BMW 7-Series E38 (1994 - 2001) - 728i Cold engine -- light knocking

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Sat 1 Dec 2007 21:28
728i Cold engine -- light knocking - Cheeky
Hi all. Went to see a E38 1999 728 today. 90 000 miles and good money. Everything works, good history (BMW and independent) -- however, I walked. Didn;t test drive yet as car boxed in the forcourt. No nasty smoke and smooth idle expect for a light knock which got faster with engine speed. Dealer said it was because the oil needed to get round and hadn't been run for a while. I can accept that, however, would have thought the knocking should have stopped after 5 mins or so? The straight 6 BMWs I have seen in the past have not made this sound - am I right to walk and could it mean a top end rebuild?

Edited by Pugugly {P} on 01/12/2007 at 21:30

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Sat 1 Dec 2007 21:46
728i Cold engine -- light knocking - Aprilia
Without hearing, its almost impossible to say what it is. If it was light and from the top of the engine then possibly related to the valve/cam assy. These engines have VANOS which could be at fault. Its about 5 hours work to get at the cams and 15 hours to R&R the head, so factor this into your deal if you decide to go ahead with the purchase.

I owned one of these quite a few years back when they were the 'current model' so to speak. To be honest I think they are over-rated cars, I didn't find it that tremendous to drive. I had a few electrical problems and then cooling problems.
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Sat 1 Dec 2007 21:59
728i Cold engine -- light knocking - Cheeky
Thanks, as I figured. Presume yours was near silent as it should have been then? It is local so I may pop back for a test drive this week and see if the theory "it just needs a run round the block" is the only problem to get the oil round. If it still makes the noise once the test drive is over, I'll leave well alone...

I've had an E39 2.2litre which was very smooth and no hint of any untoward noises, so I thought it unlikely from the 2.8 relation. ONly remember my previous 520 did sound a little clattery with the bonnet up - however, put that down to it having a timing chain rather than belt assembly.
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Sat 1 Dec 2007 22:07
728i Cold engine -- light knocking - Aprilia
Cheeky

The engine in the 728i uses a chain - two in fact (a long one to the ex cam sprocket and then a short relay chain to the in cam sprocket). The VANOS unit sits in front and can be responsible for noise.
Mine was a reasonably quiet engine although it did actually have some camshaft wear (lobes) by the time it hit 90k and could sound a little 'thrashy' when revved with the bonnet up. No knocking though. I suspect the vendor is hopeful that its a sticking tappet or some such. It could be. If the noise goes away once the motor has had a run then don't take this as the problem gone away. Go back and listen to it again the next day and see if it knocks when you start it cold.

Edited by Aprilia on 01/12/2007 at 22:08

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Mon 3 Dec 2007 07:27
728i Cold engine -- light knocking - Collos25
Little end knock common on 728i's especially when cold will run for years with it .
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Mon 3 Dec 2007 08:55
728i Cold engine -- light knocking - Aprilia
Little end knock common on 728i's especially when cold will run for years with it
.


Not so sure about that - little end knocking tends to get worse as the engine warms up (the oil gets thinner).
Whatever the reason, it is difficult to diagnose without hearing, so I would get someone on the spot to check it out.
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