timing chain replacement

[Summershandy]

Does this look like the set up for the sprockets to change the chain on a '54 straight 8? The cam pulley has 3 lines and not a dot. Do those 3 lines represent the diagram at the top right? TDC and 5 degree marks? (Sorry for the terrible pic) There is also a line on the other side of the sprocket 180 degrees. Timing is my downfall and I really don't want to mess up an already good running engine. I happen to be in there already and would like to do it then. 

[Bloo]

The diagrams just show what the valves actually do when everything is correct. I have no idea why there would be 3 marks. This looks like the standard setup used on most cars except for the 3 marks. I would verify which mark you have now. I am guessing the center mark, but check it. Line it up so that a line between the center of both shafts goes through the timing marks. You might have to rock the crank and cam back and forth a bit (easier with the plugs out) because of slop in the old chain, but there shouldn't be a whole tooth of slop, so you should be able to tell which mark it really is. Make a note for later.

 

Are you just changing the chain and sprockets? Or maybe just the chain? Is the head off?

 

The diagram tells you that on TDC OVERLAP (a whole turn away from firing) the intake opens the same number of degrees before TDC that the exhaust valve closes after TDC. If there is any need, you can use this information to verify the valve timing is correct. If the head is off you can just watch.

 

On my Pontiac 6, I did this with a dial indicator with an offset foot. I stuck it in through the spark plug hole. I could reach the head of either valve this way. On some Pontiacs, the spark plug hole may not allow this. The dial indicator could similarly be used directly on the lifters if the side covers happened to be off. I used this information to verify that the valve timing was correct, even though neither the head nor the timing chain cover were off.

 

Valve lash affects the readings. So does chain slop. The absolute number of degrees is not important, just that the inatke closing and the exhaust opening are the same distance from TDC OVERLAP.

 

You can divide 360 by the number of crank sprocket teeth you have to see how many degrees a whole tooth is. Since you know how many degrees a tooth is, if the error you find is less than that, the timing chain has to be on properly.

 

 

Edited November 28, 2017 by Bloo (see edit history)

[Summershandy]

Change the chain for sure maybe sprockets. Heads are on making me think checking valves would be difficult. Again, this field is new to me and the diagrams mean nothing but thanks!

[Bloo]

To put it in a really easy way. On any cylinder, on TDC, one whole crank turn from where that cylinder fires , one valve opens just barely before the piston goes over the top, and the other one closes just after.

 

If you can verify that somehow, the valve timing HAS to be correct. Good luck!

Edited November 28, 2017 by Bloo (see edit history)

[maok]

What Bloo is saying is that both the inlet and exhaust valves will be slightly open equally at TDC, not the firing TDC. If you can confirm this, then your timing marks are correct. If there is a side plate to access the valve lifters/followers then it would be possible to confirm. Or you could pull the head off.

[RussJagoau]

So the crank pinion looks to be at TDC given the orientation of the key. But the cam gear looks to be 180 degrees out... ..a full turn of the crank should see the correct marks line up together. I would think given the current  crank angle thats indicated then that engine is on the exhaust stroke of the No 1 cylinder.... the Inlets on these engines have a 224 degree duration  whereas the exhaust is 230 degree and minimal overlap so they are quite simple to valve time...
To check that with the head on is quite simple, remove the plugs and install a piece of tissue into the #1 plug hole. Rotate the engine in the normal CW direction, if the tissue is drawn in its intake , conversely if its blown out its compression. this combined with the position of the rotor in the distributor should be a giveaway as to the what stroke in the cycle that the cylinder is on.  As the engine has been running ok, then its also a simple matter of re-placing the chain with the same number of link s / pins of the timing chain   from the timing marks used. You dont have to use the factory timing marks, as long as the phasing of the cam to the crank goes back in exactly the same position that you removed it.  So if the car was a runner prior, replace the chain and ensure the timing marks are in exactly the same location before you pulled the chain.....  

[Summershandy]

I was happy to see when I got the nut removed that the other gear was keyed also. I matched up the new marks best I could and replaced the gears and chain. The shafts never moved so nothing has changed. Gotta be a shade tree mechanics dream!