Just when I thought I understood A timing...

Art Newland

Art Newland

Well-known member
I was about to button-up my engine project when I thought I'd take a look at how the timing pin mark in the cover and the timing alignment marks on the crank and cam gear equate to the position of the piston/valves. While the timing marks are aligned, the #1 piston is at TDC and the exhaust valve is wide open. Is this correct?:confused:
 

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With the timing pin engaged in the cam gear through the cover, the valves are closed and the piston is headed down the bore, considerably ATDC. I thought while the pin is engaged #1 is supposed to be at TDC?:confused:
 

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I though maybe I have a weird-o timing cover, but looks like pretty standard fare?
 

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In the red book, the pictures of the gears show the position of the crank gear key-way in a different place than my engine, which is correct?
 

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Any other engine I've worked on, while the timing marks were aligned, #1 piston was at TDC. Obviously that can't be the case on the A motor if TDC is supposed to happen with the cam timing pin moved way over to where the timing pin is located.
 
Your's is very different from mine......

Seems to me I've read here that there were some crank gears that were improperly marked....

Others will respond!
 

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I can not tell clearly from your pictures, however remember the crank makes 2 revolutions to 1 of the timing gear. Your crank might be 1 revolution off. What is the position of the number 4 piston and the valves for cylinder #4? 1 and 4 should be at TDC with the indent in the timing gear lined up for the pin however the exhaust valve for #4 should be open and all valves for #1 closed.

I think if you took the timing gear off, rotated the crank 1 full turn so your marks line up again I think you will be fine.
 
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If you turn the motor till the valves are rocking on No 4, No 1 will be at TDC and ready to time it. It's easy to see when that happens since you have the head off. I bet the dimple in the timing gear lines up with the pin when you do that. That is, unless the crank is one turn off, in which case the dimple will be directly opposite the pin.
 
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The location of the timing indent in your pics is not where it will be when the timing pin is used for timing. Place the cover on loosely with a bolt or two, rotate the engine so the pin falls in place, then remove the cover and see if the valves are closed then and if the piston is at TDC. They will be, but do not take our word of it. Check it yourself.
 
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frank55a said:
I can not tell clearly from your pictures, however remember the crank makes 2 revolutions to 1 of the timing gear. Your crank might be 1 revolution off. What is the position of the number 4 piston and the valves for cylinder #4? 1 and 4 should be at TDC with the indent in the timing gear lined up for the pin however the exhaust valve for #4 should be open and all valves for #1 closed.

I think if you took the timing gear off, rotated the crank 1 full turn so your marks line up again I think you will be fine.
Click to expand...

TDC is TDC, if I rotated the crank one turn, it would be right back in the same spot.
 
PC/SR said:
The location of the timing indent in your pics is not where it will be when the timing pin is used for timing. Place the cover on loosely with a bolt or two, rotate the engine so the pin falls in place, then remove the cover and see if the valves are open then and if the piston is at TDC. It will be, but do not take our word of it. Check it yourself.
Click to expand...

But you have to initially "time" the gears by aligning the crank and cam gears, they both can't be TDC...:confused:
 
Henry liked to be different, so he timed the cam to the crank without caring where the ignition timing was at that time.

So they are two completely different operations, and NOT done at the same time.
 
Well, try it with the cam gear mark aligned to the crank gear on that tooth just to the right of the key way. Then fit the timing cover, insert the timing pin in the dimple and see where the #1 piston is and which way the distributor rotor points....

Then write a note for the next guy that rebuilds that engine!
 
Synchro909 said:
If you turn the motor till the valves are rocking on No 1, the piston will be at TDC and ready to time it. It's easy to see when that happens since you have the head off. I bet the dimple in the timing gear lines up with the pin when you do that. That is, unless the crank is one turn off, in which case the dimple will be directly opposite the pin.
Click to expand...

PC/SR said:
The location of the timing indent in your pics is not where it will be when the timing pin is used for timing. Place the cover on loosely with a bolt or two, rotate the engine so the pin falls in place, then remove the cover and see if the valves are closed then and if the piston is at TDC. They will be, but do not take our word of it. Check it yourself.
Click to expand...

See post #2
 
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