I have heard it said that the bright links of the timing chain will "line up with the timing marks ever now and then" when you spin the engine over.

Well... I'm here to put a number on it and that number is eleven.

I lined up my timing marks and then rotated the crank to see how long it would be until the marks lined up again, and the answer is that they line up every eleven rotations of the cam (twenty-two rotations of the crank). Not being satisfied with only experimental results, I counted teeth and links and stuff.

There are 20 teeth on the crank gear.
There are 40 teeth on the cam gear (makes sense since the cam spins at half the crank speed).
There are 110 "teeth accepting holes" in the chain.

The common multiple (modulus maybe?)  of all of those numbers is 440 and it takes eleven cam rotations or twenty-two crank rotations to move 440 link holes.

The links of the chain will line up in the same position every eleven rotations of the cam.

And because everyone likes pics... Timing chain and pulleys:

Edited August 31, 20195 yr by Captain Obvious
Dirty Harry Moment

Amazing how you made that head disappear!

Glad to hear this, I've freaked the heck out on this before. Thank you!

Oh, it's still there. I had the head work done by Dr. Marcus Nichols at Plexicorp.

I've been out geeked out smarted and out done. Your the man Scotty!

 

Bright ideas come from bright people!

Thanks!

Now we'll have to cone up with a 15-36-24 always remember line...

11 is too young!

The Spinal Tap Chain.

11 bothered me because it's not an even number. 11 turns of the crank turns the cam 5.5 turns, right? How can the dot line up with the link other than on a full turn? 

110 chain links / 40 teeth on the cam = 2.75 cam revolutions for one complete chain revolution. 2 complete chain revolutions = 5.5 cam revolutions. 4 chain revolutions = 11 cam revolutions. 11 cam revolutions = 22 crank revolutions.

11 cam revolutions * 40 teeth = 440.

22 crank revolutions * 20 teeth = 440.

440 is the first number we can get to that is evenly divisible by 110 chain link holes, 20 crank teeth, and 40 cam teeth - isn't it?  (110, 220, 330, 440)

Somebody check my math - and logic...

(11 cam revolutions bothers me - because it isn't even.)

 

Yes, 440 is the lowest common multiple.
https://www.calculatorsoup.com/calculators/math/lcm.php

And 440/#cam teeth = 11

Oh crap... So when I said crank revolutions, I meant cam revolutions.

I was spinning stuff and counting, but in all the excitement, I kinda lost track myself.

I changed the original post to fix that mistake. Thanks for the help guys!

Edited August 31, 20195 yr by Captain Obvious

Yes, you are RIGHT.

440 is the lowest LCM. And one more thing is that cam teeth =11.

You can do the same with LCM Calcualtor: https://www.lcm-calculator.com/

Lowest Common Multiple.