Missing VVIS plate - parts required for reassembly

[RedCarsGoFaster]

My NSX is in for a service and a boroscope inspection of the intake has shown that the screws holding one of the VVIS butterfly plates have backed out, and the plate has fallen into the lower intake plenum.


There are no signs of poor running, so I'm crossing my fingers that nothing has been ingested into a cylinder so far . . .


I've asked the workshop to strip down the intake system, retrieve the plate (and hopefully both screws), and reassemble.


Is it considered advisable to re-use the screws, plate, and rod currently fitted to the engine? What other parts would be required for reassembly?


What fixing methods are considered acceptable when installing the screws? Just Loctite, or something more robust?

[Kaz-kzukNA1]

For the parts, this, plus the the EGR gasket 18721-PR7-A01 x 1;
http://www.nsxcb.co.uk/showthread.ph...ently-required


Process;
http://www.nsxcb.co.uk/entry.php?227...esistor-etc-17
http://www.nsxcb.co.uk/entry.php?228...esistor-etc-18
http://www.nsxcb.co.uk/entry.php?228...esistor-etc-19


If using Loctite, you will need to use the high temperature spec one but personally, I won't use it for the following reason.




In order for Loctite to work properly to the spec, you must create oil free surface at both the screw thread as well as at the mating thread on the shaft.
You can't clean both threads without first backing off the screw completely away from the shaft/plate and by doing so, you will very likely to widen/deform the shaft thread because the end of the screw is already staked at the factory.

Backing off the screw partially enough to apply Loctite is not recommended as you will never be able to create oil free surface with that method.

Instead, the proven method is to use the liquid gasket designed for the oil pan gasket purpose.

On our NSX, there is a rubber gasket between the eng block and the oil pan to seal the mating surface.
However, there are many production cars without the rubber gasket in use at the oil pan and relying on just the specific liquid gasket designed for this purpose.






I normally just tighten all of the screws without backing off at all (unless it has already fallen off) and clean the plate and shaft as well as the exposed surface of the screw head and staked section as much as possible to create oil free surface.
Then, use this specific liquid gasket at both end of the screws so that it will increase the initial torque if ever it wants to turn anticlockwise in the future.
Not perfect but minimum risk.

You could stake the screw end further but I don't know how strong the shaft is so too scared to do so.

Regardless of the method used, the key is to check the screw once a year.
It will take years before the screw to completely back off and fall off.
You can spot the initial rattle just by operating the VVIS with your finger.

You don't need any special tool.
Operate the VVIS with your finger while keeping TH at WOT and look for the rattle at each plates.






Nowadays you can get cheap fibre scope connecting to your mobile phone, etc so you can even look for the tiny gap between the plate and the screw head to detect the first sign of the issue.

You still have months/years before the screw backs off completely from that point so plenty of time to react.

Just make sure to operate the VVIS with your hand. The screw hole is offset from the centre line of the plate so depending on the angle of the shaft, it may hide the gap at the base of the screw head as the plate will shift its position.

Kaz

[britlude]

Kaz posted on this very subject a few weeks ago....

the missing butterfly
http://www.nsxcb.co.uk/entry.php?227...esistor-etc-15

where it was hiding...
http://www.nsxcb.co.uk/entry.php?227...c-16&goto=next



edit.. tooo slow!

[RedCarsGoFaster]

Thanks Kaz, much obliged. I wouldn't have thought of using the liquid gasket, but it seems a neat solution!

Just to clarify - you're happy to re-use the screws that backed out, once you have retrieved them and cleaned them up?

[Kaz-kzukNA1]

There is a reason why these material and coating are in use inside the VVIS so I'll re-use the original parts even though the staked screw has already backed off.

You will notice some increased friction at the very beginning of turning the screw into the shaft due to the staked screw end.
You also have 50% chance of placing the screw back into the different mating thread.

Just make sure to use the specific liquid gasket designed for the oil pan usage.
There are many different spec on the market and some of them are not suitable for this purpose.

Please check the screw once a year.
This fix is only to increase the initial friction.

Because of the offset of the screw hole on the plate and engine vibration, as some of the owners experienced including you, once the screw backed off a little, there is enough toque generated to back off this screw.
You will be amazed how much initial torque is required to back off this screw.....


Kaz

[RedCarsGoFaster]

Thanks Kaz!

[Papalazarou]

Kaz,
I sell the gasket maker you refer to, and as you stated, the right product is very important. There are three main products out there; acetoxy, oxime and elastomeric. The cheap factor ones are usually acetoxy, it is old tech and not recommended for modern engines. They can cause corrosion problems and aren't always oil resistant.
The oxime product is good. It is oil resistant, non corrosive, sensor safe and has a shorter curing time.
Elastomeric is the best. It cures even faster and is stiffer than the other products.
In summary, avoid acetoxy. Oxime and elastomeric are both great.
Here are some recommendations;
35044 Permatex "the right stuff" 158ml (pressurised container) (elastomeric
35134 Permatex ultra grey 80ml (oxime)
Innotec easy gasket 275ml. (Similar to elastomeric)

[Kaz-kzukNA1]

👍
Thank you for the extra info.

Kaz

[RedCarsGoFaster]

Now that's what I call specific. Thanks guys!

[RedCarsGoFaster]

Update - the workshop reported following disassembly that the thread on the screws that had come loose was worn smooth to the extent that they were not happy to refit them. In the end I sourced a replacement VVIS assembly from Christian at ATR Racing, which has now been fitted.

Apparently the replacement unit seems to be of a later standard, with a different method of swaging/staking the screws to prevent them backing off. I did not see it in person, but the tech considered the new method of fixing to be sufficient to prevent the screws backing out, so the additional precaution of a dab of sealant on the screw heads has not been applied. Will continue to check the screws annually.

I'm told the idle has now smoothed out a little, but I will have to confirm that when I'm reunited with the car. We did also change the injectors, so if the car is running smoother it might not all be down to the missing VVIS flaps. Nice bonus though!