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Worn Distributor Drive Gear

Engine

Vehicle Information: Model: 911S Targa; Year: 1977; Body Type: Targa; Total Mileage: 150,000;

I own a 1977 911S Targa, Its an occasional driver and I do participate in DE track days.The motor was rebuilt 2 years ago and has about 3000 miles on it. I kept the 2.7l motor with CSI. I did regrind the cams to the 964 profile and installed JE pistons, 9.5:1 CR, new piston barrels, SSI heat exchangers, MSD6al ignition. Beside the limited mods, the motor is balanced and all 77 2.7l upgrades have been complete (Race Ware head studs, oil feed tensioners, 911 turbo camshaft oil line restrictors, and all the chain sprockets and intermediate gear has been replace).Just lately I have noticed engine detonation (pinning) at 4000 RPM and up when the engine is warm. Checking the timing I was unable to get a steady reading, it would sometimes fluctuate 5-7 degrees. Upon closer inspection I noticed excessive play in the distributor rotor, not back and forth but in the rotation. I pulled the distributor and looked at the distributor drive gear on the crankshaft, it looks very worn. The distributor drive gear was replaced at the time of the rebuild, the distributor is new and I compared the new gears on the distributor and crank to the old ones, they look the same, minus the wear on the crank gear.Only one way to replace the distributor drive gear, split the case. Any ideas what may have caused such quick excessive wear would be very much appreciated.As long as I keep the pistons and bores matched, is it ok to remove the pistons from the bores, or should I leave them in?Any words of wisdom on a breaking down and rebuilding a fresh motor for this type of repair?Lastly, I have though about PMO carbs, I dont have much in the way of engine mods, however Id like your opinion if carbs would make any difference, I have had received many opinions supporting keeping CIS as well as going to carbs.

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