Discussion in 'Buick FAQ' started by LARRY70GS, Jan 2, 2005.
never mind i found an old chat i had with you larry thanks anyway
I see a lot about how to better modify the Crane vacuum canister but how about the Mr. Gasket vacuum canister? Does the adjustment give you a wide enough range of controllability to avoid knock at light and medium throttle?
Not sure about the Mr. Gasket cannister. The Crane unit alows ajustment for amount of advance as well as the rate. I'd limit it to no more than 8*
I noticed with the vacuum pump that the Mr. Gasket canister (when adjusted ccw for minimum advance) requires more vacuum to start advancing. It takes around 8psi to initiate movement of the pin and does not move to its maximum range until you have ~18psi vacuum. Since I only have ~12psi it will never make this full sweep. I'm thinking I may still need a positive stop modification.
I'll check it out at least by this weekend and give an update. Thanks Larry.
This thread has really been a good reference for me, thanks Larry!
Thought I'd share what I did.
I use the Mr. Gasket adjustable vacuum advance kit (#6011), and made my own adjustable stop to limit vacuum advance. For my street/strip set-up I run 34* total mechanical advance, and limit the vacuum advance to 9*. The advance at idle with the vacuum canister connected is 43*. I also have the canister adjusted 6 turns counter-clockwise. Have not heard any engine knock yet. My mechanical advance starts at 1300 and is all in by 1900.
The dimensions given below in the picture is the distance between the rod and the end of the stop (right side).
I also took some readings with my vacuum gauge connected directly to the vacuum canister (before I installed it in the distributor). With the adjustable stop installed and adjusted to the "Gap 1" position here are the vacuum readings at various canister adjustments (hex key turns). The first reading is with the hex wrench turned all the way clock-wise, the last reading is the hex wrench turned to the maximum counter-clock-wise position (7 3/4 turns).
Vaccum (psig.) @ Initial rod movement / Vaccum (psig.) w/Rod @ stop position.
max. cw = 3.2 / 5.2 psi (more knock potential @ part throttle)
1 turn ccw = 3.7 / 5.6
2 turns ccw = 4.1 /6
3 turns ccw = 4.7 / 6.3
4 turns ccw = 5 / 6.8
5 turns ccw = 5.5 / 7.1
6 turns ccw = 5.9 / 8
7 turns ccw = 6.2 / 8.2
7 3/4 turns ccw = 6.8 / 9.5 (less knock potential @ part throttle)
Here's the installed canister, notice the position of the mounting screws, for the positive stop I made, they are far enough away from the rod to allow hex wrench access without removing the rotor.
Of course I had to use the mill to create the slot in the adjustable stop. As mentioned before make sure any mounting screws do not protrude on the bottom and limit rod movement. This was my first mistake
:beer :beer :beer :beer :beer :beer
THEN U CAN DO MINE MARCO
I was going to post "What advance should I use" but hit search first. Bingo!
Followed the basic instructions of having 31 degrees advance when the mechanical advance is maxed. First I cut a piece of tape to 1 3/4" length and put it to the right of the TDC slot on the flywheel. Then scribed a line with a sharp drill bit. Fired it up and set the advance to "1" degree at the scribed line. That's with the vacuum advance disconnected so a total of 31 degrees without the vaccum advance.
I've got an HEI unit off some sort of '74 Buick (I think a Riv.) and the idle timing w/o vacuum advance was roughly 14 BTDC which is about aligned with the end of the timing tab.
It needed a bit less throttle opening at idle with that much advance. Previously it was set for 10 BTDC at idle. Idles smooth in and out of gear.
Took it for a quick drive and it really ran well. Might get back for more playing with it but a good result. I want to get a weight kit now.
Thanks Larry and all!
Glad it worked for you Glen,
Just make sure the mechanical advance was truly maxed out when you set the total to 31*. The stock springs will not let the mechanical max out until upwards of 4000 RPM typically.
Should have said that the timing was done when holding the RPMs up. Some throttle blips showed the mechanical advance was maxed.
Factory total timing for HEI
I'm going over my distributor now and on the Crane adj.vacuum advance kit's instructions it reads that "The GM HEI distributor has a centrifugal advance of 20 crank degrees with stock weights.Using advance weights other than stock may change the centrifugal advance curve and total advance.".Is this information accurate?Are all HEIs about the same and can total advance be affected by the weights? The way I see it is unless the weights are binding with the center plate somehow they will only affect the rate at which the advance comes in not the amount. o No:
No, that is not accurate at all. Most HEI's have quite a bit more than 20*. They are all different. No, changing the weights will do little if anything to the total. Heavier weights will swing out quicker with the same spring tension. To change the total, the distributor must come apart (To do it right anyway)
Thanks,Larry,that's what I tought.On your original post you mention on Dave's stop that .086"=8* and .104"=10*, is this the norm for the Crane canister?I'm planning on making a gauge to those dimenssions to set the stop in my unit.Also on my canister there is a second thickness of sheetmetal so thread engagement will be plenty.I will elongate the holes on mine so it can be adjusted,if need be.Great thread.
one thing that hasn't been covered
The heaviest (blue) springs that came with my crane kit have the mechanical advance coming in at 800 rpms. If I go with the silver or yellow they have the advance coming in at 500 rpms.
Larry, how are you keeping the advance out until 1300 rpms?
Also just a curious question. If you put a bushing on the pin to limit the total advance won't it also limit the travel of the pin at the other end thereby keeping the advance from going all the way out at idle?
Those RPM numbers will vary with the different weights out there. Have you actually observed this with your engine? Sometimes, you can bend the hooked ends of the springs to modify things somewhat. I use the 2 silver springs. My engine will idle at 750 in gear in low stall. There is a small amount of advance, but it is not a problem in my application.
There is some space at the end, even with the weights pulled all the way in. The pin doesn't touch that end of the slot, so no, putting a bushing on does not change how far the weights pull in, but even if it did, it would accomplish what you were looking to do anyway, which is shorten the mechanical advance.
Yes, they work just like crane says they will. With my GS113 cam I idle at 800 in gear and 850 in park. I also need to run 22* initial timing with that cam so I really don't want the mechanical advance coming in at 500 rpms but, I need the lighter springs to get my total in by 2000 or so. o No:
To elaborate on Larry's response, bottom line is it does not matter even if the bushing does keep the advance from returning "all the way." You just compensate for that with the initial, "twisting the distributor in the hole" initial setting. The only thing that matters is how far it moves at maximum travel.
I too have had issues with loose springs letting there be advance at idle. Bottom line is, it is usually not an issure, if you can not correct it. As long as the car will start, some mechanical advance at idle is not a problem. Getting the advence in in time is MUCH more important.
What I do when curving a new distributor is initially install it with NO springs at all. As long as the motor is warmed up, it should have no problem starting. Yes, it will idle high, but rpms are irrelevent at this point. Set it for maximum advance. Then you know that what ever you do for springs, weights, etc., this is the true mechanical total advance.
This is SO not true, as Larry stated. Both the shape of the oblong top plate that holds the inner ends of the springs, as well as the shape of the skinny arms on the weights effect the advance curve. In my experience, HEIs have way more variation in these areas than points distributors, and are that much more in need of true tuning to get right.
OK, so I got my total to 34* by welding up the slot and my initial is at 22* which I arrived at by advancing until it turned over hard then backed it off slightly. Seems happy here. The funny thing is that no matter what springs I put in it, the total is all in by 1400 rpms. The lightest springs have it in around 1200 and the heaviest by 1400. o No: I know I can run it like this but is it optimal for a street motor and should I still run my vacuum advance?