I changed the serpentine belt, tensioner and idler pulleys on the wifes GLK350 at 150k miles this weekend. I noticed that the ones that came off still seemed to have plenty of life left in them. I roughly determine how worn they are by how fast/long they spin when spinning by hand. My experience with these items off of BMW's are that they spin quite freely after about 120k miles. I'm not going to run till failure on her car because of obvious reasons. What is longest anyone has seen these items last - mileage wise?

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Jim

Free spinning isn't a measure of bearing wear, it is a measure of how much grease is still in the bearing.

Whenever I get a car with over 100 K, I lube alternator / idler / AC bearings if they still feel smooth. Don't fully pack the bearing as this creates excessive friction and can burn the grease leading to a bearing failure. Something like 50 % fill is plenty with less grease used if the bearing sees high speeds. To some extent excessive grease will be expelled from the bearing during use so fill volume isn't hyper critical.

About 8 years ago I got a 99 Blazer with 125 K miles for Dad to drive. I lubed all of the bearings and it now has 230 K on the original idlers / AC bearing. The alternator and water pump were replaced due to non bearing related failures.

How do you lube them?

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Jim

Most bearings in this type of application are rubber sealed, see farther down for shielded.

Use a eyeglass screw driver to pull the seal lip off the inner race then insert a grease needle and give it a pump or two. An alternate method is to pop the seal out of the outer race then apply grease to the bearing. In either case you only need to do one side on a single row bearing because most idlers / alternator bearings are single row. If double row, like some AC clutch bearings, pop a seal on each side. If the bearing seal gets slightly damaged it usually isn't an issue.

Some bearings are shielded. This is more or less a steel washer that snaps into the outer race and is close to the inner race. With these I pry up the inner race side then pump grease in.

In theory, old grease should be removed as mixing greases " could " cause a problem but I haven't had any issues over the years.

Find any sealed bearing and practice / just pry the seal off to see what you are up against.

I'll try it on some of the old spare pulleys I have laying around, thanks.

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Jim