Help, C3 won't pass inspection

[acmsal]

Took my 1978 (L48/auto,completely stock) Silver.Ann. to be smogged. It
failed, bad egr valve the mechanic said. And, the timing mark at the
crank
was floating all over the place. Took it home and tried to check the
timing
but 6 degree mark kept moving all around. What would cause this? Took
off
the cap and rotor, look worn and tired, will replace. But should I also
replace coil and module inside dist? Plugs and wires are new. Took off
egr
valve and the rubber diaphram looks worn, will replace. Help, what's up
with the timing? Oh, by the way the car runs fine, only hesitates
slightly
when cold.

 

[Stallion]

I'm not sure and I don't know, but is this when you need to do a "tune-up" to your Vette? Isn't that when the timing is off? Can somebody explain what this "tune-up" is and why/when it is needed?

Thanks!

 

[acmsal]

I was thinking along the lines of worn dist shaft or timing chain. I know how and when to do a tune up!

 

[Vette/Berlina-coupe]

-Hello ------name? -am down the pike from you in SanDiego and am also very worried about facing the Smog-gun shortly myself (350ci engines were banned in Calif. during 1980, --they could only sell 305-ci's; --thus am going to just have them "pipe it" for me off the computer-record initially to see where I stand). With your engine-timing wandering around like that, it indeed would lead one to suspect the Timing-chain for sure; -but still, it could be the distributor vacumme or centrifugal advances are sloppy as well, or likely the HarmonicBal.-hub (slap-on a much superior FluidDamper-hub to forever end that source of trouble). Some GM V8's had timing-chain sets (that is, non-rollerchain and mating two gears) that gears were coated with a thick-layer of nylon. --Thus if someone ever got the engine really over-heated, it can actually melt the nylon to the point that the chain is so loose that one can lift it off the gears (without removing the gears). If you are not sure about the sort of mileage/history on the engine, I'd be inclined to pull the radiator & waterpump to get at the timing-cover. Be sure to install a completely new double-roller Timing-chain and mating-gears set, as it will be an essential improvement to your engine (for spot-on timing accuracy) regardless, --if it turns out that the original is a non-roller type chain. jus my 2-pacos worth! --BerlinaBob
---or you could just do this to it... :L

 

[vette-dude]

You might also want to check your Harmonic balancer. These have a tendency to go bad after alot of miles and the outer ring may be slipping around on the rubber inertia dampening device. The other things that could cause this have already been mentioned. If you have an HEI dist they have a tendecy to wear out the advance limiting pins in the dist which will cause the timing to move around at all RPM ranges. Take the cap off and look and I bet you will find alot of brown residue and some rusty looking parts inside the dist. Like everyone said before, get it rebuilt or buy a perf. dist. While your at it, recurve it so all your advance is in when the cam reaches it's peak RPM range. Might as well go ahead and put in a perf. module and a perf. coil, new sparkplug wires, new plugs, and then see where you are at. I would check this first before I blamed the timing chain. True, the chain is probably worn and could use a replacement repair but it will do no good if the dist. is toast.

Randy
:cool

 

[acmsal]

Sure enough it was the harmonic balancer. Seems like a pain in the ass to replace!!! Thank you to all for your expertise!!!

 

[Stallion]

So how do you do a "tune-up" to your Vette? Somebody I was looking to buy from mentioned that the Vette needed a tune-up. What's involved with this? Thanks!

TR

 

[page62]

Nowadays, a tuneup consists of replacing the spark plugs -- maybe the cap, rotor, and wires. And you only need to do it every 100,000 miles!!!

In the early '70s, a tuneup consisted of replacing the plugs, cap, rotor, perhaps wires. Points and condenser were also replaced. Timing and dwell were checked and adjusted. The carburetor and choke may have needed adjustment, too.

By the late '70s, electronic ignition eliminated the points and condenser. But everything else still needed to be done!

Times sure have changed...

 

[Stallion]

How would you tune up the timing? Would that be the little cam (not the main camshaft) that you would have to change for the sparks?

Thanks!

TR

 

[Bob Chadwick]

You time the car by rotating the distributor. You measure the spark of the number 1 cylinder with a timing light, basically a strobe light that fires when electricity is sent down the plug wirne you are measuring.

With the car running, you rotate the body of the distributor which affects where on the firing cycle the coil sends electrity to the plugs. The strobe on the timing light helps you to read timing marks on the front pulley and set it.

The manufacturer sets where the recomend based on a stock engine and as you can see from the posts here, that once you start modifying your engine that the mark may change.

Bob

 

[Stallion]

Okay, I think I see what you mean. But, I don't know what this distributor does yet. I haven't gotten there in my automotive learning stage. When I do, though, you'll probably know by the questions posted by me.

Thanks!

TR

 

[Bob Chadwick]

The distributor distributes the electricity to the pistons. There is a cap on it that has 8 wires, on an 8 cylinder car anyway, and a button inside that rotates around. As it passes under each wire it sends electricity from the coil into the wire and causes your spark plug to spark igniting the fuel in the piston.

By rotating the distributor body it changes when the spark is generated to each piston and controls the timing.

Bob

 

[Stallion]

Okay, I now understand how the distributor works. But, if you were to change the timing then what would this do to the rest of the engine and its timing? Like the cam. How would that affect the cam?

TR

 

[BlackNBlue95]

Okay, I now understand how the distributor works. But, if you were to change the timing then what would this do to the rest of the engine and its timing? Like the cam. How would that affect the cam?

TR

No shure if the 78 had a computer or not.. I would guess yes.. make shure to disonnect the computer from the iginition module other wise you will not get accurate timing.. that is when checking base timing.. other wise the computer can mess you up..

now turning the dist. base only effects spark timing.. or iginition timing.. not cam timing.. when the timing chain gets worn out you see it as the timing moving back and forth with the light because the dist is ran off the cam and the link between the cam and crank is the timing chaing when the slop is moving back and forth you willl see it in the timing with the timing light.. one way to check the timing chain is to take the dist cam off and wiggle the crank and see how much slack there is between the rotor and you moving the crank shaft..

-Rick

 

[Stallion]

:confused I don't think I understand. This chain regulates the timing between the cam and others?

TR

 

[BlackNBlue95]

:confused I don't think I understand. This chain regulates the timing between the cam and others?

TR

The timing chain is basically a change betweenthe crank shaft and cam shaft.. it's what allows the crank to turn the cam shaft.. and if there is slop bewteen the 2 shafts.. it messes up the ignition timing because the dist is driven by the cam... also causes the valves not to be completely synchronized with the crank.. hard stuff to explain just typeing stleast for me easier to show someone or have a picture..

 

[Stallion]

So this chain connects the cam and crank. And the distributor controls the sparks, which control the combustion, which exterts force on the crank, exerting force on the cam.

Is that right?

Thanks!
Tr

 

[Evolution1980]

No shure if the 78 had a computer or not.. I would guess yes.. make shure to disonnect the computer from the iginition module other wise you will not get accurate timing.. that is when checking base timing.. other wise the computer can mess you up..

I don't believe computers were introduced "to fix a problem that didn't exist" until '81

 

[MoeJr]

First Vette with computer was 1981. Other GM cars started in 1980 though the 1978 Buick Regal 3.8 turbo had a small computer on the radiator support that adjusted the timing to keep ping away. If you have a hestiation acsmal I would rebuild the carb. This may also help with emmissions if you are having nozzle drip which is common on QJets.

:bar

 

[BigBrakeFuelie]

The California Corvettes in 1980 had the first computer.The CCC system.I know I unfortunatly have it.:cry