Timing and TDC

[71-440]

I picked up a timing light today and checked my timing against the scale on the balancer just to see
what the previous owner had it set at. It showed 18* BTDC. I am having a hard time starting when cold. (Back fired through the carb last time I started it)
I bumped it to 24* BTDC. Ran good no problems. I have yet to start it from a cold start though.

I would like to check the balancer to see if the scale is accurate though. I know piston #1 has to be on the compression stroke.
Can I use a piston stop and do the forward/back thing on the crank pulley to find true TDC. Or would that possibly do damage.

440 bored .060 over.
Mopar Purple cam 484 lift / 284 duration
Mopar aluminum heads.
Roller Rockers
MSD Distributor

I found in the receipts the previous owner game me, diamond forged flat top pistons, Hopefully that's in my engine as he owned several Mopars.

Any advice on the use of a piston stop would be appreciated and  what should the idle timing be at?
Also what RPM  for the advance timing and what max. * BTDC for the advance.

I also ordered the MSD kit with springs and stops for the mech. advance and timing tape for the balancer.

Thanks again in advance for any help!

[Cuda Cody]

You'll often find that an engine will need to have the initial and max timing set separately.  If you are running vacuum advance, most of the time there is a small allen screw inside the hole where the hose hooks to the distributor.  You can turn that to adjust the timing gap between initial and all in (max).  After that you'll need to change springs and stops.  I normally get the biggest increase in power, driving and start up when I take the time to set both. 

[LinceCuda]

The piston stop is great for checking the TDC mark to make sure it's correct, Then after that what Cody said is good way to proceed.

[RUNCHARGER]

You're on the right track. I always verify TDC on these old engines. 24 will make starting more of a problem than 18.

[73_Cuda_4_Me]

I may be way off, and am not stirring up trouble, but I think that the screw adjustment Cuda Cody is talking about only adjusts the amount of vacuum necessary to overcome the spring tension... You can screw it CCW (loose spring) for low vacuum advance starting point, or turn it CW to increase spring tension to the point where it is not capable of having enough vacuum to move it.

The total amount of vacuum advance is hard-coded in the canister arm... there is a slotted area that allows arm movement equating to the total degrees vacuum advance stamped in the arm (x2 for crank degrees, i.e. 8.5 = 17 degrees at crank).

Circled area of picture shows notched area of arm that controls total amount of advance...

[1 Wild R/T]

I may be way off, and am not stirring up trouble, but I think that the screw adjustment Cuda Cody is talking about only adjusts the amount of vacuum necessary to overcome the spring tension... You can screw it CCW (loose spring) for low vacuum advance starting point, or turn it CW to increase spring tension to the point where it is not capable of having enough vacuum to move it.

The total amount of vacuum advance is hard-coded in the canister arm... there is a slotted area that allows arm movement equating to the total degrees vacuum advance stamped in the arm (x2 for crank degrees, i.e. 8.5 = 17 degrees at crank).

Circled area of picture shows notched area of arm that controls total amount of advance...

Absolutely correct....

[Chryco Psycho]

Actually if you back the screw out 14 turns to the max & put vacuum on the diaphragm it will not longer move the arm at all

[71-440]

The distributor is a mechanical advance not vacuum. MSD 8546.  Wasn't sure if using a piston stop would hurt anything.
What would be a good idle timing to start with?
What would be a good rpm to check and set advance with stops? The MSD has stop  bushings to limit the advance and different springs to set the curve.

The reason I bumped it was the two times it back fired through the carb and rough warm up. I thought advancing it would be the way to go.
I'll see how it starts in the morning.

Thanks!

[73_Cuda_4_Me]

   I knew I'd get the CCW and CW mixed up bass-ackwards! Thanks, Chryco!

Back to the timing... almost everyone here would suggest disabling vacuum advance if it's present, and just use mechanical...

With larger cams, you need more initial at idle. That poses a problem when you then rev up, and mechanical goes above the 34-36 degree 'all in' at higher rpm's. You will need to limit total amount of advance. The amount to limit depends on what cam likes at idle... set timing for best vacuum reading at idle (rpm will increase, too), and then reset idle speed. Test timing for best vacuum a couple of times, trying to keep idle speed as low as practical with the cam. You should not get any mechanical advance around idle speed! You may have to use stronger springs to keep it off until you get to 1,100-1,400.

Once you find out what it likes, then you can set the total mechanical limit so it falls into the 34-36 degrees all in around 3,000-3,500... If cam likes 20, you limit it to 15 more on mechanical... if it likes 25 best, you only get another 10 to work with.

[RUNCHARGER]

I like vacuum advance if the engine will take it without pinging.

[71-440]

  I knew I'd get the CCW and CW mixed up bass-ackwards! Thanks, Chryco!

Back to the timing... almost everyone here would suggest disabling vacuum advance if it's present, and just use mechanical...

With larger cams, you need more initial at idle. That poses a problem when you then rev up, and mechanical goes above the 34-36 degree 'all in' at higher rpm's. You will need to limit total amount of advance. The amount to limit depends on what cam likes at idle... set timing for best vacuum reading at idle (rpm will increase, too), and then reset idle speed. Test timing for best vacuum a couple of times, trying to keep idle speed as low as practical with the cam. You should not get any mechanical advance around idle speed! You may have to use stronger springs to keep it off until you get to 1,100-1,400.

Once you find out what it likes, then you can set the total mechanical limit so it falls into the 34-36 degrees all in around 3,000-3,500... If cam likes 20, you limit it to 15 more on mechanical... if it likes 25 best, you only get another 10 to work with.

That's what I was thinking or trying to remember.  Large cam more initial timing.  Like I said it's been 30+years since I messed with timing on a car and I don't know a whole lot to start with...lol
The idle did increase when I tweaked it up so I backed off the idle screw and brought it down to 900. Probably a little high still.

I don't have a vacuum gauge but will pick one up tomorrow for sure.

Thanks!

[73440]

http://www.hotrod.com/articles/ignition-timing-free-hp-heres-get/

[71-440]

http://www.hotrod.com/articles/ignition-timing-free-hp-heres-get/

Good article!

Thanks!

[Chryco Psycho]

the piston stop wil;l work well , take all of the plugs out , put the stop in #1 or #6 cylinder , turn the engine one way until it stops , then put a mark on the damper & go the other direction until it stops & put a second mark on the damper , TDC will be 1/2 way between the two marks .
Generally you want the initial timing between 16-20* with total timing limited to 34-36* range .

[Cuda Cody]

  If you can get around 18 initial timing (at idle) and maxed out all in around 36 degrees (about 3,500 rpm) I think you will have a great starting point.  Those are some good starting numbers to target for.