# Sticky  Pilot Bearing or Pilot Bushing?



## PontiacJim (Dec 29, 2012)

The factory used a pilot bearing. The inspection & replacement process is covered in the factory chassis/service manual. But when replacing the bearing, the question arises, *"Bearing or Bushing?"

My opinion and choice* has always been a sintered bronze bushing over a pilot bearing. Pilot bearings can disintegrate and fail given enough years, mileage, abuse, etc. My guess is that the clutch/pressure plate will need changing out long before the bearing would fail because it will be replaced at that time.
You will also find arguments for the pilot bearing, so it once again boils down to choice.

If I am correct, our cars came with a roller bearing type sealed bearing, not a needle bearing. Roller bearings are a little more forgiving with regards to slight mis-alignment, just as the input shaft of our older transmissions use as opposed to the modern day needle bearings and tight clearances these transmissions are built to. Needle bearings of high quality are great, however the average shop guy laying on his back with the engine in the car might not get the bearing seated in the crank perfectly square. If the engine is already assembled and in the car, the bronze bushing is a better choice as it can tolerate slight misalignment.

Something one should consider and check when rebuilding your engine. If using, or upgrading, to a manual transmission the bellhousing and block's accuracy should be verified with the dial indicator method or the Browwell Alignment Tool. This is especially important when using a modern type transmission having needle bearings like the TKO. This is even pointed out in the instruction manual. Damages can result.









How To Align Bellhousing - High Performance Pontiac Magazine


Read about how to align your bellhousing on your Pontiac's manual transmission. Check it out only at www.highperformancepontiac.com, the official website for High Performance Pontiac Magazine!




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

A "good" pilot bushings that GM used and the good NAPA brand bushing is a bronze oilite made of sintered bronze. If a magnet is attracted to the bushing, I would suggest not using it and keep looking for a good bushing.

A cheap or offshore made pilot bushing may contain a good amount of iron or steel in the material's composition can and will cause galling of the pilot shaft end of the transmission's input shaft. The high amount of steel and an under lubricated or over worked condition that causes microwelding of the shaft to the bushing under extreme conditions of heat and load.

More info to enjoy.

*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.

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 .002 total. The bronze bushing type should be a press fit in the crankshaft bore. It must be installed carefully. It should have between .002 and .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 (see below). If the bore runs out more than .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 .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.

Clutch alignment is critical to installation. Otherwise, expect the transmission to not line up with the pilot bushing.

It is always a good idea to use an input gear (of the proper diameter) or clutch aligning tool when installing the clutch on any engine. With the clutch disc aligned on the pilot bushing it becomes a simple matter when installing the transmission to engage the splines and bolt up the transmission . If this simple procedure is not done, the transmission shaft won't line up and the temptation will be great to "pull it up with the bolts" which damages the front transmission bearing, pilot bushing, and more than likely will break an ear off the transmission or adapter. The transmission should slip in freely to mate up with the face of the bellhousing.

Full article here:






The Novak Guide to Clutches, Linkages & Bellhousings for Jeep® Conversions


The Novak Guide to Clutches, Linkages & Bellhousings for Jeep® Conversions




www.novak-adapt.com


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## GtoFM (Mar 23, 2018)

Thanks Jim!


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## dadspackard31 (Dec 2, 2019)

Once again Jim, Nice writeup thanks.


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## armyadarkness (Dec 7, 2020)

On my last two builds I used Centerforce Bearings. Not sure what MDL included with my Tremec Conv. I havent installed it yet.


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## geeteeohguy (Feb 2, 2008)

I'll add my 2 cents here. I agree with Jim. I used to install the bearings, and in fact have a bearing in my '65 GTO that has been in place, sight unseen, since 1984. 38 years. Is the grease dried up by now? Likely. Is it making any noise or giving me issues? No. I have seen dried up bearings weld themselves to input shafts and wallow out the crank and mess up the input shaft. Bronze or brass bushings won't do this, ever. Oilite bronze is an oil impregnated non-ferrous (not magnetic) bushing that will go decades without causing problems. Brass bushings are much the same, but not oil impregnated and I use wheel bearing grease with them. But even dry, they won't take out a trans input shaft. Also, if you are running a scattershield and a block saver plate, the extra distance the trans is moved back from the block requires a longer bushing to fully support the input shaft. Paul at 5speeds.com explained this to me when I did the clutch on my '61 Chevrolet, which runs a Lakewood shield and a plate. I used the longer bushing. I'll also add this: many new clutch kits come with what LOOKS like an Oilite Bronze bushing, but it is actually not bronze, but magnetic. If you decide to go with a bushing instead of a bearing, put a magnet to it and verify that it won't stick. You do not want to use a magnetic bushing. Next time I pull the trans out of the '65 for a re-fresh, I'll likely install a bronze bushing and get rid of the steel bearing. Main reason: the new bearings are likely no longer quality USA made items. I'd hate to have a cheap off-shore bearing derail my car.


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## armyadarkness (Dec 7, 2020)

I put a roller in my Vette, but the GTO is getting an oilite


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