camshaft markings/valve timing

Here's a bit from the repair manual. If you don't have the whole manual at hand, though, I would encourage signing in so you do; there's a lot of info scattered through there about what to do and not do with the lock pin in the timing adjuster, and so on.



I've been hoping somebody will post the number of links in the timing chain, in case you have the cover off and you can count them. The number isn't in the book. It's easy to find good enough online pictures of the sprockets to count their teeth, and knowing the number of chain links too would make it possible to do the math to tell people (if they don't have the timing cover off) how many crank revs they might need before the colored links show up in the right spots.

 

This video may help you, he shows in detail the alignment marks. Also, for next time, a tip for locking the cam shafts, preventing them from rotating.

 

That's the idea but not quite how the math works: you could have to turn the crank 2(L / gcd(L, T))−1 times in the worst case, about half that many times on average, if L is the links in the chain and T the teeth on the cam sprocket. (Here's a Euclid's algorithm link if rusty on finding the gcd.)

But that's why it would be nice if somebody actually counts the links in the chain, because the difference between "55" and "about 55" can be huge when the formula has gcd in it. (Consider a case where one guess for L could be an exact multiple of T, and the guess just one up or one down from that could have no factors in common with T at all.)

So the links-in-chain question is still out there, for anybody who has one handy and doesn't mind counting them.

 

Screen-grab from the video:

 

Nice framegrab, thanks! I've counted (outer plates) a couple different ways now and got 70, anybody else get something different? So 140 rollers.

Now if I could just remember where I saw a good photo of the sprocket....

 

I just got 70 also

 

Here's a Repair Manual excerpt, with alignment info:

 

Some more screen grabs, the camshaft sprocket:



And the crankshaft sprocket:



Are these needed? The Timing chain cover is back on?

In the video, they say it takes something like two or three revolutions to get the marks aligned. That's assuming no misaligned cams.

There's pics in the pdf too.

 

The intake cam uses the double link, and the exhaust cam uses the single. The crankshaft must be correct if the cams are correct. It takes 10 revolutions to bring the marks back around if I remember correctly.

I rotated mine until I saw the links lined up two more times. Just to make sure nothing slipped.

 

KInd of a funny angle on the cam sprocket, but I'm pretty confident that's 18 teeth on the crank sprocket, which would make 36 on the cam. Yeah, does look like 36 on the cam, funny angle and all.

If that's 140 rollers in the chain and 36 sprockets on the cam, 140 = 2⋅2⋅5⋅7 and 36 = 2⋅2⋅3⋅3, the 2⋅2=4 is common to both, so it would take 140/4 = 35 cam revolutions to get all the way from aligned to aligned again, or 70 crank revolutions. Not sure why cnc is remembering ten.

Kind of a pity Toyota didn't just make the chain four rollers longer (couldn't they? just make the tensioner a little deeper?). 144 would be an exact multiple of 36, and you could get from aligned to aligned again with just 4 cam revolutions (8 crank revs).

On the other hand, thank your lucky stars they didn't split the difference and make it 142 rollers long. That would have no common factor other than 2, and you'd be stuck needing 71 cam revs, or 142 crank revs, to get from aligned to aligned.

 

In the video they mention it just takes a few revolutions of the chain for everything to realign.

 

"revolutions of the chain"? Maybe that's really what they meant ... how many times do you see the marked links come around the top of the engine?

One revolution of the chain (140 rollers) is nearly eight revolutions of the crank (18 teeth).

So you would need fewer than ten "revolutions of the chain" in the worst case (and typically fewer than five, if you didn't know where you were starting).

 

Not sure why ten stuck in my head either. But I do remember rotating the crank until the marks came back together two times for sure.

 

If we've got the tooth and roller counts right, it is indeed every 9th time the chain marks come around: one full chain loop is not a whole number of crank or cam revs, but 9 chain loops = 70 crank revs = 35 cam revs.

 

Yes that's what they meant. Had to think, but yeah: when the chain mark came around about four times, you were back where you started. And with the spark plugs out you can get there pretty fast.

It's about a third of the way into the video iirc.

 

Now I've watched it. Yeah, he ends up at aligned on the second time around the chain. But that's starting from an unknown point (just wherever the engine last came to rest before he started taking things apart).

If you ever were to start with the marks already aligned, it would take nine times around the chain (70 full turns of the crank) to get back there. (Though I imagine that most people, finding the marks already aligned, would elect to go zero turns and call it good.)

Starting from an unknown point where the engine last stopped, you don't know how many turns away you are from alignment, but it'll be under nine times around the chain, and if you do the same job a bunch of times, you'll average around 4½, or 35 crank revs.

 

I believe you Chap, cus my brain is full.