machining 273 crank for later 904 converter

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65TerrorCuda

65TerrorCuda

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Alright, so I'm looking at getting my crankshaft pocket/register/etc. enlarged for the later easy-to-find converter. I've seen two sizes listed for the bore, both 1.81" and 1-13/16" or 1.8125". Can anybody verify this? How much clearance is there for the converter hub?

And for anyone who's worked on a crankshaft, how do you hold it without damaging the mains?

All help appreciated, I sure don't wanna junk this crankshaft due to some rookie mistake.
 
Not much help, but im removing 904 that has smaller hub converter. When I put 340 in, I had to have a spacer/bushing made. I can get dimensions once trans/converter is out.
 
4spdragtop said:
Not much help, but im removing 904 that has smaller hub converter. When I put 340 in, I had to have a spacer/bushing made. I can get dimensions once trans/converter is out.
Click to expand...
Much appreciated, but I'm trying to get away from the small hub. I've called 10+ torque converter places and I'm looking at minimum $850. I've got the opposite problem, later 904 with the 273. I should just go 340 and call it a day, I'm considering it.

RustyRatRod said:
I'm unsure the crank register is thick enough to do that.
Click to expand...
This is my concern too, but I asked another member that's done it himself multiple times and I guess it wasn't an issue. Every crank is different though, so I'll have to take a close look once it's sitting on the bench.

4spdragtop said:
Here's thread where I did the opposite, went from 340 crank to 273 converter. Might help?
Flex plate bolts witness marks on torque converter
Click to expand...
Hey thanks! That's a great reference for sure! I enjoyed that read.

My plan is to borrow a converter and take it with me when I get the crank machined.
 
65TerrorCuda said:
Alright, so I'm looking at getting my crankshaft pocket/register/etc. enlarged for the later easy-to-find converter. I've seen two sizes listed for the bore, both 1.81" and 1-13/16" or 1.8125". Can anybody verify this? How much clearance is there for the converter hub?

And for anyone who's worked on a crankshaft, how do you hold it without damaging the mains?

All help appreciated, I sure don't wanna junk this crankshaft due to some rookie mistake.
Click to expand...

RustyRatRod said:
I'm unsure the crank register is thick enough to do that.
Click to expand...
I had an early small block steel crank machined for the larger register. Cost $65 bucks 10 years ago.
 
Killer6 said:
What You are doing has been done, there are pics either here on FABO, or on the Slant Six Forum .org site. It works...
Click to expand...
I will give that a look here soon, thank you!

Illahe said:
I had an early small block steel crank machined for the larger register. Cost $65 bucks 10 years ago.
Click to expand...
Local shops have quoted 100-150 minimum for 1 hour. So long as it doesn't become a paper weight I'm happy with that.

Hope y'all are doing good,
 
65TerrorCuda said:
Much appreciated, but I'm trying to get away from the small hub. I've called 10+ torque converter places and I'm looking at minimum $850. I've got the opposite problem, later 904 with the 273. I should just go 340 and call it a day, I'm considering it.


This is my concern too, but I asked another member that's done it himself multiple times and I guess it wasn't an issue. Every crank is different though, so I'll have to take a close look once it's sitting on the bench.


Hey thanks! That's a great reference for sure! I enjoyed that read.

My plan is to borrow a converter and take it with me when I get the crank machined.
Click to expand...
You know what they say. Measure twice, cut once. But somehow I still always get it wrong.
 
So I got the crank register machined to 340 specs, handed over $150. Seemed like a good deal...

As I'm leaving, shop owner says, "it may not be perfectly centered."

Why would you leave a customer with a doorknob confession like that?
 
65TerrorCuda said:
So I got the crank register machined to 340 specs, handed over $150. Seemed like a good deal...

As I'm leaving, shop owner says, "it may not be perfectly centered."

Why would you leave a customer with a doorknob confession like that?
Click to expand...
Did they machine the crank register in a lathe?
 
Illahe said:
Did they machine the crank register in a lathe?
Click to expand...
Not sure. I asked them this before they did it, the answer was it would be held by a fixture clamped around the seal journal at the back end, but nothing more detailed. The guy said he'd done it before without issue.

They have a few big lathes and I don't see how else they'd turn it.
 
65TerrorCuda said:
Not sure. I asked them this before they did it, the answer was it would be held by a fixture clamped around the seal journal at the back end, but nothing more detailed. The guy said he'd done it before without issue.

They have a few big lathes and I don't see how else they'd turn it.
Click to expand...
If the crankshaft pilot was modified in a lathe, there is not much room for runout error.

Perhaps he was just being smug.
 
65TerrorCuda said:
So I got the crank register machined to 340 specs, handed over $150. Seemed like a good deal...

As I'm leaving, shop owner says, "it may not be perfectly centered."

Why would you leave a customer with a doorknob confession like that?
Click to expand...
But it MUST be centered, or else it will tear the front pump bushing all to hell and then...more stuff. What a tool.
 
Illahe said:
If the crankshaft pilot was modified in a lathe, there is not much room for runout error.

Perhaps he was just being smug.
Click to expand...
How would someone do that? The crank register is on one end that gets clamped in the lathe.
 
RustyRatRod said:
But it MUST be centered, or else it will tear the front pump bushing all to hell and then...more stuff. What a tool.
Click to expand...
I'd think if you can't do the job, let the customer know. I'm going to lay the crank in the block and dial indicate the bore. If it's off by much I'll get a 4" stroker and mill the pistons. Lol
 
65TerrorCuda said:
I'd think if you can't do the job, let the customer know. I'm going to lay the crank in the block and dial indicate the bore. If it's off by much I'll get a 4" stroker and mill the pistons. Lol
Click to expand...
That's what I was gonna come back and recommend. Not the stroker part. lol
 
65TerrorCuda said:
Mill ain't tall enough I don't think.
Click to expand...
You can hang the crank off the side of the table to machine it.. But why would you...

Snout in the chuck, use a live center in the tailstock to support the flange end of the crank while setting up a steady rest... Remove live center & bore the damn thing..

And yes, now that it's done throw the crank in the block & indicate the bore to see if you have a problem... Or a joker...
 

Alright, just got the ID done,

At this shallower position, I got .006" max
PXL_20251210_055142826.jpg


This deeper one I got .002" max, more like .0015"
PXL_20251210_062259385.jpg


Both I'm estimating are 30 degrees from perpendicular so the actual runouts are higher than what I saw.

If I go deeper the gauge will be at 45 degrees and will probably deflect, but it's better the deeper I go so far.

The OD runout I'll get here soon, good call! Hadn't thought of that one
 
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