Compression Stroke

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carbuff

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Hi all. As stated in my intro, I am restoring a 1965 Dodge Dart GT with a 273 Charger engine. I know this has been discussed previously; but I am still confused. If my cam timing mark is at 6 o’clock and the crank timing mark is at 12 o’clock, is that the compression stroke? Thanks.
 
carbuff said:
Hi all. As stated in my intro, I am restoring a 1965 Dodge Dart GT with a 273 Charger engine. I know this has been discussed previously; but I am still confused. If my cam timing mark is at 6 o’clock and the crank timing mark is at 12 o’clock, is that the compression stroke? Thanks.
Click to expand...
As post #2 says, it is but not for #1. With the dots both at the 12 o'clock position, then you are at TDC for #1.
 
Last edited:
The position you described is commonly called "dot to dot". Mderoy is correct, your are on #6 compression. For #1 compression, both dots at 12 oclock.
carbuff said:
Hi all. As stated in my intro, I am restoring a 1965 Dodge Dart GT with a 273 Charger engine. I know this has been discussed previously; but I am still confused. If my cam timing mark is at 6 o’clock and the crank timing mark is at 12 o’clock, is that the compression stroke? Thanks.
Click to expand...
 
When the timing dots are aligned (6 o'clock & 12 o'clock) that is firing at TDC on #6.
 
The dots have NOTHING to do with the compression stroke ....... until you correctly install the cam.

You yourself have to positively locate the Crank to TDC#1,
Prior to installing the timing set,
that has been previously meticulously aligned dot to dot.
If the top sprocket does not fit, you have to rotate the cam until it does ........ without moving the crank sprocket.
After
this is done, you have to verify the crank is still at TDC#1, and the dots are still aligned.
After that is done, you should be able to slowly rotate the crank two full turns with no valves getting slapped by any pistons.

But you really don't know if any marks are accurate.
To sleep better, I would still figure out where "split-overlap" is occurring, relative to #1 TDC. Split overlap is when both valves for a given cylinder are open the same amount. The window for this to occur is about 4* retarded to maybe 8* advanced, and you want to be somewhere close to, in the middle of that.
On an SBM with hydraulic lifters, this can be a tall order, and
if you don't do it, it's no big deal; if the sprockets are accurately marked.

Before you put the distributor back in, make sure #1 cylinder is at TDC compression. Then back the crank up to say 10 * advanced, then stab the D in with the rotor ending up under the #1 Tower, and continue.
Good luck.
 
Thanks for the info. I did measure TDC #1 with timing marks lined up, then I rotated two crank rotations to get two compression stroke. Then I stepped thru every 90 deg and created a cold lash at the correct valves. I admit I didn’t meticulously look at “split-overlap”; but have rotated it a couple times with no valves hitting. I will take into account your 10* advanced position before installing distributor.
 
carbuff said:
Thanks for the info. I did measure TDC #1 with timing marks lined up, then I rotated two crank rotations to get two compression stroke. Then I stepped thru every 90 deg and created a cold lash at the correct valves. I admit I didn’t meticulously look at “split-overlap”; but have rotated it a couple times with no valves hitting. I will take into account your 10* advanced position before installing distributor.
Click to expand...
To make it easier than a convoluted bunch of boosheet, put a degree wheel on it.
 
carbuff said:
Sorry, meant to say I rotated crank one turn from “split-overlay” to get to compression stroke.
Click to expand...
I wasn't talkin about you. I was talkin about the clear as mud BS in post #7.
 
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