I’ve read every post on this I could find, but I still haven’t seen a clear answer to this specific issue.

Swapping a Muncie M21 into my '70, 442 with a 455 that originally had an automatic. As expected, the crank has:

• The usual ~1.690" converter register
  
• And forward of that, a factory-started tapered hole, roughly 1.2" in diameter and about 0.25" deep
  

Here’s the part I can’t wrap my head around:

RockAuto and others list multiple 1.094" OD pilot bushings (like the Pioneer PB656), which obviously require cutting a smaller bore.
But how is that even possible when the crank already has a larger 1.2" hole started? Wouldn’t the smaller bore be partially unsupported? Will there be slop? Or is the 0.750" bushing recessed far enough past the taper that it ends up fully seated in fresh material?

Also, RockAuto lists the Dorman 690023 (1.381" OD × 0.363" deep), which appears to match the original Lansing machining diagrams and fits the existing bore size far better. That seems like the more logical route.

So now I’m stuck wondering:

• Why is the smaller OD bushing (PB656) even listed as a fit?
  
• Can you actually machine for a 1.094" bushing when the crank already has a 1.2" taper started?
  
• Which bushing is better overall for durability and support — the shorter/wider Dorman, or the deeper/narrower PB656?
  

I already have the PB656HD in hand (not noticing the OD difference prior to ordering) and I know machining is needed either way. Just trying to make the smartest call before handing it off to the machine shop.

Any insight from those who’ve done this is appreciated. Thanks.




RockAuto listing of bushings for 70 Olds 455

Dorman 690023

Pioneer PB656

Machine Info for Pilot Bearing

 

Have you done any measuring on your crank ? I believe the .592" I.D. is the pilot diameter of the Muncie input shaft.

 

Hi, Ralph!
I had posted this:
As expected, the crank has:

• The usual ~1.690" converter register
• And forward of that, a factory-started tapered hole, roughly 1.2" in diameter and about 0.25" deep

This is what my auto crank currently is. I am concerned with the OD, not the ID.

 

I was a machinist for many, many years. There were Inside Diameters (I.D.), Outside Diameters (O.D.), bores, counterbores, countersinks, chamfers and depths.

"Register" means nothing to me, could you describe it ?. This tapered hole you mention, did you measure it at the beginning or down part way ? Or, are you calling a straight hole with a drill point shape at the end ?

The blueprint drawing you attached to your post was the machining diameter and depths to convert an "automatic crank" to a bearing recess for a manual transmission. The 1.381" O.D. bushing you show would replace a roller bearing that would have been used in "Manual transmission crank". .

 

I should mention that others may chime in and provide information.

 

Hi Ralph,

Thanks for the reply — I think I might not have explained my terms clearly enough. By “register” I meant the large ~1.690" bore in the back of the crank where the torque converter snout locates on an automatic setup.

Forward of that is the feature I’m asking about — a secondary hole that is clearly tapered like the end of a drill bit, not a straight bore. The opening at the face of this taper measures roughly 1.2" OD, and the taper only goes about 0.25" deep before it bottoms. I’ve attached a photo of my crank so you can see exactly what I’m talking about.

This is an automatic crank and, as expected, it has never been fully machined for a manual pilot bushing. I’m just trying to clarify machining options — specifically, why so many parts listings show a 1.094" OD bushing as a fit when this factory-started hole is already larger in diameter.

My concern is:

• Can a smaller (1.094" OD) bore even be machined when this 1.2" taper is already there?
  
• Will there be enough solid material for a press fit, or would the smaller bushing need to be set deeper to avoid the tapered section?
  
• Or is it better to finish the crank to the 1.377–1.381" OD shown in the factory diagram and use the wider Dorman-style bushing?
  

Hopefully this clears up what I meant and why I’m asking.

Thanks,

Auto Crank

 

I quoted you to keep things simple and not have to scroll back and forth between posts. What you need to be concerned with is two diameters and two depths.
1.378-1.380" I.D. and to a depth 1.190-1.230"
1.219" I.D. and to a depth of 1.440-1.560"

the 1.378-1.380" is the most critical size because that where the Dorman 690023 fits. You want about .001" press fit. So if the bore comes out 1.380" you freeze the bushing for a few hours and pop it in fast. If the I.D. comes closer to 1.378" I.D. polish the bushing down to give .001" press fit and freeze it.

The 1.219 I.D. is not real critical. It clearance behind the bushing and the 1.440-1.560" depth is to provide end clearance for the .592" O.D. pilot on the input shaft on the Muncie. This1.440-1.560" depth is to keep the Muncie from bottoming out in the hole.

I think I covered what you need to know. Print out and take the drawing and bushing with you. A good machinist will readily understand it. If you want to take post along also, thats fine. I hope this helps.

 

I just recently had this done. When I dropped off the crank at the machine shop,
I gave them my pilot bearing (National 7109) and the drawing above.
They drilled the crank and fit the bearing with no issues. Was not cheap.

 

I just want to add one thing. Have you asked your machine shop about this yet ? There are very few "normal" automotive machine shops that are really equipped to properly do this job. It takes a pretty good size lathe with a good size steady rest. I am fortunate that I have a friend with a precision type machine shop who I can get to do this stuff for me when needed. I have a 12x36 lathe which is medium size but I would not feel comfortable doing something like this on it.

 

The machinist didn't just drill the crank. He could drill some of it, but he had to set up a boring bar and cutting tool to finish the 1.378-1.380" diameter to size and depth. Thats unless he had a precision reamer.

Thats one way to do it in a large lathe, but its a lot of set up. I would think two v blocks on a horizontal boring mill or an old Cincinnati horizontal mill with the convertible head would set up much easier.
....Just my two cents worth.

 

Either way but my point was that probably half of the strictly automotive machine shops do not have the equipment to properly do the job.

 

Don't place too much faith in parts catalog listings. RockAuto is my go-to, but they just publish what the manufacturers give them. That smaller bearing is for something else and just got incorrectly labeled for Olds.
There's lots of good threads already:
https://classicoldsmobile.com/forums...earing-169947/
https://classicoldsmobile.com/forums...g-help-154309/
https://classicoldsmobile.com/forums...ushing-163381/

It helps to be clear on your crank - it sounds like what you have is an automatic crank.
In the manual crank, the 0.75" area is clearance for the input shaft. The same area in the Auto crank has to be drilled deeper to provide enough depth. Size isn't critical there, just big enough that the input shaft doesn't hit anything.
1.38" is the Olds bushing OD. The manual crank is machined to that size. The auto crank is ~1.2" in that same area. That isn't a critical dimension - it's just clearance for the torque converter snout - so the machining isn't precise.

You can either get that 1.2" area bored out to the correct ~1.38" dimension and use the correct Olds bushing/bearing, OR find a "conversion" bushing that has an OD that fits the auto crank. Mondello used to make them, there are probably some floating around.

 

[QUOTE=OLDSter Ralph;1643585]The machinist didn't just drill the crank. He could drill some of it, but he had to set up a boring bar and cutting tool to finish the 1.378-1.380" diameter to size and depth. Thats unless he had a precision reamer.

I wasn't there when the crank was machined. I don't know his exact process,
you would have to ask him. My point was, he had the bearing in hand and
the drawing for reference. He machined the crank to the bearing for the correct press fit.

 

Oddball- Thanks for the clarification, and answering my OP. I should have cross referenced a parts book vs. assuming RockAuto to be accurate.
I have since ordered the correct, larger OD bushing and having it shipped to the machine shop to bore it correctly.

Appreciate everyone for the feedback.

 

this is what you need. Your converter snout hole in the crank is probably closer to 1.703”

you have one of the oddball cranks that were depth machined deep to the converter snout O.D.

 

I have gotten auto cranks bored out for the Olds sie bearing or its equivalent bushing, and also some for the
Chevy bushing, which will hang out some but work well. It also depends somewhat on whether you are using an aftermarket housing with block plate or not, The block plate spaces the trans back about 0,14". Iirc, I got the crank bored 0,55" deep for the
Chevy bushing when using a block plate.