Cam timing guides

[Jamo]

Has anyone got any good links to explaining cam and crank timing?

I'm failing to grasp a concept here that Pisobiker has done with the stroker.

He states that because the block is 16mm higher then the cam / crank timing will be different.

But if the cambelt belt is the same length as OEM in both configuration how is this so?

As the belt is what links head to block and as the belt length is static surely the timing is no different?

[HPmuirt]

Has anyone got any good links to explaining cam and crank timing?

I'm failing to grasp a concept here that Pisobiker has done with the stroker.

He states that because the block is 16mm higher then the cam / crank timing will be different.

It is not the overall length of the cambelt that changes the timing, but the distance between the crack and cam pulleys (measured in no. of teeth from crank to cam pulley)

This is how some engines employ variable canshaft timing. By having 2 belt tensioners, one before and one after the camshaft pulley and then moving them in opposite directions (as one moves in the other moves out) so that the tension remains the same, but the belt distance changes and thus the timing changes. In your case this change is caused by the block length change of 16mm of about 2 teeth

Well that's what I think, but I am sure a real mechanic will now come along and embarrass me

Cheers n

Si

[urquattro-island]

hmm

Does not sound right to me, if timing is set right on cams and cranck, new belt is fitted and tensioned right. Then timing is right, the belt only does the same rotation, it can not change the timing unless it jumps.

its doing a circle and will continue on this circle with same distance travelled until its changed, brakes, jumps or tensioner fails...

[mcandmar]

Take this pic as an example, the left hand pulley is the tension adjuster, and imagine the other two lower pulleys are locked solid so they cant rotate. i.e. locked at TDC

Now add a 16mm spacer between the block and head, in order for the belt to take up the extra distance the tensioner will have to slacken off, and the top pulley will rotate clockwise as the head is raised. This is your problem as the timing between the top and bottom pulley has moved in the process.

In theory having a block and head skimmed or a different thickness of head gasket will have an effect on the timing. Adding 16mm is a huge difference that can be measured in teeth never mind degrees. Your going to have to find true TDC, then set the cams to the TDC position, and then adjust your cam pulley so the belt fits. When all said and done the adjustable cam pulley will read something like 10 degrees away from 0, maybe more.

The tricky bit i can see will be finding the TDC position on the cams, as a rough guide you could use a stock cam pulley and line up the timing mark with the valve cover, then find a way to lock the cams to stop them turning and change over to your adjustable pulley, then adjust the pulley so you can get the belt on.

[Rusty]

If the crank and cams are correctly set at TDC when the belt is on and tensioned then you'll not have an issue, it's whether there is a small change (fraction of a tooth) that can't be sorted, in this case a Vernier pulley can be used to make the small adjustments and allow the timing to be perfic

Shirley, you must have a longer belt to make up the 30mm extra travel?

[Fat Audi 80]

If the crank and cams are correctly set at TDC when the belt is on and tensioned then you'll not have an issue, it's whether there is a small change (fraction of a tooth) that can't be sorted, in this case a Vernier pulley can be used to make the small adjustments and allow the timing to be perfic

Shirley, you must have a longer belt to make up the 30mm extra travel?

Andy is right, If TDC is set correctly, the 16mm will not matter unless makes the difference of less than one tooth on the belt. I am assuming that Jamo's belt has enough slack in the tensioner to make up the 30 odd mm required in the extra height of the block.... A longer belt would not make any diffrence either as long as the Cam(s) and Crank are set relative to each other.

The stoker will just make the piston travel a little quicker to make up the 16mm difference between the two engines.

@ Jamo, this is where your dial gauge will come it to allow you to acurately set TDC and then ensure the cam pully/wheel is in the correct position for TDC....

Hope that makes sense!

Cheers,

Steve.

[urquattro-island]

tdi

blocks have been used in Norway for some time, and they use oe belts no issues. Like I said in my previous post, timing right on head and on bottom, put on belt and no probs. One should not make it more difficult than it is

[Rusty]

One should not make it more difficult than it is

Sound advice but where's the fun in that though

[Jamo]

Andy is right, If TDC is set correctly, the 16mm will not matter unless makes the difference of less than one tooth on the belt. I am assuming that Jamo's belt has enough slack in the tensioner to make up the 30 odd mm required in the extra height of the block.... A longer belt would not make any diffrence either as long as the Cam(s) and Crank are set relative to each other.

The stoker will just make the piston travel a little quicker to make up the 16mm difference between the two engines.

@ Jamo, this is where your dial gauge will come it to allow you to acurately set TDC and then ensure the cam pully/wheel is in the correct position for TDC....

Hope that makes sense!

Cheers,

Steve.

Now that makes perfect sense to me Steve, I trying to understand these posts

http://www.s2forum.com/forum/showthread.php?t=6941

http://www.s2forum.com/forum/showpos...4&postcount=15

[Fat Audi 80]

Not exactly. You still may want to adjust the PHYSICAL timing from when the intake port opens relative to the position of the piston in that cylinder as per the discussions above, regarding the timing belt and TDC positions.

The ignition timing is related but also a separate problem. I need to thoroughly read the above links to fully understand these stroker issues I think.

Cheers,

Steve

[Jamo]

I'm getting confused sorry, the pulley works differently to how I though initially, it keeps the ecu ignition timing static not the other way round

[Flat on my back]

Q.

Is this pully adjustable for the belt wheel about the camshaft and also the sensor disk with the window...therefore 2 different adjustments.

1. cam timing to crank position,
2. hall sender signal relative to TDC.

[mcandmar]

The answer is here "Taller deck produced half a theet of timing difference on the camshafts which makes about 13 crankshaft degrees (way too much to make it usable). So I had to build a custom pulley having the right phasing not only for the camshaft position but also for the hall sensor disk's slot."

So the difference is half a tooth on the timing belt or 13 degrees, the only way your going to get the crank/cam timing in spec is by adjusting the difference out with an adjustable cam pulley.

The second part is in relation to the hall sensor window, it must adjust with the cam pulley or else the ECU would see a Hall signal 13 degrees out from the actual cam timing.

[Fat Audi 80]

Brilliant.

Your answer in one paragraph.

[Jamo]

The thing is i've checked his posts and emails and I have the cam wheel he built, it is set to OEM timing which he confirmed in his later posts and it does only move the magnetic disk.

So how did he adjust the physical cam timing?