Thursday, October 2, 2008

Bearing Down on Things

Yesterday my old friend and neighbor Rob came in and purchased a pulley bearing while I was out visiting a client.

Change a pulley bearing on a General Motors compressor ..... piece of cake, right.


Rob took the bearing and gave it to one of his employees instructing him to change it. This is a relatively simple task if you know how to do it.

A few hours later Rob returned with a clutch assembly in hand and said "it worked perfect before. All we did was change the bearing and now it slips.....Can you check it out for me?"

"Sure Rob. Be happy to."

The first thing I did was check the coil with an ohm meter.

"Coils good."

Next I looked at the pulley.

The first thing I noticed was the bearing seal was damaged, obviously from the way they installed it.

"Rob, look at this."

"Whoever did this used the wrong tool. You never put pressure on the face of a bearing seal."

Rob replied, "I know Joe, what did they do?" all the while with a look of disgust on his face.

I said, "Look ....." and I proceded to peer across the face of the pulley and show Rob what had happened.

His employee used the wrong tool to install the bearing and damaged the bearing seal. Then he did not support the pulley properly and proceeded to bend the "face" of the pulley so it was now concave. Of course the perfectly flat "hub" or "drive plate" which mates to this was slipping. It had to because it was only grabbing on the outer edges of the pulley's circumference.

So ....

Here are a few useful do's and don'ts about changing a pulley bearing.

The first rule to remember when installing a new bearing is to never put pressure on the inner race. This stresses the ball bearings and will ultimately cause the bearing to be noisy. When installing a bearing the tool must rest on the outer race so it does not put pressure on the ball bearings or the inner race. Remember, the whole assembly is held together by polished steel balls riding in a polished groove. Damage the balls or the groove and the bearing becomes noisy or, worse yet, it comes apart.

Removing the old bearing is a whole other matter. In most instances, you are forced to put pressure on the inner race to remove it. But that doesn't matter since you are changing it any way.

Above I mentioned that when installing the new bearing the tool must rest on the outer race.

Hmmmm .... this could be a problem for the DIY'er......

Well ..... not really.

Of course, you could get on line and go to your favorite Auto AC parts and supplies dealer, Polar Bear, Inc. and spend a lot of your hard earned dollars with that nice guy Joe over there. This in an of itself is always a good idea ....

but,.... if this is a once a year or once in a life time project, it kind of defeats the purpose of doing it yourself. So, consider ..... what will fit perfectly over the outer race of your new bearing?

How about the outer race of the old bearing?

Simply clean any grease or grit off your old bearing and line it's outer race up with that of the new bearing. Line both bearings up perfectly straight with the bearing housing of the pulley and use a flat piece of metal to press it in.

But .... nothing is as easy as it sounds.

You must be careful to keep everything straight. If the bearing cocks to one side it will jam and cause you problems. It might even damage the bearing or the pulley. All of which brings to mind Rob's original problem ....Notice that the bearing in the pulley pictured below presses out from the rear.

You simply lay the pulley on its face and press the old bearing out of the pulley (or drive it out with a special tool and a hammer). Then wipe it clean and install the new one doing the reverse using your improvised old bearing and scrap metal tool.

Well, .... not exactly. You must be sure to support the bearing housing when you install the bearing. If you support it from the outer edges, as Rob's employee did, you will collapse the face of the pulley, making it concave and rendering it useless.

Keep in mind also that if you use the old bearing as a tool in order to install the new bearing you will usually have to drive part of the old bearing into the housing. It will probably get stuck. As long as it does not to go too far into the housing you can remove it by holding the pulley and tapping it with a small hammer. If the bearing sits too deeply in the housing you will either have to buy the correct tools or bring it to a properly equipped shop. Another thing to know is that most automotive bearings are secured in place by either a snap (or lock) ring OR they are staked. When working with a snap ring you simply remove and replace it. You need the appropriate snap ring pliers. When working with a bearing that is staked you will need to "re stake" (if there is such a word) the bearing. If there is no snap ring, you will notice a series of "punches", "indentations" or "dimples" on the open side of the bearing housing. These punches slightly collapse the wall of the housing over the outer race of the bearing. When you remove the bearing you expand those "collapses" (another new word) so when you replace it you must stake the bearing again. You do this with a small, very pointy punch and a hammer. Place the punch next to or on one of the original marks on the pulley and give it a sharp rap with the hammer. Do this following the old marks until you get them all and the bearing is now "staked".

While we are at it ... A word of caution about presses.

Even the lowly manual arbor press exerts several tons of force when you use it. A hydraulic press exerts much more....* Any* hydraulic press, even the bottle jack style. When you stack objects such as these be aware they can fly out of the machine with deadly force when not perfectly straight. Never stand directly in front of the machine. Always stay to the side and try to use the frame of the press as a "shield".

So, the lesson learned here is that Rob, a seasoned pro, didn't assess the job with respect to the resources he had available. Obviously, his employee was not familiar with changing this type of bearing in this type of part. In terms of time, lost opportunity, damaged parts and wasted labor, Rob would have been better off changing the whole clutch OR, bringing it to someone who has the proper tools and fixtures to do the job.

As a DIY'er, it is critical you think this way since as a general statement, you do not have a complete shop or a network of shops you can bring your mistakes to and get professional help. When in doubt feel free to call us (1800-365-3516). We will tell you what is involved in doing the job and if you need special tools. And, when we don't know, we are not ashamed to say so. But, we will find out for you.

So, till the next time something worth discussing happens, thanks for reading this.



Mikes said...

Changing the bearing in your car is easier. You can easily learn yourself and can complete by your own.

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