E-Bodies.org Cuda Challenger Forum

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. :notsure:

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!

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. 

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. :burnout:

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

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...

Quote from: 73_Cuda_4_Me on January 21, 2018, 05:11:51 PM
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....

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

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. :notsure:
I'll see how it starts in the morning.

Thanks!

 :('  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.

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

Quote from: 73_Cuda_4_Me on January 21, 2018, 07:10:27 PM
:('  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!

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

Quote from: 73440 on January 21, 2018, 07:33:59 PM
http://www.hotrod.com/articles/ignition-timing-free-hp-heres-get/

Good article!

Thanks!

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 .

 :iagree: 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.

Thanks for all the replies! :bigthumb:

I started it this morning and it started right up.  :cooldance: I have to goose the gas a little to keep it running until it warms up. Choke is not working properly.
It's a Edlebrock thunder series 800cfm with electric choke.

I picked up a vacuum gauge this morning also.



I will wait until I get the timing tape in and piston stop. The balancer is graduated but a little hard to see as it's
chromed. Then recheck everything using both the vacuum gauge and timing light.

On a side note I got my horn relay from Roseville AND NOW MY HORNS WORK.  8)

Very informative thread as I have to do the same.  ;)

See I never worried about the timing marks & tune by ear , threw out my timing light a long time ago

Usually the more initial timing you run the harder it is to start the car.

I'd be interested in seeing what kind of vacuum you are pulling. The most common setup w/o vacuum advance is 14-16 initial and 20 degrees of mechanical. I don't care much for vacuum advance so this is why I don't bother.

Quote from: Chryco Psycho on January 22, 2018, 06:10:30 PM
See I never worried about the timing marks & tune by ear , threw out my timing light a long time ago

:iagree: Yup, that's what I do, timing is pretty much different for each engine and setup, altitude, humidity etc., they are just guidelines, that's why they usually give you a range to follow. I do hook up the vacuum gauge to see where it's at though.  :alan2cents:

Be certain to disconnect your battery before you get started.  You could imagine the bad day you would have with an accidental blip of the starter with a piston stop installed.  Like others have said, remove your plugs because it will make rotating the engine by hand possible.  Sneak up slowly to each side of TDC as you nudge the stop and make your marks precisely. The use of a dial back timing light comes in handy and eliminates the need for timing tape on you chromed balancer.

Quote from: Mopar451 on January 22, 2018, 09:01:16 PM
Be certain to disconnect your battery before you get started.  You could imagine the bad day you would have with an accidental blip of the starter with a piston stop installed.  Like others have said, remove your plugs because it will make rotating the engine by hand possible.  Sneak up slowly to each side of TDC as you nudge the stop and make your marks precisely. The use of a dial back timing light comes in handy and eliminates the need for timing tape on you chromed balancer.

Good advice! 
Thanks!

Quote from: HP_Cuda on January 22, 2018, 06:25:11 PM
Usually the more initial timing you run the harder it is to start the car.

I'd be interested in seeing what kind of vacuum you are pulling. The most common setup w/o vacuum advance is 14-16 initial and 20 degrees of mechanical. I don't care much for vacuum advance so this is why I don't bother.

I eliminated the hard start part by putting a switch on the small red wire to the MSD box.
I hit start, which begins the motor turning over, then flip MSD switch.  Better than
timing retard at startup.

Got the piston stop and tape today. Unfortunately have to work this weekend. I will try and get started on it Sunday late afternoon.
If not may have to wait till end of week.

I'll post up how it goes as soon as I get working on it.

Thanks everyone for your advice!

I'll finally get some time this weekend to work on the timing.

One question- How far in do you thread the stop portion ( center rod all thread)of the PS.
When you reverse the direction of the crank
and come up on the exhaust stroke the exhaust valve will open, correct?
Don't want to damage a valve.

Aluminum Mopar heads.

Thanks!

Put the engine @ TDC & thread the stop in until it hits the piston , back the piston away & turn it in approx another 4 full turns

Quote from: Chryco Psycho on January 31, 2018, 07:44:50 PM
Put the engine @ TDC & thread the stop in until it hits the piston , back the piston away & turn it in approx another 4 full turns

OK. 

Thanks for the help! :bigthumb:

OK so today I had a little time to play with the new timing light and new vacuum gauge.

I figured before I use the piston stop let me see what the marks on the balancer with both timing light and vacuum gauge hooked up
tells me.
Warmed the car up to 180* which is normal operating temp. No problem starting and warmed up in a couple of minutes.
Looked at the vacuum gauge and was reading 10-11 in.hg. Timing 22* rpm 850.  So I advanced the timing untill the vacuum gauge read 15in.hg car smoothed out
Not real choppy rpm increased. timing light read 30*. Ran it up to 2500 rpm timing read  40+*.

So I went back to 22* on the timing light. Shut it down. Pulled the distributor cap to see if any bushing was installed for the advance before I continue(MSD DISTRIBUTOR)
No bushing installed but I did find corrosion on the magnetic pickup and the reluctor.

I will cal MSD to se if I can get a new magnetic pickup and clean the reluctor.

Any thoughts and suggestions?

I guess I need to pull the plugs and use the piston stop to see if the balancer is that far off.

(440 Mopar purple cam 484 lift 284 duration aluminum heads.)

Thanks in advance for any suggestions and thoughts.

If the timing marks are correct you only need to limit the timing curve .
At least cleaning the reluctor & pick up is a must but it sounds like it is working well even being corroded . :bigthumb:
The initial timing seems to high for that cam , the vacuum & running deosn't lie though

Quote from: Chryco Psycho on February 14, 2018, 08:45:11 PM
If the timing marks are correct you only need to limit the timing curve .
At least cleaning the reluctor & pick up is a must but it sounds like it is working well even being corroded . :bigthumb:
The initial timing seems to high for that cam , the vacuum & running deosn't lie though

I'm going to clean up the reluctor and buy a new magnetic pickup.
And I think your right just limit the advance.

I found a site that makes 2 bushings to limit the advance to 10* or 14*.
MSD's only goes from 18* to 28* in six different increments.
Once I get it cleaned up and get the new pickup I'll start off with 26* initial and get the 10* bushing  for the advance and see how it goes.

Thanks!

I would use 8* , 28-36*

I'll be doing some tuning on timing and carbs this weekend and was wondering how do you determine if vacuum reading is correct for your car?

Depends on your setup I believe.
Chryco Psycho would better explain it.

Vacuum is directly related to your cam and how much compression you are running.

The cam manufacturer should be able to let you know a vacuum range that cam should fall in.

Quote from: Aar1064 on February 15, 2018, 04:09:51 AM
I'll be doing some tuning on timing and carbs this weekend and was wondering how do you determine if vacuum reading is correct for your car?

Vacuum is ambiguous  , there is really no right vacuum spec .
There are a number of factors the biggest is the camshaft design , more duration = less vacuum type & size of the ports in the heads [small or large , swirl or straight],this will affect the velocity inside the engine  , type of intake [single or dual plane] & size of the plenum & ports , simple tuning can make a big difference , if you adjust the timing to factory spec the vacuum will suffer , advance the timing & you may find 3" of vacuum as demonstrated by the original person posting , idle RPM makes a difference , TQ converter load if auto , all affect vacuum

Thanks for the replies.

340 TA Engine was built to stock specs if that helps. No torque converter, a four speed.

Wish I knew more about this. Thanks for the help.

Keep working on the engine & you will gain experience & knowledge just as we did , I was not born with any knowledge either  :idea:

Update on my original post about timing. Had some time to mess around with it. Balancer marks were ok with the pointer.
Changed out the Mopar Box, which is a MSD-6, and installed a FBO box. Bypassed the ballast resistor.
Ran heavier gauge wire down to the box and wrapped the wires in that harness with a heat reflecting wrap.
Got them off the manifold with two cable clamps.
Installed the 10* advance bushing in the distributor. Cleaned the pickup and reluctor.
Set initial timing at 25* with the heavy springs installed on the advance otherwise the timing would jump around.
The heavy springs held it steady at idle. 900 RPM.
3000 rpm the timing went to 30-32.(with the heavy springs still installed) Should have went to 3500 RPM but will check that tomorrow.
Vacuum was between 12 and 13 with  it fluctuating between those two numbers.

Took it out for a test drive but was only able to get on it once. Too many cars on the road.
From about 10 MPH jumped on it and it lit up the tires going a little sideways but not too bad.
Ran it through 3rd. gear with no hesitation.
Rev limiter is set at 7000 RPM.

Torque converter, from what I understand, is a 2600-2800 stall. Might have to eventually go to a 3000.

That's where I am now. Still more playing to be done. The carb will be next after I fine tune the timing.
The fluctuation in the vacuum has got me a little puzzled. 12-13 With the needle fluctuating between them.
Not rapid but up and down.

not enough varience in the vacuum to worry about IMO

Quote from: Chryco Psycho on March 29, 2018, 07:19:59 PM
not enough varience in the vacuum to worry about IMO

I was hoping you would say that...lol

Thanks.

@Chryco Psycho (https://forum.e-bodies.org/mlist/chryco-psycho_4) I have a basic ignition timing question. My factory timing spec. on a 383 auto engine is 2 1/2 * btdc. Most of the recommendations I've seen is to run somewhere around 10 - 15* initial timing and around 34* total timing. Question is: why are we not running the 2 1/2* btdc initial timing that Chrysler recommends?