Timing advancing - Not Returning
 

On my 418W, with MSD dizzyand 6al box, if you bring up the rpm to get full advance all goes well!! The problem is that it stays at full advance when you let the rpm return to idle. If you shut off the engine the timing then starts at where it should be and the cycle starts all over again.
A friend put the MSD in a distributor machine and everything works fine, timing advances and retards as it should, but put it back in the engine and the symptoms described above take place all over again.
The distributor gear is fine on the cam and the dizzy.
Any ideas because I am stumped??

Bad Box?
Distributor?

Which springs do you have on the advance weights? If they are the very light silver ones (weakest, that allow the quickest advance rate) and if the nylon pads under the advance weights are worn there may be some resistance or drag preventing them from returning to baseline. You may also need a small amount of lube in and around the advance weights.

I am currently using one silver and one blue spring!! I am going to change to the heavy springs and lube it up and see what results!! Thanks for the input!!

It should work with the light springs, it will advance faster IE at lower RPM. Changing springs to one stiffer will slow down your rate of advance.

Terry, If you continue to have strange timing readings, try using a self powered light, or a seperate battery.
Usually see strange readings with advance type lights.
Jerry

Check the height of the dist gear
 

also take apart the distributor and clean and lube the shaft. I encountere the same problem with mine and that is what MSD told me to do. Go to the website to check proper gear height.

Ditto what Morgan said. Check the bottom of the distributor gear for wear as it may be out of spec on the gear height and rubbing.

I just spoke with MSD tech Joe and he walked me through a repair process!
He said that the distributor machine will not simulate real "in the engine" performance because the gears are cut to pull the distributor shaft down and the dist machine will not do this. He said that it sounds like I have something binding and to remove the bottom collar and slide the shaft up to see what is going on and to check the nylon bushings and make sure everything is free to spin! I will update when I have some results!
Thanks again for your suggestions as it sounds like you were right on the money!!

Terry:

I offered this on a previous thread, in response to a similar problem experienced by another member:


"I have had similar experience to Rick Lake with MSD service. I replaced a Mallory Unilite distributor with the MSD billet unit. Less than a year after installation, I began to experience all sorts of difficult/backfire-through-the-carb-during-starting problems. After tearing down the carbs and cursing Holley and all his offspring numerous times, I discovered that the real problem was that the advance weights on the distributor had rusted and stuck in the full advance position. I talked with MSD and they explained that they had briefly tried a "new and improved" anti-corrosion treatment which, apparently, didn't anti-corrode. I returned the unit to MSD and they essentially replaced all of the guts for free (minus shipping, of course). No more problem since then. They seem to really stand behind their products."


Some of MSD's distributors had the internals coated with an anti-corrosive which, apparently, didn't wear well. The centrifugal force generated at the higher RPM was enough to move the advance weights out, but the friction caused by the corrosion was also enough to prevent them from retracting as the RPM dropped.

As Mr Parker points out, the springs affect how quickly the advance comes in, while the nylon bushings determine how much advance is allowed.

Joe LaPille (sp?) was the technician I dealt with; I assume this is the same Joe you with which you dealt. He was very helpful and MSD took care of the problem with no difficulties whatsoever. They seem to understand the concept of "customer service."

This was a problem also with the old GM distributors that the MSD advance system is patterned off. The weights or the shafts would bind up--solution was to take it apart clean shafts and all weights, pivot pins lube, etc

Another area to check is on engines that the dist goes thru the manifold, if the block has been decked or heads milled the distributor gear is loaded against a boss in the block causing the upper end to be jammed!! Also a oil pump drive shaft that is too long can do the same. An assortment of aftermarket parts exposes to a tolerance stackup that gives results out of the norm, but none of us use any aftermarket parts in these cars, correct???

Jerry

An Afterthought: Some of the HD aftemarket drive shafts have different length hex reliefs machined on either end, the broached recepticals on the oil pump and the distributor shaft are different depths and if the drive shaft is installed upside down it will jamb the distributor shaft upwards causing it to bind as it is tightened down.

Problem is fixed!! Did as you gentleman suggested and took the distributor apart and lubed everything that looked like it needed it and now it advances and retards with engine rpm!!
Thanks again!!