Camshaft timing when the sprockets are ONE tooth off from straight up.

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Kern Dog

Kern Dog

Build your car to handle.
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Here we go....
This is not purely hypothetical.
Years ago I had a 318 in a Duster that was a S-L-U-G ! I tried all sorts of things to improve it but it was still slow. I pulled the timing cover to find that the cam sprocket and crank sprocket did not line up at the 6:00 firing position. With the crank at 12:00, the cam sprocket was off by at least one tooth.
Here is the question.....How much cam timing is in one tooth?
I realize that you just divide the number of teeth on the sprocket by 360 but which sprocket do you do the math from?
I don't remember the amount of teeth on either sprocket. I'm also curious if the number of teeth is always the same no matter who makes the timing set. It is always a 2 to 1 ratio though since the crank sprocket is 1/2 the size of the cam sprocket.
If the cam sprocket could be rotated ONE tooth to line up to the crank sprocket, that is one thing. In theory, that is 1/2 tooth of timing at the crank, right?
This would mean that the cam sprocket could be off 1/2 of crank timing per cam sprocket with a chart as follows:
1 @ cam = 1/2 crank
2 @ cam = 1 crank
3 @ cam = 1 1/2 crank, etc.

Back to the Duster 318. This was in 2008 and the memory is a bit fuzzy. It was off the mark enough that the engine ran smooth but was gutless no matter how much spark timing was put to it. I tried different intakes, carburetors, distributors and even uncorked the exhaust. Once I put a new timing set in it, (Installed correctly) the car was great. Before, it wouldn't peel out even on light gravel over hard packed dirt.
What say you? What amount of cam timing difference do you see per tooth ?
 
What what its worth Mopar Joe on u tube has a video on a similar topic?
 
Skipping a tooth could be combined with an offset key to get a desired intake centerline.
 
Yeah, many decades ago, I had a lazy 318 too. I advanced a used double-roller with a loose chain, one tooth, and shazzam! From 17s to 12s just like that............ not. But it was a noticeable improvement.
 
If the top sprocket has 26teeth @360 degrees, then one tooth is 360/26=13.846, by the math. and so on.
I can't recall the tooth count either.
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With an 8/1Scr-318 running the factory cam, with a loose chain at say 2* retarded(Ica of 54*) , which is 6* from where it shouldda been;
to one full tooth advanced on that same loose chain, at say
54 less 14= 40*ICA, the pressure is predicted to rise from 134psi to 147, at sealevel. At Ica of 40*, in this case, it is only 8* advanced from the factory install, using that stretched chain.
The overlap moves the same amount, but since the 318 cam only has 20 degrees to start with, and she is running logs, this is almost meaningless.
The Power stroke shrinks the same number of degrees as the compression increases, but since the 318 cam, in at split overlap, already has an excessive amount of power-stroke, 8>10 less degrees is almost nothing...... IMO.
Mine ran fantastic. Well, I mean I was very young lol, and to me it was light years more powerful.
I had/still have, an egg-crate full of stretched 340 chains and used sprockets, still to use up, so, I did it again on my winter motor, in year 2000. lol.
Com'on think about it, it's sort of like VVT! Advanced under power/ retarded by engine-braking; it seemed good to me. With a 2800 Stall, I liked it. I might do it again someday.
 
PRH said:
With a double roller, a tooth is about 14 degrees.
Click to expand...

If the crank sprocket is 25 tooth, 360 divided by 25 works out to 14.4 degrees per tooth.

Inertia said:
12 - 14* one cam tooth .
Click to expand...

If a cam sprocket has double the teeth of the crank, then the cam sprocket has 50 teeth. That would make each cam tooth 7.2 degrees.
Part of the curiosity is if all aftermarket timing sets have the same amount of teeth on the sprockets. I've never thought to count them. I have a few engines here and a few low mile timing sets I've saved. I just haven't thought to look and count them.

I found a notebook where I wrote about the work that I was doing with the car.
In there, I wrote that the cam sprocket was 3 teeth off advanced. That technically is 1 1/2 teeth at the crank, right?
The Engine Masters TV episode where they ran the 440 on a dyno showed a power loss with the cam advanced 10 degrees. Being advanced the 3 cam sprocket teeth is what then...almost 22 degrees? The only reason the valves never hit pistons in this low compression 318 was because the pistons probably sat .80 in the hole and because 318 cams had a paltry .373 of lift.
The timing set was not stock, so someone either made a mistake or stupidly thought that advancing the cam timing this much made sense??
 
I was taught to check if a timing chain had jumped a tooth (particularly cheb plastic gears), that to put #1 or #6 (or#1or #4 on 4 cyl. cyl) in equal overlap.
If the timing mark was more than 12*, the chain had jumped, not stretched.
Proved true time and again.
That was my test
 
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Inertia said:
I was taught to check if a timing chain had jumped a tooth (particularly cheb plastic gears), that to put #1 or #6 (or#1or #4 on 4 cyl. cyl) in overlap.
If the timing mark was more than 12*, the chain had jumped, not stretched.
Proved true time and again.
That was my test
Click to expand...
the chain has to have stretched a lot to jump teeth, if it's not stretched ie correct tension it can't jump. now installed a tooth out? that's entirely possible, lol.
 
The “classic” timing set mistake, which I have witnessed several times, is to put the crank key straight up and line that up with the dot on the top gear.
This puts the cam advanced 2-1/2 teeth on a BBM with a double roller chain.
Most times this results in 8 bent intake valves.
But some engines actually have enough physical room to run without damage occurring.

Had a customer who was working on a 455 Olds.
Very low power, 200psi on the compression tester, no spark knock.
I told him it was likely cam timing way off.
They didn’t want to tear it down and look so they spent a summer with it being a dog while they messed around with timing, carbs, etc.
They finally pulled it apart…….and it had the “classic” mistake.

Put the timing set on correctly, way more power everywhere.
Lost a bunch of cranking pressure.
 
PRH said:
The “classic” timing set mistake, which I have witnessed several times, is to put the crank key straight up and line that up with the dot on the top gear.
This puts the cam advanced 2-1/2 teeth on a BBM with a double roller chain.
Most times this results in 8 bent intake valves.
But some engines actually have enough physical room to run without damage occurring.

Had a customer who was working on a 455 Olds.
Very low power, 200psi on the compression tester, no spark knock.
I told him it was likely cam timing way off.
They didn’t want to tear it down and look so they spent a summer with it being a dog while they messed around with timing, carbs, etc.
They finally pulled it apart…….and it had the “classic” mistake.

Put the timing set on correctly, way more power everywhere.
Lost a bunch of cranking pressure.
Click to expand...
and used a bunch more fuel all summer too :lol:
 
Kern Dog said:
If the crank sprocket is 25 tooth, 360 divided by 25 works out to 14.4 degrees per tooth.
Click to expand...
Geez....that sounds familiar. :rolleyes:

1734283326978.png
 
mygasser said:
the chain has to have stretched a lot to jump teeth, if it's not stretched ie correct tension it can't jump. now installed a tooth out? that's entirely possible, lol.
Click to expand...

And if chain is installed wrong, same test .

I've actually watched an old stiff one of those link-belt timing chains, walk a tooth over, when the engine was rotated backwards, - like when shut off, the engine "runs on" then goes whoof, with a shot of something outta the carb.
The engine actually runs reverse rotation, and has/does walk an old stiff timing chain over the cam sprocket. It'll push a straight section of stiff chain straight UP, - till it finally flops over, - a tooth over from where it should be .
 
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PRH said:
The “classic” timing set mistake, which I have witnessed several times, is to put the crank key straight up and line that up with the dot on the top gear.
This puts the cam advanced 2-1/2 teeth on a BBM with a double roller chain.
Most times this results in 8 bent intake valves.
But some engines actually have enough physical room to run without damage occurring.

Had a customer who was working on a 455 Olds.
Very low power, 200psi on the compression tester, no spark knock.
I told him it was likely cam timing way off.
They didn’t want to tear it down and look so they spent a summer with it being a dog while they messed around with timing, carbs, etc.
They finally pulled it apart…….and it had the “classic” mistake.

Put the timing set on correctly, way more power everywhere.
Lost a bunch of cranking pressure.
Click to expand...

I bought a rebuilt slant six long block from Southeast Engines in Atlanta back in the late eighties. Ran smoothly, but had no power. I tried this and that, finally pulled the front cover off to check the cam timing. It was one tooth off. Corrected that, and got the power back that it was supposed to have (not a whole lot, it was a slant six, but way more than when it had one tooth off).
 
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In the "old" days, cars with a lotta mileage on it always seemed to have better "top end", speed .
It did, - cam was sooo retarded totally changed power band to top end.
Loose as hell bottom end also helped, lol.
That's just before they blew-up, lol . .
 
This engine did have a loose chain although it was aftermarket.
Here is how the car looked when I got it...

IMG_1439.JPG


The car was a real roach, so I nicknamed it that.

IMG_1441.JPG


IMG_1449.JPG
 
At least we're not spending valuable time trivialising over a slant six or something equally as pathetic.
 
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