Re: HEI - one failure mode

[Terry M.]

I had a long post all written about determining top dead center (TDC), when a recent experience came to me - one of those light bulbs going on over my head.

You do have one of those infernal HEI systems, right. They are both good and bad. I'll bet you have encountered one of the bad.

Take the distributor cap off and try to turn the rotor a little each way by hand. This checks if the mechanical advance is operating. My guess is you will find it is not.

HEI creates big spark as cap and rotor age. This spark creates ozone, a highly corrosive gas. This corrodes (read rust) the centrifugal advance mechanism solid. It sometimes stops in the advanced mode - thus car runs better at what appears to be weird timing marks.

Cure: Take off the rotor so you can see centrifugal mechanism under the rotor. Take off weights and springs and soak the mechanism with WD-40 and a apply force with ball peen hammer. No jive. Be a little careful and keep working the mechanism back and forth. Look at what movement you are trying to get. Tap from the side - first one side then the other.

If you really want you can take the distributor out to do this, but it is not necessary, in fact it is easier with the distributor in the car as it is held securely there.. Just look at the mechanism to see which way it has to move and apply the taps that way.

Try it you will like it.

Want to prevent it happening again. A little silicone grease on the tip of the new rotor, which you will want to install along with the new distributor cap. Done deal.

Now you want to know how to adjust the timing by levering the distributor with a three foot screw driver? That is another post, but you really don't have to loosen the distributor hold down bolt to adjust the timing with this tool.

FINE PRINT NOTICE: if all this sounds like heresy to you, don't send flames - just ignore it.

Terry

[Duke W.]

Another HEI tip

The HEI uses plastic bushings on the advance weight pivots. These are usually overlooked and are probably severely worn on on all HEI distributors. Don't know if GM services them, but I just buy Borg-Warner replacements (part number DG 13, 2 per kit) at Pep Boys.

Duke

[Jim T.]

Re: HEI - one failure mode

Terry I learned many years ago with my 64 Vette that the centrifical advance can become stuck. Mine would be okay when the car was first started after overnight cooling. From that early experience I have always made the disassembly, cleaning, and lubricating with ole Blue Streak point block lubricant part of routine maint. This can happen to convential distributors as well.

[Terry M.]

Re: HEI - one failure mode

Guess I have not lived long enough to experience THAT failure mode on conventional distributor, but I can see it happening.

You don't want to hear about the centrifugal spring that broke and let the weight fly out and hit the distributor - rotating it out of time and stopping the engine dead in it's tracks. Happened intermittently. What it took to find that is more than you all want to hear. Happened on an old C1 straight six. Can't happen on "newer" conventional system with weights under rotor.

None of you want to hear how I learned about the HEI corrosion I posted above either. Sum it up: Some of us (read me) learn the hard way.

Terry

[Rob Brainard]

Re: HEI - one failure mode

Fellas, All of your suggestions are good things to watch out for in a dist, but they all would have the same effect in that they would not allow advance. Michael states the timing marks won't line up. Regardless of what the dist. is or is not doing the timing marks have to line up. The cycle of the engine could care less what the dist. is doing so long as it gets spark at the proper "time", thus timing marks lining up.

[Terry M.]

Re: HEI - one failure mode

Rob,

There are three components to ignition timing.

1) initial - as set by rotating distributor. 2) vacuum - as controlled by dashpot (when present) 3) centrifugal - controlled by weight & spring system

My suggestion was that the centrifugal advance stuck in the advanced position. That is what happened in my case. This alters timing, so mark does NOT line up with tab when engine runs best as set by "ear."

You are right - there is no centrifugal advance when it is stuck, and if the centrifugal stuck in the "at rest" position it would cause lack of performance, but no problem at idle. Initial timing (as set by rotation) can be adjusted to compensate for stuck centrifugal advance mechanism if it is stuck in advance position, but you wind up with exactly the symptoms described.

Easy to check with little labor and no cost of parts. Keep an open mind - could it be something else? Sure, but rule this one out before moving on to more complex theories.

Terry

[Rob Brainard]

Re: HEI - one failure mode

Terry, You are correct that if the mech. adv. stuck it would "alter" where the timing marks "now" lined up, assuming it stuck in an advanced position and not at the rest position. If someone checks the timing,unaware that the mech. adv. is stuck advanced, he would find that the intial timing is too far advanced, as you stated. To bring the intial timing back to specs, the dist. would be rotated to retard the timing, thus lining up the proper timing mark. A frozen mech. adv. is the same as moving the plug wires one spot on the dist cap and rotating the dist. to compensate for that.

[motorman]

Re: Another HEI tip

also make sure that the dimple on the dist gear lines up with the contact point on the rotor, you can install the gear 180 degrees off and make setting the timming a bear.

[Terry M.]

Re: HEI - one failure mode

Rob that is exactly the experience I had. I would be embarrassed to tell all of you this publicly how long I chased that gremlin. Finally buried my pride and went to a mechanic friend - a pro, 5 minutes to diagnose and 15 to fix and I was out the door. A lot wiser for the experience. We still laugh about it. And I got the free demonstration of the 3 foot distributor adjusting tool I referred to.

Maybe that is why I can not find a real distributor hold down bolt wrench anymore.

Terry