Variable Valve Timing - How?

[gregoir]

My BIL is having his "dephaser" pulley changed, expensively on a Clio 182. This provides variable valve timing and is hydraulically operated to vary the valve timing. The cam belt, drive belt and alternator are also being changed, expensively.

I know my 1.4 TSI engine has variable valve timing - is this also a potentially a financial time bomb?

[Bristolf2b]

Many modern vehicles have some element of VVT, including VAG diesel engines

 

One of the original ones, the Honda VTEC system, apparently had zero failures if serviced properly (regular oil changes as it relied on oil pressure to move pins to lock the high lift cam). So if designed properly it should be reliable.

[SC03OTT]

Have a read of this if you can. From my very limited knowledge it's nothing like VTEC. Certainly WRT the Clio engine anyway.

http://www.cliosport.net/threads/5000rpm-why.775073/

[Gabbo]

Owning any car is only ever going to cost you money.

All you can do as the owner is make sure its properly & regularly maintained and driven & cared for sensibly.

 

The current generation of VAG engines are made in extremely high volumes & even a small problem with reliability should become well known quite quickly.

On the forums I don't recall many people complaining about mechanical failings with thier petrol VAG engines so I think so are reaosnably safe provided you look after the car.

[gregoir]

Thanks for that re-assurance. I'm old enough to remember mechanical failures A-Z even on humble engines. Granted diesel turbos, AGRs and dual mass flywheels, I can not think of any serious failures with the petrol VW engines recently. There was the cam chain hiccup in older TSI engines. Frequent, annual, oil changes and decent fuel- fingers crossed.

[gregoir]

But does anyone know where the variable valve timing mechanisms are and how do they operate ?

[MoggyTech]

But does anyone know where the variable valve timing mechanisms are and how do they operate ?

It's done by the camshaft pulleys. They are two part, outer driven ring and inner hub, and control is done by hydraulics using oil pressure.

[glosrich]

Another reason for regular oil changes of the right quality and keeping it topped up. These longer oil change intervals may work for the warranty period, but gummy deposits are building up because its not being kept clean, allowing for problems later on.

I've read on a Honda forum about VTEC stopping working because it was gummed up with oil sludge. A clean out and an oil change and it worked again.

[MoggyTech]

Another reason for regular oil changes of the right quality and keeping it topped up. These longer oil change intervals may work for the warranty period, but gummy deposits are building up because its not being kept clean, allowing for problems later on.

I've read on a Honda forum about VTEC stopping working because it was gummed up with oil sludge. A clean out and an oil change and it worked again.

Absolutely, oil isn't just used for lubrication these days, but also as hydraulic pressure control for VVT. These engines are modular design, and if you strip a main end bearing shell then you need a short engine, the crankshaft cannot be removed, been that way since 2005 Polo range.

[gregoir]

OK, I guessed it was by hydraulic pressure. But what is the actual mechanism that enables two concentric rotating parts to shift relative to each other?

I know the use of higher octane fuel enables higher power and better mpg to be achieved- presumably by advancing the valve (and ignition?) timing/overlaps etc.. I guess the engine management constantly reviews this and adjust the timing quite frequently. So needs to be a fast and reliable mechanism.

[KenONeill]

OK, I guessed it was by hydraulic pressure. But what is the actual mechanism that enables two concentric rotating parts to shift relative to each other?

 

It's called a "water sheep" ;) Ok, a hydraulic ram!

[MoggyTech]

OK, I guessed it was by hydraulic pressure. But what is the actual mechanism that enables two concentric rotating parts to shift relative to each other?

I know the use of higher octane fuel enables higher power and better mpg to be achieved- presumably by advancing the valve (and ignition?) timing/overlaps etc.. I guess the engine management constantly reviews this and adjust the timing quite frequently. So needs to be a fast and reliable mechanism.

The outer and inner camshaft drive sprockets can move in relation to each other. This of course alters the valve timing. It's also how they do exhaust gas re-circulation these days. Rather than use an EGR valve and all the mess and problems that can cause, they simply shut the exhaust valve early under certain engine loads thus trapping some exhaust gas in the cylinders. It's certainly more elegant than the old EGR system, and the ECU can give more precise control over the process. 

 

This also separates the EGR and PCV system. In the old system, PCV went through the EGR valve, so you had soot and oil vapour mixing, resulting in the gummed up EGR valves we used to see. The new PCV is a separate process with a much better oil trap, so PCV is now simply bottom end blow-by gas with very little oil vapour going though the inlet manifold.

 

It really is a very clever engine design, plus it sounds sweet, which is something VAG engines were never really known for. 

[Gerrycan]

ACT (active cylinder deactivation) adds another level of complexity into the variable valve equation.

Again it is technology which has been around for some time and I am not aware of any real issues with it although the benefits in some applications do not seem to meet the claims.

Edited 12 January, 2017 by Gerrycan

[norsko]

Her you can see how its done on the TSI engines:

 

https://www.youtube.com/watch?v=gWrrS4FoAQI

[gregoir]

The outer and inner camshaft drive sprockets can move in relation to each other. This of course alters the valve timing. It's also how they do exhaust gas re-circulation these days. Rather than use an EGR valve and all the mess and problems that can cause, they simply shut the exhaust valve early under certain engine loads thus trapping some exhaust gas in the cylinders. It's certainly more elegant than the old EGR system, and the ECU can give more precise control over the process. 

 

This also separates the EGR and PCV system. In the old system, PCV went through the EGR valve, so you had soot and oil vapour mixing, resulting in the gummed up EGR valves we used to see. The new PCV is a separate process with a much better oil trap, so PCV is now simply bottom end blow-by gas with very little oil vapour going though the inlet manifold.

 

It really is a very clever engine design, plus it sounds sweet, which is something VAG engines were never really known for. 

So the cylinders may/do  contain some exhaust gases on the intake stroke? Is it always the same amount or are there some parameters to adjust the quantities?

PCV =Positive Crankcase ventilation? My old BMC A series engines vented the crankcase fumes into the air intake after passing through a wire mesh oil trap Doesn't really sound a new idea in principle!

Still none the wiser as to how two rotating parts can be moved relative to each other using a hydraulic ram. Is this ram also whirling around between the components and pressurised oil is somehow injected into the assemblage?

[patchie]

[MoggyTech]

So the cylinders may/do  contain some exhaust gases on the intake stroke? Is it always the same amount or are there some parameters to adjust the quantities?

PCV =Positive Crankcase ventilation? My old BMC A series engines vented the crankcase fumes into the air intake after passing through a wire mesh oil trap Doesn't really sound a new idea in principle!

Still none the wiser as to how two rotating parts can be moved relative to each other using a hydraulic ram. Is this ram also whirling around between the components and pressurised oil is somehow injected into the assemblage?

Under certain engine loads yes, they retain exhaust in the cylinders for the next intake charge. I think the amount is variable but don't quote me on that. :D 

As an ex Morris 1000 Traveller owner I remember that PCV system all too well. That and the two gearboxes I wrecked, and the three clutches, and the burnt out exhaust valves, and the diff, and the joy of lying on a cold garage floor doing oil changes every 3000 miles. :x 

 

Too old for that malarkey now. Service = Phone call and a coffee or courtesy car :clap: I could rebuild A series engines and gearboxes with my eyes shut a few years back. Mind you, I had that moggy for 11 years and got all my money back and change.  

[James@RRG_Skoda_Rochdale]

There were some failures on early 1.4TSI engines that were dealt with very quickly. The pulley mechanisms were replaced and production changes were made.

[gregoir]

I see that interesting video is for a Nissan. Is the VW system similar and is the change in timing also a fixed 'jump' and not variable?

Thanks for the information and inputs.

My knuckles have almost healed from all the BMC repairs; my mind is still scarred. Modern cars are ,on the whole , greatly improved and certainly much more reliable and durable.

[MoggyTech]

I see that interesting video is for a Nissan. Is the VW system similar and is the change in timing also a fixed 'jump' and not variable?

Thanks for the information and inputs.

My knuckles have almost healed from all the BMC repairs; my mind is still scarred. Modern cars are ,on the whole , greatly improved and certainly much more reliable and durable.

Knock yourself out with the following VVT self learning guide.

http://www.volkspage.net/technik/ssp/ssp/SSP_246.pdf

[gregoir]

That's very interesting MoggyTech and answers my questions. Clean oil is very important in the mix. Just hoping none of my sensors fail.

[MoggyTech]

That's very interesting MoggyTech and answers my questions. Clean oil is very important in the mix. Just hoping none of my sensors fail.

To be honest, modern cars scare the bejesus out of me. Fine when they work, nightmare when they fail. I stopped worrying about cars and just accepted if it goes wrong, it's either big money or warranty.