73-87 Chevy _ GMC Trucks > Engine/Drivetrain
Vacuum Advance on HEI 350
kopeck:
--- Quote from: TexasRed on November 08, 2021, 12:23:51 PM ---OK, I would look/google "vacuum advance stop plate". I don't know how much this forum likes linking. You can use pretty much anyone's adjustable vacuum advance kit. The crane kit was nice because it had almost everything. You had to do a little machine work but it wasn't bad.
The parts you'll need:
Adjustable vacuum advance
a limiter plate you'll have to make
some screws (you'll need the drill and tap for these)
the springs from one of those kits for adjusting mechanical advance (the weights are junk)
timing light
There's a guy that used to post on other forums called ignitionman that has the setup that you need in terms of initial, how fast you want to see the mechanical and then the additional timing for the vacuum advance.
Clear as mud?
--- End quote ---
MSD makes a plate that has multiple options, it's $12 bucks so it seems like that might be were I start. See what I have for full in timing and then start backing it down.
K
kopeck:
--- Quote from: VileZambonie on November 08, 2021, 05:46:47 PM ---You are going down a rabbit hole. You could simply retard the timing if it is over-advanced. Figure out why it is pinging:
What plugs are you running and how do they look?
What is your initial timing and total timing?
Do you have a borescope? Can you get a look in the cylinder to see if you have excessive carbon buildup? You can buy a cheap borescope for your phone for like $10 bucks on eBay.
--- End quote ---
No doubt about it, there is some underlying issue.
I'm pretty sure I'm running NGK 7052 now, I was running some flavor of AC Delco before that. The plugs looked good when I replaced them, no oil fouling or anything like that. The only reason I replaced them as I needed to replace wires and I figured why not.
The timing is whatever's on the sticker, off the top of my head something like 20 BTDC @ 2000 RPM but don't quote me. I have checked it multiple times. That's with the canister unplugged, I can't exactly remember where it goes with the canister plugged in, mid 30s?
The valve guides must be pretty worn on this old girl as she gives a good-sized blue puff on cold startup. The engine undoubtedly needs to be freshened up but it also runs well, makes good oil pressure, and moves the truck around. I'm just trying to make it happy until I can pull it and see how worn it really is.
K
Mike81K10:
Should not be much wear on a 90K engine unless it has been abused.
TexasRed:
--- Quote from: kopeck on November 09, 2021, 07:21:47 AM ---
--- Quote from: TexasRed on November 08, 2021, 12:23:51 PM ---OK, I would look/google "vacuum advance stop plate". I don't know how much this forum likes linking. You can use pretty much anyone's adjustable vacuum advance kit. The crane kit was nice because it had almost everything. You had to do a little machine work but it wasn't bad.
The parts you'll need:
Adjustable vacuum advance
a limiter plate you'll have to make
some screws (you'll need the drill and tap for these)
the springs from one of those kits for adjusting mechanical advance (the weights are junk)
timing light
There's a guy that used to post on other forums called ignitionman that has the setup that you need in terms of initial, how fast you want to see the mechanical and then the additional timing for the vacuum advance.
Clear as mud?
--- End quote ---
MSD makes a plate that has multiple options, it's $12 bucks so it seems like that might be were I start. See what I have for full in timing and then start backing it down.
K
--- End quote ---
The reviews on amazon for the MSD leaves a little to be desired.
Well, I found an extra scroll plate from crane. You have to drill and tap the advance in front of the pin on the vacuum advance. NOT like what Crane describes. Each notch should be about 2 degrees.
https://static1.s123-cdn-static-a.com/uploads/278432/2000_593f642430b4c.jpg - not my picture, but it's kind of what it would look like.
I would think with the vacuum canister plugged in, you'd get around 20 extra degrees of advance.
kopeck:
--- Quote from: Mike81K10 on November 09, 2021, 10:13:27 PM ---Should not be much wear on a 90K engine unless it has been abused.
--- End quote ---
It hasn't been abused at all. It was bought new by my Grandfather and he used it as his chore truck around the farm and then I inherited it in 2000. I drive it but I've always been easy on it, I guess I wasn't "normal" in my younger years. :-)
It's one of the things I've struggled with. I suspect it's not all that worn but the heads need some attention and it leaks from all the usual spots. You don't know until you look but through the years I've learned that you shouldn't just tear down engines just for the fun of it.
K
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