KV6: using timing service tools

[p2roverman]

Originally Posted by SD1too

Hello David,

When the front belt is removed both inlet camshafts move. Because the rear belts link these to the exhaust camshafts, they move as well. The result is that the engine's timing is destroyed. By far the easiest way to restore this is to fit the front timing tools, leaving your hands free to lace the new belt and to loosen the sprockets to assist this operation (I will shortly be trying this for myself). If you don't use the special tools then you'll need to rotate both inlet camshafts against valve spring pressure and, whilst holding them in a precise position, lace the new belt around the crankshaft, tensioner and idler pulleys and both camshaft sprocket wheels which are held stationary. I'd like to know how that can be possible single handed.

Simon

Agreed it's easier to do the job with the tools, but note that with the engine locked with a pin, the front tools will only fit if the wheels are slackened. And with the tools, belt changing is a simple one-person job.

However it can be done without the tools single handed, use a spanner to turn the inlet cam, one at a time, back to its original position (which you have marked with Tippex, of course, and not slackened the wheel) while lacing the belt with the other hand. Start with the front camshaft, once the belt is in position on it the camshhaft will not slip back again if you keep a bit of tension on it; you could alternatively wedge the spanner.

Then do the rear belts. The exhaust cam will turn by action of the valve springs. Rotate the whole engine so the inlet cam turns by the same amount using a spanner on the crankshaft bolt. Rotate the wheels and belt assembly and fit.

Most difficult job when using the tools? - trying to fit new exhaust cam end cover seals; I gave up and refitted the old ones.

[marinabrian]

Originally Posted by chris75

Got to disagree with this one ! They don't pop off if they are fitted properly
Never had a problem with them

There was a duff batch of these, once bitten twice shy

Brian

[Ennine]

If one intends to simply replace the belts and not release the front cam bolts a couple of very simple home made locking devices with hold everything in place without the need to turn the cams with a spanner at all.

[p2roverman]

Originally Posted by Ennine

If one intends to simply replace the belts and not release the front cam bolts a couple of very simple home made locking devices with hold everything in place without the need to turn the cams with a spanner at all.

Inlet or exhaust cams?

I don't disagree, but presumably you are using home-made tools on the REAR wheels to hold the cams still while you fit the main belt, as it's not possible to fit this belt with tools fitted to the front.

I didn't make clear that you have to position the main belt, then turn the inlet cam by spanner back to its original position to then fit the belt; this is the method specified in Haynes for doing the job without tools (apart from one to hold the rear wheels to work on the bolts)

[Ennine]

Originally Posted by p2roverman

Inlet or exhaust cams?

I don't disagree, but presumably you are using home-made tools on the REAR wheels to hold the cams still while you fit the main belt, as it's not possible to fit this belt with tools fitted to the front.

Correct. One can lock the rear wheels very easily. One device per sprocket on the rear allows the rears to be changed. The same device left in place allows the front belt to be replaced with nothing moving at all.

[Mike Noc]

Firstly I'm not selectively quoting you Kaiser - all of your post is here. Just easier to respond in parts.

Originally Posted by kaiser

1 degree or 1.6 degrees, is neither here nor there.
These will be well within other tolerances affecting the engine and it's operation.

Is this an assumption, or do you have documentation from an engine manufacturer to back this up?

Originally Posted by kaiser

When/if poor Simon eventually gets his engine timed, ask him to make a picture of all timing marks. Then rotate the engine a couple of turns, and you will find it difficult to replicate the timing marks exactly, unless you rock back and forth around the safe mark. That is why Rover said that is the timing is correct, when the belt is installed, one should not worry too much, if the marks are not exactly on the spot when the engine has done some revolutions.

Absolute nonsense - if you need to do that then it could be due to the belt tolerance after the replacement if you haven't adjusted the floating sprockets to account for it! Or of course another problem.

On the cambelt changes I have done the marks always align after a couple of revolutions. On pinned engines, where alignment is more objective than looking, once the crankshaft is locked the other sprocket holes align perfectly if the job is done correctly.

Originally Posted by kaiser

But here we are, and the thing has been worked down to a degree (excuse the pun) that we are talking about 1, maybe 1.5 degrees adjustment of a camshaft, in the worst case.
That is about 1/10 of a tooth on the belt, maximum 1/7 of a tooth if you are really unlucky, that is the maximum you can expect, if the belt is at maximum tolerance, belts will be well within these tolerances.

I think we agree on quite a few things - the ballpark figure for the possible variation in belt length, the amount of timing variation that could arise from it, and, as you haven't disagreed with my suggestion, the reason the floating sprockets are fitted.

Of course skimming the heads could possibly increase the variation slightly (or may even help with a shorter belt), but we are probably only talking about around 2 degrees at most.

Originally Posted by kaiser

The fact is, the V6 can, will and DOES!! maintain timing, if you just change the cam belt like on any "normal" car. If you want to use any tool, do so to hold the rear sprocket when you lose the bolt. That is it!

As for the rest.

A complete and utter waste of time and resources.

The very fact that Rover (and the many other maufacturers that use them) fitted floating sprockets would tend to suggest that they wanted a far tighter tolerance than the 1 or 2 degrees that you are happy with.

As I have said before, each to their own.

[kaiser]

Mike, tell me what accuracy YOU think would be appropriate.? I am really keen to see how your mind works.

One of the most difficult things for a new engineer to accept, is that things never work perfectly. They come bright eyed and bushy tailed and start calculating to the third decimal, until an experienced engineer pull them aside and tell them about accuracy, or tolerance, if you want.
In engineering you are useless, if you strife for zero tolerance, when it is not required. I can make a drawing and specify a very high degree of accuracy on a radius or a length, or whatever.
Any high degree of accuracy requires special additional work to be able to accomplish, it might be surface treatment, it might be special fixation or even high precision equipment. An engineer specifying these high tolerances is likely to get a call from the machine shop, to make sure that they are really needed and a small chat about time and cost, and a question about relevance. Does it make a difference to the end product. And surprise surprise, often it does not. It is not sensible to make one product with extreme accuracy, if the whole machine does not benefit from it.

Let me ask you another question. Have you ever timed an engine? If you have, you will know that you sit with a degree plate maybe 400mm in diameter, marked in degrees. You also use a dial gauge accurate to 100th of a mm, and when you want to find the top of a cam, or the TDC or many other specific points, you realize that you cannot measure it correctly, unless you approach it from both sides, measure an equal amount of lift before and after, read the degrees and take an average. Can you be out by a degree? You bet!

Or have you tried to find the timing marks and time a distributor? If you have, you will know that the point will be a compromise of your best readings an estimate if you will, but a qualified one at that. Could you be out by one degree on the distributor? Well, what do you think?

We have had this endless argument about the timing of the V6. There is nothing special about this engine. It can be timed with the accuracy of any normal engine using a belt, without any tools. I have shown you that the belt variation is minimal, and that the engine will be timed, if you follow good normal practice and don't stuff the job up.

If 1 or 1.5 degree accuracy stomps you, we are talking different languages, and what is more, this accuracy here, is going to be drowned by real life.

It is simply neither here nor there, and totally inconsequential to the operation of the engine.

But, let me repeat my first question to you. What accuracy are you striving for? and, if you achieve this by using a tool that places the markings of the rear sprockets in a different place from the ones shown by Rover, will that make you happy?

I will take my engine and time it like I have timed numerous engines. If there are markings made by the factory, cast into the metal, I will go with them.
If it has got a belt, I will fit it as fitted from the factory.

It just makes common sense.

[Mike Noc]

Well cars are a hobby for me so my opinion on accuracy is pretty much neither here nor there, but seeing as you ask, it depends on the engine.

For the KV6, and similar engines of this era, I'd be happy with anything under 0.5mm belt deviation. If you use the tools then it depends on how accurately they are made and the clearance they have, and let's face it if you aren't using the tools then the timing marks, such as they are, don't give you much accuracy at all with the engine still in the car.

Whether they actually show the correct timing position still hasn't been established definitively for me anyway.

With engines timed with pins, and they are a tight fit in the holes, you can get within 0.1 to 0.2mm accuracy. The last two types I have done both had timed injection diesel pumps with floating cams even though the belts were relatively short. I assumed this was for precise fuel injection.

Now the other thing about me is I'm not a new engineer by any yardstick.

I'm an old service engineer nearing retirement, and yes I have timed an engine from first principles (I did an apprenticeship in Marine Engineering way back) and yes you are quite right, very difficult to be accurate when doing so. I agree with you on distributors as well. But more modern engines are built with far tighter tolerances.

In my day job I work on high speed packaging lines. We use, and replace many timing belts, and you would be surprised with the accuracy that some of them are set to. On modern machines the belts are driven by servomotors, so you can assemble them without worrying about the timing, and the servomotor will find the reference datum and reset to it.

From there we can adjust the timing by increments of 0.1mm belt movement using the software accurately, and it is repeatable every cycle. So it is fair to say that I'm probably more used to accurately setting up timing belts than most people.

Back to the KV6, and there really isn't any other reason I can see that Rover fitted floating cams, other than to set the position of the camshaft timing more accurately than the tolerance of fitting a new belt would allow if they had used solid sprockets.

The same company didn't do it on the four cylinder K Series, and it is plain to see that there is no need to because the deviation is minimal. I agree with you that the KV6 is nothing special, but there is more room for error due to the length of the main cambelt, the length of the belt from the front bank to to the rear bank sprockets, and the relative position of the tensioner.

Again the real question is, if they didn't go for the floating cam arrangement for timing accuracy when replacing the belts, why did they?

[SD1too]

Originally Posted by Mike Noc

... the real question is, if they didn't go for the floating cam arrangement for timing accuracy when replacing the belts, why did they?

To make it easier to fit the belt I’d suggest Mike.

Having refitted the sprockets with new bolts tightened “sufficiently to allow gears to rotate without tipping” [i.e. “floating”] the front tools are then fitted [camshafts locked together].

The next instruction is to rotate both sprockets fully clockwise [utilising the “floating feature”] and fit the belt to the sprockets [i.e. engage the teeth] “turning the gears only a minimum amount anti-clockwise to fit drive belt”.

It seems clear that a small amount of movement is required to engage the belt teeth properly on both sprockets.

Was that your experience when you did it?

Simon

[Mike Noc]

They only mention that because you have already locked the camshafts in position though Simon.

If the engine wasn't fitted with floating cams then, with it in the safe position, you can move the cam sprockets, just as you have to tweak them a bit on the K Series if you don't have a locking tool.

I knocked up this tool many years ago from bits laying around the workshop. Fully adjustable to suit all sprockets, and very useful it is too.



I have mentioned previously that I've never done the cambelts on a KV6, so all this is academic to me, but you never know I may buy one in the future. As Kaiser says, there is nothing special about this engine.