Odd crank throw issue on 383

[396 Signet]

The 1-2 crank throw on my 383 is 0.004-005" shorter than the other 3. Doesn't affect things much as far as my build goes but wondered if anyone ever saw this? All the others I've fooled with were always within 0.001-002". This is an untouched factory unit circa 1965. Maybe just sloppy QC on a Friday.

 

[mopar 3 B]

Have you measured journal sizes? How did you measure the throw?

 

[396 Signet]

Didn't measure stroke directly. Measured journals, rod length, deck height from mains all 4 corners. Assembled piston depth in hole was off (exactly same) on 1-2, stroke mismatch was only possibility I see.

 

[mopar 3 B]

Assuming the block has been checked and deck height verified.
All rod journals did measure the same size?
Are there any special stamping on the id pad at the distributor?
If something out of the ordinary was done at the factory it would be noted there.

 

[396 Signet]

Assuming the block has been checked and deck height verified.
All rod journals did measure the same size?
Are there any special stamping on the id pad at the distributor?
If something out of the ordinary was done at the factory it would be noted there.

Block decks slightly tapered (0.003") front to rear, same both sides, did not resurface. All journals in spec, very close, just polished & left standard. Nothing on ID pad, just basic 383HP & date. FYI also cc'd heads & measured depth in hole prior to taking apart, had no where near advertised 10:1, more like mid 8's. it will be better when I'm done.

 

[mentor70]

this VERY common, most people dont pay it any mind.

my old machine shop used to "index" my crank shafts, you can "pull" the stroke on that journal by going a .010 grind on the all the journals and offset grinding the one that is out to pull it to a true 90* to the remaining journals.

 

[396 Signet]

this VERY common, most people dont pay it any mind.

my old machine shop used to "index" my crank shafts, you can "pull" the stroke on that journal by going a .010 grind on the all the journals and offset grinding the one that is out to pull it to a true 90* to the remaining journals.

Thanks, what I wanted to hear. I'm just a putzer, done a half dozen or so motors & never saw this. All previous I saw had stroke on the money. Probably should have asked my machinist who has seen thousands.

 

[miller]

This is an untouched factory unit circa 1965. Maybe just sloppy QC on a Friday.

The guy probably dropped his drink!
Your talking about rod end play, right?

Ahh...re-read the post. Understand now.

 

[moper]

Assuming that the decks are not the culprit - that's "within spec" in terms of the crank grinder who did it originally. This is why I/we blueprint the engine when it's rebuilt. It costs me extra but I have all my cranks indexed and stroke corrected when I have them turned. You say it doesn't affect you, but the reality is it does. Two cylinders will be different, and not in a good way. While it's minutia for many enthusiasts to me a performance build that is looking to exceed the as-produced quality and performance should not overlook these details. That's why I use the shop I do, and why I have the machining operations done that I do.

 

[396 Signet]

For practical purposes it doesn't affect much. It will still have acceptable quench and the engine did run fine for 135k miles with this "condition". It would be nice to have everything perfect but it's not like I'm racing in super stock. This will just be a very durable & reliable motor that I can drive anywhere. I want to see the mechanic that listens to a motor & says "yeah, it runs good but I can hear a 5 thou stroke mismatch".