Camshaft alignment problem

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273 Commando

273 Commando

mooser's dad
Joined
Dec 27, 2008
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San Jose, CA
Am I a dumbass or don't I get it? Ok, here's the deal. I set my 273 at TDC and insert the new bump stick ( on engine stand ), I go to install the timing chain with the timing marks set to "dot to dot" per instructions and the cam is 180 degrees out of time according to the Mopar valve lash chart. I spin the crank 180 deg. more so both the timing dots are at the 12 o'clock position (both facing "up") and No. 1 is at TDC again and its correct. After installing the valve gear and checking the dot positions, this is correct. The closed valves for rocker arm adjustment are in the correct position when the timing dots are "up".

We fired the engine this way and it started and ran....any ideas why this is? I'm not sure how this occurred or why since I'm a novice carport mechanic LOL but an insight would be great. I'm sure many of you will say just go with it, but I like to know how things are supposed to work. Thanks gang!
 
That is correct. Dot to dot is easier to line up when at 6 and 12 which is #6 TDC. You should always spin it around before dropping the distributor.
 
Yes Steve, you are right on. When the dots face each other, my engine is at #6 TDC. Is that normal? I always assumed that dot to dot meant #1 TDC. Well this why one asks and learns I suppose. Thanks.
 
273 Commando said:
Yes Steve, you are right on. When the dots face each other, my engine is at #6 TDC. Is that normal? I always assumed that dot to dot meant #1 TDC. Well this why one asks and learns I suppose. Thanks.
Click to expand...

Its normal in the sense that this how timing chains are installed. Remember the cam rotates once for every 2 crank revolutions. You then spin the crank once, then the cam only goes 180. THAT is #1.

We will always learn something as long as we are alive. Its a great thing.
 
Steve's right. The cam only turns half the amount the crank turns. And to add to that there's 2 top dead centers for each firing cycle. TDC compression stroke and TDC exhaust stroke. When #1 is on TDC compression stroke #6 is on TDC exhaust stroke and vice versa.
 
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