This has been shown using a Kenworth with a Cummins engine but the principles are pretty much the same for most manufacturers. It’s important to find the idler bearing before it seizes and the truck is broken down on the side of the road. As part of every service or anytime you have the engine running you should be listening for a squeak that could indicate an idler bearing on its way out. If you do hear a squeak the next step is to remove the belt and spin all your tensioners and pulleys. Do yourself a favor, before removing the belt draw a picture.
To remove the belt put your half-inch drive breaker bar or long ratchet into the square drive cutout in the tensioner and lever back on the tensioner to take the weight off the belt. Then slip the belt off the pulley. A square drive is common on a tensioner but it could also be the head of a bolt.
Square drive can also be a bit more hidden in behind the tensioner like in this case, so we use an extension on our ratchet once the belts off spin all the pulleys and listen for a dry bearing. If you find a noisy bearing on the tensioner or a pulley the next step is to remove it. Before removing the tensioner I recommend putting a mark so you know what orientation the tensioner was on the housing. I’ll explain why in a second. Most tensioners are held in with a single bolt with the tensioner removed you can see the locating lug. This locating lug fits into a hole in the housing. The reason I told you to mark the tensioner before pulling it off is because some of these housings can have more than one hole. So the tensioner can fit in more than one spot.
The next step is to remove the pulley from the tensioner. You might need to use a vice to undo the pulley some of them can be very tight. If the tensioner is levered by the bolt head there’s a good chance that this will be left handed thread. Remove the circlip make sure you’re wearing safety glasses these circlips can have a habit of flying out. Select an appropriate size socket to hit the old bearings out. Also select a socket that will allow room for the bearings to come out the other side. Then simply hit the bearings through. On a side note you technically shouldn’t hit a socket but what are you gonna do? if I break one I’ll buy another one. Wherever you are purchasing your bearings from make sure you tell them the application which is a fan idler bearing and say that it needs to be high speed. The bearing part number should end in c3 or c4. This is a classification of the internal clearance of the bearing and is most suited for high speed. It’s very important when you’re hitting or pressing the new bearing in that you choose the appropriate size tool. This type of bearing is made up by an inner race an outer race and the ball bearings in the middle. In this application the outer race is pushed into the housing.
The housing being represented by the red area. Pushing or hitting on the inside race, the force goes through the ball bearings to the outside race. This damages the ball bearings and the inner part of the race. You’ll find that your bearing no longer spins freely.
With the correct tool hit your new bearings into place. Keep an eye on the bearing make sure it’s going evenly in. Fit the circlip. Fit the pulley back on to the tensioner. Use Loctite 243 on the thread because we don’t want that bolt coming loose. it’s important then to give it a spin make sure it’s turning smoothly. Some manufacturers have a cover probably because they don’t want you to dismantle it and replace the bearings. They want you to replace the whole tensioner but it runs perfectly fine without the cover. If you can get sideways movement in the tensioner or it loses spring pressure then the whole tensioner needs to be replaced.
Instead of using a hammer you can use a press. The principles are still the same. Replacing the bearing in an idler pulley is also exactly the same process. Now that you’ve replaced the bearing it’s time to fit the tensioner. Put some Loctite 243 on the bolt and fit the tensioner making sure to get the locating lug in the correct position as shown earlier in the video. Note that the bolts for these two tensioners are different lengths. You can screw them in and they will start but one will only turn in a few threads and the other one will bottom out. To replace the fan belt it is necessary to slide the belt past each fin. Fit the belt taking care to align it in the grooves. It can be a little bit fiddly and when you move the belt onto one pulley it can make it come off the other pulley. So make sure you check each of the different pulleys at the end once you’ve got the belt on. Tiny pieces of rock or contaminants that get in the grooves on your pulleys will destroy your belt. The best way to deal with this is get a little screwdriver or a seal pick and run it along the grooves. For the ones like the alternator you can spin this pulley and just sit your screwdriver in the groove that cleans it out well. If you’ve had a failure where the belt has split this is something that you would particularly take notice of.
If you’re tensioners, idlers and pulleys have been running for a couple of years but they’re still good it’s a great idea to replace them and keep the old ones under the seat or in the dog box in case you ever have a breakdown. On a final note at the end of the job make sure you run the engine and inspect the belt as it’s going around. Make sure that it’s sitting properly in each pulley
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