Timing marks are moving

CarMichael Angelo · Jan 1, 2012

Ok. I just finished timing the cams on my 2v head swap. Got the dots on the gears matched up w/ the darker links on the chains. The crank gear dot was at 6 o clock. I used a pretty reputable source to be sure I was in the proper places w/ the two cam gears.

I released the tensioner pins, and spun the engine around by hand to be sure there were no interference issues. ( did not sense any interference) Spun it around about 4 times. Noticed that the passenger side chain (especially) would slacken at one point in the revolution but would go tight within about 15=20 degrees of additional rotation.

In addition to that, the dark links have moved exactly 7 teeth from the dots on all gears on both cams.
When you bring the motor around to what should be TDC, the dots are where they're supposed to be but the marked links are not.

WTF?

98COBRA281 · Jan 1, 2012

it's normal, the dot's and blue link only realign once ever like 48 revolutions i believe, but DO NOT realign ever revolution

trinity_gt · Jan 1, 2012

madmike1157 said:
In addition to that, the dark links have moved exactly 7 teeth from the dots on all gears on both cams.

When you bring the motor around to what should be TDC, the dots are where they're supposed to be but the marked links are not.

WTF?

This is normal. You will not see the links re-align with the timing marks for many crankshaft revolutions.

Th chains have a total of 116 link pins. This means there are about 58 pins from one marked pin to the next. The camshaft sprocket has 42 teeth. If you rotate the engine two full rotations, you bring the cams into alignment again (one complete Otto cycle) but you've only pulled the timing chain along 42 pins (i.e. one complete revolution of the camshaft.) This advances the marked pin from the bottom of the crankshaft up toward the cam. Since 58 pin separated them originally, the marked link that was down by the crank should now be within 58-42 or 16 pin of the cam sprocket timing mark. Depending on how you're counting "links" -- I count the pins -- you can see how this basically explains what you're seeing. Another two crank revolutions will move the chain another 42 teeth/pins along moving them apparently further out of phase. However, the relationship between the cams and the crank is maintained.

It will take a lot of crank revolutions to get things all lined up again.

If we assume the marked links look the same then there would need to be an integral multiple of 58 pin advancements to appear to line up the marks again. In order for the cam timing marks to be lined up there would be the additional constraint of having turned the crankshaft an even number of revolutions (2, 4, 6 etc.) Since each double-crank revolution accounts for 42 pin advancements, we need to find the smallest value of "double crank revolutions" that, when multiplied by 42, also equates to an integral multiple of 58.

The smallest value of double crank revolutions that meets this criteria happens to be 29 (or 58 total revolutions.)

58 revolutions of the crankshaft produces 58x21 or 1218 pin advancements which happens to be an even multiple of 58...

I believe that if you were to rotate the crankshaft through 29 complete cycles (or 58 revolutions) you would end up with marked links lined up with dots that were also in the correct positions.

Or something like that...

CarMichael Angelo · Jan 1, 2012

trinity_gt said:
This is normal. You will not see the links re-align with the timing marks for many crankshaft revolutions.

Th chains have a total of 116 link pins. This means there are about 58 pins from one marked pin to the next. The camshaft sprocket has 42 teeth. If you rotate the engine two full rotations, you bring the cams into alignment again (one complete Otto cycle) but you've only pulled the timing chain along 42 pins (i.e. one complete revolution of the camshaft.) This advances the marked pin from the bottom of the crankshaft up toward the cam. Since 58 pin separated them originally, the marked link that was down by the crank should now be within 58-42 or 16 pin of the cam sprocket timing mark. Depending on how you're counting "links" -- I count the pins -- you can see how this basically explains what you're seeing. Another two crank revolutions will move the chain another 42 teeth/pins along moving them apparently further out of phase. However, the relationship between the cams and the crank is maintained.

It will take a lot of crank revolutions to get things all lined up again.

If we assume the marked links look the same then there would need to be an integral multiple of 58 pin advancements to appear to line up the marks again. In order for the cam timing marks to be lined up there would be the additional constraint of having turned the crankshaft an even number of revolutions (2, 4, 6 etc.) Since each double-crank revolution accounts for 42 pin advancements, we need to find the smallest value of "double crank revolutions" that, when multiplied by 42, also equates to an integral multiple of 58.

The smallest value of double crank revolutions that meets this criteria happens to be 29 (or 58 total revolutions.)

58 revolutions of the crankshaft produces 58x21 or 1218 pin advancements which happens to be an even multiple of 58...

I believe that if you were to rotate the crankshaft through 29 complete cycles (or 58 revolutions) you would end up with marked links lined up with dots that were also in the correct positions.

Or something like that...

Thanks. And I appreciate the explanation. I was figuring that there some math/geometry involved.
I set out to find out that on my own. I don't know how many revolutions it took, (something like 10-12) but the dots and links remarried each other.

Timing marks are moving

CarMichael Angelo

my rearend will smell so minty fresh,

98COBRA281

trinity_gt

CarMichael Angelo

my rearend will smell so minty fresh,

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Timing marks are moving

CarMichael Angelo

my rearend will smell so minty fresh,

98COBRA281

trinity_gt

CarMichael Angelo

my rearend will smell so minty fresh,

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