Pilot Bearing Design
 

I bought two 7109 pilot bearings. The BCA (the one BOP and Butler sell) is open on both sides. The Timken is open on one side and sealed on the other. Which is the better design? And if I go with the Timken, should the sealed side face the transmission or the engine?

Open side faces the engine, so if you desire to force grease into the bearing from the front side it won't be able to get on the flywheel surface.

By partially filling the back of the crankshaft and sliding a shaft that fits tightly on the inside race you will force grease into the front side of the bearing. If you put too much grease in you'll either blow the seal off, or force the whole bearing out of the crankshaft cavity.

That's the way I've been doing it for 50 years, and I really never have had the bearing fail if I followed that procedure. I know that the bearings are supposed to be not as durable as a bushing, but if you follow that procedure, it should outlast the clutch. When the bearings fail, or get noisy they're dry of grease. I never see any leftover grease in the back side of the crank cavity of failed bearings. I believe they just hammer the new bearing in, and reassemble the clutch, never bothering to fill the new bearing with grease.

Centrifugal force at 5000 RPM should also push some grease into the bearing too, not proven, just my theory.

The extra step does make a difference.

:2cents:

Timkin all the way!

Tom V.

If your using the bearing make sure you stake it in place. 7109 Timken is the one I used. The bearing really only comes into play when the clutch is pushed in.

only takes 1 little bitty prick punch to keep it in forever!!...don't go all "hammer Joe" on it or you will NEVER get it out!!! ;)

ive always heard that you dont want to grease roller bearings like these or modern pulley bearings in serpentine systems, the thin clear grease they come with is what they are designed for & all thats needed. been told that adding the wrong thick grease like chassis or wheel bearing grease causes the balls to not roll right & can or will make them slide on the race & not roll.

not sure if thats 100% true but ive been told that by reputable long time mechanics as well as bearing manufacturers when i asked about greasing them. yes the factory installed grease can dry up but usually not until the end of its service life, maybe adding some grease at that point can extend the life a bit but ive always trusted the dont add grease thing & left them alone with what they come with. just mentioning what ive heard a lot more than one time on greasing roller bearings.

for removing a pilot bearing thats a bugger to get out i did use the trick of packing the crank bore with grease & using a rod just a tad smaller than the bearing opening to pound it in & have the grease force the bearing out.

Is it necessary to stake the bearing if it fits real tight/needs to be tapped in (or frozen first)?

its always recommended to put 1 little "burr" to keep it from coming out without INTENTION. FWIW a little dry ice and rubbing alcohol will get you down to about -150* F which should be worth about .0015 on the diameter of said bearing ..;) (worth about .003" change in pinion bearing race dia...due to it's size)

If the bearing fails from lack of lubrication, not putting grease in will make it last longer? Then you have the fact that they leave one side of the bearing exposed. If you wanted a sealed bearing, why is one side open? So dirt can enter?

You stick to your theory, and I'll continue doing it the way I've done it for 50 years...........;)

Hopefully you don't replace tapered wheel bearings using the same theory.

I'm wondering why someone would stake the bearing, when it can't move unless the transmission is removed?.........:noidea: It's pretty much captive as soon as the input shaft is installed.

If someone was worried that it didn't fit tightly, a couple hits with a prick punch on the interior of the crank bore can tighten it in the bore.

Most times I install the bearing, grease it as outlined, and finish the job.

The only reason I mentioned to stake the bearing as I've had them a bit too loose and staking helps to keep the outer race from rotating. If the bearing installs nice and tight Probably doesn't need to be staked. I assumed if your installing a bearing you know the procedure. That's all. like your little Emoji..

My father, also a mechanic all his life, showed me that if a bearing doesn't fit well, then you use a prick punch to raise the mating surface so it does fit tight.
I guess two ways to arrive at the same end. That bit of advice he gave me has been invaluable many times over the years. They hadn't invented Loctite bearing mount yet....:)

My impression from assembly manuals I've looked at over the years is that the purpose of staking is to keep the bearing in place when removing the transmission. Since I'd replace the bearing if I pulled the transmission, I never bothered in the past. I'm no mechanic and haven't gone through this very often (maybe 10 times over the last 40 years), but each time the same questions occur to me. I've always wondered whether there should be a little give between the crank and outer race just in case the bearing seizes up. This way the whole thing would turn and the noise might indicate a problem before the whole thing comes apart.

I've taken them apart when the only thing left is the outer race. The grease gets hard from age and the inner parts disintegrate. The balls, and inner race were MIA, and a lot of metallic dust is left. The outer race was the only piece that didn't fall apart, still stuck in the crank just like when it was installed. I can't remember if the input bearing was bad in the transmission on that one or not. Too many clutch jobs to recall each one in detail.

All I can speak for is, it definitely helps if you give the bearing a little extra grease. They seem to stay together much better, than just hoping there was enough grease when assembled by the manufacturer.

The Pontiac pilot bearings are fairly unique, most manufactures use a bronze bushing. I have seen a few trucks that use a ball bearings, but not many cars. Trucks however sit at a stop with the clutch disengaged, and if you don't have a cowboy driver, the clutches in trucks tend to last longer so maybe it was a durability reason that Pontiacs used it...can't say for sure. GTO clutches never lasted very long....LOL

I never worked on any stick shift older cars with the straight eight, or sixes from Pontiac, so not sure how far back they used the ball bearing pilot bearing.

A roller bearing would probably be more robust, but with little side loading, probably not necessary. If it gets replaced with every clutch replacement, it's probably adequate, as long as the grease doesn't dry out.

well its not "my theory" its what ive been told for years by many reputable life long mechanics & when i asked the tech dept at a bearing company. i used a pilot bearing for my car & when i saw the open back & thin clear grease i thought the same thing about adding grease, they said do not do that as its not designed for random grease to be injected at an unknown or excessive amount, they use a special grease intended for the purpose. there is a lot of info out there supporting that & they all say the same thing, that thick grease in a roller bearing like these makes the balls not rotate as designed & they will skid along the race causing excessive heat, wear & shortened life. so i chose to go with what the manufacturer recommended & trust what my mechanic friends say... im not suggesting the bearing will fail right away by adding grease & im sure its worked for you in the past, but its not what the manufacturer says to do & apparently a lot of other people & mechanics that have been doing this just as long as you know about it too.

not much dirt is able to get into the area of a pilot bearing, when i removed mine at ~50k miles & 40+ years old the inside of the crank bore was basically spotless & the bearing itself was very clean looking. these pilot bearings arent designed or needed to be sealed...

& a tapered wheel bearing is completely different than a roller bearing... they are designed for thick wheel bearing grease & operate a little different than a ball bearing, the comment about "hope you dont replace tapered bearings using the same theory" makes no sense since they are not the same type of bearing & obviously dont come pre lubed with a specific grease & require packing with wheel bearing grease.

lots of people do things different than what the manufacturer or repair manual says to do, i do it too sometimes & it usually "works" ok, but that doesnt mean its what the engineers & manufacturers of the part recommend to do.

EDIT: i just called timken to confirm what they suggest for this, spoke to the auto tech dept & asked about greasing a pilot bearing for a 1978 firebird & he looked up the part #. he said they specifically do not recommend adding any grease to these, they are supplied with a special synthetic grease that lasts the life of the bearing. i asked if it would be ok to put some other grease like chassis or wheel bearing grease & he said its not recommended & then repeated what ive heard & mentioned above, it will or can cause the ball bearing to not roll & rotate right & cause heat & premature wear. straight from the horses mouth. do what you want but i will leave my pilot bearing as designed & if/when it fails or the grease dries up i will buy another one for a few bucks.

So I decided to see if I could figure out how far back Pontiac used the 7109 (part number is 907109) bearing and the first thing I found was that Pontiac used the same bearing from`1941 through at least 1966 (the date of my parts catalog). The next thing I found was that it wasn't a 7109 bear, but a part number 907321.

I KNOW I replaced the bearing in my '57 347V8 with a 7109 when I had the tranny out.

Not a hijack but, man... I've been searching and reading about pilot bearings and bushings. I have 3 different bearings now, and 1 bushing, and I still don't know what to do.. LOL.

If you are running an automatic put in whatever you want.

If your are driving a street car on street tires put in whatever you want.

If you are running a Manual Trans car with GOOD TIRES and Power Shifting go with the Modified
(diameter cut down to fit the Pontiac crankshaft) Bronze Bushing, to support the input shaft without failure.

Tom V.

I have always ran the bearings in Pontiacs. The one in my '65 has been there unseen and un-re-lubed since 1984. Is the grease dry by now? Likely. Is it noisy? No. That said, if it were a bronze bushing (non magnetic) I wouldn't even give it a thought. The oilite bronze bushings don't dry out, and don't weld themselves to the trans input shaft like the bearings can, after they dry out and run hot. So, while I used to run bearings, if my '65 needs another clutch or a trans overhaul in my lifetime, I may go with a bronze bushing instead of a bearing. The one I installed 38 years go had a sealed side, which I faced to the trans after packing it with high temp disc brake grease. YMMV....

Funny....I've run wheel bearing grease in my '65 for the past 38 years without any service at all.....and about 50, 000 miles. I've also run wheel bearing grease in all my older cars that have----guess what?-----ball bearing wheel bearings. My Ford T, and my '61 Corvette. Ball bearings. Yet the wheel bearing grease works just fine. Funny how that is.....

Butler lists the 7109 bearing and another one that's .007" larger in diameter.