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VNT Adjustment ZD30


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Adjusting the VNT initially sounds very daunting, when actually it is quite simple. A little care and forthought makes it light going. Usually 1/2 a turn down on the grub screw is enough to put you in the right spool up rate following an EGR block/exhaust upgrade etc. Generally we are looking for a spoolup rate of 5-6psi @ 1500 and 10-12psi @ 2000, this is just a guide not a hard and fast rule. Excess spoolup can result in long term damage to the turbo from cavitation and turbo shock. Hope this helps people trying it for the first time.

Tools required: 10mm combination ring open end spanner preferably with a slight offset angle, a 2.5mm allen key, a pair of long nose pliers, 300mm of 10lb fishing line :) 30 minutes will se it done, and a bottle of Jack Daniels.

With the engine cool tightly attach the fishing line to the VNT retaining clip, otherwise when it flies off you will never see it again and you will be going to Mr Nissan for new one as you won't know the size :)

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Push the clip off with long nose pliers

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Under the VNT head are 2 x 10mm hex head set screw, undo the rear one first then the front (otherwise the rear one will be pushed by the spring loaded diaphragm and make it a bit more difficult to keep the spanner on

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Slide the VNT rod off the retainer shaft and gently wriggle the head and rod to remove it upwards

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The head and rod removed

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I had a little over 1mm end float in the rod connection after 12 years of wear and tear, not sure what a new one has

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Clear view of the grub screw and lock nut, 1/2 a turn down on the grub screw is usually enough to get you in the groove

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Adjustment of the grub and lock nut, do this carefully so you don't lose where the original position was, loosen the lock nut just enough to turn the grub screw, do not take the spanner off as you want to ensure the exact amount you actually turn the grub screw in case you need to readjust later. Firmly retighten the lock nut in the new position, no need to overtighten as you can damage the grub screw head and lock nut

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With the fishing line still attache, push the circlip back into place with the long nose pliers, the damn thing could still fly off :)

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Edited by geeyoutoo
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  • 4 weeks later...

Have been playing with the VNT again and have gotten it down to 20 minutes start to finish, so it's not hard. But I was reminded of point I meant to write up previously but didn't fully explain.

There are several ways of adjusting the VNT, some don't require the removal of the vacuum diaphragm head but I do not subscribe to that method as the big danger here particularly for a novice is losing your position, I like to be able to see and get at the adjusting screw clearly and cleanly and not have the Allen key come out of the grub screw unless I have the spanner firmly on the nut, this way I can guarantee I have moved the grub screw by the exact amount I intended, 1/3, 1/2 or 1/4 turn no matter what. That way I am in no danger of not being able to return it to the exact setting it had from the factory.

I crack the nut open by the smallest amount, less than 1/8th turn, this allows me to insert the Allen key and make an adjustment with no backlash in the thread and if I need to go more the spanner is still clearly in view and in contact with the nut so I can remove the Allen key and reinsert for the extra adjustment without fear of position loss.

EDIT: After 12 years of the diaphragm going up and down I noticed there was some wear and free play in the pivot point, a little over a 1mm, I reduced that free play today to less than .5mm, so it will be interesting to see if there will be any effect.

Hope the above helps anyone wishing to have a go.

Edited by geeyoutoo
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