Replacing a crank shaft questions

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like_A_pike

like_A_pike

that's not factory
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My engine is a 1971 340 (august I think). Externally balanced.
I have a manual for 1968 and the only thing it says regarding identification is whether I have a Maltese Cross stamped on the “numbering pad on the right side of the block” . It may have undersized one or more bearing journals by .001. If it is stamped with that cross and an X All of them are .010 undersized.
Is this Maltese Cross Id still true in 1971 or 72? Do I need to worry about it if it’s heading for the machine shop? Where is this numbering pad? Will any LA crank shaft work or is there something specific I need to target?
Thanks in advance
 
like_A_pike said:
My engine is a 1971 340 (august I think). Externally balanced.
I have a manual for 1968 and the only thing it says regarding identification is whether I have a Maltese Cross stamped on the “numbering pad on the right side of the block” . It may have undersized one or more bearing journals by .001. If it is stamped with that cross and an X All of them are .010 undersized.
Is this Maltese Cross Id still true in 1971 or 72? Do I need to worry about it if it’s heading for the machine shop? Where is this numbering pad? Will any LA crank shaft work or is there something specific I need to target?
Thanks in advance
Click to expand...


Remove the crankshaft and look at the back side of the bearing shells for both the rods and mains... They stamp the size of the bearings in the back; STD, .001", .010" etc...

They also have the date of manufacture code stamped on them...
 
like_A_pike said:
mopar casting numbers

Saw this on another post. Will the cast 72 crank work in my 71 motor? Is the only difference that they were steel up to 72 and cast after 71?
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72 still had forged cranks, the only year they put the cast crank in the 340 is 73...

You can interchange the cranks between the engines as long as you keep the original vibration damper with it so it is properly balanced... You can use the cast crank in an earlier 340 block if you use the proper 73 cast crank balancer for the 340...


As long as you keep the cranks with the proper original dampers, you should be ok...
 
I believe they went to cast crank mid year 72 after they depleted inventory of forged cranks. I have a 72 with undersize crank from the factory.
 
It's a little unclear as to what you are attempting to do......why are you asking about crankshafts and interchange?

.Krazykuda's advice to pull a main cap and a rod cap to read info on the back side of the shell is spot on. The markings will be date cod, and size. Date code is month, year ( 9-72 ) for example, size will be STD for standard, or .001, .010, .020, etc for under size. If date code is newer than 1972 means someone has been into the engine before you; not a big deal, it's a 40 plus year old car, it's kinda to be expected.
 
ch1ll said:
I believe they went to cast crank mid year 72 after they depleted inventory of forged cranks. I have a 72 with undersize crank from the factory.
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help me understand ch1ll, can one use an undersized crank if it was not “undersized” originally? The real question is; will your crank work in any 68-71 340? Or am I looking for a “Maltese Cross and an X” on my block for it to match?
 
like_A_pike said:
My engine is a 1971 340 (august I think). Externally balanced.
I have a manual for 1968 and the only thing it says regarding identification is whether I have a Maltese Cross stamped on the “numbering pad on the right side of the block” . It may have undersized one or more bearing journals by .001. If it is stamped with that cross and an X All of them are .010 undersized.
Is this Maltese Cross Id still true in 1971 or 72? Do I need to worry about it if it’s heading for the machine shop? Where is this numbering pad? Will any LA crank shaft work or is there something specific I need to target?
Thanks in advance
Click to expand...
As stated, your '71 340 was a factory forged crank- INTERNALLY balanced (if unmolested factory). Keep it as opposed to the cast 340 crank, unless it's all you can come up with. Like krazykuda said, they use their own external balance damper AND their own balance on the flywheel/TC which is unlike any other smallblock, including LA360s and 5.9 Magnums.
And no, you don't have to worry about your -.001 or -.010 crank if it's heading to the machine shop anyway. Any undersizes are dealt with with appropriately sized bearings.
 
like_A_pike said:
My engine is a 1971 340 (august I think). Externally balanced.
I have a manual for 1968 and the only thing it says regarding identification is whether I have a Maltese Cross stamped on the “numbering pad on the right side of the block” . It may have undersized one or more bearing journals by .001. If it is stamped with that cross and an X All of them are .010 undersized.
Is this Maltese Cross Id still true in 1971 or 72? Do I need to worry about it if it’s heading for the machine shop? Where is this numbering pad? Will any LA crank shaft work or is there something specific I need to target?
Thanks in advance
Click to expand...
71 340 was internally balanced. The factory didn't throw a crankshaft away if it needed a tighter bearing. They just used undersized bearings. If the crank is not worn or grooved and just needs new bearings it really should be miked to get the correct oil clearance. (within spec) Pull the engine and the crank, check it or have it checked. It might just need a polish or a .010/.010 turn to be made correct.
 
JBurch said:
It's a little unclear as to what you are attempting to do......why are you asking about crankshafts and interchange?

.Krazykuda's advice to pull a main cap and a rod cap to read info on the back side of the shell is spot on. The markings will be date cod, and size. Date code is month, year ( 9-72 ) for example, size will be STD for standard, or .001, .010, .020, etc for under size. If date code is newer than 1972 means someone has been into the engine before you; not a big deal, it's a 40 plus year old car, it's kinda to be expected.
Click to expand...


The engine is at the machine shop 2 hours away. They tell me today that the crank shaft is toast and they can’t find one??? I’m attempting to get them some information to properly identify what I have so we make the correct choice on the replacement.

What I think I understand is that any crank from 68-71 will work with this engine despite how many times it’s been line honed as long as the bearings are matched properly. Is that right?
 
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Pix please of the crank as above. Sounds like the block casting date is early August, but the assembly date would be sometime after that in the '72 model year. You want to find out if it is internal or external balance. And a damper pix too if you can.

And as said, with undersized journals, you just put in the matching undersized bearings. The 'holes' in the block and rods are the same for all undersized bearings.
 
You can use a 318 crank. You may need to ad weight to it tho.
Is there someone at that shop that could send you a picture of the crankshaft from their phone?
 
Don't know if it helps or not, but King also carries narrow rod bearings all the way to .060 under size.
 
6655EB6C-498D-4720-BE4B-DFB88DEA7F44.jpeg

this is all I have here. It needed a line hone 6 years ago and that shop said the crank was just Ok then. So I went with it....
I will try to get this shop to take pictures in the morning.
 
like_A_pike said:
My engine is a 1971 340 (august I think). Externally balanced.
I have a manual for 1968 and the only thing it says regarding identification is whether I have a Maltese Cross stamped on the “numbering pad on the right side of the block” . It may have undersized one or more bearing journals by .001. If it is stamped with that cross and an X All of them are .010 undersized.
Is this Maltese Cross Id still true in 1971 or 72? Do I need to worry about it if it’s heading for the machine shop? Where is this numbering pad? Will any LA crank shaft work or is there something specific I need to target?
Thanks in advance
Click to expand...

like_A_pike said:
mopar casting numbers

Saw this on another post. Will the cast 72 crank work in my 71 motor? Is the only difference that they were steel up to 72 and cast after 71?
Click to expand...

like_A_pike said:
The engine is at the machine shop 2 hours away. They tell me today that the crank shaft is toast and they can’t find one??? I’m attempting to get them some information to properly identify what I have so we make the correct choice on the replacement.

What I think I understand is that any crank from 68-71 will work with this engine despite how many times it’s been line honed as long as the bearings are matched properly. Is that right?
Click to expand...

like_A_pike said:
View attachment 1715546311
It needed a line hone 6 years ago and that shop said the crank was just Ok then. So I went with it...
Click to expand...

Okay, hold the phone, back up the bus, hit the "reset" button- this is starting to read like a bad dimestore paperback whodunit that keeps revealing new information after it's all over. You started out asking about block markings and factory undersize crank journals, then start talking crank swaps, and then bring up that it was already line honed when you were into it 6 years ago?
Factory block stampings don't mean chit fifty years later, once you (and who knows how many other previous owners) have had work done to the motor, replaced parts and been into the short block. You need to check and verify dimensions- isn't that what you're paying the shop to do?
Line honing is a block correction procedure and does not affect the crankshaft or the fact that it may have undersized bearing journals.
And personally, I wouldn't trust a shop that cannot find a 273/318/340 crankshaft. Grab your toys and take them home.
So, let's start this over and get the whole story all at once, not piecemeal. What you have, what's already been done to it (as far as you know), what the problem is with it, what you're attempting to have done, and what they're telling you. Asking for advice without giving all the information is just inviting more problems.
 
like_A_pike said:
If it is internally balanced then this https://www.jegs.com/i/Scat/942/1-98003BI/10002/-1 ?

plus a new harmonic balancer?
Click to expand...


Ok, remind me WHY your crank is junk.

There are still stone aged dullards who think grinding a crank .010 under is bad, and anything more junks the crank. They are fools.

I usually grind my brand new small block cranks to 2.100 and use chevy rods. That means I take a brand new crank and take it .025 under.

The last low deck BB I did had giant, worthless 2.375 rod journals. I did some figuring and turned that crank down to 2.100 so I could use SBC rod bearings and to slow the bearing speed down some. That means I had it ground .275 UNDER.

I’d do more to see why they won’t use that crank long before I bought another crank.
 
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