Crank Hole Finish Size For Pilot Bushing

-
cosgig

cosgig

MoBro Inc.
FABO Gold Member
Joined
Jul 20, 2008
Messages
12,497
Reaction score
6,486
Location
Pinckney, Michigan
Howdy all, cosgig here! I'm in need of a little help with my upcoming project! I have to install a pilot bushing into the crank and I need to know if this hole is finish reamed for the bushing or not! Does anybody have knowledge of the correct size the hole should be for the bushing? The bushing od is.940 and the hole currently measures .906! Will it fit??

4 speed gods, I call upon you! Please shine on me with favor as you look down on this project and make this hole correct for installation!! Amen!!

Thanks for any help available, Geof
 
Piss on it. Get the roller bearing from magnum cranks and move on with your life.
 
jos51700 said:
Piss on it. Get the roller bearing from magnum cranks and move on with your life.
Click to expand...

Might come to that, but already have the bushing! Its customer provided items and was hoping it was finished the right size to pop the bushing in already! .035 oversize seems like a lot though!
 
So, I think I've found my answer, and the answer is that its not finished for the bushing! The hole needs to be .9375, or .003-.004 undersized of the bushing! Now thinkin of turning down the od of the bushing to fit! It would need to have .015 off the wall thickness which is .100, leaving the wall thickness at.085. Any input on whether this is acceptable!

Also, is an unreamed hole still concentric with the crank? Can I put the undersized bushing in the unfinished hole and have it work?? Anybody ever done this??

If all else fails I can still just buy the bearing, just trying to use what I have here!! Geof
 
Chrysler made it really hard for swaps by not drilling all the cranks for a pilot bushing.

On the cranks I have that were factory drilled then I of course use the bronze pilot bushing.

On cranks that are not drilled, I usually drill them out. If you drill it out you will never get it precise enough to use the bronze bushing. The idea is just to drill it out enough so the input shaft fits in there without making interference contact within the crank. Then I get a hub bearing. This avoid cutting the input shaft down which in my world is a huge no no and it gets you close enough and you can always use a hub bearing to prevent the input shaft from flopping around.

http://www.ebay.com/itm/Clutch-Pilo...Parts_Accessories&hash=item5414a7eea4&vxp=mtr
 

Attachments

  • $_12.jpg
    54.2 KB · Views: 873
Thanks for the response there rani!! I was hoping not to go the bearing route if I could, but seeing that it is only $10 makes that route much more plausible! Thanks for the input, and give the kitties some lovin from Nella!! Have a happy thanksgiving also!! Geof
 
one word of warning about drilling it out though is plan on a workout and a half. Its a time consuming job that will make you feel like you worked out all day.

Don't be distracted at all when drilling. One of the times I did it, I got it cutting and I let go of the drill with one hand because I thought it was going smooth and it was cutting smooth but then when it hit a burr I only had one hand on it and it twisted the drill around and broke my wrist. So when your drilling its a job that you cant be distracted and you have to be patient.......its no easy task.
 
RaniDart70 said:
one word of warning about drilling it out though is plan on a workout and a half. Its a time consuming job that will make you feel like you worked out all day.

Don't be distracted at all when drilling. One of the times I did it, I got it cutting and I let go of the drill with one hand because I thought it was going smooth and it was cutting smooth but then when it hit a burr I only had one hand on it and it twisted the drill around and broke my wrist. So when your drilling its a job that you cant be distracted and you have to be patient.......its no easy task.
Click to expand...


Me?? Distracted??? Never....wait, what were we talking about?? ;-)
 
I've posted this on other threads about drilling a cast crank to accept the 4 speed imput shaft. I can be done but there is a risk. I lived through the following ordeal so it's not a myth!


This might be a stretch. But when you pull the motor stick your finger in the back of the crank thru the pilot bearing to see if you come up with fresh oil. If you have a cast crank it could be forced thru the casting. Years ago Wheeler manufacturing had the bright Idea to drill the back of the cast cranks in there 400 BB so they could be used in a auto or stick aplication. The problem was that the cast cranks were to porous and the oil would go right thru the casting and out the drilled hole. I found this out after installing one of these and pulling the pan twice and the auto trans 3 times. For me it was an easy fix i cleaned the crank real good with carb cleaner. filled the hole with JB weld and put a flat expansion plug in the center. Yours with a stick might be harder, if it turns out that is the problem.
 
Well, to clear up any confusion, this is a 66 273 motor with a forged crank! Every other motor and crank I have here is not only drilled and reamed, but all have the bushings already installed! They are 340's though, so I think that was automatically done with that displacement! The only other motor I have here is another 66 which is not reamed either! All have come from automatics!

Without further info, I am going to check the concentric of the unreamed hole with an indicator, and if it is concentric, I'm going to turn down the bushing and go that way! That will get me back on track the quickest and most economically!

Of course more input is welcomed, if anybody has anything to add please do!! Thanks, Geof
 
And the right way to turn these out is on a lathe.... drilling is iffy in terms of final size, straightness, out-of-roundness, etc. I have a drill press tall enough to take cranks, but holding them straight and securely is always the problem.
 
Typically you press fit with .002 - .003" interference.


I know a guy near you that has connections with a machine shop if you need it. PM me and I can get you in touch with him he's not far from Metro Airport.
 
So, I'm going to turn down the bushing od to size! That is the way the owner of the car decided we would go, and buying the undersized bushing is the same as turning it down!! I read the answer in the link 66fs gave (thanks for the link) and it kinda confirmed why im goin to check the runout first though!!

Thanks for all the input folks, I really appreciate it!! Happy Thanksgiving all!! Geof
 
Dorman number 690-025. ID 3/4 od .885
 
The ONLY way to drill the crank for a std pilot bushing is to put it in a lathe, INDICATE it in, and finish the hole.

You could use the already undersized OD bearing, BUT the hole in the crank is rough finished , and may not be in the center.

By the time you diddle around with turing down the OD of the bushing you have, step up to the lathe and MAKE your own bushing. Make it to the roller bearing size, and pop it in. Have done it 30 or more times.

I despise roller bearings where a pilot bushing SHOULD be. I have had to repair (at the minimum) 15 input shafts that are wrecked from roller bearings.

In fact, I am making a bushing for myself this week, for my own engine. It takes 20 minutes and you don't have to use a roller bearing.

In my life, I have not found a great many roller bearings in the places they are used the most, such as rocker arms, input shafts and motorcycle pivot points, just to name 3.
 
madscientist said:
The ONLY way to drill the crank for a std pilot bushing is to put it in a lathe, INDICATE it in, and finish the hole.

You could use the already undersized OD bearing, BUT the hole in the crank is rough finished , and may not be in the center.

By the time you diddle around with turing down the OD of the bushing you have, step up to the lathe and MAKE your own bushing. Make it to the roller bearing size, and pop it in. Have done it 30 or more times.

I despise roller bearings where a pilot bushing SHOULD be. I have had to repair (at the minimum) 15 input shafts that are wrecked from roller bearings.

In fact, I am making a bushing for myself this week, for my own engine. It takes 20 minutes and you don't have to use a roller bearing.

In my life, I have not found a great many roller bearings in the places they are used the most, such as rocker arms, input shafts and motorcycle pivot points, just to name 3.
Click to expand...

Do you mean to make a bushing that fits in the crank register where the converter snout goes, but has a pilot hole size in the middle for the input shaft?? That's not a bad idea!!
 
Is the crank drilled deep enough to accommodate the input shaft length?
I've seen a lot of 4 speeds with broken off bolt hole flanges.
Has the trans input shaft been shortened by someone already?
If yes, I'd surely go with the mad's snout bushing rather than the roller bearing replacement.
 
I have done several 440 steel cranks where the hole was drilled but the bushing didn't fit into the hole.

I don't have a lathe, but I usually turn down the OD of the brass bushing by slipping it over a steel shaft (like a 1/2 inch socket extension) and spinning it up against a bench grinder wheel.

I've always been able to get the brass bushing down to where it tapped into the hole and worked fine.
 
Daves69 said:
Is the crank drilled deep enough to accommodate the input shaft length?
I've seen a lot of 4 speeds with broken off bolt hole flanges.
Has the trans input shaft been shortened by someone already?
If yes, I'd surely go with the mad's snout bushing rather than the roller bearing replacement.
Click to expand...

The crank is drilled plenty deep enough for the bushing! All of my other cranks that have the bushing in them already have almost an inch more depth than the bushing! This crank is drilled as deep as the other cranks!

The snout of the input shaft has not been modified, and with the bushing in the correct place will work as stock!! Geof
 
Not to highjack, but has anyone ever set up a lathe type bore cutting tool bolted to the block and machined the hole with the engine running?
 
cosgig said:
The crank is drilled plenty deep enough for the bushing! All of my other cranks that have the bushing in them already have almost an inch more depth than the bushing! This crank is drilled as deep as the other cranks!

The snout of the input shaft has not been modified, and with the bushing in the correct place will work as stock!! Geof
Click to expand...

Then you can make the snout bushing, the pilot, or the roller.
You already have the pilot.
Turn the pilot bushing OD, add some lead to one OD end, press it in, and ream to size. Needs to have a solid press fit so it doesn't spin on ya.

Bottom of page..................

http://www.symmco.com/newpages/Tolerances.html
 
69MOPE said:
Not to highjack, but has anyone ever set up a lathe type bore cutting tool bolted to the block and machined the hole with the engine running?
Click to expand...
Seems a bit extreme. How about bolting a 3/8" plate on the back of the block and using a mag drill?
 
To throw another idea out there.
If original indersized hole is deep enough but is not running concentric. Turn up and press fit a solid bearing bronze insert and press it in. Then drill and bore it out to size and running true.
I have done mine long ago on a mill with crank mounted vertical hanging off side of table. You can then use boring head/tool to finish it.

Mike
 
You must log in or register to reply here.
-

Back
Top