K Series Cambelt Tension

[chris whitlow]

I've changed the cambelt on my 1.6 SS K-Series but can't find anywhere how to set the tension correctly.

It's a manual tensioner so there's no spring to assist.

Any help gratefully received.

Cheers,

Chris

[Wrightpayne]

as an aside, I was told to bin the spring on the manual tensioner, as they've been known to wear through and drop into the belt / pulleys with disastrous consequences - it doesnt really do much anyway!

I do mine up so you can deflect the belt a bit between the two pulleys but no stack. I was also told if its too tight the water pump will start to whine!

Summary from the manual, ensure the belt front run is taut ie all the stack is on the tensioner side of the belt,slacken the tensioner bolts and tension the belt and tighten bolts. Turn the engine over manually to check the timing marks are all still aligned then tighten the two tensioner bolts to their specified torque

Ian

[chris whitlow]

Thanks Ian.

I've read that in the manual before but it doesn't mention how you know when the tension is correct.

I thought there would be a more scientific method to determine when the tension was correct as both too tight and too loose can cause problems.

How much deflection of the belt do you get between the two pulleys?

Cheers,

Chris

 

[SM25T]

It's not deflection. On the longest run you should almost be able to twist it to 90 degrees mid span by hand.

[revilla]

Ian you're thinking of alternator belt!

[revilla]

Sorry about formatting I'm on mobile. There's a calibrated spring and post tensioning kit that you normally get with the belt kit but you can get separately from Rimmer. Slacken both bolts of the tensioner by one turn or so, so it moves freely. Screw the little post into the threaded hole in the head between the two pulleys and hook the spring around the post and through the hole in the tensioner, being careful not to stretch it more than necessary. Wind the engine round clockwise using the crank pulley bolt until the crank timing marks line up and check the can timing marks are also aligned. If not, remove the belt and correct. Check that the belt is nicely centralised on all the pulleys. If not, wind the engine round another two full turns and check again. Then slowly wind the engine round clockwise again through two full turns just until all the marks align again. Don't turn anticlockwise at all. The tensioner should settle to a steady position under the tension of the calibrated spring. When you get back to the alignment point again, carefully nip up the small bolt of the tensioner then the pivot bolt, making sure it doesn't move. Then torque them both correctly (not got the figures to hand). Once complete REMOVE THE SPRING AND POST so they can't come off into the belt. Store them safely for future use. Job done. For peace of mind wind it round two turns again and check that all the timing marks align correctly.

[revilla]

PS: I think there are two fitting kits, one for VVC engines and one for others. From memory I think the non-VVC one has a plastic sleeve around the spring, the VVC one doesn't and the VVC one sets a lower tension to protect the drive bearings in the VVC mechs.

[revilla]

For the non VVC engine you want parts 12 & 13 here: http://www.rimmerbros.co.uk/Item--i-GRID001209 - use a little loctite on the tensioner bolts.

[SM25T]

No .... twist method for cambelt.

[Bricol]

I've always done the twist test.

There is a bit of leeway - as long as it's taut enough not to jump teeth on deceleration, the fact the engine is turning keeps all the bits that need to be taut, er, taut.

Although, the tensioner isn't really a tensionerer on a belt - it's a slack taker-outer ;-) 

Seen a couple of engines (not mine!) where the tensioner pulley has lost all it's balls (lying in the bottom of the cover!) and the belt is very slack, but the owner of the Mondeo in one case had simply carrie don driving without stopping te engine for an hour or more - it made a funny noise at low revs, so stopped using low revs ;-)  Motion of the engine at higher revs, kept the belt taut with a hint of tension from what was left of the plastic pulley.  Noise was from valves hitting the pistons as the cams under the influence of the valve train pulled the belt tension off and mis-timed it momentarily.

Certainly designed cantenary sag to "tension" belts in the past on low power stuff.  Higher power drives need proper idler pulley systems.

[Grim Reaper]

On a similar note... my 1.8K (VVC derived) seems unable to get the belt tight, the tensioner is at full swing but the belt is still loose.

I have confirmed over several different manufacturers/part numbers that they are all the same (Gates 5416XS 143x26, Conti CT929 143x25, Gates LHN100830 143x25)

I've just ordered a Gates 5238XS 143x23 to see if that's any different.

It used to be about mid range on the tensioner adjustment range a long time ago, but with various belt, tensioner and water pump changes it seems to always be slack even at max tensioner adjustment.

Have manufacturing tolerances changed over the years?

Has the tensioner pulley diameter got smaller?

I've had a head skim but surely that wouldn't have dropped it that much.

It's almost as if I need to drop a couple of teeth on the belt to bring it back into range of the tensioner adjustment range.

[SM25T]

Recall there is a 145 and 143 tooth belt. Is one for auto tensioner and one for manual .... the VVC is manual tensioner. 26mm wide too

[Gordon GWF]

Just checked the box on the Gates belt I last fitted to my 1.6 k and it's a 5238XS

[revilla]

Sorry but the more I think about it, the more I think the "90 degree twist" method is completely wrong.

The official procedure published by Rover uses the calibrated spring and post, although it seems slightly less involved that the procedure I was taught (but can't remember where from). They are slightly less cautious about settling the belt. Basically push the tensioner in by hand and nip it, wind it round twice then slacken the tensioner and let the spring set the tension and torque up. No mention of the twisting method, in fact no mention of checking the tension on the long run of the belt on the right at all.

When the engine is rotating clockwise the long run on the right is the driven side. The crank pulley effectively pulls this side downwards to turn the exhaust cam pulley. What sets the tension there is just the pull required to turn the cams. All the slack ends up on the non-driven side and the job of the tensioner is just to take out that slack without putting excessive strain on the inlet can bearings. This last point which is even more critical on a VVC which retains the VVC mechanisms as these run in a single drive bearing each, but still important on other engines with a solid inlet cam.

Even with the tensioner backed right off to the point of being far too slack, it will pull tight to about the same extent on the long right hand side run. The tension you are measuring with the twist method tells you nothing other than how easily your cams turn.

Think of it this way; if you were to turn the engine a bit using the crank pulley then stop to check it, the crank will be subject to a lot of friction and the cams will probably pulling against the valve springs as well as friction. Neither will be just loose to turn. So if you were then to swing the tensioner in and out between a position where the belt was far too slack and a position where the belt was a bit too tight, neither the crank or cams would move and the tension in the long run on the right where the belt is pulling from the crank to the cams would therefore no change at all. So the tension there is telling you nothing about whether the tensioner is set correctly.

What you should be measuring is the amount of slack on the non-driven return side where the tensioner sits. As Bricol says, the job of tensioner is really just to take out the slack here. That's what the calibrated spring method does correctly, although I agree there is probably quite a bit off leeway and once you have done a cam belt or two you probably know what feels about right and can perfectly adequately set the tensioner to something that feels right and will be OK.

With an alternator belt the alternator bearing turns freely, there is no spring action or significant friction it is fighting against as there is in the valve train, so the tension equalises on both sides. You can't end up with one side tight and one side loose, and it then just makes sense to check the tension on the longest run with the "90 degree twist" test.

@Grim Reaper - A head skim will make a difference, and especially as the angle of the tensioner means that quite a lot of movement of the tensioner only equals a small change in belt length. It's one reason which heads which are skimmed by more than the specified limit (from memory that's only 0.25mm but I may have got that wrong) often require a shim. But it sounds like the difference you are experiencing is more that that, which is odd. Are you sure you are not expecting the belt to be tighter that it actually should be? Even a correctly tensioned belt is still relatively slack around the tensioner and the calibrated spring is only very light; you can easily push the tensioner a lot further in with one finger that than it is pulled in by the spring.

[Grim Reaper]

The tensioner used to be tightened about halfway through it's quadrant to get the tension right, now its at full 'tightness' and there is still slack in the belt.

Not to the extent that it could slip, but more than I would like.

I wonder if a Gates 5559XS at 141 x 25 could be a solution?

[chris whitlow]

Thanks for all the replies.

I've ordered the spring and post as I've never done this before and it sounds like a very fine line between the correct tension and too tight.

Cheers,

Chris

[SM25T]

GR .... A shorter belt won't affect the tension.

[paul richards]

Grim Reaper

The manual tensioner can be adjusted to provide more tension. Not got one in front of me, but it involves dismantling. From memory there is an interference fit between base and pulley. You can prise apart with a screwdriver and move round to get more tension. All goes back together ok and large bolt holds it all in place. Difficult to describe, but hope you can understand. 

[Wrightpayne]

After reading all the posts, particularly by Revilla, I'm going to redo mine.

Just proves what a fantastic technical resource this forum is and whatever experience you have, there is always opportunity to learn.

Thanks Andrew.

Ian

[Wrightpayne]

Just re-done mine tonight following Andrew's instructions which has meant the tensioner has been backed off slightly (see below). I marked the original position by drawing around the 10mm clamp bolt. I also tried to mark a line on block and tensioner but this was less effective. You can also see the marks (slight corrosion) on the block from previous tensioners - quite some difference!

I also removed the post as well as the spring this time.

 

Thanks again Andrew for the detailed instructions.

Ian

[TomB]

Hi, I picked this thread as a reasonable recent one about timing belt tension.

Im just working my way through a belt change, and am ready to start reassembly with a new tensioner. Does anyone know if there should be a washer on the bolt attaching the manual tensioner to the block? I haven’t one on the old tensioner, just wondering whether there should be a plain or lock washer under the caphead bolt? 

[SLR No.77]

No washer.

[TomB]

Cheers!