Cam chain / timing

[xlr8tn]

I installed a new cam chain today and got the rivet set exactly on top. All was lined up, cam had notch pointing straight up and TDC according to my stock rotor. I used the kick starter to cycle the Pistons and when I was back at TDC and point of my rivet, it appears to have jumped a few teeth. What happened? The chain is tight, but I did not have the tensioner in place, so perhaps something slipped. Should this rivet link come all the way around and stay at top when at tdc? Still learning. Even though the rivet link was off, the TDC was on the mark and the notch was pointing up.

 

[TwoManyXS1Bs]

Assuming you have a 74-later 447 camdrive setup, there will be 36 teeth on the cam sprocket, 18 teeth on the crank sprocket, and 106 links in the camchain. Since 106 isn't evenly divisible by 18 or 36, the position of the chain's masterlink will be different for each revolution. And, it's not important. Just the timing of the camshaft to the crank is important.

Challenge: How many crank revolutions are necessary to get the masterlink to reappear at the top?

Hint: Remember your elementary school lessons on 'least common denominator'?

 

[TwoManyXS1Bs]

Oops, forgot to post the answer.

Starting with the masterlink at the top, engine at TDC, masterlink perched atop the cam sprocket slot. How many crank revolutions to reaquire that position?

Looking at the 36 tooth cam sprocket, and 106 link camchain:

It will take 106 revolutions of the sprocket to get 36 orbits of the camchain.
Those numbers can be divided by 2:

It will take 53 revolutions of the sprocket to get 18 orbits of the camchain.
That's as far down as you can go, since 53 is a prime number.

53 revolutions of the cam sprocket will require:

106 revolutions of the crankshaft.

 

[angus67]

I thought it was 4:1? Been a while since i static timed a motor

 

[Michaelo]

Are you bored 2M?

 

[TwoManyXS1Bs]

Yesterday, all day, it was raining, cold, wet, dreary.

So, I guess so...

 

[grizld1]

Angus, here's why 2:1 gearing. Compression: 1 stroke of piston=1/2 revolution of crank, valves closed. Power: 1 stroke=1/2 rev, valves closed. Exhaust: 1 stroke=1/2 rev, exhaust valve opens. Intake: 1 stroke=1/2 rev, intake valve opens. Bottom line: to get that done, camshaft has to turn at 1/2 crank speed.

 

[angus67]

thank you