Hey guys - I posted this on 4dsc.com, so I appologize to those of you that frequent there too...


So I've read every shred of html I can about this freakin VTC problem and still have some questions... I guess what I'm really trying to find out is exactly what this nasty sound is.

I understand that inside the VTC housing there's a helical (spiral) gear, that is actuated by a piston. This piston is hydrolically controlled by the VTC solenoid, and essentially rotates the cam itself relative to the sprocket (and thus to the timing chain). Acompanying this piston is a spring that's (i'm inferring here) intended to return the cam to the normal position when the piston isn't being pushed.

So my understanding is that this spring breaks pretty reliably, which means that there's nothing holding the helical gear in place, which, in turn, means that the cam can rotate freely relative to the timing chain.

OK - so I can see how that's bad - it would mess w/ the timing giving you a drop in power. I can also see that if the spring is broken then you might hear it rattling around in there (is this the infamous ticking?)

What I'm confused about is what a Nissan tech said. He mentioned that the sound I'm hearing is actually the the slapping against the follower? He also said that it's due to a drop in oil pressure. Anyone have ANY idea about that? I know that the lash adjusters for the rocker-arms are hydrolic - might that have something to do with it? Might the hydrolic path to the lash adjusters be through the VTC solenoid? I have NO idea even where to start looking there.


The bottom line is that I'm planning on doing the VTC rebuild, but want to make sure that replacing the spring will fix the problem.

(here's the relevant page from the chilton's manual about the hydrolic lash adjusters:
http://www.cybrrpartspro.com/Chilton...61CH03_30.HTML)



thanks again guys!

 

yeah - I didn't think many people would know that level of detail.

I'm sure it's been posted before, but I'm not sure what to search for: Anyone got a link to the manual that the Nissan Tech's use at the dealership? what's it called? the service manual? sorry for missing something obvious here

 

Nice research, everything you're saying is correct. Everything the Nissan tech is saying is inaccurate. I'll make this real easy for ya. When I took out my bad VTC's, as soon as I would break loose the cam bolt holding them on, the VTC rotated and squirted out some oil. I played around a bit and tightened the bolt back down, and it rotated back the other way. Both times made a loud CLACK. This is the clacking/clicking/tapping noise everybody is hearing. The spring inside the VTC either breaks or loses its tension, and is unable to hold the VTC in the required position. Therefore, when any rotational resistance is placed on the camshaft (ie, when the cam lobes actuate the valves), the pressure overcomes the VTC spring and CLACK, the thing rotates. This will happen each time an intake cam lobe hits cam follower. So, the Nissan tech was partly right, but the noise is coming from the VTC itself.

Have you ever tried to install a camshaft and sprocket correctly on a head where you needed to apply pressure to one of the valve springs to get it all lines up right? These VE valve springs are pretty stiff, and when you throw a loose VTC into the mix, that's how the noise happens.

The result is, your intake cam timing is changing constantly. The VTCs don't cause it to change too much, so there is still decent power and most people just disable the thing. Speaking of that, by disabling the VTCs, you stop sending oil pressure into them. This oil pressure causes the VTC to rotate BACK after the weak VTC spring and high valve spring pressure caused it to rotate in the first place. This is how you can get rid of the noise, but now you will have no low end because VTCs create LOW END TORQUE, not high end power. High end power will suffer however, because the VTCs can't hold the cam timing constant.

Does that make sense to ya?

VE POWER!

 

ah - what a relief!!!!! you are the man, Ken!

I feel much better about cutting her open next weekend now - I'll let you know what happens....

So did you hit any snags when doing the surgury? Any sheared bolts or anything?

In Craig's (?) write-up, he wrote this: "There are two Nissan Technical Service Bulletins that deal with the proper installation of these items. And they should be followed if you want these new assemblies to last. They deal with making sure the oil gallies are clean. If not, even the new ones will fail again. Warning! Even if you get these done at Nissan, that is not guarantee that they will follow the TSB! Some Nissan techs are lazy-asses! If you have Nissan do the repair, make sure they are aware of the TSB and make sure you they follow it! "

Anyone have the TSB that says this stuff about the oil gallies? In NTB95-022 (the one with the picture of the VTC assy) I didn't see anything about oil-gallies?


Thanks again!!!!

 

Yeah I did some major surgery, I removed both heads just to make sure everything was done correctly. The big reason I removed both heads was to drill out and replace broken exhaust studs. It was CAKE with the heads on the bench! The VTCs can be taken out easily without touching the heads. The only big parts you'll need to remove are the intake manifold (upper, actually called the plenum), the valve covers, and the head timing chain covers. Doing this there are no tough bolts that might shear off. Actually, I broke off two tiny bolts that hold a flimsy aluminum arm that holds the engine subharness up, this comes up from the front (passenger) side of the rear head. Oh well. While digging in there, you might want to remove your lower intake manifold and replace the knock sensor ($130 for the sensor and $50 for the intake gaskets for that).

My oil galleries were perfectly clean. I ran pipe cleaners through them and only got some oil, but it looked fine. The TSB also deals with installing new oil galley plugs and jets, some which you can see, others you can't. The ones you cant see, you'll have to drill a hole in the aluminum head to find them. It looked HARD. Needless to say, I didn't bother.

Removing the VTCs are quite simple. The FSM has a process of moving the crank 30 degrees this way, then 30 degrees that way to make sure you dont have any valve spring tension on the cams when you remove the cam pulleys. Otherwise they will jump. CLEARLY mark with white-out the position of the VTC, chain and sprocket. There is a timing hole on the VTC itself, but there is another mark that looks like it might be a timing mark, but isn't. The actual timing mark is on the sprocket, and is very difficult to see when the chain is on. I actually installed mine wrong but luckily when I did a test rotation of my engine (by hand, just but a big socket on the crank or cam pulley), it didnt line up and I figured it out easily.

I replaced my VTCs with new ones (found a Nissan dealer online going out of business that was selling stuff for 30-40% off with free shipping). That was 15K miles ago and it's been running great. I still need to replace my knock sensor though.

Let me know if you have anymore questions.

 

The TSB talks about needing Special Service Tool kit (J-41471) and a press capable of generating 1 Ton of force.

Well - I have access to the press, but my question is if I really need the tool-kit? It appears to contain a 20mm steel ball used to disassemble the VTC assy, and then a couple pieces of round stock (one is 1 3/16" in diameter by 5/8", and one is 1 1/8" in diameter by 1 1/8")

I called Kent-Moore (1-800-NMC-2001) and it's $76.56...

So those pieces of round stock look suspiciously like socket sizes, and I may be able to round up a 20ish mm steel ball.. I know having the right tool for the job is pretty crucial, but for 80 clams?

see what I'm askin here?