My Gap and Dwell story for 1971 350:

Using brand new INNOVA timing light with dwell meter, set new Accel points (w/ condenser) to 30 deg dwell (8 cylinder mode). The engine runs terrible, sputtering, the ballast resister becomes scorching hot, voltage to coil drops below 8V and engine dies. To me the hot ballast resister means the points are closed for too great a duration. I tried three times with same result. (I have a dedicated switched ignition circuit directly from the battery, to switch, to 0.8 Ohm MSD ballast resister, to + of MSD Blaster 2 coil)

Next with meticulous care, I set the points gap to .018 inches. The motor starts immediately, runs fine, ballast resister stays cool to touch, 12+V at the coil. (Timing is ~15 deg initial and ~36 deg at 2500 rpm) Using the INNOVA timing light/dwell meter, I get a dwell reading of 17 deg. If I gradually increase the dwell with motor running it will eventually die when I reach a dwell of ~22 deg, resister screaming hot.

Is my INNOVA dwell meter totally broken? Is there anything else that can explain this discrepancy? A gap of .018 should yield a dwell very close to 30 deg. After all there is only one adjusting screw on the points.

Thank you!

 

A long, long time ago. This was and so many like it were late model cars people like me drove everyday. And I was a poor young person. So a paper match book was a feeler gauge. Or, approximately .018.
And they ran fine. Then I managed to actually own proper feeler guages. But still no Dwell meter. And still, they ran fine.
So, if you can properly gap your points, (I absolutely hate everything Accel). And your car runs fine. But this new guage shows readings out of wack
Certainly sounds like a bad guage to me! Perhaps borrow a dwell meter from someone else and see how it compares.

 

Takes me back...lol....and your girlfriends nail file was used to clean up the points....good times!!

Freiburger says: Don't get it right, just get it running!!

60

 

We'd run the allen wrench in 'til the motor stumbled, back it out 1/4 turn and we'd
almost always be within a couple of degrees of proper dwell. DR8HV was the
Niehoff part number for 8 cylinder GM points

 

(I'm posting before my morning coffee, so I reserve the right to edit later if needed. ) Things you're seeing make sense to me, with no laws of physics being violated. Some notes:

1) A coil doesn't care what point gap or dwell angle reading you see on a gauge. It only notices time, and will continue to charge during that dwell TIME until it hits its peak current, determined by the system voltage, the primary circuit series resistance, and the dwell TIME at that RPM..
2) If I understand things correctly, you have a .8 ohm ballast and a .7 ohm coil. Assuming an alternator output of 13.2 volts, that allows a peak coil charging current of 8.8 amps, given sufficient time. At idle speeds, there is almost always excess dwell time. When the primary current hits that peak, and afterward until the points open and stop the current, your ballast is dissipating 54 watts. (Your coil is getting similarly heated.) You might notice some warmth emanating from the ballast during this time.
3) When you later set the points to .018", I am assuming (and please correct me if I'm incorrect) that you increased the gap. This did three things: It advanced the timing (improving the low-RPM efficiency of the engine), it reduced the dwell angle/TIME (reducing the peak current and duty cycle of the primary circuit), and it reduced the wattage being dissipated in the primary circuit wiring.

I think it's always good to check the accuracy of your instrumentation, so a check of your dwell meter is wise. GIven how low your primary circuit resistance is, you may have to compensate for that by running a shorter dwell angle than production specs that use higher resistance ballasts and coils.

 

I have consistently seen bad readings on the newer dwell meters and timing lights. I have an old engine analyzer/scope that I know to be correct, and I check every other dwell meter I own against it. Half of them are so far off that they are unusable. I don't think the manufacturers of those bad dwell meters (Innova) care about the dwell performance since nobody uses points anymore. Do not trust the dwell readings on the new, digital timing lights - it's more often wrong than right.

Keep in mind that the reason your engine runs bad when you incorrectly set the dwell away from the .018" gap is that every degree change in dwell changes the timing by one degree. So if your dwell is actually around 30 with the .018" gap and you change the dwell from 30 (indicated as 17 on the Innova) to the Innova-corrected reading of 30, you have just retarded your timing by 13 degrees. If your initial timing was around 12 degrees, you are now running timing at 1 degree after top center, which is, obviously, going to run like crap, if it runs at all...

Lars

 

Match book feeler gauges and Ohms law! Definitely my kinda people. I will order up some AC Delco points from Amazon and swap out the Accel and put aside the INNOVA gear. I really wanted the MSD combination of tach drive distributor and 6AL which will also require a new set of plug wires. All this together was around $1000 from Summit so I opted for the fancy pants point and condenser set. I need to detune my brain and curb this kind of logic. Perhaps a few cold snacks will help. Thank you!!!

 

Use NAPA/Echlin hi perf points set CS786 with condenser RR175. This will rev past 6500 rpm with no problem and holds a solid, steady dwell for years. The MSD components won't outperform it.

Lars

 

Match books also were used in my 8 track player ....kept Bob Seager and Black Sabbath playing!

 

I was about to say, go to NAPA for top quality points, but Lars beat me to it.
So I'll second that from Lars. !

 

Lars

 

Thank you! On my way to NAPA now!!

 

Everything I would have offered has already been said. I can add that my 50+ year old analog dwell meter is also no good and I don't bother to pick it up. I learned many years ago to manually roll the engine to open the points and then set them with a feeler gauge. I did that this spring with my recently acquired '72 base motor car and it starts promptly and runs great!

 

The matchbook reference is awesome. Believe it or not, a maintenance manual for a helicopter I worked on had .005-.007 clearance measurements and the manual recommended a piece of cigarette pack paper with a slight drag!

 

I have the MSD tach drive distributor and the 6AL box with the matching coil and yes, it has run great for 15 years but I know in the back of my mind that 6AL box is going to crap out someday in the middle of nowhere and leave me stranded. You can keep an extra set of points with you and be back on the road in minutes.

 

Thanks @lars! That's a really interesting observation. I had learned (from this Forum) that certain timing lights, such as the Innova 5568, do not work well with some MSD systems. I hadn't seen the dwell measurement called out before, though. But I've never had need to measure it, so I never noticed. Perhaps an O-scope and a Sun machine would make for an interesting experiment with some pretty plots.

 

Points can work fine. I ran a single point setup in my car for many years...and even dyno'd them at well over 800 HP and they ran 9's in the 1/4. And lots of street miles. In fact they were 7 year old Accel's using an old VW Bosch coil I had laying around. That coil is currently on my 8-71 blown 408" Clevor engine using an ancient Mallory dual point setup.

We also dyno'd back to back with the 7+ year old points against a full MSD system. Up to 7100 or so RPM the HP was identical....but we did start to see some point bounce at the top end. I'm sure a new set of points would have done better. The MSD DOES help a lot with low speed driving keeping plugs clean with a big cam.

I love newer electronic systems, but there's not a thing wrong with a well functioning point system especially considering the miles most folks run annually. Cheap, reliable and easy to maintain,

JIM

 

Thank you all very much for a wealth of valuable information.

I feel compelled to ask a question I have wondered about for decades..... Why is the wire from the (-) coil to the points such a small gauge? If it has to carry ~9 AMPS when the points are closed, shouldn't the wire be thicker? (Obviously it doesn't need to be) Or is it just the same diameter as the primary windings?

 

Your setup is, shall we say, unique. Production primary current requirements are usually in the four amp range, as the ballast and coil primary usually have about 1.5 ohms each (3 ohms total).

 

Ok thank you. I just don't ever remember anyone recommending increasing the negative coil lead to a larger gauge like 12 AWG when using coils and resisters of lower ohmage. I think i will do this, but have already discovered that those little flag terminals that connect to the points are hard to come by. Wondering if I should stop fretting all these little issues, but to a certain extent, they are fun. Weird...