Cam-crank re!ationship

highmileage · Aug 21, 2017

If through the course of events camshaft and crankshaft move independently and end up out of sync, one way to restlore is to put cam qnd crank sprocket at tdc with timing tools in place to verify and hold tdc. The belt can then be installed with tools in place. Remove tools rotate 2 times with no problem and then reinsert tools. They fit at DTC. Rotate engine 2/more times for good measure. Always good to go? Any exceptions? Is smooth rotation of engine by crank bolt always an indication to safe start? Thanks in advance.

Windex · Aug 21, 2017

Pretty well as you have described. If you insert the correct timing tools in the correct places, the cam and crank should be back in the correct orientation/relationship.

How would your cam and or crank have become misaligned?

highmileage · Aug 22, 2017

Thank you.

Thank you for your response, Windex. As I continue thinking about it, I am not so sure that the cam and crank were out of sync, but at the time I had my doubts. Regardless, I figured the best thing would be to go to TDC and reset everything to be safe. I changed my camshaft, lifters, bearings, etc. and to bypass opening fuel system I rotated cam to make slot in cam that fits to tandem pump vertical for removal. My TB components only have 14,000 miles, so they stayed put. The video for this method showed rotating the cam backwards 90 degrees for vertical slot, but also having read that backwards movement can stress components, I decided to go forward 270 degrees to get to same cam relative position. This worked well and I changed cam components. Then I started thinking about 2 crank revolutions to one cam revolution and started questioning relationship between cam and crank. That was when I decided to remove TB, put cam and crank sprockets at TDC, which took a little back and forth movements and jiggling, but I got to TDC and locked with tools and then reinstalled belt and did checks for smooth engine rotation and reinsertion of TB tools to verify TDC again. Then I rotated engine two more times for good measure and to check for smoothness which was there.

highmileage · Aug 23, 2017

Believe the key was going back to TDC and going forward. Finished up today, started the car and it runs and sounds fine.

James & Son · Aug 23, 2017

highmileage said:
Thank you for your response, Windex. As I continue thinking about it, I am not so sure that the cam and crank were out of sync, but at the time I had my doubts. Regardless, I figured the best thing would be to go to TDC and reset everything to be safe. I changed my camshaft, lifters, bearings, etc. and to bypass opening fuel system I rotated cam to make slot in cam that fits to tandem pump vertical for removal. My TB components only have 14,000 miles, so they stayed put. The video for this method showed rotating the cam backwards 90 degrees for vertical slot, but also having read that backwards movement can stress components, I decided to go forward 270 degrees to get to same cam relative position. This worked well and I changed cam components. Then I started thinking about 2 crank revolutions to one cam revolution and started questioning relationship between cam and crank. That was when I decided to remove TB, put cam and crank sprockets at TDC, which took a little back and forth movements and jiggling, but I got to TDC and locked with tools and then reinstalled belt and did checks for smooth engine rotation and reinsertion of TB tools to verify TDC again. Then I rotated engine two more times for good measure and to check for smoothness which was there.

Yes I have been in the same boat doubting the relationship of crank to cam. If you move the cam from the (locked) relationship the doubts can creep in.

It is important to remember that there is only one locked position for cam and crank when both are locked. The two to one ratio can not interfere with this relationship.

If for some reason the relationship between cam and crank has been lost. Likely it is best to lock the cam in position first, remembering once locked it is in the one only correct position. This is only done if you know the crank is offset from top dead center by 90 degrees.

The cam cannot bet locked first until you are curtain the crank is offset by 90 degrees. You now then can bring the crank back to top dead center for #1 piston which is the one and only correct position possible. If you turn the crank the wrong way you will hit open valves as #2 comes to TDC at 180 degrees. Remember it may not be compression when you can't move the crank, try going the other way very carefully.

highmileage · Aug 24, 2017

Thank you for sharing your experience. I recall at a point in time after I had locked the cam at TDC, I was going to rotate crankshaft to TDC and as I rotated crank clockwise, I must have had valve contact as I felt a resistance that I knew I should stop. So, I went counter clockwise to crank TDC and went from there. And thankfully, all went well.

afarfalla · Aug 27, 2017

setting the torque value gets you in the ballpark, the only way to be 100% sure is to scope the two signals and see the true relationship of each signal compared to the other

Ol'Rattler · Sep 1, 2017

afarfalla said:
setting the torque value gets you in the ballpark, the only way to be 100% sure is to scope the two signals and see the true relationship of each signal compared to the other

Huh? What is the correlation between cam to crank timing and your post?

Ol'Rattler · Sep 1, 2017

I don't think the procedure is fully understood here.
Advanced cam change method setup:

Set engine at TDC.
Remove T/B.
Turn crank 90 degrees CCW.

You can now turn the cam anywhere you want because the pistons are all safely at the mid point of their bores.
Going back together:

Pin cam at TDC.
Turn the crank 90 degrees CW to TDC and pin.
Install T/B.

This procedure does not stress anything and causes zero damage. When Frank explained it to me and I understood it, it was like a revelation. How could something so stupid simple be so goof proof at the same time?

James & Son · Sep 2, 2017

Where words and memory are involved nothing is goof proof.
Your first words proves that.

set engine to top dead center? Is that goof proof.

For accuracy and not simplicity one would say, Set crank and cam to #1 piston TDC by rotating crank and inserting crank locating pin.

We are both assuming you are starting out with the timing correct and the the old belt installed.

Now what about a novice and both the crank and the cam are rotated out of a know position. What do you do. That is what I explained and that is easily possible.

Ol'Rattler · Sep 2, 2017

Well sure, nothing is entirely "goof proof", but there's no reason to over think it either. My post was not directed at you, just at the way the thread was going.

Why would you bother to pin the crank? Being at or close to TDC on the cam is all you really need at this point. With the belt still on, the crank and cam relationship is still good.

Almost forgot. To avoid stressing the tensioner, if you turn from the crank, go clockwise. if you turn from the cam, go CCW. For accuracy, when you do your final 2 turns to check, turn CW from the crank.

I do appreciate that you helped a newbie recover from his mistake. Were all human and "Goof" every once in a while, don't we?

afarfalla · Sep 2, 2017

Ol'Rattler said:
Huh? What is the correlation between cam to crank timing and your post?

there is a magnet on the crank which represents TDC, you can stick whatever you want in whatever hole you want it won't be as accurate as when the magnet and Hall sensor connect. This is TDC.

The cam has the same setup, when the magnet and Hall sensor connect, the valves are closed, you can strap things stick things in holes, put sprockets on gears...but...if you scope the crank and cam sensors then and only then will you get the true relation between TDC and what the valves are doing.

The cam is adjustable so you should be able to super impose one signal over the other, perfect timing!

afarfalla · Sep 2, 2017

Ol'Rattler said:
I don't think the procedure is fully understood here.
Advanced cam change method setup:

Set engine at TDC.

Remove T/B.

Turn crank 90 degrees CCW.

You can now turn the cam anywhere you want because the pistons are all safely at the mid point of their bores.
Going back together:

Pin cam at TDC.

Turn the crank 90 degrees CW to TDC and pin.

Install T/B.

This procedure does not stress anything and causes zero damage. When Frank explained it to me and I understood it, it was like a revelation. How could something so stupid simple be so goof proof at the same time?

this is the proper way to install a timing belt, yes, but when you start it up and the torsion is 0.0 is this really TDC, or should it be 0.5 or maybe -1.0, maybe 5.5 will be true TDC?

afarfalla · Sep 2, 2017

I bought two spare ECU's to test my theory but couldn't break the glues seal, here is what I expect to see...when the crank signal peaks, we have TDC, when the cam sensor peaks, all the valves are closed. The two signals should completely superimpose on each other, if they don't I adjust the cam. I don't really care what the torsion value reads, irrelevant.

Ol'Rattler · Sep 2, 2017

afarfalla said:
this is the proper way to install a timing belt, yes, but when you start it up and the torsion is 0.0 is this really TDC, or should it be 0.5 or maybe -1.0, maybe 5.5 will be true TDC?

TDC is indexed by the timing tools. A valid torsion value different than zero is a deviation of of the cam timing from cam TDC.

The tell for an valid zero Torsion indication at idle is that when you rev the engine the Torsion value will change. If Torsion value is set out of range, the indication will not change when you rev the engine.

afarfalla · Sep 2, 2017

Ol'Rattler said:
TDC is indexed by the timing tools. A valid torsion value different than zero is a deviation of of the cam timing from cam TDC.
The tell for an valid zero Torsion indication at idle is that when you rev the engine the Torsion value will change. If Torsion value is set out of range, the indication will not change when you rev the engine.

I agree with your first 2 sentences.

I am trying to digest your second statement...but having a tough time. If your engine is brand new, when the timing belt is installed, however it is done at the factory, we all agree that piston 1 should be at TDC and the valves for piston 1 should all be closed at that time. Do we care what the torsion value is? The ECU must be reading the relation of crank and cam to arrive at a number for torsion? I don't see this number changing at any RPM if nothing is worn out.

If the belt gets a little worn, then the ECU would see the relationship change and post a different torsion value than when the car was new.

I strongly believe that when the cam crank signal relationship is one superimposed over the other that maximum engine efficiency is achieved.

Ol'Rattler · Sep 2, 2017

afarfalla said:
I bought two spare ECU's to test my theory but couldn't break the glues seal, here is what I expect to see...when the crank signal peaks, we have TDC, when the cam sensor peaks, all the valves are closed. The two signals should completely superimpose on each other, if they don't I adjust the cam. I don't really care what the torsion value reads, irrelevant.

I don't quit understand what your "theory" is or why an O-scope would even be needed. All the values you need are already reported in VCDS

The ECU uses a Hall sensors for the crank and a Hall sensor for the cam to report crank and cam position, both of which you can monitor with VCDS.

To make life simple, you set crank TDC statically with your extremely accurate crank tool and can fine tune the cam to crank torsion value (cam deviation from crank TDC) using the handy torsion measuring block in VCDS.

So please, expand on what you are trying to accomplish..........

afarfalla · Sep 2, 2017

with the engine running and the vag connected tell me what windows you plan on using to set the relationship of crank to cam? and whatever windows you plan on using what will the numbers represent?

If I scope the 2 hall sensors and see a 3ms delay on the cam side I can then adjust it out, what number in your vag window represents 3ms?

Ol'Rattler · Sep 2, 2017

afarfalla said:
If your engine is brand new, when the timing belt is installed, however it is done at the factory, we all agree that piston 1 should be at TDC and the valves for piston 1 should all be closed at that time. Do we care what the torsion value is? The ECU must be reading the relation of crank and cam to arrive at a number for torsion? I don't see this number changing at any RPM if nothing is worn out.

Belt flex maybe? On a new or old engine the value does change some with RPM. If Torsion is out of range, the ECU assumes the value is implausible and reports a set value of zero which will not change with RPM.

afarfalla · Sep 2, 2017

think about this...we have an old engine on our 3rd belt, using the tools we have to assume the crank ends up TDC, we really don't know where the cam is, it could be dead on or off a hair? Using the vag you somehow determine the cam is advanced, what's the solution? Increase or decrease torsion value? The engine will stay advanced but the ECU will try to correct electronically by what? delay injection advance injection? No matter how the ECU corrects for the misalignment the engine will always be out of time. This I believe is why possibly some cars get better mileage then others

Ol'Rattler · Sep 2, 2017

afarfalla said:
with the engine running and the vag connected tell me what windows you plan on using to set the relationship of crank to cam? and whatever windows you plan on using what will the numbers represent?
If I scope the 2 hall sensors and see a 3ms delay on the cam side I can then adjust it out, what number in your vag window represents 3ms?

It's not a window per say it is a measuring block called Torsion. IDK what the number represents, could be degrees or something else, nobody has ever explained that that I could find on the inter webs.

I don't think that the measurements are in the time domain. Probably more like a series of snap shots and no I don't know what the sampling rate is. Kinda like a an audio cd is a series of digital samples of an analog waveform.

afarfalla · Sep 2, 2017

QuickTD said:
Measuring block 4, field 4, "torsion value". This is a value in degrees of the crank to cam relationship. A positive value is cam advanced and a negative value is cam retarded. The value will remain fixed at zero if the crank and cam are too far out of sync (7º or so?)

If the torsion value is within range it will tend to fluctuate +/-0.5-1º when the engine is revved due to belt stretch. If the value is fixed and unchanging, it may be too far out to read properly. The engine will probably also show some running problems if the value is out this far.

this answers a question the ECU makes no corrections it only monitors an advanced or retarded state.

This is more reason to make sure no advanced or retarded state exists when you install the belt and the only way to ensure we are at TDC and all valves are closed is with a scope

afarfalla · Sep 2, 2017

I'll get one of these ECU's apart and experiment, but for now I'm tired, let me check and see how far the water has gone down and we will continue on this very interesting subject later

afarfalla · Sep 3, 2017

at 2000rpm's my torsion value is 0.5, what is this number telling me.

and remember the torsion value can be changed by the cars owner. the owner bumps it up 0.5, what did he accomplish.

torsion is just a number, it cannot and does not relate to cam position and TDC, it can only tell you if and when its in error.

Ol'Rattler · Sep 3, 2017

afarfalla said:
at 2000rpm's my torsion value is 0.5, what is this number telling me.
and remember the torsion value can be changed by the cars owner. the owner bumps it up 0.5, what did he accomplish.
torsion is just a number, it cannot and does not relate to cam position and TDC, it can only tell you if and when its in error.

It is telling you nothing of value. Torsion is checked at idle on a warm engine, not at 2000 RPMs.

The owner advanced the cam .5 Torsion units relative to the crank.

It is telling you the cams relationship to the crank. Torsion is derived by comparing the Crank position sensor and the cam position sensor readings.

120 MPH is just a number but in most places it will get you a reckless driving driving ticket and a trip to jail if you are caught..................

afarfalla · Sep 3, 2017

Ol'Rattler said:
It is telling you nothing of value. Torsion is checked at idle on a warm engine, not at 2000 RPMs.
The owner advanced the cam .5 Torsion units relative to the crank.
It is telling you the cams relationship to the crank. Torsion is derived by comparing the Crank position sensor and the cam position sensor readings.
120 MPH is just a number but in most places it will get you a reckless driving driving ticket and a trip to jail if you are caught..................

why did he advance the cam 0.5 Torsion units relative to the crank, what told him to do this? is a torsion reading of 0.0 TDC for both crank and cam?

What am I missing?

afarfalla · Sep 3, 2017

QuickTD said:
I think the part you are missing is that the crank and cam are manufactured with fixed, positively indexed tone rings. They are aligned with the cam and crank at the time of manufacture and are equipped with a skipped tooth on the crank to indicate TDC and a single tab on the cam to indicate TDC on cylinder 1.

Positively located sensors are positioned to be triggered precisely at TDC on each of the tone rings. The ECU collects the data from the two sensors and displays the position of the cam TDC relative to crankshaft TDC as "torsion value" in degrees of crankshaft rotation. Positive numbers are advance, negative are retard.

The reasons for adjusting the cam/crank relationship (torsion value) are the same reasons you mess with the cam timing on any engine, to obtain better performance. The factory specifies 0.0 as the best compromise. Like everything, there are differing opinions on alternate settings of cam timing. I like to set them up to 0.5-1.0 so that the value approaches 0.0 as the belt settles in. You can set it to anything you want and the results will vary a bit from engine to engine due to manufacturing tolerances. Some engines may run better 1º advanced, some better 1º retarded. You can determine your favorite setting experimentally. The torsion value gives you a positive, repeatable reference to work with. If you don't care about performance and don't care to tinker, set it for 0.0 and move on. The engine will run fine.

so that's what I missed "skipped tooth and the single tab"

so see if I'm right...I follow the standard timing belt installation procedures using the pins and clamps and that should put me at 0.0 torsion value. The crank will be TDC and cylinder 1 will have all valves closed.

afarfalla · Sep 3, 2017

QuickTD said:
The tools will get you close. I would expect to see +/-1-2º in the torsion value field, the tools have some slop. Most shops would never bother looking at torsion value and the engines will run ok. Maybe not optimal but the average driver would never notice.

That's my problem I'm a perfectionists. +-1 to 2 degrees after I did all that work would bother me because I know the car could run better and be more efficient.

If and when I put a timing belt on my 05, I will have no choice but to use the tools with built in slop, I will run the engine and monitor crank and cam sensors, (with my scope) and make the necessary adjustment to the cam sprocket. I will then know for sure that the engine cylinder 1 is perfectly timed, I will check torsion value just for the heck of it.

The only way you know for sure that the engine is timed perfectly is when Hall effect sensor signal for the cam and crank align overtop one another. That why they put them where they do. When the 2 signals peak together, your engine is running perfect!

afarfalla · Sep 3, 2017

QuickTD said:
The crank sensor is not a hall sensor, it is a variable reluctance sensor (coil around a magnet). It produces an AC sine wave with a skip or missing tooth at TDC in 2 locations for cylinder 1/4 and 3/2. I'm not sure what trigger level is in the ECU or if it triggers on the rise or the fall of the waveform, or perhaps at zero crossing. One thing is for sure, it will be difficult to get any useful information with a scope.

The good news is, the ECU provides this info, all conveniently packaged, tidied up and ready for use.

It is called "torsion value", located at measured value block 4 field 4.

And I give up...

Baloney, you thru the towel in once and came back, this is too interesting to give up on.

I understand it works like ABS, didn't want to get too technical

The crank is manufactured like a gear with a couple of teeth missing, so each time a tooth passes thru the magnetic field of the energized magnet (this sensor has 3 wires) a pulse is generated, if you trigger the scope on the speed sensor pulse and the engine is perfectly timed one of the blank pulses should fall right over that speed pulse, will torsion read 0.0?...if you see no blank pulse your advanced, if your blank pulse is farther down the trigger your retarded....or maybe I'm retarded?

afarfalla · Sep 3, 2017

Its my understanding that if the torsion value is something other than 0.0 you are either advanced or retarded, is this right or wrong.

If I start my car up now and read a torsion value of 1.0 what should I do? anything? is my car in perfect time?

Cam-crank re!ationship

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