KV6 crankshaft pulley

[kaiser]

Originally Posted by Mike Noc

I'm not talking about a longer belt with more teeth, but a tolerance variation of the belt with the same number of teeth.





Take a look at the photo (ignore the arrow) and imagine that the entire belt is 1% longer. The tensioner will move in to accomodate the extra length, but the slack will be in all of the free sections of the belt.

So starting from the right of the crank pulley, as the slack is taken up both cam sprockets will move anti clockwise, advancing the timing.

That is why the front cam sprockets float; so that the tension and length tolerance of the belt can be accounted for.

Well, I have found one reference, stating the accuracy of a timing belt to be 0.8mm/m. In other words they are identical to within 0.8mm for each meter.
That makes the maximum length difference you should expect 1.41mm between any two of our 1.76 meter long front cam belts. That takes the error down to 0.6 degrees on the sprocket.(going through the calculations with 1.41 in stead of the assumed 5mm)
You must be mad to think you can adjust your sprockets with that accuracy!

[Mike Noc]

Did you get that reference for these particular belts, or is it just a general tolerance?

Variations in belt tension can also affect the timing if you don't make use of the floating cams.

So Rover either added the floating cams so that the belt tolerance and tension can be accounted for independently of the timing, or it is as you stated below:

Originally Posted by kaiser

The only advantage, if any! of the floating cams are, that you CAN change the timing for specific purposes if you are dead set on tuning the engine.

Everyone can make their own minds up, 'cos I don't think we are going to agree on this one.





.

[SD1too]

Originally Posted by Lovel

Has the outer part of your pulley slipped some distance?

Good morning Gary,

I have placed my pulley horizontally in the vice and inserted the special tool into the large hexagonal recess and pushed! There is absolutely zero movement between the outer and inner parts of the pulley.

Inspecting the rubber ring on both sides it has light crazing on its surface, very impressive after 19 years' service I'd suggest. It has no cracks, no evidence of separation from the cast iron parts and no shredding.

I absolutely agree with you that the factory notch is in the wrong place but how did it get there?

• Rotation of the outer part relative to the inner? No obvious evidence of damage caused by this.
• Manufacturing error? How would this have not been noticed during assembly and alignment?

I guess that replacement is probably a wise choice but I never like to do that unless I understand why I am doing it!

Simon

[Lovel]

Originally Posted by SD1too

Good morning Gary,

I have placed my pulley horizontally in the vice and inserted the special tool into the large hexagonal recess and pushed! There is absolutely zero movement between the outer and inner parts of the pulley.

Inspecting the rubber ring on both sides it has light crazing on its surface, very impressive after 19 years' service I'd suggest. It has no cracks, no evidence of separation from the cast iron parts and no shredding.

I absolutely agree with you that the factory notch is in the wrong place but how did it get there?

• Rotation of the outer part relative to the inner? No obvious evidence of damage caused by this.
• Manufacturing error? How would this have not been noticed during assembly and alignment?

I guess that replacement is probably a wise choice but I never like to do that unless I understand why I am doing it!

Simon

If its not moving with a decent length of lever and force then it probably wont move, perhaps good for another few years, and at least you have tested it to an extent, perhaps its a heat related thing allowing it to creep over time. If nothing else at least you know the timing mark for the moment, and when you come to replace in some more years time you might need to ignore that mark

In future I'll be keeping my eye on this type of event for all the k engine types, as its a good case history and lesson learned.

[Mike Noc]

Originally Posted by SD1too

Manufacturing error? How would this have not been noticed during assembly and alignment?

Simon

Whilst they should have noticed it Simon, I doubt that the factory would have used the mark as a reference when building the engine up as everything would have been set up before the pulley went on.

It would have been quite easy to miss it on the line, but QC should have picked it up when the pulley was manufactured, unless of course it was a correctly manufactured part for a different engine.

[kaiser]

A storm in a glass of water?.
That mark is only used to find the "safe" position. After that, no use.
Go by the-cut out on the small pulley for the belts, and move on.

If you like, and if the mark is really not there, make a mark in the appropriate place.
The position of the engine for timing the cams is in any case determined by the peg in the flexplate, where the rear sprockets of the cams are in line.

Really curios, but totally irrelevant, provided there is no de-lamination of the pulley. I would clean really well, and then check again. I would also paint the pulley, as it seems it is very vulnerable to rust.

As for an earlier question regarding the tolerance of cam belts, it was a generic tolerance and not specifically aimed at our belt. No reason to believe that does not apply to our belts as well.

[SD1too]

Originally Posted by Mike Noc

... I doubt that the factory would have used the mark as a reference when building the engine up as everything would have been set up before the pulley went on.

Good point Mike. I too am inclined to believe that’s likely.

... unless of course it was a correctly manufactured part for a different engine.

Indeed, that’s another possibility.

Originally Posted by kaiser

A storm in a glass of water?.
That mark is only used to find the "safe" position. After that, no use.

Yes, we know kaiser. We’re just interested to understand how this extraordinary (though not exclusive to me) situation came about.

If you like, and if the mark is really not there, make a mark in the appropriate place.

I think you acknowledged my recent post showing that I found the notch and that it is 130 degrees in advance of the correct place. I also declared that I have made a replacement correct mark.

The position of the engine for timing the cams is in any case determined by the peg in the flexplate, where the rear sprockets of the cams are in line.

We’re agreed on that, but if for any reason the engine needs to be placed in the ‘safe’ position it’s a lot easier to rely on the crankshaft pulley mark than grappling around with a locking pin and removing parts to reach timing covers.

Thanks for your interest anyway.

Simon

[Ennine]

I have some more images somewhere but this will show you what I mean. I've found a laser line very handy when wanting to make reference marks across stepped or uneven surfaces. A dab of typex here and there using the laser line and you can always get it spot on. Trying to use a straight edge and mark a backplate or similar, whilst also trying to get ones head in a place where you can see what you are doing can be a nightmare. It was during the mark up on the V6 that I thought of it and it made life so much easier and I have reached for the laser a few times since.

[SD1too]

Originally Posted by Ennine

Trying to use a straight edge and mark a backplate or similar, whilst also trying to get one's head in a place where you can see what you are doing can be a nightmare.

But it pales into insignificance compared with trying to get access to the two air con. compressor bolts which are inserted into the front mounting plate.

Simon

[Lovel]

Originally Posted by kaiser

A storm in a glass of water?.
That mark is only used to find the "safe" position. After that, no use.
Go by the-cut out on the small pulley for the belts, and move on.

If you like, and if the mark is really not there, make a mark in the appropriate place.
The position of the engine for timing the cams is in any case determined by the peg in the flexplate, where the rear sprockets of the cams are in line.

Really curios, but totally irrelevant, provided there is no de-lamination of the pulley. I would clean really well, and then check again. I would also paint the pulley, as it seems it is very vulnerable to rust.

As for an earlier question regarding the tolerance of cam belts, it was a generic tolerance and not specifically aimed at our belt. No reason to believe that does not apply to our belts as well.

Consider what would happen if the mark slipped on a K-series four pot engine. I think it very important to be aware of this issue for all owners, hence this is an important issue that should be highlighted.
I also envisage that if an owner entrusts their KV6 or K-series to a professional outfit they for sure will not appreciate this issue, and may engage the timing pin on any random hole on the back of the flywheel (KV6).