NF Mod/Nissan Master Tech
Join Date: Jan 2006
Location: Prospect, VA
The ol' Z24 and the KA24 are two entirely differant animals. While I have seen a couple of Z24 chains fail during my time with Nissan, it was very rare.
The NAP-Z engines used two fixed guides with a tensioner foot at the bottom of the chain and the double row timing chain. The KA24E started off with a plastic, fixed timing chain guide and a metal backed "slinger" guide that was pushed by the tensioner to take up the slack in the single row chain. (The GA16i engine used in the 89-90 Sentras/Pulsars had a similar design and similar problems.)
Initially, the first of the KA24E engines were recalled and the tensioner and "slinger" guide were replaced to a modified design .
The next issue started when people started hearing chain rattle during start-up. What happens is that debris can sometimes enter the oil feed channel to the tensioner and restrict the flow and pressure. Once the engine was running, there was sufficient oil pressure to the tensioner to properly tension the chain. However, at start-up situations, the chain would remain "slack" and rattle and would eat away at the top of the fixed, plastic chain guide. In worse cases, the fixed guide would break apart so bad that the timing chain would start cutting into the back of the front cover and could cut into the coolant jacket behind the water pump! Nothing like aluminum shavings and coolant for your engine bearings!
Eventually, Nissan finally smartened up and designed a fixed guide with a metal backing. This didn't necessarily address the main problem, but did keep the fixed guide from breaking apart and making the situation worse. 1995 models and up have the updated guide. 1994 models and earlier have the plastic guides unless they have been replaced with the updated parts. The twin cam, KA24DE, also had a similar design change on the lower chain guide, but they didn't really suffer from the problems that the KA24E did. The KA24DE did suffer from the same problem of sludge build up (usually behind the timing main gear) which caused upper chain rattle, which was "fixed" by eliminating the fixed guides of the upper chain (not really fixing the problem...just the noise).
The KA24E engine would also encounter jumped timing in some cases when the guides failed and the chain slacked. This would also retard the ignition timing as the distributor ran off of the camshaft. This I would usually see on U12 Stanzas and B12 Sentras and generally one tooth seemed to retard the timing about 8 degrees. One tooth jumped, the engine would run, but have little power. More than a few teeth would often result in bent exhaust valves.
As stated, the chains actually held up pretty well. They do not have a recommended replacement interval, like timing belts. Personally, I have a 97 H-body (which came with the KA24E and new style guide). Conventional 5W30 oil was used and Nissan filters with maintainance performed by the factory schedule. I have 200,000 miles + on the engine, which has never been apart and have no chain rattles (knock on wood) so far. I highly recommend the Nissan filter (and recommend you NOT use the Fram) and keep up on the oil changes (3000-4000 miles).
If the chain is rattling for 3 to 4 seconds at startup, it is NOT normal unless the oil has just been changed or the vehicle sits for an extended period of time (several weeks). If it is rattling that long of a period, I would recommend new guides and a tensioner. When the tensioner is removed, one can see the oil port. Remove the oil filter and clear out the port by spraying brake cleaner into the tensioner port until it sprays out of the oil filter adapter. Follow that with compressed air, if available. If there is a lot of mileage on the engine, to me it would be foolish not to replace the chain and gears while the cover is off. Obviously replace the old filter and oil prior to startup. 5W30 is recommended, regardless of whether you prefer dino oil or synthetic. It is better for the tiny ports of the hydraulic lifters, which is sometimes another problem with the KA24E engine (valve tap).