OK, here's the skinny... Rebuilt 68 396, .30 over, all stock parts. Heads rebuilt as well, new springs, valves, guides, etc. Stock Rochester 4MV, rebuilt (twice). Standard points distributor, not rebuilt. I can get this thing to run, although it's a hard start. Runs rough, hard to get an acurate timing light reading. I've re-installed the distributor three times now, finding TDC with a compression gauge and then bumping the crank around until the mark on the ballancer is at zero. I have purchased a Pertronix Ignitor to replace the points, but have not yet installed. Question(s)... Do I need to rebuild the distributor? Specifically, if there is a chance that the point cam is worn, will that have an impact on the Pertronix unit? Secondly, If I assume that the outer ring of my harmonic balancer (purchased used) has slipped, is there a more acurate way to find TDC, than the way I have described above? Can the improved spark from the Pertronix possibly make a big enough difference to solve the problem? What about the valves? I adjusted the lash with the engine still on the stand. Should they be re-adjusted, even though the engine has not run cumulatively for more than 20 minutes yet? I even disconnected the exhaust from the headers for a brief run just to assure myself that there is no restriction in the pipes. Apologies for the long post... just trying to get a feel for what thing(s) I need to check next. Any input here is greatly appreciated.
Patrick

Have you set the point gap with a dwell meter?? That will give you fluctuating timing if the point gap is way off. If there is excessive play in the distributor shaft, either side to side or up and down, that will make the timing vary. I am assuming you have stock hydraulic lifters. They should be checked/ final adjusted with the engine running. This is a messy procedure best done with an extra valve cover cut in half length wise and a set of oil diverters, but gets the most accurate setting.

The Pertronix unit does NOT depend on the 8 sided cam on your distributor. Installing the Pertronix unit makes the cam obsolete. Its still there but its not needed. In fact I think you get rid of that cam don't you? Someone else can verify that for you.


Finding TDC with the heads on ( to see if your balancer has slipped) will require modifying a spark plug such that it projects into the cylinder enough to touch the piston such that it will positively stop the piston. Remove all of the spark plugs, insert your modified spark plug into the #1 plug hole , turn the engine over BY HAND until the #1 piston contacts the tool , make a mark on the balancer at the zero reference on the timing tab , turn the engine IN THE REVERSE direction that you turned it the first time until the #1 piston again contacts the tool you installed in the #1 plug hole. Make another mark on the balancer adjacent to the zero reference on the timing tab. Exactly 1/2 of the distance between the two marks you now have on the balancer is TDC for the #1 piston. Hopefully that will coincide with your balancer reference line and it will be evident that no slippage has occurred.

With respect to the valves being adjusted , if you have hydraulic valves it might not be a bad idea to adjust them again with the engine running. Loosen each valve adjuster until the valve starts to clatter and them tighten the rocker nut 1/4 to 3/4 turn. That should silence the valve if its noisy AND you will find any valves that were too tight also. As Second chance SS said its messy but its a quick way to get valves set right.

Good Luck

I forgot to mention that a "modified spark plug" is nothing more than a spark plug with the guts removed and a bolt welded into the body. The end of the bolt should be ground smooth and round so that it doesn't nick the piston.