1958 Distributor Change

[highcking]

Anyone know why Buick changed distributor specs during 1958 production? The earlier builds used a distributor adjusted for initial timing of 5 degrees BTDC. The later ones called for an initial adjustment of 12 degrees BTDC, but used a different centrifugal advance mechanism. I believe the 1959 engines continued the 12-degree setup. My '58 Roadmaster has the earlier distributor and draws about 14 inches vacuum at idle, correct by the shop manual. Was this found to be too low and the more advanced setting used to draw a higher vacuum? It's certainly an unusual change and 12 degrees BTDC was very high for the time.

Bill Shields

Virginia

[JohnD1956]

Just guessing but does that coincide with discontinuance of the oil-pump vacuum enhancer?

[highcking]

John - it does in a sense. In 1959 Buick went to electric wipers and dropped the vacuum/oil pump. But no 58's were made that way, yet this distributor change was made during 58 production. The actual change was a different centrifugal advance - the vac advance unit was left alone. Twelve degrees BTDC would probably increase idle vacuum, though, and lead to greater advance throughout the rpm range at the risk of serious pinging. I wonder if octane numbers jumped that year? I need to see if any other GM makes also made a mid-year shift.

Bill

Just guessing but does that coincide with discontinuance of the oil-pump vacuum enhancer?

[Guest kaycee]

Remember, the distributor advance weights and springs are going to be different.

kaycee

[Guest kaycee]

As well as the vacuum advance unit!

kaycee

[highcking]

Centrifugal advance was changed and given a different number--that's how you can tell the difference. My references show the vacuum unit was left the same. Probably too expensive to order a different vacuum advance. What puzzles me is the 12 degrees BTDC -- that's a lot of initial advance. Yet there had to be some reason to make the change. I'd like to find a 12-degree centrifugal advance set and see what happens when I retune the car. The ID number is on the underside of the centrifugal unit.

As well as the vacuum advance unit!

kaycee

[Glassesguy]

Guys: Per Buick Product Service Bulletin 2.436 and Special Service Letter #236 dated February 1958 entitled "Noise and Vibration Complaints". The change was made in reaction to fan noise complaints. The 5 blade 20" fan on A/C cars was changed to a 20" 4 blade fan. Non A/C cars originally had a 20" 4 blade fan. This was changed to a 4 blade 18 1/2" one.

"Since the 12 degree advance distributor allows the engine to run slightly cooler than first jobs, it is possible to omit one blade from the air conditioner fan and reduce the diameter of the standard fan" per the Service Bulletin. This change was for Dynaflow equipped cars only. Synchromesh cars kept the 5 degree distributor. The Bulletins also cautioned that if the new fans were used with the 5 degree distributor, overheating may be experienced. No recall was made on this. This change was to be made only if there was a customer complaint. The change was made in production cars in late January while the new fans etc. were to be released for service in March. No mention made of changing the vacuum advance.

There's the info right from the factory.

[highcking]

Wow, great information! I would never have guessed that explanation. I need to go back and look at my service bulletin set - not sure it's complete. I have noted the the vast majority of service problems discussed in the bulletins dealt with the ill- fated air suspension system (which my Roadmaster had when first sold) and the AC system. I owned an air conditioned 1959 Cadillac and had a hard time keeping the system working right.

Since the timing change was not carried into 1959, they must have solved the fan issue another way.

Guys: Per Buick Product Service Bulletin 2.436 and Special Service Letter #236 dated February 1958 entitled "Noise and Vibration Complaints". The change was made in reaction to fan noise complaints. The 5 blade 20" fan on A/C cars was changed to a 20" 4 blade fan. Non A/C cars originally had a 20" 4 blade fan. This was changed to a 4 blade 18 1/2" one.

"Since the 12 degree advance distributor allows the engine to run slightly cooler than first jobs, it is possible to omit one blade from the air conditioner fan and reduce the diameter of the standard fan" per the Service Bulletin. This change was for Dynaflow equipped cars only. Synchromesh cars kept the 5 degree distributor. The Bulletins also cautioned that if the new fans were used with the 5 degree distributor, overheating may be experienced. No recall was made on this. This change was to be made only if there was a customer complaint. The change was made in production cars in late January while the new fans etc. were to be released for service in March. No mention made of changing the vacuum advance.

There's the info right from the factory.

[buick man]

Interesting info here. The 12 degree would also improve in town driving I would think for fuel mileage as the new 5* BTDC 364 in 57 had gotten a bad rap regarding fuel mileage and this may of also been an attempt to change this and in the process the noise of the fan as well at the same time with the heating problems experienced throughout 57 and into 58. It would be interesting to have a 57 or 58 5* BTDC A/C 20" 5 blade car running next to a 58 12* advanced 18 1/2 inch to see both the sound, vibration/quietness at idle and on the road in a comparison test to see to what extent the change really made.

[NTX5467]

With the additional base timing amount, there would be less heat rejection to the coolant, which would relate to the need for the larger fans and such. BUT they could also have changed the pulley diameter, but that change would not have been that evident to untrained eyes.

The additional base timing would make the car come off-idle with more torque, which would relate to less throttle input needed for a given acceleration, which could positively impact fuel economy. In order to control spark clatter, the mechanical advance specs would be slowed down a little, I suspect, but with the same general total advance as the 5 degree distributor at higher rpms. Many mechanical advance schedules start the mechanical advance at about 1000rpm, so having the additional advance built into the base timing would give better response than just speeding-up the advance curve. Kind of the same thing, but different ways to get there.

The vacuum advance unit could have had a hidden adjustment, but doing everything mechanically is more reliable (the increased base idle timing degrees) than relying on springs to do the deal.

Seems like there were some issues with the '59s having wilder camshafts in them, which would require more initial bast timing to compensate for any low rpm torque loss from the wilder timing specs of the cam.

Of course, all of these fan noise issues would be dealt with by "fan clutches" in later years . . .

Just some thoughts,

NTX5467

[JohnD1956]

Can anyone describe how, or why, increasing advance results in less engine heat? I 'm just wondering aboit the theory, but looking for that in laymans terms.

[NTX5467]

The timing increases are "within a range", rather than just "increases". If timing is advanced too far, then it cooks the spark plugs and causes other detonation-related issues in the engine. In one case, just one heat range hotter put holes in the pistons of a late model (1989 or so) Chevy V-6, which resulted in a service bulletin as the hotter plug was "production-installed".

In about 1969 or so, "Hot Rod Magazine" was doing a dyno test of a Ford 351 (Windsor, I believe). At the stock timing settings, the exhaust manifolds glowed red at WOT, but with about another 4 degrees of advance, it made more power and the exhaust manifolds weren't as hot. That's what I recall.

Back when emissions controls were in their relative infancy, it was common for CA-spec engines to have a base timing setting several degrees "retarded" from "Fed-spec" engines. There were even some retro-fit kits for vehicles going back to 1955. It was reported that with the retarded base timing, the engines had overheat issues in city traffic. On the factory-production vehicles, though, the retard in the base timing was compensated for by a faster advance curve such that by 2500rpm, the total combined advance was about the same for both engines.

Remember, too, we're talking about an engine at "closed throttle" rather than at "road throttle".

In these lower-demand times, having an engine that's "happier" with things will send more power to the flywheel. Intake vacuum will be higher, throttle response will be sharper, plus better energy utilization from the fuel. Take the spark advance "retarded" and it might make the engine perceive it's more "under load", which means it's working harder for a specific result. That "harder work" usually means more combustion and exhaust heat.

Perhaps I was using incorrect rememberances of things I've read decades ago, or getting "heat rejection to the coolant" confused with what happens when the compression ratio of an engine is lowered (which CAN increase exhaust temperatures on a stock engine, by observation)?

I'll do some diggin' to see if I can find what I think I read, back when I thought I read it.

Enjoy!

NTX5467

[buick man]

As usual NTX is right about things. So it is prudent to take your distributor to a qualified rod shop and have your distributer re-curved which involves assembling different advance springs with a change in adjusting resulting timing BTDC or however the case may be. One cannot just simply change the timing and nothing else associated with the advance curve nor just the vacuum advance unit itself. Everything has to be dialed in including the carburetor's off throttle channel changes ( enlarging ) being part of the big picture. All of which combined facilitate a complete recurving of the timing for that given engine.

[JohnD1956]

I agree Dave, you prescribed the fix. I was just wondering what the theory was for how increased advance results in a cooler engine. My nailhead does not seem to be overheating so I'm not tempted to mess with success. But I am interested in how the engineers came to this conclusion.

[Smartin]

Experimentation?