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1991 964 C2 Valve Seals and Guides

Engine

Vehicle Information: Model: 964 C2; Year: 91; Body Type: Cabriolet; Total Mileage: 25,600;

I purchased this car in 2002 from the second owner with ~23k miles. The car was in showroom condition and had seen limited use for the last several years. The previous owner had oil changes completed by a local shop that had also replaced the dual mass flywheel and completed a complete valve job with new valves and guides. The valve job was completed when the car had ~ 22k miles costing around 6k and was recomended after there was a short period of oil smoking after the car was started. After I purchased the car I returned to this mechanic for an oil change in 2003 and no other service was recomended the next season in June I was driving and noiced a hard knock and had the car towed back to the same shop that did the valve work and after the engine was removed the mechanic reported there was a broken intake valve, which damged both the cylinder and head. There was also evidence that other valves were starting to hit the top of the pistons. The explanation was that the factory oil seals were prone to be tight and had restricted the oil flow and although there had been only ~3,600 miles they felt their work didn't cause the problem. Their explanation was it was one of those 964 engine issues.With limited experiance his explanation didn't convince me to spend the estimated $8k at this shop without any participation in the repair. I made the decision to research an alternate shop where they observed that both intake and exhaust valves were stuck in almost all of the guides. This shop send the heads out to Ollies in Santa Ana where the valves did have to be pounded out of the guides prior to preping the heads. Their note was the 9.00mm pin guage didn't fit the guides. My question is. 1. How normal is a valve job in a 964 with low miles? 2. Have you heard of similar engine failures with if the guides were too tight? 3. Is the original shop likely to be making more out of the tight fitting valve seals than warranted?4. Any guidance on sorting this out, I was surprised by the problem given the condition of this low mile 964? Thanks in Advance

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