On 1990-1993 Infiniti Q45's there is a problem widely known as the 'Chain Guide Problem'. When Infiniti built these cars the chains were made of metal and according to 'should last the life of the car' (Q45Tech).
The problem lies in the guides on these chains. Rather than being backed with metal, they were backed with plastic which obviously is not as durable. These plastic guides tend to crack and break. This can cause the chain to some loose and do anything from rip off the piston heads to completely destroy the engine. This problem is real. Owners that aren't sure if their car's guides have been replaced are recommend by this forum to 'not drive the car any more miles than is absolutely necessary to get to your mechanic'(palmerwmd).
The only option for this problem is to have the guides replaced with the new metal-backed guides used in the 94-96 Q45's. This is not a cheap fix either. T3, a well-reknowned Infiniti shop in Atlanta, will replace the guides for $1200. Your dealer will replace but they list the job under a chains job and can cost upwards of $3000. The chains do not need to be replaced as they can last for the life of the car. Most dealers will charge just shy of $2000 for this repair.
If you don't want to go the dealer route, this can be a DIY project but it is quite difficult. Owners here recommend having an independent Infiniti Tech do the work. The parts list that you will need for this repair is the following: (courtesy of DAEDALUS)
2x 01121-04711 - bolts for new guides NA
4x 11051-60U04 - cam end seals NA
2x 13021-60U00 - crank/cam sprockets NA
2x 13028-60U00 - timing chains $99.88
1x 13070-60U03 - chain tensioner(RH) $49.90
1x 13070-60U12 - chain tensioner(LH) $49.90
4x 13075-60U02 - tensioner bolts $ 5.20
1x 13079-60U01 - tensioner gasket(LH) $ .56
2x 13085-60U01 - chain guide $13.18
2x 13085-60U11 - chain guide $13.18
1x 13091-60U01 - guide(tension RH) $49.85
1x 13091-60U11 - guide(tension LH) $49.85
2x 13094-60U00 - guide bolts NA
1x 13510-60U00 - front cover seal $ 5.34
1x 15041-60U00 - oil pump chain $33.88
1x 15043-60U00 - crank/timing sprcket NA
1x 15044-60U00 - crank/oil sprocket $33.88
1x 15072-60U00 - bracket oil pump NA
1x 15073-60U00 - oil pump chain guide $ 4.87
1x 15073-60U10 - oil pump chain guide $30.85
2x 13270-60U00 - valve cover gaskets NA
8x 14032-60U01 - intk manifold gskts $24.80
After various opinions and experiments, it has been determined by this board that there is only one way to check to make sure you have the new guides. You must pull off the front cover to check the engine.
NOTE: There are 4 guides, a slack-side guide, 2 tension guides and an oil pump chain guide. The slack-side guide has ALWAYS been metal backed and is NOT part of the problem. The problem lies with the tension guide and oil pump guide. These are all plastic and must be replaced.
If you think you may have old guides on your car and you can't get to a mechanic right away to get the problem fixed but don't have another car to use, palmerwmd suggests the following driving habits:
"Minimize your trip distances and especially the number of starts.
Staying under 3000 rpm is a good idea and remember to allow a full 8-10 minutes for the car to warm up, especially if it is cold outside."
Contributors to this article include: palmerwmd, daedalus, landtodd, ardvaarkus, Q45Tech