Turbo Failure and VNT Actuator Repair

[davegsm82]

Not on a T25, but still on a VW. My 290,000 miles old MK4 Golf TDi ate its turbo last thursday, it had been making an odd buzzing noise for a few days while under load, I thought it was a boost leak but after a sustained high speed run I pulled off the carriageway onto a winding country road at which point the engine began to surge and lose power for a few seconds before lurching violently and going into what I thought was limp mode.

Managed the next couple of miles to Go-Karting ok without excessive noise or smoke, just no power.

Upon leaving the Go-karting track I started up and still had no power, decided to swap the N75 valve for the N18 thinking it may be the actuator valve that had failed. When I tried to drive away I left a smokescreen which looked like something off of the 1980's batman programs.

After about 4 miles I had to give up as I was becoming a hazard to other road users.

Got carried the next 20 miles home on the back of a flatbed and only today managed to get a look at it. The following picture is the intake side of the turbo;



It should look like this...



Needless to say, the impeller has disintegrated and ingested parts of itself. There was probably 3-4mm of play in the rotor shaft, the exhaust turbine had fared any better and had clattered the VNT vanes so the whole thing was a write off, not even a new 'core' would save it.

The second turbo is my 'spare' but I'm going to fit something more suited to my engine, i.e. a VNT17 from a PD130.

Dave.

[davegsm82]

After fitting a VNT17 from a PD130 I have been test driving the Golf this weekend, I was massively unimpressed by the lack of boost below 2000 RPM.

I figured something was wrong, although I suspected jammed VNT vanes. What I didn't suspect was the same failure I had actually seen early on with my AFN/DHL install -----> https://club8090.co.uk/forum/viewtopic.php?f=12&t=141442" onclick="window.open(this.href);return false;

Turns out the VNT actuator had a hole in it and was not 'pulling in' because it was taking so much vacuum that the lower engine rev's just weren't enough so it would only pull in when the engine was over 2krpm.

I stripped the knackered VNT actuator down to show what happens to them all apparently...



This is the Actuator... I ground around the edge with a bench grinder.





Inside there is a spring on the vacuum side (where the pipe connects) and a piston with a rubberised diaphragm round the outside.






When you push out the piston you can see the diaphram.






....But this is where the problem lies, a great big hole (and some others) on the diaphragm.





All because of this, this rusty junk was in the top side, i.e. the side of the piston open to atmosphere.





Something in the top side has rotted away to nothing. looks reasonably intact but I guess it's just flaked away. Eventually that crap all collects round the outside of the piston and rubs a hole in it when it goes up and down.

[davegsm82]

Since I have 3 vehicles under my duty of care which use this same actuator I decided to try and repair it as I don't have a spare.

After stripping the piston down I found that the actuator rod was so badly corroded that I wouldn't be able to re-use it reliably, the old one is on the left, the one I came up with is on the right.





The new rod was made from a socket cap bolt which provided enough threaded and unthreaded sections. The head was cut off and a Die run down the unthreaded end as per the picture below.





I found a ridged rubber diaphragm which was removed from and old piece of equipment after maintenance. The outside was trimmed down to the correct diameter and the center cut out to accomodate the bolt etc.





The diaphragm is then sandwiched between the piston and the large washer and all tightened up.





The whole unit is then reassembled in the original housings, after they have been severely de-rusted and cleaned up with a shot blaster.






This actuator now functions normally.

[Aidan]

nice work

[lloydy]

Well done, lot of work there. You can see why garages don't repair these for customer though, a lot of labour there.

[syncroandy]

The actuator cans are available as a spare part if needed. If fitting a used turbo, their function can easily be checked using a Mityvac.

[davegsm82]

Thanks chaps, yes I can see who no one bothers to repair them, massive pain in the a$$.

I only repaired this one as a spare really since replacements seem to be about the £40 area. It proves that they can be repaired in a pinch if you have the appropriate bits and pieces paying around (and some spare time!)

Dave.

[Oldiebut goodie]

Man after my own heart - I will always attempt a repair on things that have a chance of being repairable before condemning them. It was the way that I was raised - I started with straightening used nails for my father!

[syncroandy]

Agreed with attempting a fix before bin and replace, my spares stash is healthy and my local scrapper is friendly ! If anyone on here is short of the odd TDI part it might be worth giving me a bell as I have spare spares.. I have an exc. head, pumps turbos ECU's, etc.