HELP, Cam Belt tension problem

[rusty55125]

I finally got to the cam belt tension on my 98 esprit, I hate to say it but it took me a year to just get the time to start working on setting the tension. Anyway, every time I set the tension, rotate the engine two revolutions and went up to check, the tension went up or changed enough to require a new setting. I figured the belt had some type of set in it. So to get the belt worked in little, i ran the starter a few seconds. Only did this when the tension was set to the range given by the manual. Everything was going very well and I was getting much more consistent reading. Mind you, I only ran the starter a total of three separate times. Most of the checks were done with the recommended method, checking the timing with the pins at sever point during this whole process. Well, on the third time running the starter everything seemed to be fine, but when I went under the car to set the position for testing the tension, the crank turned over maybe 1/4 a rev, or so before it was to hard to move. I didn't want to force it to much so I stopped.

I checked all the belts and nothing appears to be in the way and they are both if anything tight and still looks to be in good condition. One reads 180Hz but that is not set where it needs to be for testing. That is just as far as i dare try to turn it to.

My question is, could the belts have jumped a tooth? Shouldn't it have been fine to run the starter to get a more stable belt tension? I only ran the starter for maybe 5 seconds or less each time. I didn't hear anything, and the engine turned over fine. I just don't know what to do. One possible thought is that the motor is vapor locked. Could that be the case?

Help me

Scott

[mike_sekinger]

Hi Scott,

From my experience, rotating the engine two revolutions is enough for the belt tensioning change to be registered with a repeatable accuracy. It should not be necessary (or even advisable) to turn the engine on the starter when you are making amendments to the tensioning. You would in any case always have to re-establish the firing stroke when doing this.

If you are worried about vapour lock, then simply remove the spark plugs. This should also make it easier to turn the engine as you will have zero compression. Just make sure that you cover the plug wells and don´t drop any foreign matter in there.

I would then go back to the start and make sure that your cam positioning is good. This being the case, carry on with the tensioning. If you need more revolutions to settle the belt, try four revolutions on the crank - see if this makes a difference.

Cheers,

Mike S

Edited July 8, 2011 by mike_sekinger

[rusty55125]

Part of my problem is that I doesn't seem to want to move at all and I don't want to damage the valves if they are hitting the pistons. Like I said before, I checked the timing with the pins several times during this process and it has always been fine. I just figured that running the starter wouldn't be any different than if i was to start the motor and I was happy with the setting I had at that point. I was almost ready to just put the car back together but being the way I am, I wanted to do one more check and that's when this happened. Anyway, I will remove the plugs this evening and see if that is the problem.

Is there any possibility that the cam got out of time from running the starter?

Thanks Mike for your quick response.

Scott

[mike_sekinger]

Hi Scott,

In principle, provided that your tensioning was reasonable, then there should not be a problem with the belt shifting. As you rightly say, this would be no different to starting the car normally.

Whip out the plugs to discount any vapour lock theory and try to turn the crank. If the belt tension is very tight, then you will find it more difficult to turn. Have a feel of the belt - is there any flex in it at all?

Let us know what you discover.

Cheers,

Mike S

[rogerch]

I found that if I set the tension correct when cold, it got too tight when hot. So it ended up a compromise. then having run the engine to full heat, allow to cool and it's different again.

So within safety margins I wouldn't worry too much until the engine has been run a few times before finally setting the tension, and in my case returning the borrowed gauge.

[rusty55125]

The belt seamed to be very tight on the left side and I can't remember on the right side but it wan't slopy loose, maybe just a little loose. Will check when I get home this evening.

Thanks

Scott

[lotus4s]

I found that if I set the tension correct when cold, it got too tight when hot. So it ended up a compromise. then having run the engine to full heat, allow to cool and it's different again.

So within safety margins I wouldn't worry too much until the engine has been run a few times before finally setting the tension, and in my case returning the borrowed gauge.

Roger,

That's not practical on a V8. Setting timing on a V8 is totally different than a 4 cyl., much more difficult to access and more things to get wrong. Best to do it by the book IMHO.

[rusty55125]

I feel so stupid!!!

When i got out of the car, i didn't notice that i had bumped the shifer leaver and put the car in gear. Took it out of gear and everything is working. Sorry for the panic, but i just didn't want to screw anyting up.

Mike, thanks for your help!!

I have to start the tension over again but al least nothing is wrong, just a brain fart.

Thanks again

Scott

[mc21.8]

and the played on

well found the problem mate thats the main thing

[rusty55125]

Another question

Something that was mentioned as the reason I was using the starter earlier. I again have been finding that the belt tension goes up significantly when I rotate the motor over two revolutions, or even 4. I believe the reason is that the valves don't have to much oil left in them, the car has been sitting for a year. I think i got the tension set correctly, but every time i move the crank it goes up to 150 to 170Hz or so. I believe that because there is minimal oil left up in the head and its a little sticky. When I grab the belt between the two cam pulleys and pull, I can get the tension to come back down. I think I need to get Oil in the valves to get a good reading on the belt tension. Can I run the car for a few minutes with these settings to get oil up in the cams to help? Or, do I need to replace the belts? Also, the left bank tensioner doesn't seem to want to set when I torque the bolt to 20-m. Do I need a new tensioner?

Scott

[mike_sekinger]

Hi Scott,

The oil left in the tappet has no relation to the belt tensioning. You are not measuring valve lift - simply the mechanical tensioning of the belt at specific rotational points in the cylce.

If you are finding variations in your belt tension simply through rotation, then I would start to question for play in the intermediate shaft idler. It is difficult to imagine that the belt tension is increasing due to a worn tensioner.

If the tensioner is not clamping properly with 20Nm, you should check that the threads in the head are not stripped.....

A few things to check there.

Cheers,

Mike S

[rusty55125]

I have a digital Torque wrench that vibrates when the set torque is reached. I don't have a problem with getting the bolt to 20N-m but at that torque I can still move the tensioner special wrench. Should I remove the tensioner and check for interferences or other problems? I could put in the locking tools on the crank and the cam so the belt doesn't move.

What are the positions the crank should be in when setting the cam belts? I have been using 80deg and 120deg ATDC, these are the values that are on my tools.

Scott

[mike_sekinger]

Hi Scott,

From what you have said, I would be looking to remove the tensioner, inspect the mating faces of the head and the tensioner and de-grease them. It is a pure mechanical clamp that is holding the tensioner in position. If there is any damage to either face, then that will need addressing.

Those crank positions are the correct later specified ones for #2 cylinder on a firing stroke.

Cheers,

Mike S

Edited July 12, 2011 by mike_sekinger

[rusty55125]

I will remove the Right bank tensioner tonight and see if there is any grease or damage. The Left bank clamping works fine and locks in place very well, but the belt tension still moves around a little bit on both belts. I don’t believe that in either case that the tensioner is moving, and causing my changing tension. I will also try to measure the Frequency every 90 degrees on the wheel to get a better understanding on how the tension changes throughout the revolution.

Thanks again Mike!!

Scott