1966 Ignition and Cam Timing Issue - Pontiac GTO Forum
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post #1 of 15 (permalink) Old 04-21-2014, 09:07 AM Thread Starter
 
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1966 Ignition and Cam Timing Issue

I have a 66 with a tri-power set-up on a 389 that was rebuilt in 1990 and finally started for the first time last week (yes - a 24 year project). Cam is not factory (Cam Dynamics), installed by previous owner. It has 0.437 lift and duration of 224 at 0.050, so by my understanding, this is not too aggressive. Engine is bored 0.090 over. All else is largely factory.

Adjusted outer carb linkage to eliminate vacuum leakage. Finally got engine to idle at 750 rpm, but idle timing HAS to be in the range of 25 BTDC and seems to like 30 even better. Will not stay running at anything below 25 unless idle is cranked up. There is an inconsistent and somewhat deep knocking sound, which I suspect to be pre-ignition at idle. Engine revs and sound fine at higher revs. At idle, the engine runs consistently, but constantly shaking (not terribly bad, but certainly not smooth). Total timing is about 40-45 BTDC at 1800 rpm. Vaccum advance is disconnected and plugged for all of the above.

Could valve timing being off by a tooth? I hate to pull this nicely finished engine apart to check since I doubt it's wrong, but I don't know what else would cause such advanced ignition timing. Any idea's and other thoughts?

Side note - Interior is not installed, so car has not been driven on the road to see how it behaves. If it wasn't for the overly advanced timing and slightly rough idle, I wouldn't think anything was wrong at this point.

David
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post #2 of 15 (permalink) Old 04-21-2014, 05:14 PM
 
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Just to make sure that was not a typo .090 over on a 389?
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post #3 of 15 (permalink) Old 04-21-2014, 06:08 PM
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Ok. A rebuilt engine sitting for 24 years could likely have these issues: rock hard cam lube on the cam lobes (if lith grease was used, this is a certainty), surface rust in the bores, dried up gaskets, and weak valve springs. If coolant was installed in the engine, then a corroded timing cover, as well. Engines don't have spark knock generally at idle or in neutral without any load. Suspect a mechanical issue. I would: verify that the harmonic balancer has not slipped (bad rubber) giving you erroneous timing mark references; I would verify #1 cylinder static ignition timing, and go from there. I have heard of a couple of 389's going .090 over, but they were the thick walled '59-'62 castings. Generally speaking, if it's a '64-'66 block, .060 is the maximum overbore allowable before cylinder collapse failures start to occur. Keep us posted.
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post #4 of 15 (permalink) Old 04-22-2014, 06:50 AM Thread Starter
 
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Originally Posted by the65gto View Post
Just to make sure that was not a typo .090 over on a 389?
I will check my notes tonight on the bore. The work was done by the previous owner - I just measured it, wrote it down, and probably don't remember correctly at this point.
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post #5 of 15 (permalink) Old 04-22-2014, 07:07 AM Thread Starter
 
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Originally Posted by geeteeohguy View Post
Ok. A rebuilt engine sitting for 24 years could likely have these issues: rock hard cam lube on the cam lobes (if lith grease was used, this is a certainty), surface rust in the bores, dried up gaskets, and weak valve springs. If coolant was installed in the engine, then a corroded timing cover, as well. Engines don't have spark knock generally at idle or in neutral without any load. Suspect a mechanical issue. I would: verify that the harmonic balancer has not slipped (bad rubber) giving you erroneous timing mark references; I would verify #1 cylinder static ignition timing, and go from there. I have heard of a couple of 389's going .090 over, but they were the thick walled '59-'62 castings. Generally speaking, if it's a '64-'66 block, .060 is the maximum overbore allowable before cylinder collapse failures start to occur. Keep us posted.
Lithium grease was used. Cylinder walls were coated with something too - either engine oil or lith grease. Coolant was not added until now. Engine was stored in a dry garage most of those years. I peeked under valve covers before starting and saw no evidence of rust on anything. So hopefully, no lasting detrimental effects from this.

I will check to see if there is evidence the damper slipped or is loose. Is it possible to have spark knock at idle if the timing is too advanced (as it appears to be) or if valve timing is off?
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post #6 of 15 (permalink) Old 04-22-2014, 08:59 AM
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No. I've never seen it, and I've been tuning up/repairing cars for over 35 years now. You need to remove the intake manifold, and remove the valley pan to inspect the camshaft. My guess is that it is damaged from the solidified lithium grease left on the lobes and bearings. If lithium grease was used on the engine bearings, an entire teardown will be necessary to replace the bearings and to check the crankshaft, rods, etc. for damage. I have never seen white lithium grease NOT turn to cement after 10 years or so. 24 years is waaaaay too long to let a newly built engine sit and plan on bolting it in and running it.
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post #7 of 15 (permalink) Old 04-22-2014, 10:10 AM
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^Agreed 100%^. Honestly engine should have been at least partially disassembled to check everything over. Agree also on the Lithium grease. That stuff will set up hard and now all your oil passages on the lifters could be clogged. Hopefully you haven't damaged anything but at the minimum I would invest in new lifters and valvesprings just to be safe.

A "broken in" engine would be better to let sit for 20+ years than a freshly rebuilt one IMO. Good luck.
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post #8 of 15 (permalink) Old 04-23-2014, 07:19 AM Thread Starter
 
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OK - I gave some incorrect information and learned not to trust my memory too much as I get older. The engine is only bored 0.030 over per my notes. And I dug through the shelves and found the assembly lubes I used. The cam and parts got red-colored cam lube by TRW, and everything else got Lubriplate engine assembly grease. As far as I can tell, this is not a lithium grease as I thought. Does this reduce the concern of cam and lifter damage after long-term storage?

How can I tell if the vibration damper slipped? I looked at it, but I'm guessing it needs to be removed and carefully inspected...

Would the engine run if the valve timing was off by a tooth or two, and if so, could this explain the need for the too-far-advanced ignition timing and slightly rough idle?

I sincerely appreciate the input so far and the opportunity to learn some things.
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post #9 of 15 (permalink) Old 04-23-2014, 12:51 PM
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The Lubriplate is the stuff that sets up like cement. And yes, the engine will run with the timing off by a tooth or even more. You need to remove the engine, disassmemble it, and inspect it carefully. There are no good shortcuts here....it has simply sat about 15 years too long to be placed in service. As Alky said, if it had been a used engine, well broken in, the only issue you might have is dried out gaskets. With a fresh build, it shouldn't sit for more than a couple of years, maximum. The last newly rebuilt 389 I looked at that had sat after its overhaul for 20 years ended up needing cylinder sleeves and a total overhaul due to corrosion and solidified lubes. It was a sad sight.
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post #10 of 15 (permalink) Old 05-01-2014, 09:47 AM Thread Starter
 
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I just can't bring myself to remove and disassemble the engine yet without further diagnosis.
UPDATES:
Oil is clean as a pin.
Finally got drivers seat in and drove a little. Pings under light load (as expected given too-advanced timing).
Rebuilt distributor - it had significant end-play in shaft - 0.050.
Pulled spark plugs - all but one are very black, almost sooty.
Finally able to measure vacuum. It is bouncing between 15 and 5 at idle. Based on what I've read - this seems to indicate something mechanical in the valve train (wiped lobe, broken spring, bent valve, although I've read a couple cases where the carb caused this too).
I hope to check compression, and then pull the valve covers to check valve travel, and then the timing cover to check cam timing.
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