Distributor Tear Down, Vacuum Advance Replacement...TURTCEL

[marlinh]

Another question. Has anyone ever come across a vacuum advance with only one port on it? This distributor I regreased had one on it. Not sure where it came from, but it works. Would you connect it to ported vacuum?

[dlb]

i used some high temp teflon stuff generally used for bicycles that 4wdchico thought would work well but i feel it is too thin. i was thinking i would just use the good old fashioned esso or chevron wheel bearing grease my dad has in bulk. not sure if it's correct or not but figured it should hold up fine. someone please tell me if i'm out to lunch on this.

mark gave me a dizzy recently that has a single port vac advance unit on it. it looks like the port and bottom diaphragm from our usual 2-diaphragm units so i assumed it would connect to ported vacuum too. easy way to check if you install it in a car: with the engine idling and a timing light on the crank pulley, temporarily hook the port up to manifold vacuum. if the timing advances by only 8*, the unit should remain connected to manifold vac. if it advances by 13*, the unit should be connected to ported vac.

i should be replacing the blown advance unit on my friend's terc eventually with the good single diaphragm unit so i'll try to remember to post what we find if you don't get to it first, marlene.

[marlinh]

Ported vacuum only kicks in when the throttle is open, correct?

I have some spare distributors that I thought I'd spruce up. The first one I did, I used lithium grease. It was rated for high temps.

[dlb]

Ported vacuum only kicks in when the throttle is open, correct?

yup, it is present at partial throttle during hwy cruising conditions.

[Petros]

the load on the bearings is related to 1) rpm, 2) both lateral and axial load. there is a bearing formula that determines size of bearing based on these inputs. since the distributor is fairly low rpm (half engine rpm) and very low loads, the type of grease is likely not critical, it is also not particular high temp, max around 200 degrees (unlike say the wheel bearings in the front hubs can get very hot with the brakes so close, or the CV axles, very high load). However, you do not access the distributor bearings very often, so any quality grease that will hold up over the long run.

I think a light axle grease would work well, I like the Ford type axle bearing grease; it is infused with graphite particles and it is cheap. It is designed for the truck axle bearings. The lithium and graphite type lubes should also be good, as long as they are sticky enough to stay in place after many many miles and years.

[marlinh]

Dlb said "with the engine idling and a timing light on the crank pulley, temporarily hook the port up to manifold vacuum. if the timing advances by only 8*, the unit should remain connected to manifold vac. if it advances by 13*, the unit should be connected to ported vac."

If I hook up the vacuum line to ported vacuum at idle, the timing shouldn't change. So, how do I know what port to hook up the single ported advance to?

[irowiki]

He means to connect it to manifold vac at idle and see if it advances 8 degrees, or 13 degrees. If 8, leave it on the manifold, if 13, route it to ported vac.

[marlinh]

Thanks Paul, that ends my confusion. Except, wouldn't you want vacuum advance to occur under throttle application, instead of at idle?

[irowiki]

The 8 degrees of advance from the manifold is also applied at part throttle, it goes in conjunction with the 13 degrees from ported!

[dlb]

paul's got it. sorry, i should have been clearer.

wouldn't you want vacuum advance to occur under throttle application, instead of at idle?

manifold vac is present at both idle and part throttle, and ported vac is present on part throttle. the first supplies 8* of advance and the second 13*, which means the total amount of vac advance at idle is 8* and the total at part throttle is 21*. there is also the centrifugal advance caused by the weights in the dizzy but i have no idea how much advance they supply.

[marlinh]

So, depending on the amount of advance determines which port to hook up to? That works if you have two ports, but what about only having one. Which is more advantageous?

[irowiki]

You put a tee on and connect both?

No, okay just kidding

[marlinh]

Ha, ha thanks, Paul.

[irowiki]

I dunno, it might actually work if ported vacuum pulls harder than manifold vacuum! With good use of check valves, anyway...

[Petros]

you will not have vacuum advance occuring with throttle responce, when the throttle opens the manifold vacuum drops. you do not in fact want a lot of advance when you stomp on the throttle becuase it will ping, the purpose of the vac advance is so when you are at part throttle curise speeds, when the manifold vacuum is high (lean fuel air mixture) to advance the spark timing to improve part throttle curise economy. the lean part throttle fuel air mixture burns slower so the timing has to be advanced to improve part throttle efficiency.

the mechanical advance in the distributor just advances the spark timing purely based on rpm, again since the fuel burns at the same rate, it has to be advanced as the rpm increases to get the peak pressures to occur at the optimum point in the combustion cycle.

If the mechanical advance is not working the engine might start and idle fine, but will lack power at higher rpms. If the vac advance is not working you would not notice it other than perhaps a small drop in MPG (fuel economy) on long distance trips. The first five cars I owned did not even have a vacuum advance, cars from the late 50's and 60's.