When Should I Change The Timing Belt?
The US service manual states that the timing belt should be replaced at 72 months (6 years) or 90,000 miles. The vast majority of NSXs hit 6 years well before they are anywhere near 90k miles so many owners are wondering if they really need to change the belt at 6 years.
The "safe" answer is to replace it per the maintenance schedule. However, considering the way many NSXs are pampered and the conservative nature of most timing belt replacement schedules, it is probably fairly safe for most owners to go beyond 6 years on low-mile cars.
Though one other thing to keep in mind is that Honda will have no sympathy for you if it is beyond the recommended service life and breaks, damaging your engine. Repairs for such a belt failure are likely to be a fair amount of money. But if this happens when the belt has been replaced according to the maintenance schedule there is a chance that they will help with goodwill on the repairs.
[KS - 99/12/11] I asked one of the top NSX technicians in the country about this, and here's what he said: "Acura says 7 years or 90 k miles. Period. I have seen Integra belts break at lower miles and years, but NEVER a Legend or NSX. I have seen Legend owners go as high as 110k miles, but rarely, if ever over 8 years. Years ago I developed the quirky habit of taking every belt I remove, and twist it like wringing out a wash cloth. I listen to the number of fiberglass strands that snap and break, and predict how close to breakdown the car may have been. This sound of glass breaking is very distinctive. I have done NSX T-belts that were 7 or 8 years old with only 30 or 40 k miles, and when I twist the belt, all I get is red hands. The moral of the story is that while other cars may be in the danger zone at your cars age and miles, I would plan to do yours no later than, say, 8-9 years, or at about 50k. If this sounds arbitrary, it is based on the experience of others. If nervous, disregard [everything above] and get it replaced"
[DL - 99/12/11] The problem with a timing belt failure is that you are never again sure everything is "as new." It bends valves, which can be replaced, as well as valve guides (sure, they can be replaced, too, but it's a big job), stresses the heads, tappets and cams, and generally makes a mess of the top end.
I've always believed that the less a factory-made machine is touched by anyone away from the manufacturing process, the better. My rule when I was racing was "don't change plugs between practice and the race," which means for anything you touch expect side effects that will take additional time and work to recover (I won a lot of races, also blew up plenty of motors during development). It's a lot better to do the timing belt a little early rather than a little late.
We lost a belt on our old Honda Prelude, exactly at 90K, and it's come back OK but I don't have the same confidence in its longevity. Just the hassle of being stuck on a freeway (if you're quick enough to recognize what's happened and can coast across a few lanes to safety) is a bummer. Even the tow into the dealer has some risk of tweaking something.
From what's been posted, I'd guess 50-60K or 7 years sounds like a safe bet, but who knows? I've got a '93 with 34K miles, so I guess I'll put it off a while. On most cars, the miles match the years, but not on a special-purpose toy like our NSX's. I'd ask around for any examples of failure, just to have some real data rather than more opinion. But it's much better to do it when it's just a simple belt replacement (complex though it is) rather than a full top end teardown and machine shop job.
[AT - 99/12/30] I finally had the chance to do some comparison of my old timing belt and a new one. To also check on the belt I also brought along a tool I've used in the past to check on spark plugs. This is a special flashlight with a magnifying lenses attached which then magnifies and illuminates any small 1 1/2" square area in greater detail.
First I checked the old belt to see if it had stretched to any degree as compared to the new belt. I could find no difference between the two belts. This is a good sign, but considering new belt technology, I didn't really expect this to be as much of a problem as it had been in the past. By the past I'm referring to the infamous Fiat timing belts of the 70's. If you didn't change these belts on the exact mileage they specified, then you could almost guarantee that it would break and total the engine. Their expected life span was no more than 30,000 miles max if I remember correctly.
Then I checked the rubber surfaces on both sides of the belt. From a normal viewing distance the main difference between the two belts was that the old one had some minor glossy areas on the outside of the belt which corresponded to the teeth on the inside of the belt. Also it was missing all markings of the belts part number and the like. On the inside of the belt it looked almost identical to the new belt. Under the magnifying lens I had a much better look at the rubber surface and texture. I fully expected to see small cracks and excessive wear on the old belt. But to my surprise it was remarkably similar to the new belt. Both surfaces looked very similar, no dry cracks, no separation, cuts or any damage. On the inside of the belt where the teeth reside, I also noticed that the surface texture exhibited on the old belt looked almost identical to the new one. The tooth pattern was very uniform, no cups, overly rounded or squared edges, either leading or trailing.
The last area I could inspect were the internal plies used to support the belt and give it a majority of it's strength. Since I couldn't get into this area, I can only surmise that it was probably in very good condition since it exhibited no dryness, cracking when stressed or twisted. Again this is speculation on my part so this is where the weak point of the belt would come if it were to fail. Originally my biggest concern was that the tooth shape would have changed enough along with some belt stretch to cause it to jump a few teeth on one or more of the cam sprockets. Now I think that this would be unlikely unless something else mechanical or chemical affected the belt. Possibly the belt tensioner failing to do it's job properly or oil getting on the belt causing it to slip or break down more quickly.
All in all this is a well made part from Honda. It would be one of the parts I would least worry about on this engine.
[DD - 99/10/19] Even though most NSX's are way under the recommended mileages for this service, owners must recognize the established time-period of the useful life for this equipment. We've had a few owners that "took their chances" and got burned.
What Else Should Be Changed With The Belt?
It is normal to replace the water pump and other engine belts (alternator and
compressor) at the same time. They should not charge you labor for
The parts costs on the other belts is minimal but the labor to get to them is substantial (mostly the same labor as replacing the timing belt). So it makes a lot of sense to change all the belts at the same time and only pay for the labor once.
The water pump is almost always replaced, but on a well-maintained (fresh coolant) car it's not really clear how long they will actually last. A few have been disassembled and inspected after being replaced and they looked almost new inside on low-mile cars that were having the timing belt changed based on time instead of miles. But again the water pump parts cost (about $200) is less than the labor to replace it, so most owners replace it during the timing belt change as suggested.
[MBA - 99/10/29] You should always do the Timing Belt and Water Pump together. Its about 7 hours labor for one, or 7 for the other, or 7 for both. Also, the Water Pump is Timing Belt driven so a broken pump equals a broken belt.
Water Pump Note
The the vendor in Japan who was casting the pumps changed ALL the molds and can not cast the old pump any more. The weep hole was moved in the 1997 pump. The new pumps are the same price as the old pumps. The new pump will fit the 91-96 cars but one of two things must happen:
If you buy a new cover you will need a grommet.
19200-PR7-A03 Water pump
Many dealers who do not work on many NSXs are still not aware of this change. They will get halfway through the job and call to say there was a parts change and they need to get a new timing belt cover. Some owners have been able to get the dealer to give them a discount on the new belt cover when they get a call like, especially if they negotiated a flat fee for the work first.
When Have Owners Reported Changing Their Belts?