300TDI Enigne Rattle.

Hello All,
Apologies for dropping this in as a new guy, I'm a long time lurker and would like some help with an engine problem. I did pitch up on LRO but suspect I might get better coverage here.

I was driving into the office this morning all was going normally. As I pulled away from a roundabout and changed gear from 1st to 2nd, I heard a horrible, heavy, fast, metal-on-metal bang/rattle that stopped as soon as the engine rev's dropped down.
To cut a long story short, it's starts to rattle at anything over 2500rpm, happens on or off load, its really sharp and loud (reminds me of a blown big-end type of noise) but stops completely when the revs are low. If kept under 2500rpm, the engine is quiet and smooth with no smoke. In other words, normal.
I've read about vacuum pumps failing but nothing that I've spotted on the forums so far mentions anything about noises only at certain engine speeds.
Becuase I'm at work, I cant really spend long on the details of it this morning, but will take a closer look at lunch. I *think* it should be ok to get back to the yard tonight as it seems to be fine if driven slow.

I'd appreciate any idea's you may have, if anyone can confirm a blown vacuum pump, I'll gladly grab another at lunch (LR indy just round the corner from my office).

I hope its not terminal because I've just done an awful lot of service work on this one. No upgrades yet, just servicing. It would be a shame to junk it all for another engine..

After a closer look and a bit of a test-drive during lunch, it would appear that the horrid rattle-of-death is not the Vac-Pump, big-ends or mains but much further up the block. I would hazard a guess that it's the cam or follwers at the front end of the engine. Certainly thats were the noise sounds loudest/worst.
The odd thing is that as I drove it back to the yard (about 10 miles on country back roads) the rattle was coming and going. To begin with, the rattle was exactly how it started this morning, quiet under all conditions until 2500rpm then a nasty heavy rapid bang/tap until revs drop below 2500 again. After about 2 miles of quiet and steady 1500RPM-in-top and very gentle throttle work up the A10 , the rattle reappeared in a smaller, more frantic way and much more 'external' sounding. Fearing a stranded-by-the-A10 type scenario, I changed the route to county backroads and discovered that the rattle is much lighter now, happening at any rev's but not is affected by load . It makes no difference between light throttle, heavy throttle, overrun or other wise - it sounds the same only getting louder/faster with more RPM's. Wierd side-note: (you knew that was coming huh?), when holding a steady light throttle in any gear at about 1100rpm, the tappy noise will appear and disappear. Most Odd.

Another bit of oddness is that when going downhill, the noise completely stops. Even under reasonably hard throttle and mid high rev's. Go uphill again and it starts back up again. For little bit. And then stops for a few seconds. And starts again. You get the picture.

It did get me back though, and I manged to get to where I needed to be by deploying the Sunday Car :twisted: (which is supposed to be resting up for winter) but suffice to say I am confused.com about the Disco problem.

Next step: pull the Vac pump off (not a problem as I wanted to perform the nut&bolt trick on it anyway) and then pull the head off. Thats more of a PITA as my head is good. It's flat and it seals beautifully. Not for much longer it seems. Bugger.

Hold this beer, pass me a breaker bar and watch this...... :twisted:

You say you have done a lot of service work on the engine - cambelt replacement by any chance ?
The reason i ask is that I had a problem that sounds very like the one you are having.
Turned out to be a faulty timing belt idler bearing. The noise was dependent on revs and also inclination of the car and going round bends. The noise took several months and about 5000kms to develop into something worrying but I,m very glad that I investigated it as it would have certainly ended in disaster if the bearing had broken up.
I bought the cambelt kit from a well known LR parts supplier in Derby (not sure if I,m allowed to divulge names !!!!) and to be fair, they did honour the 12 months parts warranty.

does it do it at idle, when you can stand next to the open bonnet?
try applying a bit of pressure to the fanbelt tensioner. use a decent long screwdriver or similar, and stop the tensioner bouncing up and down.
then replace the tensioner.