Any idea what interval the belts and plugs should be replaced on the 03-04 M45?

Thanks,

Mark

EdBwoy might know, he's our resident Y34 expert...but belts I'd do whenever I start to see cracking and spark plugs, at least on my 07 M35x and 11 M56x were at 100kmi I believe.

I agree. My service rep at the dealer told me "leave them until they cause a problem and don't worry about time or mileage". I think most change them at 100k miles. But me? I like to be different .... so I had mine changed at 90k miles - not a bloody thing wrong with them - I just did it.
In fact: I had them done along with other maintenance items and ran a contest for the members to see who came closest to guessing my final bill. And the winner was (drum role please) Ilya! Here is the thread:
https://forums.nicoclub.com/post6748178 ... g#p6748178

Spark plugs
From different sources that I can't seem to find right now, I recall seeing 120,000 miles. All Infiniti tells you is that the iridium plugs last longer than others, but they don't call for mileage-based replacement anywhere.
Just do them as frequently as you please (or as frequently as you can afford, lol). In the same way as changing your oil or taking a shower, there's nothing wrong with doing it before you need it, but it could get unnecessarily expensive.
Technically, you're supposed to check the gap and replace if the tip is wearing or have the cylinder misfiring confirmed to be due to that plug. [Don't regap or clean old plugs to reuse them!!] I have removed plugs as old as 190K miles and found the gap to be just fine. I replaced them with brand new plugs anyway and could feel no perceivable difference.

For the nominal cost of a spark plug compared to the labor required to pull them and look at them, some people would rather just install new ones on the way in [make sure you buy good quality, original NGKs]


Drive belts
The manual calls for regular checking (every oil change) and replacement at 60,000 miles.
What you are checking for is cracking and glazing as mentioned above (I don't see your odometer mileage indicated, but I recommend you remove the belts and check the idlers/pulleys as well)
Even when there are no cracks, you need to monitor belt stretch by looking at the indicator marks on the tensioner. If a belt stretches too much and exceeds the range of the tensioner, it is likely to start skipping, slipping etc...which generally speeds up other forms of failure along with your accessories not working correctly.
To bring out a little variability, the manual is written with OEM components in mind. You might have aftermarket belts (longer, shorter etc, which will wear at different rates)

But like I said with the plugs, belts are cheap and there's no point in playing the game of chance with the system. $100 every 60K miles isn't too much to ask of the car so just replace them.

Thanks much all. I decided to have them done (plugs and belts) and also had a nuisance oil leak at the valve cover gasket repaired. When I bought it there was some history - car was dealer serviced until about 90k, and then serviced locally at
a gas station until I purchased it at 106k, but I have no details on what was done. I have 112,000 miles on it and daily drive the car, so this gives me peace of mind. I love this car and want to keep it a long time.

If they aren't cracked and the belt tensioners show they are within tolerances, I wouldn't change them. Both tensioners have a indicator that should indicate belt tension. If they seem to be to pointing to one side or the other, i would check deflection of the belts. You should be able to determine belt deflection by pushing them inwards, they should have hardly any. That being said, the actual replacement is pretty easy, I highly recommend using a long reach allen wrench for the the tensioners and a long breaker bar and a deep socket for the main pulley (you'll see what i mean).

plug gap for 04' M45?

The plugs are pre gapped. Recommend NGK for your car. That is a factory plug that nissan/infiniti use. On the belt tensioner there are marks to show the tension of the belt

The factory recommended gap for the V8 is 0.043 inches or 1.1 mm.

It is advisable to check the gap of any plugs you buy before installation. It is a fairly quick and effortless exercise that you do before installing the plugs in the engine for a very long time. Refusing to check seems like a reckless gamble to me.
I have bought spark plugs straight from various dealers and I can certainly confirm that they are not all pre-gapped for your specific engine.

Example 2 and a half minutes into this video: