Talk Morgan Forums Morgan Sports Cars Morgan Aero 8, 2012< Plus 8, SuperSports, Coupe & Aeromax The BMW Engine

I’ve been trying to work out exactly how the very complex valve system of the BMW motor in my Plus 8 functions.
After a lot of reading of BMW documents and posts on BMW forums I think I understand it all.

The BMW N62 B48 V8 has “Double Vanos” and “Valvetronic”.
But what are they?

Double Vanos is relatively simple to understand: in essence it is a continuous alteration of both inlet and exhaust cam shaft position based on engine speed and throttle opening. In essence a fully automatic “advance and retard” control for the valves, and indirectly, spark timing.

At low engine speeds timing is retarded so the valves are open later to improve idling quality and smooth power development. As engine speed increases the timing is advanced so valves open earlier: this enhances torque, reduces fuel consumption and lowers emissions. At high engine speeds the valves move back to a retarded position for full power delivery. The cam shafts each have a range of movement of +/- 12 degrees, which is quite significant. But it isn’t quite that simple as the timing change of inlet and exhaust cams can be altered independently so altering overlap: this is used to manage gas flow and keep the cats as hot as possible. The timing also works together with Valvetronic, which gives continuous and precise control over variable intake valve lift.

Valvetronic-equipped engines use the amount of valve lift for air flow control, rather than a butterfly valve in the intake tract. In other words, in normal driving, the "accelerator pedal" controls the Valvetronic software rather than the throttle butterfly plate: true "drive by wire". There is a butterfly, it is used for starting and as part of the “limp home” mode if the main system fails…!

The operation of Valvetronic is complex as there are an extra set of rocker arms, called intermediate arms positioned between the valve stem and the camshaft. These intermediate arms are able to pivot on a central point, by means of an extra, electronically actuated third camshaft. This movement alone, without any movement of the intake camshaft, can vary the intake valves' lift from fully open at 9.9mm for maximum power, to almost closed, at 0.18mm, for idle.

Add Double VANOS and Valvetronic together you end up with a very flexible engine that is both powerful and efficient, easy to drive due to good low end torque. I think it is an excellent device, particularly when connected to the ZF 6HP 26 automatic transmission, which is almost as complex as the engine!

But it is all very complex, controlled completly by computer and probably almost impossible for the traditional DIY engineer to work on!

If anyone can add more to this description, please do so!

Excellent description - and like all complex engineering solutions, a real b*gger when it goes wrong.

And things do seem to go wrong on them at high but not stratospheric mileages ie. under 100K miles.

And, while my 2011 BMW with double vanos was recalled last summer for 13 hours investigation and remedial action on the vanos (at no cost to me) I'm not convinced Morgan would take the same approach!! And they returned the car with major engine issues so it had to go back again. Happily ok now...

But the engine is a peach and works seamlessly when on song. I don't think they like very high g forces in any direction for long so don't do any loop the loops!

One comment from the factory.

If you knock the sump, even slightly, at the front then change it. The oil pick up used to drive the clever valve gubbins is there and so it can cause a shortage of oil to the system leading to expensive issues.

Peter, you are probably aware that the VANOS shafts are adjusted by solenoids, which can fail if the oil seals on the shafts harden and cause a level of 'stiction' that the solenoids can't overcome. This has two implications:

1) drive your car regularly and hard !! Oil seals will stay flexible for longer if they do not dry out.

2) if buying an aftermarket warranty, be wary that the provider may need quite some persuading to accept that the VANOS shafts are effectively auxiliary camshafts (and therefore on the list of covered components) and not some weird item that is not on the list of parts covered. Mate of mine had quite the battle, but won in the end. Just saying...

I'm very aware that the VANOS system requires a perfect oil supply and that aged and hardened oil seals are bad news. The answer is to use exactly the quality of oil specified, change it every year and never let the level drop.

As far as Tarka is concerned, 19800 miles in 15 months would seem to be "regularly" and using the revs sensibly is also a good idea, so holding lower gears when having "fun" cannot do any harm!

So, all being well another 80,000 miles should be possible, but nothing is certain. The VANOS/Valvetronic system can be rebuilt, but it is wings off, if not engine out.
Fingers crossed!

There's advice out there that says the VANOS system really appreciates a 5,000 mile oil change. Something worth considering.... Not that expensive to do.

Interesting Peter - thanks.

The alternative is to just change your car before it starts to cause problems.

If you think the ZF 6HP 26 is good in "standard" BMW guise you should try it with the Alpina programming

I change my oil every year with a service every two,I use a Marine pump with a tube that goes down the dipstick.You just pump it up and the oil comes up and collects in the base of the pump,no mess no fuss.


Em