Camshaft sudden failure?

[mike-f]

OK I have a Avant 1.9Tdi B7 with 248K . Doing around 65 on the motorway, the car developed a sever vibration, slowing down onto the hard shoulder it was obviously misfiring on one cylinder. I completed the journey slowly. Restarting when cold it shows the same problem. I have a basic vgate 505 code reader which showed no stored codes, so decided to try swapping the the injector loom which did not help. So then decided run it with individual injectors disconnected, and found it was the same with #4 disconnected (would not run with the others pulled). So tried it with a secondhand injector fitted and its just the same. So digging deeper, I have measured the cam lift on all the cams:-

Cylinder 4 Ex 5.6mm In8.7mm (gouge in PD cam also)
Cylinder 3 Ex 5.95mm In8.7 (gouge in PD cam also)
Cylinder 2 Ex 7.2mm In5.25
Cylinder 1 Ex 8.7 In5.35

The question is could this suddenly cause it start misfiring? I cant see if any of the tappets have broken through though they do look worn.

What else should I check before i start to remove the Cam?


I don't want to spend a load on parts just to find its something else wrong, and it does sound very rough!

Thank you

[mike-f]

OK some great replies from the forum!

I have now replaced the cam and tappets. The car now runs perfectly. So to answer my own question, yes the cam can suddenly wear and cause the engine to sound extremely rough, almost like big end/ little end failure.

On removal of the cam, the lower cam bearing shells had worn through the bearing material. One tappet had a hole in it, and several others were very dished, but several perfect. I must admit I am not impressed by German engineering! In fact on the whole i would not rate Audi VW engineering above an old Lada / Trabant. The sheer number of faults that span years of model updates is astounding. Every fault I have found on my 2008 B7 A4 seems to have been around since the 1994 B5 !

[Gazwould]

Servicing interval and what oil was used ?

[mike-f]

9000 or less using 505.01 spec oil, as it should be.My last non Vag diesel went to 339,000 on the original clutch, turbo and water pump. This is not a maintenance issue just bad engineering, and design. Looking at the top end, the design is pretty poor. Tappets are to thin on the top face, and cam bearing surface to small for the given loads. This along with poor quality of materials is a recipe for disaster. Its only when it happens and you start looking into this that you realize how poor VW/Audi are. Most other company's would have redesigned at the first sign of problems, but it seems the Germans just shrug and blame anyone else but themselves. In the last week read some pretty dreadful stories of early cam failures, even cars with full dealer service history.

[Gazwould]

Yeah for sure a PD camshaft etc is inferior because of it's narrow lobes thus high loads .

You're not using the best VW oil spec and oil and filter cheap , engine expensive , change every 6 months .

[Rob69]

That is a fair old ammount of wear on the lobes! I'm surprised it was not more apparent prior to your motorway incident. I think when they introduced the PD cylinder head and stuck it on the older VE block they were cramming a lot onto a relatively short camshaft and the lobes had to be narrow to fit it all in. Bearings are also narrow and badly supported. I've worked a lot on Cummins engines with PT unit injectors and the cam lobes are proportianly far wider than the vw PD shafts, with rollers also on valve followers, but a lot more space on the shaft to play with on them.
I think as car diesels went for lower emmissions, higher outputs and better driveability along with manufacturer cost saving they lost the longevity and simple reliabilty of the old school set up. You don't say what your previous high miler diesel was but I suspect it had rotary injection pump and simple wastegate turbo with solid flywheel?
Sorry i didn't see your OP , i would have probably chipped in and rambled on if i had! Hope you have many more miles on the new top end.

[mike-f]

Great reply Rob,

Well yes it was a 1.9 XUD, I am sure the engine would have gone on for ever, shame the rest of the car was not so keen. I think what upsets me more as a Engineer, is the lack of design progression. I have seen other manufactures have problems with engines and introduce updates and mods in latter versions.
It seems to be a German problem that they just don't like to change anything after they have found a problem. This seems even more apparent after the problems that BMW are having.
On the PD engine I can see why they are stuck with the narrow cams, but cant see why then could not have increased the Journal diameter and also improve lubrication to the tappets. The latter seems to be totally lacking, just relying on oil thrown off I don't know where! Lack of lubrication is possibly why failure of the first (inlet cam on cyl 1) and the last cam (Ex cylinder 4) is so common. The strange thing is that it was running OK up to the failure, over the previous few months I had noticed a drop off of MPG from 55 down to 50 and also a slight engine wobble on tick over. I had put this down to slight timing belt stretch as it was due a change (done 70K). It was surprising that the failure was so sudden, I guess cam wear progresses until the tappet has no further compensation left.
One thing to come out of this is that I am not sure you can trust injector testing. I sent the injector off cylinder 4 for testing, it cam back as being faulty (open circuit) hence I fitted a replacement. It was only when the replacement did not solve the problem that I suspected something else. I guess that the removed injector is most likely fully working! A quick test shows 0.6 ohms which seems to be correct, and not open circuit.