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There is a limiter bushing on the advance rod that rots and falls off, causing too much advance (55+ degrees) at cruise. The bushing can be replaced, or an adjustable advance unit can be installed. These engines actually like 48-50 degrees under light throttle cruise for fuel economy, but tend to surge and buck with too much advance. It takes some tweaking to get it in the sweet spot.
 

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Thanks, Bear and Jeff. Bought a new timing light with all the trimmings, hope to have time Sunday to try to sort it out. Work, wife, band in the way for a few days....
 

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Come over and tune my junk!! 20* initial is ok with cam and exhaust? I lack the intelligence to use the final timing light.
 

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Well after searching for the data on the Mr. Gasket kit for my distributor and finding no/conflicting info here is what I found.
The gold/copper colored springs were all in at around 1,700 and change, the silver ones all in at 2,100 and change and the black were all in at 2,700 and change.
I went with the black and timing at 34 at 3K.
Idle at 750 and with the TH-400 it goes into gear smoothly and the idle drops to 700.
Runs great and no overheating like with the tropical fishes.
Pretty much stays at 195.
I think she is ready now for the Route 66 to Williams run I just need to put a couple hundred more miles on the break in oil and then change it before I go.
I can't wait to get it on the hwy and see what she does.
I think I have everything, Grand Funk, Bonetime by James Harman, Lee Michaels etc.
 

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This is an old thread, but my head is spinning after reading it. I was planning on doing a "tune up" on a 68 I picked up yesterday, but I think I have allot to learn to get it right.
 

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Help understanding Lars recommendation

Lars - "Yank it out, shim out the endplay with Moroso part number 26140 (setting shaft end play to .005 - .007” for cast iron units and .010 - .015” for aluminum housings), clean it up, and make sure the advance system is working right."

Following Lars statement that this is an issue for most of us - the recommended fix is ~$10 and some garage time. I ordered the Moroso shim kit, but would like to confirm my understanding of where these shims get installed. Based on Figure 6E-26 in the 68 service manual these look like they could go between the washer above the drive gear and the stationary housing tube.

Is the end-play I'm trying to limit between .005 - .007 accomplish a more consistent gap between the rotor and distributor cap?

So it seems the trick will be to assess how much initial end play there is to begin (dial indicator?) then install the correct shim(s) to leave .007" with a cold engine.

Thanks in advance for any help.
 

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To continue - have the distributor apart and worked out the end play question above. I also got the moroso spring and weight kit. Going to use the medium springs to get full 23 degree mechanical advance by 3000rpm with the stock weights. That kit came with a brass bushing the is supposed to be pressed onto a pin in the lower surface of the rotor mount. My stock distrib did not have this and it is not shown or discussed in the 68 service manual. Car ran fine below 5000rpm before this - so thinking this is a generic kit and this bushing is used on small block chevys or other applications.

Can someone please confirm the Pontiac distributor does NOT use this bushing. It looks like it would fit - but also would use up a bunch of the rotational travel/practical mechanical advance. My inclination is to not install - but this is the first time I've ever done this, and don't want experiment or do it twice to get it correct.
 

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Geez, I started looking at my out of engine distributer today and have .067 end play. Wow! I also noticed a chunk broke off the boss that gets clamped on. Previous owner had a bunch of silicone on it. Now I know why. It probably leaked. I had been thinking I might go with something electronic to put in my rebuild. I just might.
 

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Geez, I started looking at my out of engine distributer today and have .067 end play. Wow! I also noticed a chunk broke off the boss that gets clamped on. Previous owner had a bunch of silicone on it. Now I know why. It probably leaked. I had been thinking I might go with something electronic to put in my rebuild. I just might.
I had that much end play too. Now will be .018" PJ also pm'd me and provided this (link below) - I found very useful and after measuring my parts decided I will install the bushing and secure with an e-clip. Thanks PJ!

How to Optimize the Centrifugal Advance in Pontiacs - High Performance Pontiac - Hot Rod Network
 

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I figured I should tell the whole story. Some of you will get a kick out of it...

I recognized the need to recurve my distributor. In setting the timing I noticed the timing would advance about 8 degrees as I tightened the distributor down. I also noticed the vacuum advance wasn't working at all. So I went and bought the items listed in the OP.

I pulled the distributor, remembering that I needed to mark the position of the distributor before I yanked it out. I forgot I needed to mark the inner part until afterwards, but I had marked the position of the rotor by scratching a mark in the advance weight. Brilliant, right? Yeah, the rotor only installs one way, and I changed the weights...

Anyhow, After setting the end play and changing the advance, weights and springs, I reinstalled the points and reinstalled the distributor. Nothing. No worries, I figured I had it 180* out of phase, still nothing. Checked for spark using a screwdriver - nothing.

OK, out it came again, making sure the wires were connected properly (they were), then I found the points weren't actually closing. Oh, I should also tell you I had bought a point/condenser integral unit, and the condenser effectively blocks access to the points with a feeler guage. I had to 'eyeball' it.

I reinstalled the distributor, pulled the coil wire and stuck a screwdriver in it, holding the driver close to the block while teh wifey cranked it to check for spark. This time there was plenty. I told her to stop cranking and started moving away from the block, only to become the ground and getting about 10 jolts before she let off the key. Once the tingling wore off I had her bump it to TDC, looked at where the rotor pointed and reset the cap and wires.

I asked her to crank while I moved the distributor, which was working great until the distributor came up out of the block. I had forgotten the clamp that tightens it down, and now the dizzy needed to get indexed to the oil pump shaft too. Crap.

I had to crawl on back there to be able to see the shaft. I figured I was in for an hour of 'move it, try it again', but the damned thing dropped right in on the first try!! This time I set the clamp on first, found TDC, set the cap and wires, and it was running about 5 minutes later.

Moral of the story? Let someone who knows what they are doing at it next time. Any 'real' mechanic would have had it done in an hour. It took me a week...
 

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Bear, thank you for sharing your knowledge and experience! I have a 1967 GTO with the original YS code engine that has been rebuilt to HO specifications with the Melling SP7 "068" cam, Ram Air Exhaust Manifolds, original 67 intake, and a 1970 7040264 Quadrajet with a fresh kit and #73 jets. It has ICON forged pistons and forged steel rods. It is balanced. Heads are the 670. It has stock single point distributor with a new Vacuum Advance {V280}. I don't plan to race it, just like to do cruise ins, local car shows, and some cruising around our lovely part of upstate SC. My question is would setting my total timing at 34 degrees be enough to keep it running cool, and run OK on 93 Octane with ethanol? It has an aluminum radiator, shroud, 7 blade fan, and a severe duty fan clutch, 160 thermostat. It will run about 180 to 190 at 45 mph or so, but jumps up to 195-205 when slowing down or stopped.
Thank you for your time and help!
Richard
 

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Is your water pump plate that goes over the impellers clearances to .040 (most important)? Also shroud should be set centered over fan blades. I am running the same set up and even stuck in stop and go at Woodward Dreamcruise for 2 hrs never got hotter than 180.
 

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Is your water pump plate that goes over the impellers clearances to .040 (most important)? Also shroud should be set centered over fan blades. I am running the same set up and even stuck in stop and go at Woodward Dreamcruise for 2 hrs never got hotter than 180.
my engine builder set up the clearance on the plate to the impellers and said he got it as close as he could. Fan blades are approximately half way in the shroud. This is an 8 bolt water pump. I am thinking of getting a flowkooler pump and trying that. Thank you for your reply!
 
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