Timing belt tension '98 XC70 B5245T Engine

Post by **pfeener** » 15 Apr 2007, 13:47

It looks like you don't have the tensioner adjusted correctly. It looks to be adjusted too loose. Assuming you're adjusting the tensioner when the engine is cold and the ambient temperature is around 70 degrees F, the needle should be centered in the middle of the posts, not off to the left as yours is. (unless you're outside and the temperature is below zero) After the engine heats up the needle will be off to the right as shown in the adjustment picture. This adjustment is very temperature sensitive because the aluminum block and head will expand and contract when it's heated and cooled which effectively moves the cams and the crank closer and further apart with the temperature changes.

I would readjust the tensioner and see if that makes a difference. If not I would check the crank and cam position as I mentioned in my previous post.

Post by **MadeInJapan** » 15 Apr 2007, 14:11

I agree with peefner if this were a manual tensioner, and not hydraulic like yours is....but I might be wrong. I would say that the entire belt needs to move backwards a tooth without moving the cam gears, and that way the tensioner will pull up the slack.

Post by **pfeener** » 15 Apr 2007, 14:58

Sorry MIJ, but this is a mechanical tensioner we're dealing with here.

five40i · Post by **five40i** » 15 Apr 2007, 16:26

Now let me explain the pictures.
#5 is when I started the vehicle, cold about 50 degrees and the engine is running in the picture.
#4 is after a 20 mile drive to Home Depot and back. The engine is idling in the picture.
#3 and 2 is when I shut the engine off. The needle always goes all the way to the right, everytime I shut it off and I get the slack in the belt between the intake cam and the crank.

I appreciate all your assistance.

Post by **pfeener** » 15 Apr 2007, 17:23

Ok, that makes more sense. The only way I can tell if the tensioner is correctly adjusted is for you to do it this way. When you park the car for the night, rotate the crank CW a little bit so you take the slack out of the right side of the belt. Let it sit overnight and take a picture before you start the car in the morning. Also take note of the outside tempature. If it's around 70 degrees F, the needle should be in the middle of the "goal posts". If it's a little colder it will be to the left a little bit.

Post by **MadeInJapan** » 15 Apr 2007, 18:17

You're right pfeener...I went back to page 1 and you guys are dealing with a '98 XC70....that was the split year so ones made later had the mechanical tensioner. As I know nothing about these things, the best of luck to five40i...I hope you figure this thing out.

five40i · Post by **five40i** » 16 Apr 2007, 16:27

Okay. I checked the tensioner today. This morning when the temp was at 34 degrees the needle was in the middle of the window, I started the engine and it stayed in the middle.
I drove the 80 miles to work and rechecked it when I got there. The needle was just to the right of the window. I shut the engine off and it stayed put, just outside the window, on the right.
I rechecked it when I got home and it is in the same place.
I ran next door to the Volvo dealer at lunchtime and spoke with my Tech friend, He says he has never heard of such a thing or seen any tensioner do the things this one is doing. We spoke for a while and have come to the conclusion, the only thing it can be is a defective tensioner as it acts so erratic.
I am going to get an original Volvo tensioner and try again. It is the only thing that makes sense to me.
I want to thank you all for your assistance and help with my problem and I will let you know how it works out.

Hugh Wilson.

Post by **pfeener** » 16 Apr 2007, 18:21

It won't hurt to try a new tensioner, but I doubt that it will change your symptoms. Your current tensioner is acting just as it should. If you have a little bit of slack on the right side of the belt with the engine turned off, the tensioner needle will be moved off to the right because the left side of the belt is tighter than it would otherwise be if the slack wasn't there on the right hand side of the belt. The tensioner is not strong enough (nor is it intended to be strong enough) to move either the crank or the cams to remove any slack on the right hand side of the belt. The tensioner is there to maintain a constant tension on the left hand side of the belt while the engine is running and to maintain that constant tension as the engine grows and shrinks as it heats up and cools down.

Bottom line: your tensioner appears to be adjusted correctly. At 34 degrees the needle should be just to the left of center and when the engine is warmed up it should be to the right of center because the engine has heated up and expanded which "grows" the engine. If it were me and the car is running OK, I would leave it alone. I don't think you have a problem. If there's some small amount of slack on the right hand side of the belt when you shut off the car, so what. It's not going to be slack enough to jump teeth and when the car is running the tensioner is doing it's job maintaining the correct belt tension.

five40i · Post by **five40i** » 17 Apr 2007, 19:30

I really appreciate your input on this, you have been very helpful. I have rechecked it again. I took the tensioner back off and checked it, I really can't see anything wrong with it. I put it back on and set it up according to the instructions, It is correct when it is running and the engine does run fine. The belt doesn't jump around when the engine is running, the tensioner needle stays pretty much in the middle for the most part.
But I'm still not comfortable with the way it goes all the way over to the right when I shut the vehicle off. As you say it maybe normal, I don't have that much experience with this kind of set up.
I had a thought though. Could the rear part of the timing cover have anything to do with limiting the movement of the needle, like having a stop built into it. As you can see from the pictures, there is no rear timing cover on this engine. It got destroyed when the tensioner, idler and belt grenaded????????

Post by **pfeener** » 18 Apr 2007, 06:52

Your missing the point. The tensioner has nothing to do with your issue. The issue is the slack on the right hand side of the belt when you shut off the engine. What's happening is the crank is backing up slightly when you shut off the engine. You can simulate the condition by turning the crank CCW by hand just a little bit. You'll see slack in the right hand side and you'll see the tensioner needle move off to the right because the left hand side of the belt has tightened. The response from the tensioner is completely normal.

If you want to solve your issue (I didn't call it a problem, because I don't really think it is) find out why the crank is backing up. The only thing that will push the crank backward when the engine is switched off is compression from the cylinders. My theory is that your cam timing is slightly off whiich I asked you to check in a previous post.