impalaman

Well, I tweaked the mixture screws as everyone advised. I'm getting 16 to 16.5 on the gauge. Also when I turn on the A/C, the vacuum gauge reading goes to 12. At this point the engine is idling very weak. It just doesn't feel "healthy" at all. But, when I give it the gas it revs up fine, and it has excellent power. It cruise around town fine and out on the highway.

The timing mark still jumps around at idle. Probably about a degree of variation either way.

I put a rubber band around the mech advance, and this did not affect the base idle timing.

The vac advance works fine.

My opinion: Either the intake manifold is leaking, the distributor is still flaky, or the nylon teeth on the cam sprocket are worn.

By the way, the intake gasket was replaced a couple of years ago due to a coolant leak. However, I do notice a very small amount of oil leaking from the middle bolt on the driver's side. I checked, and changed out all the plugs yesterday. They looked good.

impalaman

[QUOTE=73StreetRace;1570955072]These small fluctuations are pretty normal, I think. Nothing to worry about...
Try to blip the throttle quickly and see if the vacuum varies from 2 or 3" ( acceleration ) to 23 or 25" Hg ( deceleration ). This is an indication of a good engine condition.


I blipped te throttle as you said.... and yes the gauge goes to around 3 or so, and then back up to around 24 or 25.

73StreetRace

That's good news ! If engine is idling very weak when you turn on A/C, you're probably a bit lean. Try to richen a little bit the mixture screws with A/C on until you get a more stable idle.
A timing mark moving by +/- 1° is very acceptable at idle. Probably timing gear / chain or distributor gear related.
I think you can use it like this for a few thousands miles and then check again to see if it's not worse.

Rich's'78

You have had a lot of good input on this one, but I'll throw in my 2c for consideration too. The engine is low mileage and probably driven fairly gently (?). My cam is very similar to yours and I get 17" vac at 750 rpm and would see 18"+ at 900 (4 speed). Both are quite steady, especially the 900 rpm. So I think your vacuum is a bit low and unsteady. Variable vacuum = variable rpm = variable timing.
Maybe your rings are sticking a bit. GM used to sell a top-end cleaner / decarbonizer. You pour it into the primaries at 2000 rpm until the engine almost dies, and then finally does (lots of it used). Expect lots of smoke! Let it sit for a while, restart, run 2000 rpm until she stops smoking and change the oil. Full tank of fresh premium.
Now take it out and and do some full throttle runs to 5000 rpm! See if it idles better and gives higher vac numbers. I did this years ago on a '78 305 with no cat and it certainly ran better. My Vette always gets enough WOT use I have never had to this.
If you have cats you will neeed to use a product that won't kill them.
Good luck.
Rich

impalaman

Well, I did a compression test today. Here are the numbers:

1 - 132
2 - 133
3 - 137
4 - unable to test
5 - 132
6 - 132
7 - 138
8 - 128 (falls within the 10% rule)

If I have a longer hose on the gauge I could get to #4. But I'm going to call it good.
This engine is supposed to have a 8.9 compression ratio. L-82

I really appreciate all you guys listening to a novice rant about this engine.

Rich's'78 - On occasion, I run her up to the 5000 mark.... maybe a tad bit past. (red line is 5600) This 4-speed 220hp L-82 will definitely surprise you..... especially with that 3.70 posi behind you!

But, I think you are correct about the cleaning. Do you have a product in mind that I could try? I can always pick up a can of Sea Foam.

The only thing not stock about this engine from 78 is the water pump and the A/C compressor. I changed the pump a few years ago because I didn't like the idea of a 25 year water pump. I always use AC Delco parts.

The cat has been removed and I had a professional hot rod shop install a nice set of dual exhausts with magna flows. He installed a cross over pipe near the rear of the car. The frame already had the other hole in it. I guess Chevy had a bunch of frames left over after they stopped using true dual exhaust in 75. The new pipes are welded onto the existing ones, below the stock manifolds. (And just below the E.F.E. on the pass side) From the top, you can't tell....... until you crank her.


Anyways, if nothing else works, I'll just run it like this until next year some time. I'll change out the timing set and have the distributor rebuilt.

impalaman

Figures: I just read some other posts on how to perform a compression test. Seems there are people saying that all plugs need to be removed. Is this correct?

I did mine one at a time. I cranked each one five times.

Should I have removed all the plugs?

Does this affect the numbers?

73StreetRace

Yes, you have to remove all spark plugs to perform this test.
It affects cranking speed, and the numbers. I think I've got the same engine as yours ( 1973, L-82, 9:1 comp ratio ), and I get about 165 on each cylinder ( 86000 miles ). It also depends a lot on the cam...
Do the test again and it will raise your numbers. Don't forget to open throttle wide during the test. This will also affect the results. You can keep the throttle wide open with a small wire if you are alone, or have someone fully depress the pedal and crank the engine at the same time. I often remove the air cleaner to do this test, so It's easy to check that the carb butterflies are wide opened.
Always allow the engine to make enough turns until the readings don't go any higher. Generally at least 2 or 3 seconds for each cylinder.
Always recharge your battery before ( and after ) this test if you want accurate readings

Rich's'78

I have never seen this product so I did a google search. Here is what one guy said "I let the engine warm up, and poured 1/3 of the bottle in the gas tank full of about 4 gallons of fuel. I then slowly poored (without letting the engine die, it will bog down) the rest down the carb. WHen I was almost out, I poored the rest down the carb to make it bog down and die. then as the directions state, I let it sit for five minutes then started her up. she will smoke like crazy, but it does work. My idle quality was about a hundred times better. must have had a lot of gunk somewere that the seafoam cleared out."
As opposed to decarbonizing the valves and combustion chambers, I was thinking of sticking rings may be part of the problem, but your compression test should indiicate that.

impalaman

sigh...... ok. I'll do the test again.

TimAT

A compression test can help with lots of diagnosis. Lots of information can be picked up by a properly done test.
1. all spark plugs out
2. ignition disconnected (don't want those nasty sparks out there!)
3. Throttle held wide open
4. Compression gauge into the cylinder you want to start with.
5. Record the FIRST stroke-
6. Record the last stroke
7. Move to the next cylinder and repeat until done.
8. If one cylinder appears low, give it a shot (1tsp) of engine oil and retest)
9. Compare the numbers

Any 2 adjacent cylinders that are EXACTLY the same- first stroke to the last. good bet the head gasket is gone. If the first stroke is weak (less than the others) then look for possible valve or guide problems. The highest cylinder should be within 10% of the lowest.

PeteZO6

^ If at all possible do it with the engine up to operating temperature.

Pete

impalaman

PeteZ06 - I do not enjoy pain. This is a bone stock 78 L-82 with all the crap that goes with it. (Including the A.I.R. system) Doing this test with the engine at temperature would be an exercise is masochism.

I did not record the very first compression stroke number.

Here are the new numbers: (Compression Ratio is 8.9)

1 145
2 145
3 151
4 145 (was able to get to it this time. practice helps)
5 143
6 143
7 145
8 143

Comments?

impalaman

I've discovered two possible problems. The cylinders seem tight, so I checked some of the manifold bolts. The book says they are suppose to be 30 ft lbs.

Many of them were only 10 to 15 ft lbs. I was able to get to about 6 of them with the torque wrench. I tightened them down to a little over 20 ft lbs. I didn't want to press my luck, going all the way to 30 because the bolts are hard to get to and I didn't want to break anything else. So it would appear that my mechanic did not torque the intake manifold bolts down to the proper spec. This instake gasket was replace 2 years ago. My guess is that since it was never torqued down properly to begin with, the manifold needs to be removed and new gasket meterial (and sealant) needs to be installed. Followed by proper installation with the proper torque settings.

Now to the other item I found:

I don't like this one. I decided to take the pcv valve out and plug the vacuum line going to it, to see if that made a difference. It didn't. But, I noticed some very faint white steamy looking smoke coming out of the PCV hole in the driver's valve cover. I also notice the same faint white steamy smoke coming out of the passenger side hose that goes into the breather.

What is causing this smoke? Improper manifold installation? Bad valve seals?

Thanks

pauldana

Didn't read the whole post... just first half... but.. Check the harmonic balancer... maybe loose on the crank snout... maybe keyway shot... Good luck

RunningMan373

I got the same thing during the compression check i did. Figured it was fuel vapor. I also torqued my manifold bolts down to spec on install- 25lbs on all bolts, a few days after running it, all the bolts were around 15-20 lbs, so they need a re-torque. The Head bolts however did not, they were checked. I re-torqued my intake bolts to 25ft/lbs on aluminum heads, plus a tiny bump. I think you cast iron heads could take 25 ft/lbs easy..

73StreetRace

White vapor is generally a symptom of some water ( coolant ) entering the combustion chamber. If you have some water vapors coming out of the PCV valve, you should also have some foamy oil in the oil pan.
You can check it with the dipstick. It also means that you would have to refill your radiator or your overflow tank with new coolant frequently...
I rather think what you see are ordinary blow-by gases. This is caused by worn, broken ( old engine ) or badly seated rings ( if the engine has been rebuilt recently ). But every engine has some.
However, check if your PCV valve is working normally ( not clogged ).

73StreetRace

I almost forgot...
About your compression test numbers, they seem really good.
They would have been probably a little higher with the engine up to normal operating temperature, but we know it now, you're not a masochist
The most important thing is that the numbers are pretty close for all cylinders.
As you removed all spark plugs, did you notice a color difference between them ?

MN80Vette

I had severe problem with timing on my HEI dist jumping all around too. A guy at a performance shop recognized the problem immediately. He took the dist cap off and showed me how much vertical play there was in the shaft. If you think about it, the teeth on the dist are diagonal. Every verticle movement results in a horizontal movement. Every bounce up and down caused equivalent advance and retard.

I went home, removed the dist, and added some dist gear shims. A very inexpensive solution to a very annoying problem.

impalaman

73StreetRace - I did notice some EXTREMELY small bubbles (one or two) on the dip stick. I did not notice any foamy look to the oil. All of the plugs appear to have the same normal type coloring. But, they been changed recently, so some more driving will be needed to see if any of the plugs appear different from the others.

I am really starting to think that the intake manifold gasket replacement that was performed a couple of years ago, was not done properly, and that there is some coolant leakage into the intake runners. I will keep a close eye of the over flow tank level.

MN80Vette - While I had the dist cap and rotor off, I checked the up and down play by grabbing the mech advance and pulling upward on it. If you hold it absolutely still (keeping it from rotating), while doing this there is no up or down play. However, if you just grab it, and pull up, it will rotate a very small amount and then the whole thing will come upp about an 1/8 inch. I assume this small amount of rotation is the vacuum advance portion???

Where did you get the shims?

RunningMan373 - I will check for the vapor again under normal operating temps, after a long drive.

By the way, I've been driving this car quite a bit this summer. It runs well, and goes like a bat out of hell when you stomp it. It just idles like complete xxxx.

MN80Vette

Think about the diagonal cut distributor gear. There can't be any vertical movement without horizontal movement. If you stop the rotor from turning, you're stopping the rotor from lifting too.

A 1/8" vertical travel is way too much. That translates to 1/8" of rotation at the diameter of the distributor shaft and much more at the end of the rotor. I don't know the length of a rotor from center, but 1/8" of travel at the edge of a 3/4" (?) shaft translates to significant number of degrees at the end of the rotor. I don't have time to do the math and I don't know actual dimensions, but the timing play is probably 15 degrees or so. You definitely need shims.

You can order them from Jeg's , Summit, eBay, or your local auto parts store (maybe). There are 2 types of shims: Distributor shims that raise the distributor on the manifold, and distributor gear shims that reduce play in the gear. You want the latter, but they may all come in a distributor shim kit. Moroso and MSD both make them.

Be careful to note exactly which way the rotor points as you remove the distributor. I make a mark on the manifold with a pen before I remove the dist. If you reinstall your distributor and the rotor doesn't line up with the mark, the dist gear doesn't line up with the cam gear the way it did when you removed it.