Adventures on Nissan Valve Timing Control (N-VTC)

If you own a Nissan S14 or 15, and you have fitted tougher valve springs while retaining the factory VTC gear then you will by now be familiar with the VTC rattle that everyone on internet forums speak of. 

 

I am very familiar with this noise now, and have now got two old gears laying around to prove it. Since my 3rd gear is now making the noise too I decided that rather then coughing up another $400 to change it out, I might as well put my two old ones to use and find out whats inside.

When I decided upon this en devour, I quickly discovered that there is virtually no information on the net about it. You can find plenty of videos about the noise, and plenty about replacing them, but hardly anything on what is inside it.

The service manual has this image of it, but it is hard to make sense of it unless you have seen the contents before. So that it what this post its trying to do. Provide the internet with a place for prospective do it yourselfers like myself to see what is in a gear before destroying one themselves.

Now how to open one. Its very simple as it turns out. First of all and most important, if you ever intend to reuse the gear you MUST mark the location of various parts in relation to each other so that you can reassemble it exactly as it came apart. If you do not you risk engine damage! Okay, now if you look at the end of the gear, there is a cap and a center “post”. Through this post with where the cam gear bolt passes. These two items are press fit together. This is all that holds the gear together when it is out of the car. When installed, the bolt and washer support it as well. I hammered mine out, but a press would probably be better. There is a spring inside, so when the two parts separate the spring will send it flying everywhere, so watch out for that.

 

Above is the center “post” and the piston. The center has the dowl hole in it for the cam shaft. The center and the end cam remain in place, and when oil pressure is introduced the piston moves backwards against the spring. The main body of the gear then rotates, resulting in a 20 degree shift in cam timing.

 

Above is the return spring that sits between the center post and the piston. When the solenoid turns off it allows oil pressure out and the return spring then pushes the piston back to the front of the valve. This is the spring that most forum mechanics believe wears out. Personally I do not know if this is the case.

 

The helix teeth on the outer gear housing, the piston and the center cause the 20 degree shift in timing. There are also several fiber based seals (the red rings) which keep oil pressure in the right places. Oil, by the way, travels into the center of the cam shaft via the #1 cam cap on the intake cam and then up the center of the gear surrounding the gear bolt. There is a hole in the center post which allows oil into a cavity above the piston inside the gear.

So what was the point in all of this. Simply to see if there was any obvious cause and then fix for these gears which would allow me to not spend $400 every 6 months to make my car not sound like a tractor (currently it does). At this stage I do not have an answer to that, but there are a couple of ideas. If I find anything worth while, I will keep you posted.

Paul.

PS, you can find some interesting information if you look up Z32 (300ZX) VTC systems. They also suffer from the same problem. The cam gears look different, but fundamentally they are the same.