Ok guys....some news...


...found out some interesting stuff during this weekends work. After checking all possible things we finally checked the vacuum advance.....

....and surprise....it does not work correctly.

Vaccum produced by enigne is by far not enough to retard ignition. So I will change this damn little thing next week and see what happens then.

The only thing that really makes me wonder is....why didn´t the shop I brought the car to for after resto basic adjustments not tell me so...because he did change the points as well....he must have noticed that. Interestingly enoug as well ignition timing was set at 6 deg BTDC....and should be 10.

...so....looking for a new shop. clearly.

...or I need to learn a little more about proper engine adjustment by myself.

I HATE BUBBA !!! :mad

 

Mikey:

I scanned this thing over twice but I may have missed something. You say you have new plugs in one post, on another, you say they look okay. If you are not SURE of their condition. put new ones in of the correct heat range. AC 45S should work fine. If this doesn't fix it, run a jumper wire from the battery to the plus side of the coil. The minus side goes to the distributor. Check for that condition also. If the jumper fixes your problem, you have something wrong in the ignition circuit and it will probably go back to your dash panel bulkhead connector contacts.

Your problem sounds to me like a coil or low voltage feed to the coil, bad points, condenser, fouled plugs or something electrical. I do not think your problem is in the vacuum advance as the advance provided by this device goes away at wide open throttle under load anyway. As far as the 6 degrees the shop set vs. the 10, they may be correct if they were setting timing based on total crank degrees which would be in the neighborhood of 36-37 degrees with the vacuum advance disconnected. Once you set this, you drop back to idle and recheck the timing, making sure you are not getting any help from your mechanical advance. You could very well have an initial setting of 6 degrees.

two last things. The FIRST thing I would suspect is a blown power valve but you say it runs well at low rpm. That rules out the power valve. You need to find your problem quickly because if you continue to run the engine this way, you will dilute your crankcase with gasoline in your engine oil which can lead to all kinds of problems including fire.

Mike :)

EDIT

Unhook the vacumm advance and see if the problem goes away. The breaker plate movement may be causing a problem with the plate ground wire. Check it for continuity also. Also, your engine should rev to 7000 rpm at least on the primary side of the carb without opening the secondaries. That is assuming, you have a soilid lifter engine in proper tune.


[Modified by MikeM, 7:02 PM 6/22/2003]

 

The proper vacuum advance for you engine is the NAPA/Echlin VC 1810 that provides 16* at 8", and this is is less vacuum than the engine should generate at idle, which is about 10". This means the vacuum advance should be pulled to the stop at idle.

What's this talk of "retard"!!!???

At idle with the vacuum can connected the total idle advance should be 12 intitial plus 16 vaccum for a total of 28.

If the distributor is against the manifold to achieve the proper initial timing, it's either installed a tooth off of the drive gear is indexed 180 degrees out. An improperly indexed drive gear will misalign the rotor tip with the cap terminals and weaken the spark. Proper indexing of the drive gear is indicated if the dimple in the drive gear points the same direction as the rotor tip. Since this trick is not mentioned in any Chevrolet manual that I know of, there are probably millions of SBs out there that are screwed up. It's one of those "system knowledge" things you learn with experience.

To test the distributor for proper high rev operation, rev the engine to 6000 with a dwell meter attached and observe dwell angle variation. If it's more than two degrees from the idle reading, the distributor needs work. The shaft may have too much end play, a worn, wobbly breaker plate, or sloppy bushings. You can also run this test while driving using some jumper wires to hook up the dwell meter and read it in the cockpit. If the engine misbehaves with not significant drop off in dwell angle, the problem is probably not with the igntion of electrical system.

In any event, the firewall electrical connectors should be unplugged for a thorough inspection and cleaning. If the igntion and electrical system checkout, the problem is likely in the carburetor.

Duke

 

I am really getting curious as to how he is going to test the high rpm operation of his distributor by revving it to 6000 rpm. His ORIGINAL COMPLAINT was that he COULDN'T get it past 4000! I'm sure you meant on a distributor machine

I'm also curious as to what the PROPER vacuum advance can has to do with it. He should be able to pull 5 spark plug wires and get 4000 rpm if everything else is right. He could even retard the timing 20-30 degrees and still get 4000 rpm if evrything was okay.

 

If it won't free rev to 6000 and the dwell ramains constant, the problem is probably not in the ignition. If it does free rev to that level, the dwell variation of lack of same will tell you that the problem is probably not in the distributor. An engine that does not rev properly under load may or may not free rev. You have to run the test to find out.

The vacuum can is probably not the issue, but it should be checked because it probably hasn't been checked for 35 years.

The purpose of running tests is to either confirm a fault or eliminate systems and components that might be at fault.

The distributor is probably the most ignored component on vintage cars. I've seen guys spend zillions on old cars and just throw the distributor back in without even giving it a second thought. They deserve all the attention they can get.

Duke

 

@ MikeM....The spark plugs have been renewd and I pulled them out to check and they looked ok. That´s what I ment. Got 45´s in there. All the rest of the electrical stuff is NEW.....that´s why I will look there last.

@SWC Duke.....I will follow your thoughts and probably pull the distributor. I do have access to a dist. checking machine in two weeks time.

And yes...the vaccuum advance sits against the intake manifold.

Great hint. Thanks.


[Modified by Mikey1, 1:18 AM 6/23/2003]


[Modified by Mikey1, 1:21 AM 6/23/2003]

 

Short update:

Took a wile for deilvery of the new vac advance.....now stuff is there and we put it in on saturday.....idles a bit better....but the problem stayed unchanged.

Eliminiated the secondaries by unhooking them.....problem stayed....

Tere wasn´enough time during that day for working on the distributor....it´ll have to wait two more weeks.

We´ll probably replace it with a later year dist. that we now is working...just to be absoltuely sure...and for testing purpose only.

I´ll keep you updated.

 

In one post you mention that you need to get timing light, are you certain that the mechanical advance weights are operating.

10* initial is not enough. Bring it up to 14*-16*.

Buy a timing light and map out the distributor. It sounds like the only thing left to be addressed.

Mark



[Modified by ghostrider20, 12:12 PM 7/7/2003]

 

Ok....so here are the news of today....finally found the time to test some stuff.

Pulled the distributor today and found that the drive gear was 180 deg off. So we pulled that and assembled it as it should be. Thanks Duke...you have been absolutely right....would have never found that....

To check further we used a distributor tester from SUN. Well....seems that still a problem exisits. On that testing bench you do have a scale with the crank angle on it and a stoboscope light flashing so that you can exactly see the time of ignitionover crank angle for each of the 8 cylinders...

...on a reference distributor these ignition points remained stable up to the test limit of 4000 rpm.

With my box on it you could see that the light...or ignition marks where wandering about....and steadily...

Put the dist. then back into the car and adjusted timing to an intial 14 deg.

The engine now revs free up to 5000 rpm´s but still for a solid lifter this is not enough. But I have to admit that the engine now runs a lot smoother which initally is great.

Question to the experts: Do I have to replace the distributor shaft ? Any other advice ?

Thanks again for all the other hints as well...it did help to exclude...!


[Modified by Mikey1, 3:08 PM 7/19/2003]

 

Dwell angle should not vary by more than two degrees to peak revs and spark scatter should not be more than 2-3 degrees, max.

Check for proper indexing of the wires. Check for excess shaft radial play due to worn bushings, excess shaft end play (should be two to seven thou), and a wobbly breaker plate. Also check for weak point tension spring, and use the 28-32 oz. breaker arm tension points.

Chances are your distributor has never had anything but new points and maybe a cap and rotor or two in the last 35 years. Give it a complete blueprint overhaul. Measure everything, and replace every component that is not up to snuff.

Duke

 

Now you have the same problem I had last summer ,a 5000 RPM rapid misfire that was like hitting a wall
I had .004 clearance at the lower bushing. When I took it apart the shaft and lower bushing were scoured requiring replacement.
There's a good post in the archives under my handle with Duke and Lars giving me advise.
Believe me, a couple of thousands clearance makes all the difference in the world with these points distributors. The manual calls for a max of .002 runout and at .004 it was a no go.
I also use a set of the 32 oz Excel points and the distributors pulls smoothly to 6000 Rpm which is the highest I've revd the motor.
Make sure you also shim the end play to .002 to .007 and when ordering parts get a new plastic seal for the grease well at the top for the upper bushing. The old grease turns to concrete after 30 yrs LOL
Bob

 

You said you had a replacement balancer. Chevrolet moved the timing mark 10 degrees in 1969 and again (about another twenty degrees) in the late seventies. Have you ever checked to see if the location of the timing mark on your balancer is really indicating TDC in relation to the chain cover timing scale?