Timing Chain the Culprit???

[Studdley]

The '72 is still being temperamental, it gets very close to starting, new dist, coil, carb, getting relatively weak spark might I add, new starter (helped get it even closer), have checked firing order again and again, new cables, solenoid, 110psi of compression on all cylinders, got the timing pretty close to the sweet spot, timing chain is unchanged, anyone have any other suggestions?

 

[73pony]

Are you running points in the new distributor? Did you set the dwell? What are you getting for voltage at the coil?

 

[Studdley]

Are you running points in the new distributor? Did you set the dwell? What are you getting for voltage at the coil?

Points, 9v, what is dwell

 

[73pony]

Dwell and point gap go together. If point gap is set correctly the dwell should be correct as well. I just read more on your first post and you have to have the car running to check dwell, sorry missed the bit that it is not starting at all. 9V at the coil is correct with the resistor wire in place and for running a points set up. Weak spark with 9V to coil leads me to believe that...

A. the new coil may be bad

B. the condenser in the distributor is bad

C. point gap is way out

D. or the new plug wires (or coil wire is bad).

Did you check all the plug wires with an ohm meter, especially the coil wire? Have you considered or thought about upgrading the distributor internals to a Pertronix I or II? Avoid the Pertronix III, I had issues with mine as have some others on here. The Pertronix I can run with the resistor wire in place but they do make a really simple relay to get a full 12v without having to cut into your factory wiring, just make sure you get a matched coil if going with Pertronix. It is a very worthwhile upgrade from a performance and reliability standpoint.

 

[Studdley]

Dwell and point gap go together. If point gap is set correctly the dwell should be correct as well. I just read more on your first post and you have to have the car running to check dwell, sorry missed the bit that it is not starting at all. 9V at the coil is correct with the resistor wire in place and for running a points set up. Weak spark with 9V to coil leads me to believe that...

A. the new coil may be bad

B. the condenser in the distributor is bad

C. point gap is way out

D. or the new plug wires (or coil wire is bad).

Did you check all the plug wires with an ohm meter, especially the coil wire? Have you considered or thought about upgrading the distributor internals to a Pertronix I or II? Avoid the Pertronix III, I had issues with mine as have some others on here. The Pertronix I can run with the resistor wire in place but they do make a really simple relay to get a full 12v without having to cut into your factory wiring, just make sure you get a matched coil if going with Pertronix. It is a very worthwhile upgrade from a performance and reliability standpoint.

I did, all the plug wires are new, are the accel coils known to be bad, dist is brand new though, how much does one of those ignition systems run?

 

[73pony]

The module is around $100 for the Pertronix II, matching coil is about $40, and the relay wiring kit is around $30. You can get them from Summit, Jegs, etc.

Also new doesn't always mean good. I have had new coils bad out of the box as well as points and condenser. I've also had new plug wires bad. I always ohm them out before I install.

 

[Studdley]

The module is around $100 for the Pertronix II, matching coil is about $40, and the relay wiring kit is around $30. You can get them from Summit, Jegs, etc.

Also new doesn't always mean good. I have had new coils bad out of the box as well as points and condenser. I've also had new plug wires bad. I always ohm them out before I install.

I tested it and it was all good, with the pertronix, do I keep my existing dist and rip out the electronics?

 

[Don C]

Dwell is the angle on the distributor that the points remain closed. Too much dwell angle means the point gap is too small, which may cause the points to arc, and not remove the ground from the primary windings in the coil, and not energize the secondary windings, which means little or no spark. Too little dwell angle means the point gap is too large, which means that the primary winding doesn't have enough time to become saturated, which results in a weak spark, more noticeable at high speeds, usually won't cause the engine to not start, unless the point gap is so big that the points barely close.

Jason is right, always check the ohms on all of the plug wires, bad connections are common, and check the ohms on both the primary and secondary sides of the coil.

Make sure the ground wire is in place on the breaker plate.

 

[73pony]

The module is around $100 for the Pertronix II, matching coil is about $40, and the relay wiring kit is around $30. You can get them from Summit, Jegs, etc.

Also new doesn't always mean good. I have had new coils bad out of the box as well as points and condenser. I've also had new plug wires bad. I always ohm them out before I install.

I tested it and it was all good, with the pertronix, do I keep my existing dist and rip out the electronics?

Yes you keep your distributor just pull out the points and condenser and install the pertronix unit. It is a very easy swap, took about 1/2 hour and that was with wiring in the relay for a full 12v.

 

[Studdley]

The module is around $100 for the Pertronix II, matching coil is about $40, and the relay wiring kit is around $30. You can get them from Summit, Jegs, etc.

Also new doesn't always mean good. I have had new coils bad out of the box as well as points and condenser. I've also had new plug wires bad. I always ohm them out before I install.

I tested it and it was all good, with the pertronix, do I keep my existing dist and rip out the electronics?

Yes you keep your distributor just pull out the points and condenser and install the pertronix unit. It is a very easy swap, took about 1/2 hour and that was with wiring in the relay for a full 12v.

Thank you, whats a sign of a bad timing chain though

 

[73pony]

You can check the slack on the timing chain by removing the fuel pump and sticking your finger inside. The bad timing chain (loose or jumped) would not cause week spark but a host of other major problems, like pistons slamming into valves etc.

 

[Studdley]

You can check the slack on the timing chain by removing the fuel pump and sticking your finger inside. The bad timing chain (loose or jumped) would not cause week spark but a host of other major problems, like pistons slamming into valves etc.

That's genius

 

[boilermaster]

Studdley,

For checking the timing chain and gears for wear, I used to do this;

bring the harmonic balancer to a known point so you can see the degree markings on the balancer by having a rachet on the balancer and turning in the opposite direction of the running rotation.

record the degree marking and remove the distributor cap.

Now turn the damper, ever so slowly and record how many degrees it takes for the rotor to move.

In all the years that I worked at the dealership, I surmised that anything more than 6 degrees meant a worn chain and gears.

If one has strong hands, can usually move the crank pulley by hand, watch out for those fan blades!

Boilermaster

 

[boilermaster]

Studdley,

While you are checking for timing chain stretch and #1 cyl. at TDC re check how close your distributor rotor is to the # 1 cylinder on the distributor cap.

You could be off a tooth on the distributor.

Boilermaster

 

[NOT A T5]

So...speaking of ohm readings on plug wires. Around how many ohm's should they read?

 

[73pony]

So...speaking of ohm readings on plug wires. Around how many ohm's should they read?

It would depend on if you have stock OEM style wires or performance wires. Performance wires should be around 50 ohms or less per foot. Stock OEM type should be around 3500 or so per foot.

 

[Studdley]

Timing chain is like new and I've got good spark, so now what

 

[Don C]

Make sure the timing is correct, and that it fires on #1 cylinder at the top of the compression stroke.

Make sure you are getting fuel into the carburetor, look down the carburetor while you open the throttle by hand and see if the accelerator pump is working and fuel squirts out of the nozzles.

 

[73pony]

Make sure the timing is correct, and that it fires on #1 cylinder at the top of the compression stroke.

Make sure you are getting fuel into the carburetor, look down the carburetor while you open the throttle by hand and see if the accelerator pump is working and fuel squirts out of the nozzles.

+1. If you now have good spark and you checked and have good compression, I think you mentioned that earlier, all you need to go with it is fuel and the spark at the right time and it should fire.