1969 427/390 timing question
Thread Starter
Heel & Toe
Joined: Jun 2013
Posts: 16
Likes: 0
1969 427/390 timing question
Hi all, I have a head scratcher I'm hoping someone has seen before and can help with. I have a newly acquired 1969 427/390 4-speed that hadn't run for 15 years. I've done the basics to get her running (carb rebuild, plugs, fluids, etc) and she's a beast, but runs a little rough. So I go to do an in depth tune-up and start with timing. The timing mark is about 2-3" from even the edge of the timing tab, basically no where even close. And yes, the gun is attached to #1 cylinder. (driver side, front cylinder). Adjusting the distributor doesn't get the timing mark close to the timing tab before it bogs out. My guess is someone was messing with the car before i got it, pulled the distributor shaft, and was one gear tooth off when they reinstalled the dist. shaft. Does that make sense to anyone out there? Is it possible to install the dist. shaft one gear tooth off, adjust the timing "by ear" so to speak, and still have the engine run relatively smooth? Would you then expect to see the timing mark a couple inches from the timing tab? Any thoughts wold be helpful before I attempt to pull dist. shaft and reinstall properly. Thanks all!
Drifting
Joined: Oct 2008
Posts: 1,369
Likes: 12
From: wichita kansas
stabbing the distributor "one tooth off" won't affect the timing or the reading you are getting with the timing light. your problem is somewhere else. i just timed my '68 427/390 last night...i set it at about 5B.which on my tab is at just above the 3rd pointer..but only maybe a 1/2" or less above zero. are you disconnecting the vac advance line and plugging it while you are timing it? if it runs a little "rough" at idle, it could be another vacuum prob or idle mixture issue..if it runs rough at all rpms, perhaps you have plug wire crossed? Rick
Thread Starter
Heel & Toe
Joined: Jun 2013
Posts: 16
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Thanks guys. Both very good points. First, no i didn't check the weights so I will do that. Second, I know i detached the vacuum line, but not sure if I plugged it. BTW, Should I plug the vacuum line or the vacuum nipple on the carb? or both? The wires are definitely not crossed because it runs pretty damn strong when just timed "by ear". I can just tell its not fine tuned. So if the vacuum line wasn't plugged, would it really cause the timing mark to be off by 2-3" from the timing tab? If i had to guess, I'd say it is 30-50 degrees off right now. But I will definitely look into all your suggestions. Thanks again!
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Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
Yes, harmonic balancer is not really a balancer; it is a damper. I had mine rebuilt by the Damper Doc. He replaced the elastomer and degreed the damper. I'm kind of a stickler for original parts...
Drifting
Joined: Oct 2008
Posts: 1,369
Likes: 12
From: wichita kansas
yes, you could be off several degrees if the vac line wasn't plugged properly...unplug it at the vacuum advance and then put something in rubber vac hose to plug the vac coming from carb(i usually stick an old fuse in the line) the vacuum advance port can remain unplugged...then check timing again. Rick
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
Thread Starter
Heel & Toe
Joined: Jun 2013
Posts: 16
Likes: 0
Hi Jeff, Thanks for the link to that other thread, definitely sounds familair 
. I noticed in the last picture of that thread it shows the two dampers side by side. Very clear difference in spacing between the notch in the center hub and the timing mark. Do you think I could use that photo to see if mine has slipped. Basically, on the new damper the notch in the hub is almost in line with the timing mark. If i look at mine and see the notch and timing mark substantially miss alligned, could I say "yup thats the problem". Furthermore, can i use the position of the "notch" to create a new temporary timing mark, just so I can time it and get it in the ball park. Or is there another way to time using vac pressure gauge. Any tricks or tips are helpful. Thanks
. I noticed in the last picture of that thread it shows the two dampers side by side. Very clear difference in spacing between the notch in the center hub and the timing mark. Do you think I could use that photo to see if mine has slipped. Basically, on the new damper the notch in the hub is almost in line with the timing mark. If i look at mine and see the notch and timing mark substantially miss alligned, could I say "yup thats the problem". Furthermore, can i use the position of the "notch" to create a new temporary timing mark, just so I can time it and get it in the ball park. Or is there another way to time using vac pressure gauge. Any tricks or tips are helpful. Thanks
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
Yes, I believe the keyway and tdc damper mark should be nearly in alignment.
The 7" damper is correct for the L36.
http://www.damperdoctor.com/
The 7" damper is correct for the L36.
http://www.damperdoctor.com/
Thread Starter
Heel & Toe
Joined: Jun 2013
Posts: 16
Likes: 0
Thanks again for your help and insight. Funny thing is, I'm down talking to my local mechanic today, saying " I think i figured why i can't time the vette". His buddy, who is also a mechanic, says, " yeah your harmonic balancer slipped right?" I accused him of hacking my computer and spying on my corvette forum thread
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
Thanks again for your help and insight. Funny thing is, I'm down talking to my local mechanic today, saying " I think i figured why i can't time the vette". His buddy, who is also a mechanic, says, " yeah your harmonic balancer slipped right?" I accused him of hacking my computer and spying on my corvette forum thread
