Timing chain marks line up but don’t stay aligned after rotation

What parts are replaced, what parts are same? Do marks line up again after 4 rotations?

 

Aren't they know to often slip a gear when putting the timing cover back on if you don't pre-tension it a bit? I assume you're unable to see the crank marks anymore since you have the cover back on.

 

Keep rotating until you've seen the painted links for the ninth time, and look where they are.

It's just the number of links there are in the chain, versus the number of teeth on the sprockets. They'll line up every ninth time you see the painted marks. That's the same as every 70th crank revolution, or every 35th cam revolution. Just math.

Those won't necessarily be the same numbers for every type of engine. Somebody just has to count the sprocket teeth and chain links and do the math. These are the numbers you get for the Gen 3 Prius engine.

 

The marks on the chain are there for initial set up, when you first install it, to make it easier.
You rotate the crank twice, 720 degrees, and all the timing marks should be correct.
Forget about the chain. The crank mark should be aligned at TDC on the timing cover,
and the cam marks should align on the timing cover.
Where the colored links are doesn't matter. Eventually, if you rotate the crank enough times
they will line up. But it is not necesary to do that. Just two complete rotations of the crank.
Exhaust and Compression strokes.

 

After rotating the crank twice, 720 degrees, the dots on the sprockets will be back in their correctly-timed locations, but the painted chain links won't be on them. They'll be a few teeth off. That's ok. If you want to see the painted links line up on the marks again, you'll need to keep turning the crank 68 more times around. That's the ninth time you see the painted links go by.

And no, there's no rule that you have to do that. It's just that if you turn the crank a couple times around and notice that the links aren't on the marks, and you're curious why ... that's why.

If you're checking an unknown Gen 3 engine to see if it's properly timed, you'll see the painted links on the marks by no later than the ninth time they go by, if it is. If it's not properly timed, they will never show up on the marks no matter how many turns you give it. But it takes a long time to check 'never', so it's helpful to know that you can give up if you've seen them wrong nine times in a row.

Again, it won't be nine for every random engine type. It's nine for the engine in a Gen 3 Prius.

 

The special links on the timing chain are there to aid assembly. However, things are designed so that the same links on the chain don't ride on the same spots on the sprockets, over and over with every revolution.

There's some fancy math involved that I don't fully understand, I think it has to do with the number of teeth on the sprockets and the number of chain links not being evenly divisible. The links on the chain and marks on the sprockets WILL line up again- only once every 30-something turns. (maybe 40-something?)

Posted via the PriusChat mobile app.

 

The numbers for a Gen 3 engine were posted in #4 above. It's every 70th turn of the crankshaft, same as every 35th turn of the camshafts, same as every 9th time you see the painted chain links go by.

You can see how the math is worked out in this post, where the key step, once you know the number of sprocket teeth and chain links, is to write out both numbers as products of their prime factors, find the ones they have in common, and cancel those. Same thing you do when simplifying a fraction to lowest terms.

For more background on how/why that works, the magic words are modular arithmetic.

 

Machining the head has NOTHING to do with timing.

I don't think you are hearing what people are saying.
After the initial installation of the timing chain, those links do not mean anything.
Rotate the crank 2 times, a total of 720 degrees. Then align the mark on the crank so
it's at zero. Then look at the 2 camshaft sprocket marks, the should align with the marks
on the head. If the do, everything is correct. If they are not, you need to reset it.

You are making this MUCH harder than it is.

MUTE the audio for this video, of still photos. It is WAY too loud and horrible.

 

Well, but the almost-not-anything that they do mean is 100% predictable, and sometimes a person is curious about it, and then it's easy enough to explain.

 

As long as both camshaft sprockets are at clearly marked appropriate orientations at the same time the crank is at clearly marked TDC of #1 cylinder, it will make no difference where the silly colored links are. (If not in the designated positions, they'll all be "off" by exactly the same number of teeth.)

 

And to a person who isn't curious about anything beyond that, that's fine.

And if a person is curious enough to start a thread with a title like this one's, it's easy to answer that question too.