ronw
Well-Known Member
Can anyone tell me anything about this distributor? Started engine with it and adjusted timing @ idle with a 508 cam about 1,000 rpm. Check timing @ 2,000 rpm, still the same, no advance. Should there be an advance? Ron
P4120701 Small Block Mech Tach drive
- Thread starter ronw
- Start date
-
You may want to talk to Ray @halifaxhops
Yout mechanical is frozen up it needs a rebuild, be carefull taking the drive gear out. And for some reason have seen the cam plate welded to the weights also no idea why? Remote pickup?
Last edited:
73 dart custom
Well-Known Member
Saw the post and immediately started looking to see if Halifaxhops name came up. He is the king of distributors!
You have that "sharp" reluctor in it also?
ronw
Well-Known Member
Dist produces a good spark, Checked air gap, Set @ 008. and have timing set @ 12Deg.
Oh no doubt good distributors. Like I stated there is just mechanical advance in it and either it is gummed up or some one welded the weights to use a external trigger on it, why no idea I would have used another lower cost distrib to do it. Can you turn the rotor a bit while it is in the car to see if the advance moving at all? Also have a pick of it from the top down by chance?
It's just going to full advance when it's running, needs stiffer springs I have 2 of them at the moment I had 5 last year, it's a great distributor. With the cap off can you turn the rotor a little if so it's not frozen. I set the balancer at 5* BTC them line up the pickup with the reluctor point and lock it down, that is your starting point now check your max advance and see what you have.
I am thinking it is frozen or welded. I am looking for one for my 440 they just have great characteristics.
I might have one for a 440, I had 3 a couple years ago. I put one in my buddy's 500 cu in motor and I know I sold one maybe both I have to look, That's the only dist I been running in my 340's for years. They have that bearing in the top and never get sloppy.
You will need more than 'about' 1000 rpm with those distributors. They can appear to be 'all in' at very low rpm.
Without that, or even with that, check the springs - in particular the primary spring. Someone may have set it up for to locked, or someone could have put even a faster advancing primary spring in. According to the Direct Connection bulletin, they should hit the secondary spring around 600 rpm. On mine, it appears to nearly stop advancing between 1200 and 1700 rpm. From there on up it is flat.
The idea is to set them up for best timing at working rpm. You can use 2500 or 3000 rpm, or even less depending on the spring since its pertty much a flat line you can count on. A long quick curve assures easy starts even when hot. If its 36 degrees at 3000 rpm, then is around 10 degrees at starting rpms. Those were the priorities for back then, and the focus was drag racing. If you want a stable timing at idle, more tension or a different primary spring will be needed. Leave the big one along - thats part of the secret so the engine doesn't see the lag in electronics at high rpm (talking 5000 rpm up here, not street rpms).
(I know they talk about the 'mechanical lag' but a good portion of it is the time it takes for each electronic component to switch and send a signal. Nothing to notice even at 3000 rpm, but at 6000 rpm that time can add up to 2 or 3 degrees. Some electronics are faster so its less noticible, and a few electronic boxes are designed to compensate.)
Without that, or even with that, check the springs - in particular the primary spring. Someone may have set it up for to locked, or someone could have put even a faster advancing primary spring in. According to the Direct Connection bulletin, they should hit the secondary spring around 600 rpm. On mine, it appears to nearly stop advancing between 1200 and 1700 rpm. From there on up it is flat.
The idea is to set them up for best timing at working rpm. You can use 2500 or 3000 rpm, or even less depending on the spring since its pertty much a flat line you can count on. A long quick curve assures easy starts even when hot. If its 36 degrees at 3000 rpm, then is around 10 degrees at starting rpms. Those were the priorities for back then, and the focus was drag racing. If you want a stable timing at idle, more tension or a different primary spring will be needed. Leave the big one along - thats part of the secret so the engine doesn't see the lag in electronics at high rpm (talking 5000 rpm up here, not street rpms).
(I know they talk about the 'mechanical lag' but a good portion of it is the time it takes for each electronic component to switch and send a signal. Nothing to notice even at 3000 rpm, but at 6000 rpm that time can add up to 2 or 3 degrees. Some electronics are faster so its less noticible, and a few electronic boxes are designed to compensate.)
Last edited:
They are basically all in at idle....makes that big cam idle a lot better...I got 4 or 5 of them....they are in all 3 bracket races and one street duster...plus a spare...lol
Make the vac a lot better also and no broken noses of a mini starter. Running a Mallory all mech now.
ronw
Well-Known Member
I took the dist. out and the advance is free. do you still have the springs I need? thanks Ron
Do you mean the weights are flopping around? or the mechanisim is free to move?
What are you trying to do with different springs?
ronw
Well-Known Member
The mechanism is moves freely and has springs and from what I have read it needs stronger springs so it is not full advance at idle. What those springs are I do not know. Can you help and do you have the springs I need? Thanks Ron
Not recommended. Those springs are too short or too weak. The short ones will work for a while but will be overextended and lose tension sooner or later.
Try a primary spring from a Chrysler distributor - Halifaxhops is probably your best bet unless you have buddies with a stash of distributors or a local speed shop with a machine.
In a Chrysler and similar distributors, one spring controls the initial advance while the second spring engages only when the the advance has moved out several degrees. (see photo, secondary spring has a long loop)
You can also delay the initial advance by increasing the spring tension on the first spring. Bend the spring perch further out. Doing this the rate of the advance will not change, only the start. If this is drag race only, that's prob going to be fine. (in the photo, the primary spring perch is bent in to reduce initial tension)
In either case, with this distributor, you will still have to set timing at 2000 or 3000 rpm. Then see where the timing at 800-1000 rpm falls. The secondary spring's engagement point can be adjusted as needed. Having someone like Halifaxhops set it up using a distributor machine will save a lot of time and learning curve.
Try a primary spring from a Chrysler distributor - Halifaxhops is probably your best bet unless you have buddies with a stash of distributors or a local speed shop with a machine.
In a Chrysler and similar distributors, one spring controls the initial advance while the second spring engages only when the the advance has moved out several degrees. (see photo, secondary spring has a long loop)
You can also delay the initial advance by increasing the spring tension on the first spring. Bend the spring perch further out. Doing this the rate of the advance will not change, only the start. If this is drag race only, that's prob going to be fine. (in the photo, the primary spring perch is bent in to reduce initial tension)
In either case, with this distributor, you will still have to set timing at 2000 or 3000 rpm. Then see where the timing at 800-1000 rpm falls. The secondary spring's engagement point can be adjusted as needed. Having someone like Halifaxhops set it up using a distributor machine will save a lot of time and learning curve.
See if this helps. This a the advance curve of a SB tach drive distributor I ran on a machine. The blue line is from the mopar book pictured earlier in the thread.
Timing is in distributor degrees and rpm.
Marked up on the graph is a circle and timing in crank degrees and rpm. The circle represents the timing on an engine when the distributor is set to 35* at 2000 rpm.
Timing is in distributor degrees and rpm.
Marked up on the graph is a circle and timing in crank degrees and rpm. The circle represents the timing on an engine when the distributor is set to 35* at 2000 rpm.
Here's what adjusting the spring perches can do.
First drawing shows that more tension on the primary spring holds the weight from moving until a higher rpm. In this example, 500 to 800 rpm. That would get 31* at 1000, and 35* just over 2000 rpm.
Now imagine if it was delayed even more, say to 1000 rpm. Then the timing at 2500 rpm would still be set at 35*, but when at 1000 rpm, timing will be 13*. That's OK for with stock cam, but really not enough with a longer duration, higher overlap cam.
Instead, what might might work better is only increase the primary spring tension a little. Also move the secondary perch out. This will get the secondary spring engaged earlier. Result would look something like this.
Here the timing at 1000 rpm is around 27* and it will still be at 35* by 4000 rpm.
Under 1000 rpm will be a little unstable. With a 4 speed, no big deal - with an automatic, it can be a little annoying for some people. That's because it will lose rpm going unto gear at say 900 rpm, and lose timing at the same time. This will causew it to lose even more rpm.
First drawing shows that more tension on the primary spring holds the weight from moving until a higher rpm. In this example, 500 to 800 rpm. That would get 31* at 1000, and 35* just over 2000 rpm.
Now imagine if it was delayed even more, say to 1000 rpm. Then the timing at 2500 rpm would still be set at 35*, but when at 1000 rpm, timing will be 13*. That's OK for with stock cam, but really not enough with a longer duration, higher overlap cam.
Instead, what might might work better is only increase the primary spring tension a little. Also move the secondary perch out. This will get the secondary spring engaged earlier. Result would look something like this.
Here the timing at 1000 rpm is around 27* and it will still be at 35* by 4000 rpm.
Under 1000 rpm will be a little unstable. With a 4 speed, no big deal - with an automatic, it can be a little annoying for some people. That's because it will lose rpm going unto gear at say 900 rpm, and lose timing at the same time. This will causew it to lose even more rpm.
Last edited:
-
