When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I'm learning about distributor ignitions and have some very basic questions. (clinging to the adage that there is no dumb question)
I'm replacing the points. 330 engine, 66 Cutlass. See picture below. The points on the bottom is the old one. The one on the top of the picture is the new one. Before I pulled the points out, I assumed the condenser was mounted on the side of the coil and I replaced that, but now understand that is a noise suppressor. I didn't see the condenser back in there and only had my replacement part to compare until I took the old points out. Anyway, I need to probably head up to the auto parts store and pick up a condenser. But, I came up with a few questions.
The old points just have a slot where the coil wire slid in - no bolt to hold it in, just tension. With the new one, it seems I loosen the screw on the bracket next to the adjusting screw and slide the contact in there. Correct? Wire just lays over the points assembly.
Where does the condenser mechanically attach? Looking online, I see that there is a bracket around the condenser, but where/how is that attached within the distributor?
Where does the condenser electrically attach? The same place as the coil wire?
Didn't really find any pictures on line of the inside of the distributor with everything connected.
The bottom one is called a "uniset" points kit that incorporates the condenser and points in one assembly for simplicity. The original condenser mounts with a "P" clamp and one screw on the point plate next to the points. Your problem is that the screw and clamp are likely long gone. The spring-loaded clamp for the wire to the points was also just a cost-saving feature. Don't spend a lot of time worrying about it. And yes, the wire from the coil attaches to the same screw on the points as the wire to the coil. You could also just buy another replacement unset point set and not worry about the missing clamp and screw.
Edit, Joe beat me to it:
If your installing the points on top, then yes you need a condenser and it connects to the same screw as the coil - wire. The bottom picture is called a Uniset, it has the condenser mounted to the points as an assy. Don't overthink the wiring connection of the screw vs a wedged friction type, just connect the wires. I prefer separate points and condenser.
You're right. No screw in the back of the plate. It looked like the condenser at O'Reilley's has a bracket, so maybe I'll try to pick up a screw as well.
Nice! The AC Delco condenser came with a bracket, and I picked up an 8-32 x 1/4 stainless screw. With new points and condenser on, I adjusted to about 30deg during crank (coil wire off) to get it in the ballpark. Fired right up on the first crank from cold. Hasn't done that since I've had it. I dialed it in at idle and it's running pretty well.
Now for a few more questions:
The manual says to disconnect the vacuum advance line and set the timing to 7.5 deg at 850 rpm. Based on my scope plot looking at the coil signal, I'm idling at about 300 rpm. I think that is actually 600 rpm on the crank. If I give it a bit of gas to get the rpms up a bit, the mechanical advance seems to kick in, and I'm not exactly sure where 850 rpm is. So, that makes it a bit difficult to really get it at 850 rpm. I might be able to stick a piece of paper or cardboard or something in the throttle to force it to 850 rpm. Is that really how I need to do that to set the timing? When it drops back down to idle, the timing will drop below 7.5 deg I think.
The old points looked ok to me, but maybe they weren't. Any input on what I need to look for to tell if they are bad or not?
Anything else I should do as part of this tune up?
How often should I need to readjust or do some maintenance to the points if I'm only putting maybe 1500 miles a year on?
Here's some pictures of the distributor after placing the points and condenser, as well as a plot from my scope showing the dwell. I'm an electrical engineer, so I had to google / sit down to figure out 30 deg dwell is equivalent to what "we" would call 67% duty cycle.
For the initial timing setting, keep in mind that the book number is a reference point that is assuming everything in your distributor is the same as it came from the factory, and setting the initial to the spec ensures the timing curve is correct. If things have been changed, such as the weights and springs, the timing curve may not be the same as it was from the factory and you would need to determine the new settings.
Keep in mind that the initial advance setting is a value that when added to the mechanical advance gives the proper amount of total advance. The total advance is really more important than the initial advance, it is just easier to set the initial when doing a tuneup.
initial advance = total advance - mechanical advance
So to set the timing by finding the total advance, disconnect the vacuum advance, connect the timing light, and increase the engine RPM until the timing stops increasing. That will be the total advance and should be set to somewhere around 32-36 degrees. you can check the timing at idle RPM and make note of it for future tuneups.
There is an adjustment screw on the throttle linkage of the carb to fine tune idle rpm. Most dwell meters have a tach setting.
- I don't have a dwell meter. I'm using a scope. I can calculate the rpm based on the scope plot. So, for the plot above I'm at idle, with a period of 0.025 sec (time between firing of two cyclinders). Converting: 2 rev * (60 sec / min) / (0.025 sec * 8) gives me 600 rpm. The service manual tells me idle for a 330 with A/C, slow idle should be 575 rpm. So, I'm fairly close. Although now that I look again, the slow idle is supposed to be in drive with the brake on, so maybe I am a bit too low.
So to set the timing by finding the total advance, disconnect the vacuum advance, connect the timing light, and increase the engine RPM until the timing stops increasing. That will be the total advance and should be set to somewhere around 32-36 degrees. you can check the timing at idle RPM and make note of it for future tuneups.
Think I follow all of that. I'm pretty sure there hasn't been any changes in the weights or anything with the distributor. But, how would I measure 32 - 36 deg though? I only have 0 to 10 on the tab by the crank pulley.
Yes, a dial back timing light, timing tape on the balancer, or degree marks on the balancer (you can measure and paint lines) would be needed to set the total timing. There are a lot of posts about this - it's really easy to do.
The simplest thing is to set the balancer to 0 on the timing tab, make a mark on the balancer at the 10º point on the timing tab, turn the engine until the new mark on the balancer is now at 0 on the timing tab, and make another mark at the 10º point (this would be 20º). Keep doing this and you can have marks every 10º up until 30º, then make marks every 2º up to 40º. Now you have a calibrated balancer!
Most of us use a dial back timing light or you'll need timing tape. To be honest I would just set the timing between 7.5 - 10 and run it.
Thanks - that's what I did. And it's running great. I took a good look at the old points, and I think they were basically gone. I'm not sure when my dad changed them last, but as I read on here, if the condenser goes out, it will take out the points quickly. I can't go by mileage so much as it would take me years to get to 15000 miles.
Earlier, when I was trying to adjust dwell with the old ones, I moved the spring with a screw driver and saw spark across the points when I separated them. My understanding is the condenser should take care of that and I shouldn't see that spark. If I wasn't working from home, I'd take the old points in to work and measure the capacitance just to verify whether it was bad or not. Regardless, it was integral to the points and that was the issue. It runs like a top now. Since I've got most everything stock on that engine other than the exhaust, setting timing to 7.5 worked fine and she runs like a champ now. Just in time for the warm weather!
I change contact points, condenser & rotor (routine maintenance) every spring regardless of the miles I've driven - which leads into performing a tune-up every spring. I reside on the coast of the Atlantic Ocean - it's humid. I used to perform the same routine maintenance every year when I was raised in the mid-west, as well (routine maintenance on different vehicles). Tuning an engine is a simple maintenance item. Contact points will go bad for numerous reasons: (1) Humidity/Moisture in the distributor; (2) Poor manufacturing; (3) Aging; (4) Incorrectly sized ignition coil; (5) Incorrectly sized condenser; (6) Aged distributor wiring; (7) Aged ground strap; (8) Various engine running conditions. I like contact points - they're easy to deal with & they're inexpensive. Others prefer an HEI system and they have excellent performance with them; others, not so fortunate. I don't use a dial-back timing light, I have this ancient inductive thing (Craftsman) I've owned for years (I think I borrowed it from Flash Gordon and forget to return it) - you point and shoot.
You are overthinking this.
Please purchase a vacuum gauge, tach & dwell meter, and a setback timing light.
Verify the point dwell is at 30* before you do anything else. It's more important than the timing, thou both should be set in parallel when fine-tuning.
At warm curb idle ~700 rpm +/- 50, set the base timing to 10-12* with the vac advance disconnected and blocked, (so no vac leak).
Next plug in the vacuum advance as see how much more it adds to the total, Should be 8-10* no more. Plug the advance canister into a full direct manifold signal not ported.
Now you're at ~20-22* at curb idle. (Adjustable travel canisters are available for fine-tuning).
Rev the engine to see how much more the centrifugal advance brings in. Your total should be 36-38* total all in under 3000 rpm. 27-2800 preferred.
Those springs I see are OEMs and are heavy. I doubt you will see the centrifugal coming in until 12-1300 RPMs.
Hook up vacuum gauge it to a straight manifold source. (not ported).
Now use the vac gauge to fine-tune.
Adjust the carb air-fuel to get the highest possible vac reading.
Now twist the distributor a few degrees in the advance direction to see if you can increase the vacuum reading? if yes verify what the timing is. This will be your new base setting.
It might want more than 12* base it might want less.
Rule of thumb, give it as much timing as it will handle without spark knock.
Go back n forth between A/F and timing settings until that highest vac signal is achieved. Road test with the distributor loose enough to adjust it on the road. If it spark knocks under hot load back it down a few degrees, restest.
To answer your other questions and repeat the timing settings:
1. The manual says to disconnect the vacuum advance line (YES) and set the timing to 7.5 10-12 deg at 850 650 to 750 RPM. Based on my scope plot looking at the coil signal, I'm idling at about 300 rpm. I think that is actually 600 rpm on the crank. If I give it a bit of gas to get the RPMs up a bit, the mechanical advance seems to kick in, and I'm not exactly sure where 850 rpm is. So, that makes it a bit difficult to really get it at 850 RPM. I might be able to stick a piece of paper or cardboard or something in the throttle to force it to 850 rpm. Is that really how I need to do that to set the timing? No its a set screw on the carb. When it drops back down to idle, the timing will drop below 7.5 deg I think. Shouldn't unless the centrifugal is actuating at a low RPM. Ditch the O-scope. A tac meter will be a better tool to know what's going on.
2. The old points looked ok to me, but maybe they weren't. Any input on what I need to look for to tell if they are bad or not? Pitting. Google it. The points and feeler gauge need to be grease-free or the points will pit and die a quick death. Contact or brake cleaner. Use a lint-free cloth to wipe both.
3. Anything else I should do as part of this tune-up? Inspect cap, rotor, plugs, wires. Replace fuel and air filters. Clean and tighten both ends of both battery cables. Inspect the ground straps to the radiator core and engine to the firewall. Inspect the date your tires were manufactured. +10 replace. Rubber brake lines likely old n brittle. Brake fluid should be flushed every 5 years. Change all fluids. Brake, Coolant, diff trans pwr steering et al.
4. How often should I need to readjust or do some maintenance to the points if I'm only putting maybe 1500 miles a year on? Check it annually with your new dwell meter. As the nylon bumper wears on the distributor cam it will alter the dwell. LIGHTLY lube the cam and bumper with the correct point set grease. Don't over lube the centrifugal weights either.
Dr. Olds. I think I've recently done at least half of the items you listed, so I think I'm on the right path. Of the other half, I had some on my list to do, and I've added others now. My dwell is spot on at the moment, but it would be easier with a dwell meter. I'm looking around for what is available. My timing light matches the Chief's at the moment, but I see the benefit to being able to have the setback A buddy has a vacuum gage I can borrow, but will put one of those on the list as well.
May 19th, 2020, 01:18 PM
- I don't have a dwell meter. I'm using a scope. I can calculate the rpm based on the scope plot. So, for the plot above I'm at idle, with a period of 0.025 sec (time between firing of two cyclinders). Converting: 2 rev * (60 sec / min) / (0.025 sec * 8) gives me 600 rpm. The service manual tells me idle for a 330 with A/C, slow idle should be 575 rpm. So, I'm fairly close. Although now that I look again, the slow idle is supposed to be in drive with the brake on, so maybe I am a bit too low.
