engine rattle diagnostic

Discussion in 'Technical' started by justinmcdougall, Oct 31, 2017.

  1. justinmcdougall

    justinmcdougall New Member

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    bit of a story but thanks in advance for taking the time to help.

    89 z32 tt jap import went from stock with exhaust making 240whp and running perfectly. to 740cc injectors, twin pod filters maf delete, Mac valve (ebcs) 14psi, ait sensor, link g4+, God speed smics making just shy of 350whp.
    the problem i have is intermittent but I'm pretty sure it's only when the engine is warm. problem is I have a rattle that's at 1000rpm and above. also when I depress the throttle in neutral the revs go down to 400rpm then go up. while driving when I clutch in the revs drop right down to 400rpm then settle out at 800rpm and idle. I'm thinking maybe something is worn after being hammered on the dyno? when the rattle isn't there the car idles and runs like a bloody dream oil is changed every 2000ks I was running 5w40 oil for the last year. if just changed to 10w40 thinking it might quiet down the noise bit it didn't make a difference.

    has anyone experienced something like this? how do I go about diagnosing the problem without opening the engine?
     
  2. QLDZDR

    QLDZDR ID=David

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    Remember that Castrol RX engine oil.
     
  3. justinmcdougall

    justinmcdougall New Member

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    never used Castrol engine oil before
     
  4. DazzaZ32

    DazzaZ32 Active Member

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    Shit i run 20/60 high performance mineral as our engines really were not suited to thin oil.
    (ok getting popcorn to watch responses)
     
  5. 260DET

    260DET Active Member

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  6. justinmcdougall

    justinmcdougall New Member

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    I thought the variable timing control needs to be at least 6 MPH or higher to activate? that's what it says on z32wikispaces.
     
  7. justinmcdougall

    justinmcdougall New Member

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    are you running a vg engine? if never heard of running 20 60 ever..
     
  8. justinmcdougall

    justinmcdougall New Member

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    not my car i cant quite get it on video but this is what my rattle sounds like. rsttling sound is at 1:28

    thanks again
     
  9. QLDZDR

    QLDZDR ID=David

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  10. brisz

    brisz Well-Known Member

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    Fit new OEM VCT springs (and o-rings), run an oil representative of when this engine was built, nothing very low or very high, some where in between 10W - 50W.

    Don't worry about the JWT springs, OEM works: https://conceptzperformance.com/nis...0-vtc-spring-nissan-300zx-90-95-z32_p_975.php

    And o-rings: https://conceptzperformance.com/czp...san-300zx-90-93-z32-c-01001-00191_p_23366.php

    I went with high zinc oil (Kendall) for run in, then I wanted a tier one oil (manufacturer Shell, Mobil, etc) as they control the stock used to manufacture the oil and are less likely over time to make substitution in formula for commercial reasons, ie the quality is reliable, I wanted what was a very available brand in Australia, I wanted to be able to buy it anywhere, I didn't want to by Mobil out of a container in someones driveway, Shell is probably the most available tier one oil in Australia. I went with a semi synthetic as both mineral and synthetic have positive and negative attributes, semi is also more cost effective for very regular changes, max 5000 k's, I found the 10W40 great but maybe got knocked about a bit in warmer weather, the 15W50 was also good but I think that 40W+ seemed to contribute to VTC rattle especially as the oil got older.

    I thought about running winter 10W40 and summer 15W50.

    But I blended the two 50:50 to theoretically get 12.5W45, as about a good an oil as I have used, no VCT rattle, near zero oil consumption, oil stands up to higher temps and lasts better out to the 5000k change imo.

    Shell HX7 (blue bottle) is on special several times a year for under $30 for five litres at SuperCheap.

    Lol Kmart are stocking Shell HX7 10W40 for $32 every day price.

    Has been as cheap as $19.99 https://www.ozbargain.com.au/product/shell-helix-hx7

    It has worked for me, may not work for others.
     
  11. justinmcdougall

    justinmcdougall New Member

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    UPDATE!!!! if I unplug the vct solenoids the rattle goes away. does this mean I need new vct solenoids??
     
  12. QLDZDR

    QLDZDR ID=David

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    There are those diagnostic cables with the LED.
    I thought I bought one, but I might have bought one of the others, connectors, cables, stuff. Put some of it in the boot, if I get stranded or a mechanic is working on my car one day, might come in handy.

    You might get lucky and just fix it with motor oil that has a cleaning agent in it, to unstick them.

    Castrol RX for diesel engines.
     
  13. AAU54U

    AAU54U Member

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    Changing the solenoids won't help because its the VTC gears that are doing the rattling not the solenoids.
     
  14. justinmcdougall

    justinmcdougall New Member

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    so I need to replace the gears?
     
  15. brisz

    brisz Well-Known Member

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    Yep that is what you need, new gears, thankfully they come with new springs.
     
  16. pmac

    pmac Z,, IT'S COMPLICATED!!!!!

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    Yes you need to replace the VTC gears.
    PS. The outer springs have nothing to do with the vtc rattle, this is a common misconception and replacing them is a waste of time. The springs that have failed are inside the gear itself and inaccessible and non replaceable.
    Here is some info for you.

    Problems
    As with any complex system, the VTC system has a couple of common problems that tend to materialize on our 20-year-old Datsuns.
    VTC rattle (or tick, knock). There are a few different theories as to why this happens, but the common understanding is it has to do with the helical piston slapping back and forth inside the housing. This is not uncommon in high-mileage engines, but will no doubt begin happening (even with new gears) on engines with heavier valve springs.
    Leakage. In a VTC gear that has begun to fail (usually exhibiting the rattle/knocking noise), the rear/inner shaft becomes "broken" from the gear housing. These two components are pressed together from the factory. When this happens, oil can leak from the rear of the VTC gear.
    Spring fatigue. A common perceived failure is that the small spring at the front of the gear becomes fatigued, allowing the piston to slap around, causing the VTC rattle noise. It is now understood that these springs practically never wear out. While JWT makes "heavy duty" VTC springs, this is essentially a "band-aid" fix for the gear assembly itself wearing out in some manner, and owners who replace their VTC springs with JWT HD springs virtually unanimously report the noise returning shortly thereafter. Some claim that the JWT HD springs actually hinder performance by essentially locking the VTC mechanism.
    [​IMG]
    Variable Timing Control (VTC, sometimes called Variable Cam Timing (VCT), or NVCS (Nissan Variable [timing] Control System or Nissan Variable Cam System) was the name given to the variable cam phasing system featured on the VG30DE(TT) and other similar engines from the era. While similar in application, it is functionally very different and should not be confused with Honda's VTEC system, which was introduced around the same time.

    183-rebuild_34.jpg
    VTC Solenoids being installed in a VG30DE's head.


    Function
    Variable Timing Control was, at least in the case of the VG30DE, used only on the intake cams. Interestingly, the exhaust side of the head features a cutout that would otherwise appear to accommodate a VTC solenoid. It was a relatively simple (yet mind-bendingly impressive, from an engineering standpoint) solution to a common problem that faces engine designers: timing the cams for good low-end torque or high-end power. Most engines compromise somewhere in the middle, but VTC allowed Nissan to have it's cake and eat it, too.
    In short, the VTC system allowed the ECU to advance the cam phasing on the intake cams, depending on different engine situations. This allowed the VG30DE to maintain good low-end torque and smoothness, without sacrificing top-end power.

    ECU Control
    The ECU controls the VTC mechanisms through the two solenoids, mounted on the back of each head (see "VTC Solenoid" below). The NA and TT ECUs use different parameters to control the VTC function.

    Non-Turbo
    For the VTC to turn on, the following conditions must be true:
    Temperature between -58°F and 230°F.
    Vehicle speed 6 MPH or higher (0 MPH on some earlier ECUs)
    Then, the ECU will enable the VTC if the RPM is between 1800 RPM and 5800 RPM. If the RPM is below the range, it will enable as soon as the TP (the calculated engine load) is above 39ms.
    VTC_Control_NA.png

    Twin Turbo
    For the VTC to turn on, the following conditions must be true:
    Temperature between -49°F and 230°F.
    Vehicle speed 6 MPH or higher (0 MPH on some earlier ECUs)
    Then, the ECU will enable the VTC when the TP (calculated engine load) is above 23ms. The VTC is cut (disabled) at 5900 RPM. The TT ECU still has a parameter to enable VTC by RPM alone, but it is set at 6100 RPM, above the 5900 RPM VTC cut. Because of this, it is essentially ignored. The TT's VTC is enabled by TP and disabled by RPM.
    VTC_Control_TT.png

    Components
    The VTC System was made up of three major components:

    Camshaft
    Main Article: Camshaft
    The Intake Cams feature a ball-spring check valve at the back of the camshaft and a hollow oil passageway throughout, with an opening towards the front. The oil passageway allows oil to enter the cam near the front, and either drain back out at the rear (VTC off) or pressurize the helical piston assembly inside the cam gear (VTC On).
    [​IMG]
    VTC Solenoid
    VTC_Solenoid_Function.jpg
    The VTC solenoid (illustrated above and pictured at the beginning of this article) is a solenoid valve mounted to the back of the head, directly behind the intake camshaft. In it's "resting state" (off), it allows oil which had entered the front of the camshaft to drain back out through the rear. Once activated, the VTC solenoid "plunger" presses on a check-valve at the rear of the cam, effectively blocking the flow of oil from leaving the cam through the rear. This forces oil to pressurize the front chamber in the VTC gear at the front of the cam.

    VTC Gear
    VTC_Gear_Function.jpg
    Credit to Ash for the original photo.

    The intake gears on equipped Zs (all but USDM 1996 models) featured an internal helical piston assembly. It was made up of three basic components:
    The main gear, which actually comes into contact with the timing belt. The inside of the gear housing had helical teeth all the way around the inside of it.
    The Inner Shaft. This part connects directly to the camshaft and has a helical teeth all the way around the outside of it.
    The Helical "piston". This part was a sort of metal "ring" with helical teeth on the inside and outside of it. This went between the two halves.
    When the VTC Solenoid is activated, it allows oil to flow into the front of the gear and pressurize. This pushes the helical piston back (towards the engine). Because the piston links the inner shaft and outer housing via helical teeth, the movement towards the engine causes the inner shaft (and thus, the camshaft) to rotate the camshaft about 20 degrees clockwise.
    [​IMG]
     
    DazzaZ32 likes this.
  17. brisz

    brisz Well-Known Member

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    Apart from cutting and pasting from Z32 wiki what is the basis for your opinion ?
     

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