Ignition timing

[WPVT]

My 1954 flat head 6 Dodge truck engine had some problems with engine noise at 40 MPH and over, so I retarded the spark, and now it runs much better, smoother, and quieter. I tried retarding it more and retarding it less, and found what seemed to be the sweet spot. The change was dramatic. Now it's quite smooth at 50 mph. 

I was curious,though, so I checked the timing with a light , and it was retarded a full 10 degrees at idle (400 rpm). So I put it back to 0 degrees at idle, as specified in the manual. Doing that gives me about 10 degrees advance at 1500 rpm. At 2000 rpm I can no longer see any marks, so it's well advanced at that speed. 

Vacuum advance is new, and centrifugal advance seems like it's working properly.  

 

I haven't road tested it yet, but I suspect I will be back where I was, with a noisy engine at 40 mph. The cure seems to be retarding the timing by 10 degrees, but I'm puzzled. 

Why, do you suppose, would my engine run so much better with the spark retarded that much ? Compression is good, and it runs smoothly. No soot on the plugs....steady vacuum at 18 or so. The crankshaft pulley is reading correctly, as I mechanically verified TDC. Carburetor was rebuilt, new ignition wires, points, etc. 

[keithb7]

Ignore the suggestion of 0 degrees timing. That was old low octane  fuel. Modern fuel has a different burn rate. Set the timing that works for your engine, using today’s fuel offerings. 
 

All you are doing is setting the ignition time in relation to the piston and valve positions. Do what works for your engine. Listen for pinging under load. Back off a little on the retarding if pinging too much. 
 

My understanding is can also set up your timing using a vacuum gauge. I’ve not done that yet. Achieve maximum vacuum at idle by turning distributor timing? 

[hchris]

As well you need to consider wear and tear, timing chain stretch, rubber moulding in the crankshaft hub/pulley, distributor springs and flyweights etc,etc.

 

Highly likely that the timing marks are not where they were when built, so what you have done is correct. 

 

With a vacuum guage you can get timing almost perfect (on a standard engine) but it requires that you connect a vac guage somewhere in the inlet manifold below the throttle (not the distributor vac port). For instance a brake booster port or similar would be ideal. With engine at idle move the distributor around until you get around 20 - 22 inches of vacuum, this will get you in the ballpark, any higher and you'll be pinging. 

 

Go for a run and if it pings back off a few degrees, might be worth looking at the timing marks when you get it right, if it's significantly of my money would be on the rubber insert in the crank pulley. 

Edited September 10, 2021 by hchris
Words (see edit history)

[WPVT]

3 hours ago, hchris said:

As well you need to consider wear and tear, timing chain stretch, rubber moulding in the crankshaft hub/pulley, distributor springs and flyweights etc,etc.

 

Highly likely that the timing marks are not where they were when built, so what you have done is correct. 

 

With a vacuum guage you can get timing almost perfect (on a standard engine) but it requires that you connect a vac guage somewhere in the inlet manifold below the throttle (not the distributor vac port). For instance a brake booster port or similar would be ideal. With engine at idle move the distributor around until you get around 20 - 22 inches of vacuum, this will get you in the ballpark, any higher and you'll be pinging. 

 

Go for a run and if it pings back off a few degrees, might be worth looking at the timing marks when you get it right, if it's significantly of my money would be on the rubber insert in the crank pulley. 

Thanks.I'm not positive, but I believe my engine has a solid pulley, not the harmonic balancer with the rubber insert.

I used the vacuum method a while back. It left me with the engine noisy at 40 mph and above. Retarding the spark quieted things down. I'll probably do what KethB7 advised and just put the timing where the engine runs best. 

I'll leave the timing light in the drawer.

Edited September 10, 2021 by WPVT (see edit history)

[WPVT]

7 hours ago, keithb7 said:

Ignore the suggestion of 0 degrees timing. That was old low octane  fuel. Modern fuel has a different burn rate. Set the timing that works for your engine, using today’s fuel offerings. 
 

All you are doing is setting the ignition time in relation to the piston and valve positions. Do what works for your engine. Listen for pinging under load. Back off a little on the retarding if pinging too much. 
 

My understanding is can also set up your timing using a vacuum gauge. I’ve not done that yet. Achieve maximum vacuum at idle by turning distributor timing? 

Good advice. I'll do what does work, rather than what should work.