During engine****embly I used a dial indicator to determine TDC on # 1 cylinder and am told I could be as much as 5° degrees off and perhaps this explains why I'm having difficulty getting engine (276 with L-100, four barrel and Mallory electronic ignition set up by Bubba's) to run smoothly. By moving 1 tooth over from where rotor should be the engine runs smoother but not as smooth as it should; moving rotor 2 teeth over engine goes back to running really ragged. I now have an adjustable digital timing light but if I'm unable to establish true TDC on my pulley will the timing light be of value in getting this engine to run smoother.
Since you used a dial indicator to determine true top dead center I doubt your timing would be off by five degrees but to get the proper timing for your motor heres what I do. First put cylinder number one on top dead center next set the rotor so that it lines up with plug wire in the cap foir cylinder number one. Next put a vacuum gauge in a port below the carbs throttle plates. Now start the motor using the vacuum gauge advance the distributor while watching the vacuum gauge your looking for the highest reading you can get before it begins falling off. This will get you close to where the motor will be happy. Your timing should be at least 12 degrees initial to get a good running motor Since your using an L-100 cam your not going to have a smooth running engine there's going to be some loping to the idol that's caused by the cam timing. Its also important to be sure the carb mixture screws are adjusted correctly if they are not that will add to the rough idol problem. All the above has worked for me during the initial tuning of many motors your experience should be similar as long as there's no other internal issues causing further troubles. Good luck.
Ronnie, thanks for replying. Will try as you suggest, but with rotor lined up with #1 plug wire in cap it runs very bad even after rotating distributor to smooth things out. I know how smooth it can run because when it was on the test stand it performed perfectly, when I installed engine in the car everything went south. In the interim between test stand and installing the engine in the car I removed the distributor and ever since engine will not idle smoothly. However, will try agin as you suggest. Am told I should see about 13" on vacuum gauge with this cam, am about 11" now.
I used a dial indicator to locate TDC the first time I rebuilt a flathead, imagining it would give me a perfect result... almost by accident I noticed that my TDC was nearly 3 degrees wide. This is why on engines with offsets and long rods like flthead and SBC you use the interference method or the equivalent dial indicator bracketing method (use it to locate an inch down on each side of TDC) that was popular in the fifties. That being said, while having a slightly sloppy result is annoying, it probably is not going to put you very seriously off base or to matter much once you start to experiment. Just try it a couple degrees up and down from your mark to see what's happiest. And you can still pin down TDC better without removing a head by a modified interference method. I don't think this is your problem, anyway, something else is going on. The slight improvement with moving over a tooth could be minor or big pointer...you could have a significant problem in****embly, or it could be a simple phasing problem...meaning a bad match of rotor position to contacts in cap aggravated by advance. I haven't had enough coffee yet to think it through, but start by drawing a line on distributor directly in line with center of #1 terminal. See how closely rotor points to it, see if alignment gets worse with advance. Mallory has been built by Bubba, so we don't need to discuss the 500 things wrong with many out of the box Mallorys!
Bruce, thanks for the help. When I initially installed the distributor I had the rotor pointing to #1 cylinder and not #1 plug wire in the cap and it ran great but am unable to duplicate that now; I do have the rotor aimed at the #1 cylinder now or 1 tooth over from where #1 plug wire would be. Am now getting about 12" of vacuum at 900 RPM idle. Carb. is adjusted per Edelbrock. Plugs are clean and compression ranges from 125-142lbs. Cam broke in at 1700RPM on test stand when it was running good. Am now getting a "snapping" sound out of exhaust but could be because have muffler on one side and no muffler on the other side, idle is improved but still not quite right. Unable to get a clear shot with timing light due to poor location of timing pointer; looked good on test stand but doesn't work in car, will have to relocate later. Will go for test spin at sunset when cooler.
If its a stock motor sure but anything with modifications needs more than that. At least thats what I find works better from my experience.
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