Vacuum advance in distributor repairable? ('72 145 B20F)

[Gary Heston]

--
Gary Heston

"Is this chicken, what I have, or is this fish? I know it's tuna, but
it says 'Chicken by the Sea'." Jessica Simpson, on MTV _Newlyweds_

 

[Gary Heston]

I suppose it would help to include something in the article...

I'm fairly certain the vacuum advance mechanism in the distributor on my 145s' B20F has failed; if I pull and plug the hose, the engine is solid on the timing mark at idle; when I reconnect the hose, timing shifts 5-10 degrees, idle drops, runs rough and pops occasionally. Pull the hose, and it smooths out again. I suspect this is the source of the rough cold idle I've had for the past year.

So; can I repair/replace just the advance mechanism in the distributor, or is this a distributor-swap situation?

My temporary solution is to set the idle with the hose connected; this gives me a fairly smooth idle, though a bit high, and power is down a bit. Much more driveable than it was, though, so at least I can get around.

Anybody know where a NOS or know-good distributor could be found for a '72 B20F with D-Jet at a reasonable price?

Thanks,

Gary

 

[Guest]

Gary,

sounds as if the vacuum advance is doing what it should. I think you may have the timing set wrong. Have you followed the proper sequence for setting the timing? i.e. vacuum hose disconnected and plugged, reduce idle to 800 rpm using air restrictor.

The vacuum advance is replaceable, if memory serves. It is not repairable by mere mortals. It can only fail two ways: leaky diaphragm, which is indicated by no change in idle when hose is removed, or frozen, which can be observed by popping the cap and looking at the linkage while sucking on the tube.

Your Volvo dealer should have a replacement or you can get one on line from gcp and others.

Go to brickboard.com for more help.

chuck petterson
73ES
73 142E for 9 years, now mostly iron oxide, I suppose.

 

[Bill Chaplin]

G
Nop high breakdown item,part of why the went to "full time injection" not too pricey last I bought. B

 

[Joe (3)]

I'm trying to remember my old Trade School days these distributors run ignition points when the vacuum advance unit pulls the breaker plate in old distributors this plate wears out and as the plate is pulled to advance the timing it also changes the point gap causing the engine to misfire ect.you can check this by placing a dwell meter on and trying the vacuum advance the shouldn't change much. There is also under the breaker plate another set of contacts that have something to do with the fuel injection it has been a long time since I have played with one I hope I have been of some help.
Joe

 

[volvowrench]

In article , by
Gary Heston dropped his wrench, scratched his head and mumbled,

In article ,
Shaun Mallonee wrote:
If the timing marks are dancing around anything more than 2-3 degrees
(the less the better), you have something wornout. Usually, it's the
distibutor that's work. I am not familar with the older Volvos so I do
not know how the distributor is connected but other components can be
worn. A streched timing chain, drive gears, distributor busings...

The distributor on a B20 is directly driven off the crankshaft. I don't know about issues with the chain/gears; I'll have to look into some way of checking them without tearing apart the engine.

...

First of all the vacuum capsule on an F motor is a retard not an advance. The vacuum holds the timing at about 5 degrees BTDC at idle. When the throttle plate opens the advance jumps to 10 degrees and additional advance is controlled by the flyweights in the distributor. One is unsprung and flies out almost immediately, the second weight is sprung and doesn't fly out until after 25 degrees. Total advance will be in the 30+ degree range.

Causes for timing fluctuation may be a result of the first weight "bouncing", a worn out distributor drive gear, or a worn fiber gear on the cam shaft.

Bob

 

[Stig Hornang]

On Thu, 18 Mar 2004 16:38:56 +0100, volvowrench wrote:

First of all the vacuum capsule on an F motor is a retard not an advance. The vacuum holds the timing at about 5 degrees BTDC at idle. When the throttle plate opens the advance jumps to 10 degrees and additional advance is controlled by the flyweights in the distributor. One is unsprung and flies out almost immediately, the second weight is sprung and doesn't fly out until after 25 degrees. Total advance will be in the 30+ degree range.

I have an "E" motor. There the springs are identical (for sure) since I have a spare distributor with to different springs. Does that mean that my spare distributor is definetely from a "F" motor?

 

[Gary Heston]

Stig Hornang wrote:
[ ... ]

Strange problem that the idle rate rices as the engine warms up... It should be very stable or even drop a bit with a warm engine.

It rises quite a bit--once fully warm, it'll maintain between 35 and 40 MPH in fourth gear with my foot off the accelerator.

Have you tried to readjust the breakers and retard the ignition by turning the distributor? See if the engine is changig behaviour. How good is the response to the gas pedal on different rpms?

Haven't tried anything this week; been too busy at work. I'll try to experiment a bit more over the weekend.

 

[Gary Heston]

volvowrench wrote:
[ ... ]

First of all the vacuum capsule on an F motor is a retard not an advance. The vacuum holds the timing at about 5 degrees BTDC at idle. When the throttle plate opens the advance jumps to 10 degrees and additional advance is controlled by the flyweights in the distributor. One is unsprung and flies out almost immediately, the second weight is sprung and doesn't fly out until after 25 degrees. Total advance will be in the 30+ degree range.

That's wider than I thought, but I haven't any way to watch the timing while driving. Maybe I need to find a general purpose data logger...

Causes for timing fluctuation may be a result of the first weight "bouncing", a worn out distributor drive gear, or a worn fiber gear on the cam shaft.

I can't see any way that any of those would stop being a problem when the vacuum line was pulled.

Gary

 

[Stig Hornang]

(Something's probably wrong with my newsreader so i couldn't reply to the original article.)

I noticed something yesterday. In the distributor there are two plates. The lower is static, the upper is mounted to the lower so i can rotate (for the vacuum timing to work).

While I was driving, suddenly the engine fell to idle and it popped a lot and had no power. I found out later that it was the "bearing" (it's a very simple thing with one bearing ball which rolls on the lower plate) that holds the upper plate to the lower that was broken.

The upper plate has to hold a force applied by the breakers. The reason for the popping and low power was obvious that the breakers didn't open every time because the plate attached to was loose.

A temporary fix I had todo to get home, was just putting a piece of rolled paper to push the upper plate against the lower and disconnecting the vacuum hose. I didn't run perfectly well on some rpms, but it was almost right. My point is that if something in the breaker appartment is loose, it could trigger all sorts of problem. It's a case of vibrations, resonance in parts etc...

In your (Gary Heston) case the vacuum mechanism may for example change breaker spacing so it runs uneven on idle, but on higher rpms the case could be that the breakers open just enough. Remember that you can never see the vacuum mechanism in action inside the distributor.

I would advice you to take out the distributor of the car (it's very easy by loosening the adjustment screw for ignition timing and lurk the distributor straight up). You should check that all parts in the breaker appartment is rock solid. If you want to you can also remove the oher parts (capacitor and vacuum mechanism) and finally the plates so you can look beneath at the centrifugal advance mechanism.