OK, I'm learning more every day as I go through each of my car's systems. I read the sticky about timing on this forum and I think I understand it. Right now the car works and runs well, but I want to verify the timing and tune the carb. I want to understand everything about the car instead of just drive it and not know what's going on. This is my first Vette and I've had it about 1 year. I don't have much experience but I want to learn istead of paying a mechanic to make it worse. (Been there, done that, couldn't afford the T-shirt.)

I have a 1970 L46 Vert with a small block 350/350. The block casting numbers and stamp pad are correct to what the car is supposed to be so I assume the bottom end of the motor is original as I haven't had it apart. Someone put on aftermarket AFR 195 aluminum heads, which are ported and polished, as well as roller lifters and rockers. A previous owner also replaced the points with a Mallory breakerless optical signal. These are all good things and help the car run better.

But in the distributor, the centrifugal weights and springs look very old and don't move well. They were sticky from old grease or something. Also, the vacuum advance was disconnected, which is probably why I get worse gas mileage than other people report. I only get about 10 in town and 12 on the freeway with 3.08 gears. I'm guessing someone did that to tune it to pass emissions.

My goal is the verify the timing and then go about setting and tuning the carb, which is an aftermarket Edelbrock/Carter AFB 600 cfm with electric choke. The carb sits on a nice little mid rise Edelbrock dual plane intake. The car starts easily (now that I have a new battery) and has lots of low end torque. Its a great setup for the street since I don't go to 6000 rpm often (or ever).

But, when I try to check the timing, the TDC #1 mark on the harmonic balancer is nowhere in sight. I can see that there is a very steady spark signal as I can see the harmonic balancer does not bounce around at steady rpm. I also see I have spark advance as the balancer does advance with revs when the vacuum advance is hooked up. I haven't checked the cetrifugal advance with the vacuum disconnected.

I suppose I will go and buy a dial back type timing light so I can see how far the mark is off. I can't imagine the timing is that far off and more likely the balancer has spun. I read that the 350 is internally balanced so what does the harmonic balancer really do?

How do I absolutely verify the #1 piston is TDC? I really don't want to pull the head or timing chain cover if I don't have to. I would rather just put a mark on the balancer or something...

Also, is it hard to pull and replace the stock balancer?

Thanks in advance! Merry Christmas

 

to verify top dead center and the mark on the balancer: pull the #1 spark plug and put your finger over the hole and turn the engine over with a socket and breaker bar. you will feel it build compreesion on the comression stroke. i use a little piece of wire or small screwdriver and stick it into the sparkplug hole and feel for when the piston reaches top dead center, now you have top dead center compression stroke. your timming mark should be on zero.

you can make your own mark there but i'd replace the balancer if its off since it will most likely slip again. to change it's easy. pull off your belts and crank pulley. you may have to pull your fan and shroud depending on how much room you have. then get a puller and use a balancer installer to put the new one on.

you dont really need a dial back light. you can buy timing tape or useing simple math find the measurements that equal what ever degrees you want and then mark the balancer yourself

 

old school works for me too

 

I'm better with theory than I am with the hands getting dirty part. Thanks. I'm gonna work on it today if I can.

Is it possible the distributor is installed on the wrong tooth and still run correctly?

 

First...Do you the pickup for the timing light on the #1 wire? I bet every one here has make that mistake at one time or another.
You WILL have to rebuild the distributor, not hard to do ...or you can send it to lars!
Hell send him your carb too!
You get your stuff back and after reading Lars paper on timing, AGAIN, fire it up and no more problems!
Simple!!!

 

It doesn't matter where your distributor is. When I installed mine on it's first run I just let it drop where it would and then put the number one plug where the rotor was on TDC. The reason it doesn't always drop is because it has to go through the cam gear and the oil pump. The oil pump will only line up where you had it when you pulled it, or 180 degrees off, but can easily be rotated with a screwdriver to fall wherever you want. In short, if the dist is all the way seated, you're fine. No matter where you put the dist, the timing marks don't need to move to be correct.

One thing that happens a lot is that the balancer's paint wears off which makes it hard to see. Make sure there's a nice white mark to look at. A paint pen or whiteout pen really does the trick here. I hightly doubt your timing is so far advanced you can't see the mark, either you're on the wrong wire (number 1 wire is on the driver's side all the way forward), your balancer has spun, or the marks are just hard to see.

I'm still learning about timing as well (I'm having detonation from setting my curves too soon), but you need all three set correctly. Vacuum advance is there for a reason and only racers have I ever seen run without it. If the dist is really bad, you'll have to get it rebuilt. If the springs are just rusty, you can order new ones from mallory (which will also let you select your own curves if you want).

Good luck!

 

I've been corrected in another forum. I still don't know all the pros and cons, but apparently a bunch of people remove the vac advace and runs just fine. I'm told it's more for fuel economy and emissions, but I'm still trying to figure it out myself.

 

I'll try to clarify here. The car starts easily and seems to run properly. I really don't believe a rebuild is necessary at this point. The engine is very clean and I can see a groove in balancer. That groove just doesn't come close to lining up with the 0 mark when #1 is TDC. It's not even visible. Isn't the groove supposed to be the 0 mark?

I have the stock distributor, not a Mallory one. I only have the Mallory Unilite points replacement inside the stock distributor. One other thing that cduemig might have cleared up is that the #1 tower on the distributor cap is one post counter-clockwise than what the shop manual says it should be. The vacuum advance is also a little twisted further clockwise than it should be and is up against the ignition shielding post. I am beginning to think that the distributor was removed and re-installed onto a different tooth.

Also, if the groove on the balancer is supposed to be the 0 mark, it may have spun.

 

I would verify that the mark actually lines up to TDC. The best way is to feel the piston move like chris75stingray said to do. You can remove the valve cover to make sure that you're on real TDC instead of 180 out. If both the valves are closed then it's TDC, if not, then it's 180 out.

If it's running good even under load, it can't be that far out so the mark must be off.

 

Actually it DOES matter where the distributor is installed if you have a mechinical tach. The drive for the tach should be close to 90° from the crank centerline to align properly with the drive cable. Proper alignment keeps the tach drive cable happy so it won't bind and break, or worse, strip the gear inside the dist. That alignment puts the vacuum can back towards the firewall. In this respect Corvettes are different than most Chevrolet passenger cars.

There were two different timing pointers used in that era and they must be matched to the harmonic balancer. If the pointer and balancer don't match, you can have everything else correct, i.e., distributor positioning and secondary wiring, and still not get the timing mark to line up for the #1 cyl.

 

Ahh! This makes so much sense. I looked at mine and my whole distributor is twisted about 45 degrees counter-clockwise from what you describe. My tach drive cable is pointing at the driver's seat instead of coming off in a 90 from the crank centerline. This twists my vacuum advance toward the #6 cylinder instead of toward the firewall.

The cable drive does look stressed... I need to fix this.

 

PeteZ06 is right, a mechanical tach should have the cable coming straight out at a 90 from the crank, but other than that, it won't affect the timing. You can turn the distributor, but you'll also have to move the wires a step or two couter-clockwise. You can also do the same by pulling the dist out just enough to rotate the rotor one tooth at a time until it points to the same position on the dist as it did before you moved the housing. That way you don't have to manually realign the oil pump and the wires will be in the right place. I would set engine at TDC, turn the dist housing, then realign all my plugs via TDC and then reset the timing.

 

Thanks, I had the same exact thought and will tackle it this weekend.

 

It looks like your distributor is pretty close to standard position. Maybe a bit more clockwise so there isn't any kink in the tach cable. Any more, and you'll start having problems with clearance between the vacuum hose and the bracket for the ignition shield.

Even if the engine is internally balanced, it needs a harmonic damper to damp out minute harmonic vibrations that would increase wear on the driveshaft. Most auto parts places will lend you a puller to remove and replace the balancer. It's fairly easy to do.

If the balancer is original, it might have rotated on the shaft and it's due to be replaced.