machine shop and rely on their expertise.
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I will try and take some pictures of the crank tonight.
 
I got one crappy picture of the crankshaft. It is rougher than I remember. I may play around with it and some 400 grit Emory cloth with some wd40 but I am aware it will most likely need to be turned down.

20170505_061659.jpg
 
I would not risk it. Get it ground to the next acceptable size. Those old steel cranks are made of good steel; so you shouldn't have any problems if they turn it .
 
340dartley said:
I have a 340 block in my garage that I would like to get running on the cheap. I don't want to cut corners per say but would like to clean up and use existing parts that I have.
My current concern is the crankshaft. It was in good shape and fresh .010 mains and rods when it was removed. It wound up sitting outside and became rusty. I glass beed blasted it and would like to repolish the journals and run it. Machine shop said if it was beed blasted it will have to be turned. Anyone ever home polished a crank or should I have if turned. I also need one 340 floating rod as one spun a bearing.
Click to expand...

If you spun a rod bearing on that crank you are crazy to run it without having it professionally measured and turned. Based on the pictures, glass beading of the journals (and subsequent re rusting?) and the spun bearing my hunch is that the crank is done. As was said, find a good 318 steel crank, they are reasonably plentiful, affordable and dimensionally identical to the 340 crank.

Everything that you want to do is cutting corners, IMO.
 
There's a difference between looking acceptable and actually BEING acceptable. You can use emery to make it look better, but it won't be flat or smooth enough to work as the engineers designed it to. Just have it turned and polished and ur good da go.
 
When it spun a rod bearing I lumped it home. There was no symptoms other than my oil pressure dropped from 50 at idle to 20 at idle. My friends thought I was crazy for being worried about it as it still had acceptable oil pressure. I removed the engine and pulled the crank. Rod was damaged and bearing wad toast but not even a scuff mark on the crank. If I had put a new rod and bearing in I could have kept going but I left it apart for several years. I moved several times and it got left outside at some point. All the damage to the crank was caused by how it was stored. The block is in similar shape. The bearing surfaces are smooth just blasted at this point.
 
Even though a 273 and 318 have the same stroke as a 340 they weigh quite a bit more a 340 has the front and rear journals drilled with a 1 inch hole to lighten it as the 340 has heavier rods. Kim
 
Ok so I got bored today and decided to see what I could do to the crankshaft with a little Emory cloth a shoe string and some wd40

20170506_113904.jpg
 
see,.the thing is, rust dont grow even, it eats away steel as it see fit so after crank rust up as bad as yours its not gonna clean up round!! its gonna have high an low area's around the journals, why you need to bite the bullit and get the crank turned right! when it comes to journals and bearings living,theres right,..and errything else is ,.not right!
 
The first picture speaks volumes of how out of round and undersize it more than likely is... to be looking the way you have it now.

Take it in and have it measured...If it's in spec, they will recommend a polish,.... if it's not, they will tell you it's now time for .020.
.020 isn't a bad thing... more bearing, minutely cooler journal temp... and if you check and built it correctly and cleanly...it will last a long time.
 
The crank is not that rusty. The pictures make it look worse than it is. Since the beed blasting it has been inside . is only surface rust. I am also planning to have it turned. Just was seeing what I could do.
 
Surface rust is the problem. Visuals be damned the journal is JUNK as it stands now.
 
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