Curious though, who has them on their own cars for extended lenghts of time with positive results?
I have several test vehicles that are still running their prototype sprockets and racking up mileage. Some of these are TT.net members: "aliaZ", "Rule12b", and "citation". Citation has surpassed 12K miles with no noise to date, he previously had bought two sets of new Nissan VTC replacements and they both made noise around 2500 to 3000 miles. AliaZ's mileage is well over 5K, maybe he'll post his actual here. Rule12b sold his car so I have lost contact with it's current mileage but his was the first to eclipse 5K. As to who my customers are and how many miles they've accrued on the actual rebuilds, I'll have to leave that to them to post here if they desire.Ash claims he fixed the problem, and even mentioned there was no oil and no noise...can you speculate why? The cushion/pocket of air?
I experienced the same conclusion as Ash with my first set of test sprockets in which aliaZ also tested. No noise until 2500 miles. The only explanation for this is air in the system. It also explains why a simple front spring replacement will quell the noise for a short period. With my next round of testing I set 5K as my benchmark to prove my fix was legitimate before selling a single pair to the public. Ash's don't leak oil because he welded the entire back cover to the sprocket (who knows how much heat was transferred to his VTC springs), as far as no noise is concerned, let's ask him when he's put 5K miles on them. Of course it would be nice to get an unbiased opinion. How do you have such detailed knowledge of the VTC's? Buying lots of them and cutting them open? Consult anyone at Nissan?
I am an engineer and I love to fix problems. The method of replacing the simple front spring to fix this problem never made sense to me, and I just happen to work for a spring manufacturer so I decided to get to the root of this seemingly spring related problem. Also, I simply feel that if I am going to ask someone to buy something from me, then I had better understand what it is that I am selling. I have not consulted anyone at Nissan regarding VTC functionality and I highly doubt that anyone there would care to comment. One sacrifical sprocket and tons of research was all that was needed to understand what was occurring. I made special tools to measure the torque from the cam required to over-power the VTC spring and tested springs with different loads at the installed height as well as no spring at all. Also tested were JWT front springs and stock Nissan ones, both had no measurable effect on increasing the amount of torque required to over-power the VTC. JWT springs do have a solid height that is precariously close to the available space under the front cover though, which could coil bind and cause a total loss of all VTC function. This is the reason I do not recommend using them. I looked at several different aftermarket valve springs currently used in the VG engine and mapped their load profiles. I then looked at the camshaft lobes to find the optimum lift at which the maximum amount of torque was imparted unto the cam (you have to consider the particular valve spring when doing this). As stated previously in my linked post, this noise is a combination of rotational torque AND residual oil pressure; if you measure the surface area of the piston and the spring pressure of a stock spring, it only takes 12 psi oil pressure to activate the VTC to full advance (assuming friction is negligible, which is a fairly valid assumption given the sprockets are full of pressurized oil when activated and there are clearances in the sprocket to allow this oil to lubricate the inner workings of the VTC). If you were to assemble them dry, you might find that it takes 40 psi to cause the same effect. In the end, the spring pressure is a fine balance between preventing the noise and allowing the VTC to still function normally without requiring excessive oil pressure to activate it.
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