When I bought my NSX it had 88,000 miles on it. The clutch slipped under hard acceleration and the 90,000 mile maintenance had yet to be done. I drove it a couple thousand miles and then dropped the engine and transaxle and put the engine on an engine stand so I could work on it with relative ease. While this isn't how a professional mechanic would do it, I figured since I was replacing the clutch, timing belt, water pump, etc. that it was worth the added time to remove the engine/transaxle and have everything easily accessible. I was also taking into consideration my nonexistent experience with this type of engine in this type of car. Taking the engine and transaxle out wasn't too difficult, and since I was doing it myself, time was not a critical issue. A nice thing about looking straight at the front (actually the right side) of the engine was that I could take a good look at the timing belt in it's installed condition. This is hard to do in the car because there really isn't much space in there to look around. The teeth on the timing belt were in good condition, but the belt was stretched a bit and the tensioner was not keeping it in proper tension. I could move the belt laterally a good inch or more without much effort, which seemed to be quite a lot to me. When I removed the belt and compared it to the new belt the amount of stretch was obvious, although I didn't measure it to get an exact figure. I just looked at it and thought that replacing it wasn't a bad thing to do, and I was glad that I hadn't run the engine over 6500 RPM more than a couple of times since I had bought the car.
While the timing belt was still fully functional it seemed to me that replacing it was a reasonable thing to do. While I was there I also replaced the waterpump, front crankshaft seal, oil cooler seals, oil cooler hoses, and all that other stuff that falls in the zone of "well, as long as I have it apart..." I also replaced the cam position sensor that is located on the front cylinder head. The potting had melted out of it and I thought that it would be best to replace it. It's one of those things that is easy to replace while you're in there, and hard to get at afterwords.
Dan-O's comments are right on the money with respect to personal health and well being. People don't usually relate the price of auto repair to their own physical well being, but cars can fail anywhere and if you're in the middle of the desert in July or driving down a steep mountain road in winter, an unexpected failure can lead to more discomfort than a call to the AAA to come and tow your car to a repair shop. I don't subscribe to the blind idea that everything Honda Motor Company says and does is irrefutable gospel, but common sense and a reasonable amount of pessimism should be used in situations like this. A fundamental maxim in the engineering business is "design for the worst case". This is equally valid in the auto service industry, but maybe it should be called "replace for the worst case".
The timing belt itself is relatively cheap. I think I paid $160 or so. But other things tend to add up, like the water pump, and new cover that goes with the water pump, the timing cover seals, etc. etc. etc. Usually when you're into it this deep you might as well take care of everything in the immediate area that needs to be serviced. Certainly the hoses need to be replaced at 90,000 miles (all of them, front to back), and there are quite a few of them at $10-$25 each. NSX parts aren't cheap (thermostat was over $20) and the dealers and/or indendent shops don't work for free either. But sometimes it's best to do things like this and avoid the unlikely but possible unpleasant events that would result if you didn't.
John Crawford
