Electronic ignition on the flywheel

[hydrolastic]

Hello some background. on the road race track I have to time the classic mini. I usually try to set it to a mark I put on the flywheel at the 30 degree mark (A series engines) and put my trusty sun NON adjustable timing light on the fly wheel marks. I like my old sun timing gun because its the brightest one I have used and I often time these in sunlight in the summer or in California. With the dismal 50 or 60 year old spiral distributer drive gear driven off the cam the timing light bounces around horribly. Once I think its adjusted I try not to move it ever! On my own car I use a 500 dollar Hall effect distributer. (123) and its better but its like saying its a 3 out of 10 vs a 2.
One of the cars I work on is a twincam with fuel injection and a mega squirt ECU This car is great in a lot of ways but the one thing I like is the timing mark is a solid light on the flywheel and you can watch it move around when timing it and the light is solid at any rpm
Here is what I want to do I want to do a system like the MSD flying magnet system but put the magnets in the front pulley or possibly the flywheel, Install the sensor in the flywheel housing. Thought I would ask you guys your opinion and or suggestions maybe a better system out there ? Hydro

[PackardV8]

Either flywheel or front works. IIRC, back in the early days of magnet triggers, when there were four for a four-cylinder, Porsche put them in the flywheel with a sensor mounted on the bellhousing.

[Rick!]

In the flywheel is a better idea than the front pulley due to the flywheel having less runout. Use a Holley hall effect pickup and it will achieve a steady timing light you are loki g for, contingent on a proper ignition box.

[oldjohnno]

How many degrees is "bouncing around horribly"? I've run A and B series engines and don't remember any significant spark scatter. A flywheel trigger would certainly be more stable but I'd still want to investigate the cause of the erratic timing, just in case it's a symptom of some kind of issue with the cam and cam drive, or perhaps torsional vibration of the crank.

[hydrolastic]

Hello guys. I am going to proceed with the flywheel option for a couple of reasons. I will keep you posted on results. For oldjohno I can't say definitively if its the spiral gear that causes the spark to scatter. Here is what I know, The engines with 300 plus duration cams scatter so much its really just guessing by averaging out the scatter visually. Both cars have similar build specs. One runs the Hall effect distributer (Light beam) the other runs a 123 distributer. The third engine I spoke about was the twincam engine that runs a 284 duration cam with a 36 tooth interrupted tooth front pulley and a sensor from a Volvo.

[Tuner]

What kind of distributors are used? Lucas? Bosch? Do the distributors limit advance against a solid metal-to-metal stop? If so, that is much more likely to scatter timing because the mechanism bounces against the solid stop. I have seen Formula Ford engines with "all in at 2500" advance curves do this and eliminated the problem by setting up the distributor with the Ford recommended advance curve (found in old Ford performance handbooks) which has a well defined slope through the racing RPM range and does not reach the mechanical stop until 1000+ RPM above the maximum racing rev peak. The distributor weights and springs act as a torsional absorber, which of course they cannot if hard against a solid limit.

[Circlotron]

The distributor weights and springs act as a torsional absorber, which of course they cannot if hard against a solid limit.

In that case there would be some merit in adding rotating mass to the rotor button. Offbeat for sure, but it may help.

[Tuner]

The distributor weights and springs act as a torsional absorber, which of course they cannot if hard against a solid limit.

In that case there would be some merit in adding rotating mass to the rotor button. Offbeat for sure, but it may help.

The large HEI rotor does just that.
Prestolite distributors for the '60s & 70s era Mopar NASCAR Hemi, both points and magnetic triggered, were made with tapered roller bearings which were preloaded with a threaded adjustment (similar to a ring and pinion), instead of floating in oilite bushings like all other Mopar distributors. For service they are disassembled, cleaned and repacked with grease, like servicing a front wheel bearing.

Above the upper bearing there is an integral full circumference 1/2" thick flywheel to which the weight pivot pins are attached, instead of the regular 1/8" thick piece swaged to the shaft like all other Mopar, Prestolite or Autolite distributors.

Those roller bearing distributors also have a constant velocity floating coupling for connection to the intermediate shaft, instead of the straight tang drive.

Not sure of the purpose for this, but also the shaft between the lower bearing and the CV joint is turned down to an odd diameter, .413" or some such, the only reason I can think of they would bother to turn the .500" shaft smaller for a few inches is for some torsional frequency cancellation in conjunction with the mass of the flywheel.

The advance curve setup in those was with an extremely light primary spring that only retarded if the engine stopped and when the engine started it advanced to the second spring at about 450 crankshaft RPM. The second spring is extremely heavy with .058" wire diameter and gives about 5 degrees advance from 500 RPM to 8000 RPM, so whenever the engine is running the heavy spring is driving the trigger and isolating the trigger from engine torsional noise.

[Rick!]

Above the upper bearing there is an integral full circumference 1/2" thick flywheel to which the weight pivot pins are attached, instead of the regular 1/8" thick piece swaged to the shaft like all other Mopar, Prestolite or Autolite distributors.

Those roller bearing distributors also have a constant velocity floating coupling for connection to the intermediate shaft, instead of the straight tang drive.

Not sure of the purpose for this, but also the shaft between the lower bearing and the CV joint is turned down to an odd diameter, .413" or some such, the only reason I can think of they would bother to turn the .500" shaft smaller for a few inches is for some torsional frequency cancellation in conjunction with the mass of the flywheel.

A necked down shaft in and of itself really won't "dampen" torsional vibrations, in my experience.
Turning down a shaft in torsion lowers its torsional stiffness. If a lower torsional stiffness is desired, then one presumption would be that its torsional mode frequencies are lowered. The reason one lowers a torsional frequency is to avoid stacking the mode on top of an operating point. There are fundamentally three inputs to vibrations into the distributor shaft; the cam drive gear tooth count, the fundamental rotational speed of the camshaft, and the camshaft rotational speed times 4, which is the number of intake valves actuated per camshaft revolution. The oil pump lobe count, or more accurately, pressure pulses, could be considered another vibration input but I haven't run into that on an automotive engine. Most hydraulic pressure pulses I've dealt with are over 2000psi at 300-700Hz and vibrate things like frames, brackets or cab floors and such and end up as audible noise.

[PackardV8]

Thanks for that, tuner. In fifty years I'd never run across one of those distributors or that technical information. It's especially interesting because I modify Mopar Prestolites to work in Studebakers and Packards. It already costs me more time and money than I can get back selling them, so the high-zoot NASCAR hemi piece would be a $2500 unit.

[Tuner]

Above the upper bearing there is an integral full circumference 1/2" thick flywheel to which the weight pivot pins are attached, instead of the regular 1/8" thick piece swaged to the shaft like all other Mopar, Prestolite or Autolite distributors.

Those roller bearing distributors also have a constant velocity floating coupling for connection to the intermediate shaft, instead of the straight tang drive.

Not sure of the purpose for this, but also the shaft between the lower bearing and the CV joint is turned down to an odd diameter, .413" or some such, the only reason I can think of they would bother to turn the .500" shaft smaller for a few inches is for some torsional frequency cancellation in conjunction with the mass of the flywheel.

A necked down shaft in and of itself really won't "dampen" torsional vibrations, in my experience.
Turning down a shaft in torsion lowers its torsional stiffness. If a lower torsional stiffness is desired, then one presumption would be that its torsional mode frequencies are lowered. The reason one lowers a torsional frequency is to avoid stacking the mode on top of an operating point. There are fundamentally three inputs to vibrations into the distributor shaft; the cam drive gear tooth count, the fundamental rotational speed of the camshaft, and the camshaft rotational speed times 4, which is the number of intake valves actuated per camshaft revolution. The oil pump lobe count, or more accurately, pressure pulses, could be considered another vibration input but I haven't run into that on an automotive engine. Most hydraulic pressure pulses I've dealt with are over 2000psi at 300-700Hz and vibrate things like frames, brackets or cab floors and such and end up as audible noise.

I suspect you have primed a Chevy with a crank speed handle, so you have felt the pump pulses. The oil pump pulsation is what causes all the damage in Chevy distributors, the worn pins and weights and weight bushings in HEI and points units both. It is amazing how few miles it takes a HV+HP pump to destroy a chineze HEI.

Have you ever experienced the same engine before and after adding the pressure balance grooves inside the gear cavity in the pump, like shown in the HP books "How to Hot Rod SBC and BBC" and Jenkins' SBC book? From 2-4 degrees of scatter to rock steady. Spark scatter is particularly bad when the distributor total advance is against a solid metal-to-metal stop.

[PackardV8]

I suspect you have primed a Chevy with a crank speed handle, so you have felt the pump pulses. The oil pump pulsation is what causes all the damage in Chevy distributors, the worn pins and weights and weight bushings in HEI and points units both. It is amazing how few miles it takes a HV+HP pump to destroy a chineze HEI.

For true. More than fifty years ago, I installed my first high-volume oil pump in a 302" SBF and ran it on straight Kendall 30-wt. When the oil was cold, in a light car, a Sunbeam Tiger, I could feel the oil pump affecting the spark timing.

[Tuner]

I suspect you have primed a Chevy with a crank speed handle, so you have felt the pump pulses. The oil pump pulsation is what causes all the damage in Chevy distributors, the worn pins and weights and weight bushings in HEI and points units both. It is amazing how few miles it takes a HV+HP pump to destroy a chineze HEI.

For true. More than fifty years ago, I installed my first high-volume oil pump in a 302" SBF and ran it on straight Kendall 30-wt. When the oil was cold, in a light car, a Sunbeam Tiger, I could feel the oil pump affecting the spark timing.

More than 50 years ago I was seeing this with a timing light and dealing with it, modifying the pumps and instead of a solid bushing using the original GM plastic bushing on the advance limit pin in Delco points distributors. The soft limit bushing helped a lot but finally following all the advice from OE sources, GM, Mopar, Ford, Bill Jenkins and Smokey Yunick, about advance curves that do not "total" limit on a solid stop but run on the springs and weights to well beyond maximum speed .... those were the Ah Ha moments when rock steady timing was achieved.

[Racer71]

Porsche used set screws in the flywheel to trigger the ignition, had a bracket that bolted to hole in bellhousing that was located with a dowel pin. System worked well, especially for what was available back then.

[hoffman900]

Hello some background. on the road race track I have to time the classic mini. I usually try to set it to a mark I put on the flywheel at the 30 degree mark (A series engines) and put my trusty sun NON adjustable timing light on the fly wheel marks. I like my old sun timing gun because its the brightest one I have used and I often time these in sunlight in the summer or in California. With the dismal 50 or 60 year old spiral distributer drive gear driven off the cam the timing light bounces around horribly. Once I think its adjusted I try not to move it ever! On my own car I use a 500 dollar Hall effect distributer. (123) and its better but its like saying its a 3 out of 10 vs a 2.
One of the cars I work on is a twincam with fuel injection and a mega squirt ECU This car is great in a lot of ways but the one thing I like is the timing mark is a solid light on the flywheel and you can watch it move around when timing it and the light is solid at any rpm
Here is what I want to do I want to do a system like the MSD flying magnet system but put the magnets in the front pulley or possibly the flywheel, Install the sensor in the flywheel housing. Thought I would ask you guys your opinion and or suggestions maybe a better system out there ? Hydro

I know of a racer who did this on their A-Series and was asked to remove it by SVRA. FYI in case you run with them.