Asking this here instead of the C2 forum because I think you guys are a bit more versed in these sorts of things:

'67 427/390
The setup: new NGK plugs, new Taylor 8mm wires, new-ish Delco cap and Echlin rotor, new Echlin CS786 points, w/new Echlin condenser.
Distributor recently disassembled, checked shaft and bearing movement (none noted either horizontally or vertically), lubed, reassembled
Timing light: Innova 5568

When checking timing and revving to 3600 and higher, the balancer indicator begins fluctuating pretty significantly -- as in rapidly swings on and off the timing tab in both directions. At all rpms lower it's solid on the tab but every time rpms hit 3600 it begins the rapid swinging. This happened with the previous points, condenser, plugs, etc. and my old Sears dial-back light.

Is it possible the harmonic balancer exhibits looseness only at higher rpms?
Might the points need to be switched out for higher arm tension (CS7860 @ 32oz.)?
What steps can I do that will help isolate the cause?

Thanks!

 

I don’t think so. Maybe try a different timing light. Chain,the people who know will
chime in soon to help you. Good luck.

 

My old Craftsman dial light and a new Innova digital light show the same behavior.

 

Do you have a regular distributor or is it transistorized. If its regular try a normal timing light. Does the engine sputter and act crazy or is it just what you are seeing visually with the timing?

 

Standard factory original distributor.
By "normal" light, do you mean non-dial back? Not sure how I'd monitor the mark if the light can't be adjusted at the higher rpm.
If I remember correctly, the engine's tone seems to break up and higher revs don't seem to come easily. It's been a bit since I did the last timing so am not remembering exactly the characteristics.

 

OK, the first question I always ask in a situation like this is: Since you've owned it, did it ever run correctly? And, if so, what, if anything, did you do to the car before it started acting up? You have given us a fairly detailed description of the situation, so I don't think this is going to get us anywhere, but I like to get it out of the way before digging any deeper.

Scotty

 

I've owned it upwards of 42 years now but for quite a few years it hasn't been driven much; life and other priorities got in the way. This past summer I took it out and it bucked, stalled, didn't run well. Figured the carb was gummed up from sitting so long so cleaned and rebuilt it. Then I discovered substantial misfiring on 3 cylinders so changed out all of the stuff mentioned in my original message. In hindsight, I believe the misfires were caused by the old AC Delco plugs and their screw on terminals. It now idles well and runs fine but I haven't had it out on the road to any degree since the new parts, due to the 6-month rains that started a couple months ago. For the one test run I did, it had very strong pull and good response though I sensed the power was maxing out and falling apart at 4000 revs.

My thoughts keep returning to the points but I wanted to make sure it wasn't something a worn harmonic balancer could cause at higher revs.

 

Well, I have had 2 balancers fail on 2 different vehicles over the years. One on my 77 Corvette. in both cases. it did not ever cause a running issue. But rather they both let go rather suddenly. Causing a extreme rattle and loss of tension to the fan belts on the non corvette car. But continued to run but over heating due to lack of water pump drive.
My Vette just slipped. picked up a vibration. and when I went to check the timing the timing mark was way out.
Your issue sounds like something else. Bouncing weights in your distributor perhaps. Not certain. But really doubt it's the balancer.

 

I had a similar issue years ago after returning from a deployment. The distributor had sized and I now longer had any mechanical advance. Take the cap off and try to twist the rotor and see if it deflects and moves the weights out. IF not then thats the reason. Another issue could be the points are worn and you are getting the points to float. At that point they either need adjusting or replacing. Yes by normal llight I meant non dial back but I dont believe the light is the issue if you cant get the motor above 3600 rpm. Thats why I asked.

The third issue is that you are getting more advance after 3600 and you are going past the advance that the engine can run at. To check that you would have to disconnect the vacuum advance and see what your advance is without it. You shouldnt be getting more than 12 addistional degrees with your vacuum advance. You should look up Lars tuning papers and see what your total advance is using those.

basically you should get the car idling, use your timing light to note the timing at idle with the vacuum advance disconnected, then slowly rev the engine to 3000 rpm and see how much the timing climbs. It should stop at or below 36*...then again at idle add the vaccum advance and see how much more advance you get. Lars explains the limits and how to acheive all this in detail

 

So it is solid at 3500rpm? No movement?
Where is the Dwell set at? You may be getting point scatter at high RPM......
The balancer is not going to move all over the place at 3600 RPM even if it is bad.......to do that, it would have to spin one inch forward and back and if it did this a few times it would just come apart.
If you think the balancer is suspect....just replace it with a quality unit that has 0-60 timing marks on it......dial back lights are great and all....but I like to be able to see the sweep from say 15 to 36 degrees and back......

Jebby

 

if timing is jumping around itis not the balancer. if outer ring of balancer was dancing back and forth 30 degrees, it would make a hell of a racket and probably leave the car. it is either your spark timing going nuts or your timing light... not saying your balancer is correct. i can't tell that from here. it could be off by a lot. probably isnt.

 

Timing gear may have lost some of the plastic teeth. Timing chain could be flopping around at high RPM.

Rotate the crank back and forth while watching the distributor rotor to see how much slop is in the chain? Worth a look.

 

So a rare sunny January day in the PNW... I changed the points and condenser just in case one or both of the replacements was a dud. I went with the higher spring weight but it still "breaks up" between 3850 and 4000. I can see the irregularity in my Innova timing light flashes – the same thing happened with my old Craftsman light. I didn't try either light at zero° and just revving up the engine to 4000 to see if the sporadic flashes still occur, but I bet they do (thinking that maybe the lights' electronics get funky when dialed up to 36°). Up to that rpm the line is pretty darned steady with only a minor fluctuation of a degree or so here and there.

The dwell is set at 30 and it idles wonderfully at about 550 @12° w/vac advance connected – right at 0° if disconnected. When measuring highest advance, it appears to be right about 36° as its highest between 3600 and 3800 but put in a couple hundred more rpms and the mark begins swinging wildly. The setting as it is seems to be great with very strong pull and no pinging.
Perhaps this is a moot point and only academic because I rarely wind it up to 4000...

I've got a Mr. Gasket distributor spring kit coming on Tuesday so I'll do a little more playing with full advance coming in earlier.
One more question: the vac advance/points plate has a slight bit of sloppiness on the vacuum arm's post. Is this a problem? Attached a video of that and this afternoon's shake-down drive. I realize the drive video doesn't show much and I need to get a go-pro or something to mount my phone to instead of handholding. It really performed well, but I still wonder about the timing at high rpms. (I'll check the crank vs. distributor rotor movement later when I experiment with the springs.)

 

I just thought of something else. What if the bushing on the underside of the distributor shaft football is the wrong size? When I rebuilt the distributor, there was a small diameter nylon bushing that I put back. The Mr. Gasket kit comes with what looks to be a much larger brass bushing.

 

A reply to someone else on the NCRS forum by Joe Lucia:
That sounds exactly like what's happening and what stingr69 commented on. I guess a bit of back breaking work is ahead of me... and I get to do the coolant flush I've been putting off!

 

you have owned the car sice 1980 or so. i assume you never changed the cam or timing chain? you might be able to pull the fuel pump and snake a borescope up in there to see if there are nylon teeth on that upper gear. a cheapie from amazon or ebay would do the trick.

 

Yes - November 1979. The engine has never been out or apart in any major way - it's really a true survivor.
Might pulling the oil pan be easier and lend a better view? If I need to change out the chain set then it has to come off anyway, right? (I hesitate to disturb anything that doesn't absolutely require it.)

 

if you are ok with pulling the pan, get a balancer puller and a timing set. buy an install tool. not the parts store rental version.

 

Thank you derekderek for the replies.
Something like this? About $70 seems to be the going range for this type of puller/installer... seem reasonable?

It was recommended by Duke over on the NCRS forum to go with the Cloyes double roller C3024. Anything to add or suggest?

 

you can use the loaner puller from the parts store. if the thread is messed up, it is in their puller. (buy 3 3/8-24 bolts though.) the end of the installer bottoms out in your crank snout thread. you do not want a tool half a dozen teenagers may have gored the thread on in your crank snout. https://www.ebay.com/itm/19200567429...AAAOSwrIxeaWjj