Need Advice! Do I Need a New Camshaft????

[YoungPup1977]

Originally Posted by garyd1961

I have thought of taking an old distributor and grinding the teeth off the gear. You could just drop it in and turn the rotor where you want it. You could also use it to prime the oil pump.
I just don't pull the distributor enough to make it worth my wild so I use a screwdriver.

years ago I had removed the teeth from the dizzy gear and used it for pre-oiling the oil pump, not sure where it went, I now use the tool to do the pre-oiling of the engine which I use quite a bit. not sure who made it but it works good.

[Atlfan65]

Well it took a while to have the time to put everything back together. The cam ended up being okay. The issue I'm now having now is with the vacuum advance. I set the timing at 8° initial, 32° total by 3000 rpm. Engine is idling great at 20 in vacuum @700 rpm.

When I connected the vacuum advance to set that side of things, it jumped to 32° at idle (adding 24° of vacuum). That's a lot more than I have ever run before. It is an adjustable vacuum can so I tried adjusting it with the allen key, but it's giving 24° at idle regardless of how I adjust it. I've only seen vacuum cans fail with a broken diaphragm giving no advance, never where adjusting it does nothing with it still giving full advance. Am I pulling so much vacuum on a stock engine that it's giving so much advance regardless of how the adjustable vacuum can is tuned? Or is the vacuum can a dud? I'll be picking up a new vacuum can one of these days after work. Until then I'm running it disconnected. I've seen a list of stock GM vacuum can part numbers and their amount of advance on this forum somewhere... Now to just find it again....

[geezer#99]

You can buy or make a limiter to control your vac advance amount.
Info in here.

http://www.crankshaftcoalition.com/w...EI_distributor

[Atlfan65]

I've heard of using JB Weld to limit the advance, but what about the fact that adjusting the vacuum advance with the allen key didn't affect the amount of advance? I don't want to limit the advance down to 10-15° vac advance if something is still wrong with the can. Someone please correct me if I'm wrong, but you are adjusting the amount of vacuum advance with the allen key right? Or is it always the same amount of advance and you are changing the vacuum signal required for the advance to kick in?

[weq92f]

Originally Posted by Atlfan65

I've heard of using JB Weld to limit the advance, but what about the fact that adjusting the vacuum advance with the allen key didn't affect the amount of advance? I don't want to limit the advance down to 10-15° vac advance if something is still wrong with the can. Someone please correct me if I'm wrong, but you are adjusting the amount of vacuum advance with the allen key right? Or is it always the same amount of advance and you are changing the vacuum signal required for the advance to kick in?

According to the article quoted above...you'd be adjusting the tip-in point of the can's full vacuum movement from about 4.5 to around 8 inches of vacuum with one turn and 8 turns respectively.

-klb

[Atlfan65]

And I didn't have enough vacuum line to run the vacuum gauge into the cab while driving to see my vacuum level at steady cruise, but in park it advanced the timing up to 60° total at some points while revving it to 4000 rpm. 32° total with vacuum at idle and 60° at some points is way too much right? I didn't hear pinging at idle but with header leaks it's hard to hear... I should be looking for about 50° total with vacuum under light cruise right? And how the hell could it add more vacuum advance while revving in park then it is at idle with a higher vacuum signal?

[Atlfan65]

Originally Posted by weq92f

According to the article quoted above...you'd be adjusting the tip-in point of the can's full vacuum movement from about 4.5 to around 8 inches of vacuum with one turn and 8 turns respectively.

-klb

What are you seeing in that article that mentions specific numbers? It talks vaguely about the concept of vacuum advance and mentions the limiter plates, but doesn't talk about what adjusting the vacuum advance can does. Point it out to me if not. I'm looking at section 15.5.

I'm confused what you mean "tip in point at 4.5 in - 8 in vacuum." My truck is running at 20 in vacuum at idle and while I didn't have long enough vacuum line to test cruising vacuum, I'm sure it's much higher than 8 in vacuum.

What I've read about tuning vacuum advance says to back out on the vacuum advance adjustment if pinging occurs. So what is this physically changing?

[geezer#99]

Your vac pot didn’t add more timing at 4000 rpm, your mechanical advance did.
On your vac pot which direction are you turning the adjustment screw to reduce the timing?

[Atlfan65]

It has 32° total timing, 8° initial 24° mechanical. At 60° total advance with vacuum, 60-32 total = 28° vacuum advance being added. At idle it was at 32° total with vacuum. 32° - 8° initial = 24° vacuum advance being added. So it is somehow adding 4° more vacuum advance while revving it in park at a lower vacuum signal.

And I'm seeing that everything says to fully seat it clockwise and back it out counter clockwise to reduce the timing at cruise. Mine was not having any effect though. Same exact timing whether it was fully seated or backed out 8 full turns.

[geezer#99]

I’m actually pretty good with the math!
Easy to add/subtract.
Do you want help or do you want to troll?

Prove your vac advance is adding 4 degrees or it’s from mechanical.
Plug off the vac pot and test again!

[Atlfan65]

Originally Posted by geezer#99

I’m actually pretty good with the math!
Easy to add/subtract.
Do you want help or do you want to troll?

Prove your vac advance is adding 4 degrees or it’s from mechanical.
Plug off the vac pot and test again!

Not trying to troll, just pointing it out. When I set the timing to start I revved it to 5500 rpm when checking full timing because I have heard of some HEIs adding a few degrees of advance at redline. It was solid at 32° all the way from 3000 rpm to 5500. I know hooking the vacuum advance up didn't magically add more mechanical advance but I can't "prove it" any other way.

[Atlfan65]

Should I just use JB Weld to limit it to 15° or so vacuum advance? Or with the adjustments not changing the 24° of vacuum advance at idle do I need a new vacuum can anyways?

[weq92f]

Originally Posted by Atlfan65

What are you seeing in that article that mentions specific numbers? It talks vaguely about the concept of vacuum advance and mentions the limiter plates, but doesn't talk about what adjusting the vacuum advance can does. Point it out to me if not. I'm looking at section 15.5.

I'm confused what you mean "tip in point at 4.5 in - 8 in vacuum." My truck is running at 20 in vacuum at idle and while I didn't have long enough vacuum line to test cruising vacuum, I'm sure it's much higher than 8 in vacuum.

What I've read about tuning vacuum advance says to back out on the vacuum advance adjustment if pinging occurs. So what is this physically changing?

Depends on what can you have exactly... the article was discussing "adjustable vacuum advance" cans. Here's the info-graphic from the link that I based my comment on...

...seems to indicate both tip-in and total vacuum advance is adjustable...

-klb

[Atlfan65]

Originally Posted by weq92f

Depends on what can you have exactly... the article was discussing "adjustable vacuum advance" cans. Here's the info-graphic from the link that I based my comment on...

...seems to indicate both tip-in and total vacuum advance is adjustable...

-klb

It looks like it more adjusts the amount of timing and it has a slight effect on the vacuum signal needed to add the vacuum advance. I'm guessing the slightly higher or lower spring tension adjusting it slightly.

[MySons68C20]

Do you have a Mityvac tool? You can apply vacuum while the engine is running and see at what vac point the timing moves and how much.
Just another way to see what the adjustments are actually doing.

[geezer#99]

When you’re checking timing curves try another timing light.
And mark your balancer to see if it’s moving at all when you do the higher rpm tests.

It’s possible your vac pot is sprung inside. I had one like that.

[Atlfan65]

Sounds like a new vacuum can is in order. Distributor work used to be the easiest thing in the world on my Ford with it up front, but on these Chevys is it easy enough to pop the vacuum can in with the dizzy in the truck or should I pull it to save myself the cursing trying to to pop the rod into place? I'm sure it can be done with it in the truck, just wondering if it's one of those "easy enough but pain in the ass" jobs where pulling the dizzy saves my sanity and an hour of trying to get the rod lined up.

[Atlfan65]

Everything is finally resolved. I threw in a new adjustable vacuum can and everything is running great. After tweaking with the timing, I've settled at 10° initial, 32° total by 3500 rpm (waiting on springs in the mail to get it down to 3000), with the vacuum can adding 13° of advance at idle to limit total cruising advance to no more than 45° total. It's funny how many "carb issues" a good timing refresh will fix! The stumble when giving it the beans is completely gone and it takes off like a rocket now with the 3.73. If you punch the gas from a stop this 65 C10 with a vortec 350 will lay 11's through 1st and 2nd gear and my gas mileage went from 10-13mpg. Next, new exhaust. Considering dual 2.5 inch with boom tubes right under the side steps to get into the bed. The adventure never ends....