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Timing question...

Started by Steve W, July 26, 2015, 09:43:37 PM

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Steve W

OK..so I set the timing on my car...about 6* BTDC...with the vacuum off and plugged, and the parking brake vacuum line plugged as well, as per manual. Stars and runs fine. Still runs warm tho, even with new water pump, new, thermostat, etc.

BTW, my mechanic switched from points to Pertronix about 2 years ago or so. Havent had a any problems.

So, after putting all the vacuum tubes back to normal...timing stayed at 6*.  Thought I would check it a little further...revved the engine to 2500 rpm and the advance goes to 22*. Is that normal for q 1968 472?

And how do you adjust the higher rpm advance?
Steve Waddington
1968 Coupe deVille
North Hollywood, CA
CLC Member # 32866

Scot Minesinger

Steve,

the only reason you are supposed to disable the vacuum release on the emergency brake is so that you can put the car in drive with emergency brake on to set timing.  If you set it while in park, you need to go back and re-do it.  This is a two person job, I get my wife or kid to put foot on brake with car in drive to set timing.  Get a tach from Auto zone (not expensive) and hook it up to negative on coil, and the battery, then you can set rpm to factory spec. while making this adjustment.  Once you have timing set you should be all done and not have to deal with setting it at higher rpms.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

m-mman

#2
The increase in the timing advance is a factor of the springs and diaphragm inside the vacuum advance 'can' and  the springs and weights under the rotor. Racers and others who are trying to get an engine to operate differently under very specific conditions sometimes make changes in these parts.

Rest assured that GM engineered the system to operate smoothly and reliability in the ranges and environmental conditions that a Cadillac owner would likely use their car.

There are specifications that describe the advance curves for each component (vacuum and centrifugal) but realistically you need to use a distributor machine to measure them accurately. All you would be checking is that they are functioning as intended. Seeing the advance change as you rev it up pretty much verifies that they are functioning. 

The reason for setting the timing in park is to have the engine spin at it lowest idle speed that it would likely experience during normal operation. If it was operated at a higher RPM the centrifugal advance might start to kick in. Over the years some makes suggested that the idle and timing be set with the headlights on such that it would make a slight drain and load on the alternator.
1929 341B Town Sedan
1971 Miller-Meteor Lifeliner ambulance
Other non-Cadillac cars
Near Los Angeles, California

CLC #29634

Scot Minesinger

The Cadillac shop manual calls for the timing to be set in drive instead of park for the 472/500 engine family.  The theory about headlights on creating some drag may be why the car needs to be in drive when setting timing, as that is way more drain on engine than park.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Scott Halver

Hello Steve,
The best way to set-up your timing is to take the distributor out of the car and take it to someone that has a Sun Distributor machine.   They can run the distributor as if it is in the car and "tweak" the rate (how fast it is advancing) and amount (total timing) of centrifugal timing.........   and then apply vacuum to see how much vacuum advance exists.    I took my distributor to a older "race car mechanic".......  has set-up thousands of distributors.    My car is set-up for 10 degrees on the crank, 24 degrees of gradual centrifugal advance (all in by around 3000 rpm), and 12 degrees of vacuum advance-   so 46 degrees of total timing although you would never achieve that much timing-   vacuum advance gone when on full throttle/say 4000 rpm/passing gear.     I found a new "old stock" vacuum advance for my car and it had 22 degrees of timing for the vacuum advance (factory specs).................   mechanic not happy with that much advance.    He said that is too much timing and that I would have a knock, I agree.  So he welded a small bar across the reach to limit the advance to 12 degree.     The car drives very nice with no knock.   The mechanic that did the distributor for me specialized in ignition and fuel most of his life.   I have watched him dyno cars to figure out the best timing curve and fuel mix.   I offered to pay him to put in on the dyno, he kind of laughed and said, I think the car is pretty close to right on ..........  considering the application etc-    not like I'm racing the car.

Note:   I think the factory was able to use 18 - 22 degrees of vacuum advance in the late 1950s because the fuel was really good, high octane.   It made the car drive really responsive, drove like a Cadillac !   That much timing on light throttle with today's gas is asking for trouble.   I actually add a little 110 octane racing fuel in the summer.

The only concern is that if you are not comfortable taking the distributor out of the car and then being able to get it back in correctly.   It is kind of hard to get to at the back of the engine.   A lot of mechanics try to avoid that procedure if possible.   The actual time on the distributor machine is like 20 minutes..........   assuming the mechanic has all the tools, extra springs/weights, oil to lube the springs, extra vacuum advances if needed etc.    My mechanic spun the distributor up a couple of times, each time getting it closer to what he wanted, but you could tell he was determined to find that "sweet spot" in the advance curve...............   no substitute for finding an older guy with a lot of experience.

Good Luck, SHalver #24920
1960 Eldorado Seville, Grandfather Bought New
1970 Corvette Convertible 350/350

Jon S

I think taking the distributor out of the car is a bit of over-kill. Either a timing light and/or vacuum gauge works just fine on a Cadillac and that is how Cadillac certified mechanics have been doing it for over 80 years.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

Scot Minesinger

Agree with Jon, not necessary to remove distributor to set timing.  The car will run great with standard factory set  timing procedure outlined in shop manual. 
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty