Timing belt tension '98 XC70 B5245T Engine

five40i · Post by **five40i** » 14 Apr 2007, 08:34

Hi;
I seem to be having problems keeping tension on my timing belt.
I bought this car with a blown timing belt, bent all the valves.
I replaced the head. I set up the timing per instruction I got on line and through a Volvo tech I know. The engine seems to run fine, it does seem to lack power and has a wee bit of a rough idle. I think those problems are related to the problem I am having with the tension of the timing belt.
When I installed the timing belt, I locked the cams and lined the crank up with the timing marks. One thing I did notice with the crank lined up with the marks, #1 piston is not all the way up. If I turned the crank a few degrees past the marks, then the piston came up to the top of its travel.
I got confused at this point. I consulted my Volvo tech friend. He told me he just lines up the marks. I went with his advice, seemed to work.
Anyway. I adjusted the tensioner per the instructions to get the pointer in the window, turned the engine over by hand a few times just to make sure the needle stayed in the window and no valves hit. I started the engine and found the needle went to the right, out of the window. I shut off the engine and the needle went even more to the right. At this point I found there was slack in the belt between the intake cam and the crank.
I turned the crank by hand to take up the slack and re-adjusted the tensioner again, got it in the window, turned the engine over a few times by hand and the needle stayed in the window. I started the engine, the needle went to the right, where is stays when the engine is running, shut the engine off and the needle goes more to the right and there is slack in the belt between the intake cam and crank.
I tried to adjust the tensioner again and again, and again and keep coming up with the same results.
Am I missing something??

Any suggestions would be greatly appreciated.

Thanks
Hugh Wilson

Post by **pfeener** » 14 Apr 2007, 08:57

First; STOP do not run the engine or you are risking wiping out the valves again.

To answer your questions:

1. when the timing marks on the crank are lined up the #1 cylinder will not be at TDC, that's normal. Just line up the marks as you have been doing.

2. I don't know how you're adjusting the mechanical tensioner, but there's not much to it so I assume you're doing it correctly. Just for background information. The adjustment will change as the temperature of the engine changes and the aluminum block grows and shrinks with the tempurature change. The needle should be in the middle of the posts at 70 degrees and will move to the right as the engine heats up and will be to the left if the engine and outside temp is colder than 70 degrees. I'll attach the link for the adjustment in case you don't have the official Volvo instructions.

3. Now to the meat of the matter. Obviously either the belt is stretching or the belt path length is changing. The cams and the crank are not changing. The water pump and idler are most likely not changing either or you'd be able to feel the play when you grab them. That leaves either the tensioner not holding it's adjustment or the belt is defective and stretching. The tensioner needs to be changed with each belt. It will not go two belt changes. I didn't see in your post if you bought a new tensioner or not, but if it were me, I would buy a new genuine Volvo (I've had very bad luck with aftermarket parts) tensioner and belt (even if the ones you have are new) and start over. For the $100 buck it'll cost you for the new parts, it would be worth it in my mind.

http://volvospeed.com/Repair/ManualTensioner.php

Post by **pfeener** » 14 Apr 2007, 08:59

One other thing. You probably already know this, but when you're turning over the engine by hand you can only rotate it clockwise, looking at the crank from the right side of the car. If you rotate it the other way the belt will loose up and you may FUBAR the tensioner.

Post by **Ozark Lee** » 14 Apr 2007, 09:39

A couple of things come to mind.

We had another member that had similar problems and, at the end of the day, the center bolt was missing from his crankshaft sprocket and it had slipped. The timing mark - such that you can see it without a microscope - should align exactly with #1 TDC.

You are also likely aware that the camshafts also have adjustable valve timing. If the camshaft sprockets have been removed at any point during your repair they are likely not properly timed. Quickbricks sells a tool to set the cam timing but it comes at a price.

http://www.quickbrickmotorsports.com/prod_camtool.html

...Lee

Post by **pfeener** » 14 Apr 2007, 09:59

Both points are good thoughts, but neither would cause the timing belt to loosen.

five40i · Post by **five40i** » 14 Apr 2007, 10:26

Hi all:
Thanks for the replies. First of all I installed new belt, tensioner and idler that I bought from FCP Groton so I can assume the parts are reliable??
Secondly, I have followed the adjustment procedure from the link that was sent several times and keep coming up with the slack. Granted it isn't much but when the engine is started the crank will take up the slack and yank on the belt, I don't think that is a good idea.
The cam gears were taken off to transfer them to the new cams that came with the new head. What I did was leave them loose with the cams locked and the crank on the mark, put the belt and tensioner on. I then turned the cam gears counterclockwise to take up the slack between the intake cam and crank, then locked them down. I then adjusted the tensioner.
I really don't like this tensioner and I don't trust its reliability, it seems to complicated for what it does. I have thought about getting a tensioner for an M40 BMW engine and see if that will work.

All comments greatly appreciated.

Hugh Wilson

Post by **pfeener** » 14 Apr 2007, 12:48

There should be no slack in the belt; period end of story. A lot of folks don't seem to like the mechanical tensioner, but it's the one Volvo has used since mid 98, so they've manufactured a ton of cars with this tensioner. I wouldn't try using anything else. The penalty for being wrong is just too great. Keep in mind, the tensioner on these engines can't be ov the fixed type because the engine "grows" too much as it heats up. The tensioner has to be able to adjust.

The timing on your cams, cam gears and crank pulley should be as follows. With the crank pulley on it's timing mark, the cam gears should be on their timing marks and the slot on the back (left hand side of motor) of the cams should be horizontal.

The procedure for installing the belt is as follows. With the crank and cams on their respective timing marks, thread the belt from the crank pulley up the right hand side over the idler, over the intak cam, over the exhaust cam and around the water pump pulley. The belt must be tight with no slack on the right hand side and over the top of the cams. Install and make a preliminary adjustment on the tensioner. Rotate the crank in a clockwise direction, which will remove any slight slack that's in the belt track. Readjust the tensioner according to the tempature of the block. Crank it through clockwise a few more times to be sure and you should be done.

If for any reason the crank turns or is moved in the counter clockwise direction the belt will develop slack on the right hand side and the tensioner needle will move off to the right. From your description it sounds like this is what's happening to you.

Question: when the belt develops slack, do you have to readjust the tensioner or if you just rotate the crank CW a little bit so it takes up the slack, is the adjustment needle back where it should be.

five40i · Post by **five40i** » 14 Apr 2007, 18:59

"Question: when the belt develops slack, do you have to readjust the tensioner or if you just rotate the crank CW a little bit so it takes up the slack, is the adjustment needle back where it should be."

To answer the question. I move the needle to the left by hand ( I don't have the timing cover on, it got destroyed when the belt came off). When I do this the slack is gone. (but it will not move back into the window). If I move the needle to the right by hand, the belt slackens up all round. Also
If I rotate the crank slightly clockwise the slack is gone and the needle will move to just right of the window.
I am going to take a couple of pictures and post them so you can see what I am talking about.

Thanks again

Hugh Wilson.

Post by **pfeener** » 15 Apr 2007, 06:40

OK I have a clearer picture now. The path lenght or the belt length isn't changing. The belt is loosening on the right side so the path lenght on the left hand side is shortening and the tensioner is adjusting accordingly. If you think about how this system works: the right hand side of the belt is the "drive" side of the belt, meaning the crank pulley turns cw and pulls the right side of the belt down which rotates the cam pulleys. So the right side of the belt is always under tension and tight. The left side of the belt has the tensioner which is spring loaded and is just there to take any slack out of the belt.

It sounds like what's happening with your system is the crank is backing up a slight bit when you trun off the car which puts a small amount of slack in the right hand side and shortens up the left hand side.

I would check the "actual" cam timing. Not the timing on the cam pulleys, but the actual cams. Bottom line, with the crank on it's timing mark, remove the distributor and the cam sensor and the slots in the cams should be lined up horizontaly.

five40i · Post by **five40i** » 15 Apr 2007, 10:49

Here are a few pictures of what is going on. I seemed to have loaded them in the wrong order.
The last picture is when I start the vehicle cold, the second to last is when I shut the engine off after a 20 mile drive and this is when the belt gets slack where my finger is pointing in the last picture. here is the link for the pictures.

http://profile.imageshack.us/user/five40i/images/

Thanks

Hugh Wilson.[/url]