Pilot bearing and bushings

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by: Cobalt327, Crosley, Eloc431962, Jon
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[edit] Overview

From the Novak site:

[edit] Pilot Bushing

"In most cases, this is a porous bronze, pre-lubed bushing rather than an actual bearing, as it is often called. A few applications still use an actual bearing and others use a needle roller type bearing, but by far, the most common type is bronze. You cannot use a roller bearing on a transmission shaft originally designed for a bronze bushing due to different type of heat treatment on the shafts.
"For a list of several versions of pilot bushings offered by Novak, jump here.
"The pilot bushing is seldom thought of as a part of the clutch system but it is one of the most vital parts of the system. It pilots the end of the transmission input gear in the crankshaft. If it is worn or not running "true", it can cause serious clutch problems or transmission failure. Pilot bushing bore runout should always be checked with a dial indicator and should be within 0.002" total. The bronze bushing type should be a press fit in the crankshaft bore. It must be installed carefully. It should have between 0.002" and 0.003" clearance on the transmission shaft when installed. The pilot bushing is only functional when the clutch is disengaged but it is a factor in input gear alignment at ALL times.
"Most people have no idea what an important part the pilot bushing plays in the life of the transmission and clutch. The job of the pilot bushing is to support the end of the transmission input (main drive) gear in the crankshaft and it only acts as a bushing when the clutch is depressed. This pilot bushing should be a light drive fit into the crank bore. Care should be taken when installing any pilot bushing as they are soft and easily damaged by crude installation techniques. A damaged pilot bushing can bind on the input gear giving symptoms of clutch drag. Transmission damage and early failure can be caused by a pilot bushing or crankshaft bore that "runs out" in relation to the transmission locating bore in the bellhousing. It is advisable to check the bore of the crank with a dial indicator before installing the pilot bushing. If the bore runs out more than 0.003" total, the crank should be set up in a lathe and the bore trued up OR a special pilot bushing should be made that runs out the same amount as the crank bore. The run out in the bore of a pilot bushing is put 180 degrees off from the crank bore run out and the pilot bushing installed. If properly done, this can put the bore of the pilot bushing well within the 0.003" required. We have used this method to save engine disassembly many times. A disadvantage of this method shows up at pilot bushing replacement time as a special pilot bushing will have to be reproduced."

[edit] Types of pilot bushings/bearings

[edit] Bushings

Sintered oilite-type bushing. GM p/n 3752487 or Doorman p/n 690-014 are similar to this

"Good" pilot bushings that GM and the good NAPA bushing is an oilite made of sintered bronze. If a magnet is attracted to it, this indicated an iron content- which isn't recommended in many cases.

A "good" pilot bushing is an oilite. Oil is put into the sintered bronze material under a vacuum- an impossibility w/non sintered material- being as how a solid bronze part has no real porosity of any kind.

An oilite bushing contains all the oil that the material can "soak up" already. The amount of pressure that's used when it is sintered will determine how much porosity- and how much oil it can absorb. Different applications will have different properties.

Adding additional lube other than a slight amount as an installation aid isn't recommended and will serve only to attract/collect debris coming from the clutch and clutch plate, dirt, etc. An oil-bearing material like oilite has all the lube it needs already incorporated into the material itself, anything additional is not needed.

[edit] Fluted bushings

GM pn 10125896 pilot bushing.jpg

The flutes reduce the load bearing capacity- even though there's not a terrific amount of load on the pilot bushing- provided the bellhousing is indexed correctly. They also present a way for contaminants to get into the bushing.

[edit] Damage caused by a pilot bushing containing iron

New input shaft
Badly galled input shaft caused by seized pilot bushing containing a high amount of iron or steel

Somewhere in the shaft's life (above), it has been used w/a pilot bushing that contained an iron/steel bronze compound by the looks of it. A pilot bushing containing a good amount of iron or steel in the material's composition can and will cause this type of galling. It comes from microwelding of the shaft to the bushing under extreme conditions of heat and load.

An all bronze oilite bushing is basically incapable of such damage; the bronze being softer than the shaft causes the bushing to be sacrificed instead of the shaft.

[edit] Needle bearing (rolling element)

Unless these are original equipment, it's not usually advisable to use them in place of a sintered bronze pilot bearing. If a rolling element type bearing is going to be used, it's imperative that the bellhousing opening to transmission input shaft alignment be within 0.002" to prevent premature bearing failure. In the case of a bronze bushing type bearing, there is more leeway for any misalignment.

It's been stated that the roller needle bearing has a Rockwell hardness of about 57 and the newer transmission's gears are rated between 61 and 63. In cases where the input shaft may be 'softer' than the needle bearings (like possibly in older transmissions), there is a chance undue wear could occur to the input shaft, possibly necessitating replacement.

Lakewood p/n 15977
GM p/n 14061685
GM p/n 12577583

[edit] Bellhousing alignment

Because of manufacturing tolerances or line boring of the mains, it's possible for the index to be off. Unless the hole in the bellhouse is in alignment w/the crankshaft, undue wear will occur to the shaft, bearings and/or pilot bushing.

More on bellhousing alignment- Bellhousing Alignment From the February, 2009 issue of Circle Track magazine.

[edit] Removal methods

Slide hammer/bearing puller

The pilot bearing/bushing is used with a manual transmission only. And, it is in your best interest for the bearing to be removed when changing from a manual transmission to an automatic transmission.

There are several ways to remove the pilot bearing from the crankshaft. Probable the safest method is to use a slide hammer puller attachment with expandable fingers. This slide hammer is sometimes called a "blind hole puller" or an "internal bearing puller".

[edit] Other removal methods

If a proper puller tool is not available, the following suggestions are just a few ways to remove the bearing either for a new replacement or complete removal.

When removing the bearing you will be removing the transmission. So, as anytime, when doing these changes be safe and have the vehicle properly secured when lifted in the air, if you do not have a lift. Be sure to use the proper jack stands for the weight of the vehicle in question, and, if possible, have someone there with you while performing the work. DO NOT place vehicle on blocks of wood or concrete blocks. If you have access to a transmission stand, use it by all means. Vehicle needs to be on a good level surface. After the transmission has been removed and cleared from the vehicle, you will remove the flywheel. Then, if you look at the end of the crankshaft, you will see the bushing. It is where the shaft of the transmission will ride when installed. The nose of the shaft sits inside the bearing. Now you can either rent or buy a puller for this. It's a small slide hammer puller with fingers on it that you will place in the bearing and use it to pull the bearing out. If you do not have access to a puller here are a few other ways of removing the bearing.

  • You can fill the center of the bearing with grease and find something that is almost the same size as the bearing and place it in through the center of the bearing and take a hammer and hit whatever you are using and the force with the grease behind the bearing will force it out. You might have to hit it pretty hard and more then once but it will come out. When using something like grease, wear safety glasses and leather gloves. The force of the grease can cut the skin, or even put your eye out. Also watch out for flying pieces of metal.
  • When using the grease/toilet paper method wear gloves or wrap a rag around whatever you are using to hit with the hammer to help prevent flying debris.
  • Another method is you can fill the center of the bearing with wet toilet paper and use the same process as above.
  • You can also use an old input shaft that has been removed from an old transmission. You might want to do some modification to the old input shaft to turn it into an easier to use tool.
  • You can also use a lineup shaft.
  • If you can't find a tool to use to fit the bearing, you can use a 3 inch 1/2 Inch drive extension to place in the center of the bearing and force it out. But by all means if you can use the small fingered slide hammer, do so.
  • If you have a brass or bronze pilot bushing, an alternate method can be used as well. Use a tap and cut threads into the bushing. Then screw in a bolt and bottom it out inside the bushing so it contacts the crank. Then just keep on turning and it will pull the bushing out. Works real well if you have a tap, where as you may not have a piece of stock to fit the bearing inside diameter.It is a little safer as it takes the hammer out of the equation.
  • Bread is also a surprisingly effective removal method. This works much the same as the newspaper/toilet paper method.

[edit] GM instructions on removal

From a Chevrolet Passenger Car and Light Duty Truck Overhaul Manual: Pilot Bearing Replacement The clutch pilot bearing is an oil impregnated type bearing pressed into the crankshaft. This bearing requires attention when the clutch is removed from the vehicle, at which time it should be cleaned and inspected for excessive wear or damage and should be replaced if necessary.

To remove, install tool J-1448 and remove bearing from crankshaft. In replacing this bearing, use tool J-1522. Place bearing on pilot of tool with radius in bore of bearing next to shoulder on tool and drive into crankshaft. Lubricate with several drops of machine oil.

[edit] Olds transmission input pilots

Olds cranks weren't all machined for a manual tranny pilot. See p/n's 450, 455 and 460- Mondello tranny pilots.

The better way to do the input pilot is to use the BBC bearing, as shown. But the other two can be used w/minimal machine work. Like they say, "down & dirty". But to do it 'right' requires the crank to be removed or at least the engine.

The image below shows a pilot bushing that is NOT going to interfere with the converter, as the bushing is below the area occupied by the converter. Note this image shows a picture of a Flexplate flywhee) or drive plate used with a torque converter and an automatic transmission. There is no need for the pilot bushing in this instance. Only a manual shift transmission requires a pilot bushing. As stated above it will not interfere with the operation of the torque converter.

At pilot bush.jpg

[edit] Resources


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