I rebuilt my 383 this winter and I have a very unusual timing issue that I really can not figure out. The initial/base timing reading is at 45 degrees, runs really well (no discernible knocking detected by me, several wrenches and 2 professional mechanics) and I can not seem to figure out why. Any attempt to lower the timing below a reading of 35 degrees and the engine dies. So either a) my reading is wrong or b) some unusual factors are making it so my engine wants ridiculous amounts of timing.

Some background....
My engine is a Class II Jasper 383 I dropped in 3-4 years ago (Jasper Link to PDF http://www.jasperengines.com/pdf/Cla...%20hp%2009.pdf ). This winter I took an a first for me which was a top-end rebuild consisting of cam (comp cams 12-433-8 profile custom ground to a 1.045" base circle), cyl heads (AFR 195) and an Edelbrock Air Gap intake. I also replaced rockers, lifters (hyd rollers) and pushrods. The carb is a 750 Speed Demon set to mfg specs. The dist is an MSD HEI set-up #8365 with no vac advance and the black 18deg bushing. The idle is about 1100-1200 rpms and I had 17 of vac. Plugs were gapped to 0.045"

The rebuild went pretty good other than some interference between the cam and connecting rod bolts which I rectified with the custom grind and then had ARP 383 clearanced bolts pressed in and the rods re-sized and re-balanced.

About a month ago, I got the engine back together had some friends come over to hold the fire extinguisher (just in case) and turned the key. To my joy she turned right over and sounded great. I took some basic drives and she drives great. Several of the local vette club wrenches were around and everyone agreed it sounded great and seemed to run great.

Here is the issue....When I started to get into actually tuning, etc the initial timing reading at idle was 50 degrees and any effort to lower it below 35 degrees causes the car to simply die.

Here are the theories, reasons, etc proposed by me, my local vette buddies and various other sources and my thoughts/ results on each:

• Theory #1 Dial Back Timing Lights is confused by HEI - Result: I checked with two other guns including a non-dial back inductive light as well as a 20 yr old Penske light. All 3 gave me the same reading
• Theory #2 Harmonic Balancer is bad and causing a mis-reading - Result: Nope. replaced the HB with a brand new one with pre-engraved timing marks and the reading is the exact same.
• Theory #3 My timing mark is not correct for TDC - Result: I verified my TDC mark on the compression stroke and has since been double checked by a professional mechanic
• Theory #4 I have a massive Vac leak - Result: I replaced 95% of my hoses last winter but still went through and visually inspected the hoses, etc but also tried the propane trick. I did not find anything.
• Theory #4 Distributor is "off a tooth" so re-install - This one did not make sense to me but I went through the install procedure again anyway. I found TDC, installed the dist lined up my post and rotated about an inch and half to add some advance in. Same result.....Car runs seemingly great but "reads" 50 deg
• Theory #6 Issue with vac advance - Result: My car does not have a vac advance on it so def not the issue.
• Theory #7 Springs in dist shot and cent advance coming in too early / wrong size bushing - Result: Installed the "blue" bushing from MSD (18 deg advance), replaced the springs with the two heavy silver springs and got the same result.
• Theory #8 - Cam degree off - Result: I verified the intake centerline with comp cams to the desired spec of 108 and I checked my measurements 3 times before completing my install. My cam came out to be 108.25
• Theory #9- Since Cam was custom ground maybe they ground in an alternate firing order - Result: Verified with Comp Cam the right cores and grind were correct
• Theory #10 - Plug wires in wrong order - Result: Triple checked that I have the plugs in the correct firing order. Also verified by professional mechanic.

The next things I am going to try are:
1) Test with a new distributor to see if, for some reason, the MSD HEI is sending a premature spark in addition to the main spark and causing the misread on the gun but still allowing it to run correctly.
2) Positive Pressure smoke test to make sure there is not some crazy leak I missed. (Maybe a leak in from the oil galley?)
3) Install new plugs and fresh gas (I know not likely the cause but I am out of ideas)

I am ridiculously stumped and everyone of my usual trusted advisors / wrenches is stumped as well.

Any help would be greatly appreciated.
Thanks
Shane

 

If no detonation, why worry about it. Drive it. I have yet to use a timing light on the '65. Find where it best performs and tighten it down.

 

You know I have had that same thought a few times as well. If there were at least a good explanation for it, I think I could do that. But I have met 2 guys with very similar combos and even plagiarized this from a magazine build and everyone agrees the timing should be in a normal range.

 

I agree that some things need to be understood like the time I heard a "chirpping" sound on the '65 on the front end of a 8,000 mile trip. After pulling a valve cover at a convience store only to have the "chirpping" go silent and continuing on, I realized when I got home that the chirpping was the roller lifter case touching the cam lobe since the needle bearings(roller hydralic) had disappeared. I to this day have no clue what keep this engine ( BBC '71 LS6 ) from disintigrating. The cam lobe and # 3 intake lifter were unbelievable.

 

I am really just starting to think (i.e. hope) it is a mis-reading on the timing light caused by the HEI distributor. I know this is a long shot but it makes more sense than some crazy factor causing the engine to need / want 50 initial and 68 total.

Going to try swapping dists today and see what happens.

 

There were a couple of timing mark on balancer/timing tab on front cover combinations used over the years. Is it possible that you have one style of balancer with the opposite style timing tab?

IIRC, the "old" style timing tab was visible from the left side of the engine, whereas the "later" tab was observed by looking down behind the water pump. I think the difference between these locations is about 35-40 degrees.....

 

quite the mystery you have....i would recheck tdc again and replace the distributor...how much total advance are you seeing?(ie at appx. 3500rpm)...good luck hope you solve it

 

So just got bac form the shop a little while ago and we tried a different distributor and WHAMMO everything worked perfectly. The mechanic and I had tried re-installing the old dist twice with the same weird timing and then we put in the other unit and timing was right on where it should be.

Since the MSD is a magnetic / electric unit, we are surmising that the dist was sending some sort premature signal / current and setting off the timing light causing a poor reading even though the car ran fine.

New dist is on it's way!!!

Anyone ever hear of anything like this before?

I am thinking of calling MSD as well to see if they have an explanation.

 

Just read this write-up and have to go to work, but here's my first impression. The nipples on the distributor cap are set 45 degrees apart (360/8=45). If the engine runs best at a static advance of 45 degrees, in theory, the rotor is actually arcing (firing) the preceding nipple to where your number one plug wire is located. Since your timing light take-off is triggered by the current flow in the #1 spark plug wire, the only way this could happen is the rotor phasing inside the cap is off AND carbon tracking inside the cap is bleeding the electrical discharge from the incorrect nipple contact to the correct one.

I'll ruminate 'bout the problem more later on, but I would definitely check for carbon tracking and rotor phasing before proceeding any further.

Good Luck!

 

Got back last night after work, read through the entire thread, and found out I was a "day late & a dollar short" as you had already resolved the problem.

I've seen this type of problem before when restoring C2/C3 Vettes with worn bushings in the original cast iron distributor. The worn bushings allow an elliptical motion for the distributor shaft resulting in the rotor tip contacting the distributor cover and retarding the rotor tip. Eventually the tip is moved further and further back to the point some incredible amount of static advance is required just to get the engine to idle.

I'll have to admit that 50 degrees advance holds the record in this category; however, I admire your persistence in tracking the problem down. (BTW, Chevy used to recommend a total of 42 degrees of advance on our L-88's back in my youth when we raced. We had to manufacture our own narrow tipped rotors by filling them down until no misfires occurred.)

Good Luck with your engine and new distributor. (IMHO MSD should swap out a new distributor for your old one.)

 

Thanks for taking the time on this. Even though we found a solution, I always like to understand the "why" on these things and this is the best explanation I have heard.