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7 Series - E38 (1995 - 2001)

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  #1  
Old 11-03-2013, 01:26 AM
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ebida3 ebida3 is offline
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VANOS rattle

I'm having a slight rattle upon start-up that goes away in 2-3 secs. It may be the tensioner but some say it could be the VANOS. The question is if this is the VANOS rattling how exactly is the noise being produced?
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  #2  
Old 11-03-2013, 05:02 AM
Podmore Podmore is offline
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My car has exactly the same rattle on start-up. Sounds awful - however I think it's a hydraulic cam-follower (valve lifter) rattle rather than either VANOS or chain tensioner. Mine never does it on a warm start-up, only on cold. If it was timing chain or VANOS, it would be every time, I would have thought. VANOS rattle generally does not occur at start-up, but only when the engine is warm, and it's more like a gentle knock-knock-knock at idle.

The valve lifters are pressurised by engine oil and automatically adjust to maintain proper valve clearance; when they wear, they leak down and do not retain oil pressure, so on start-up, there is excessive valve lash which causes that dreadful rattle. As soon as the valve lifter(s) re-pressurise, the rattle stops. I don't think there is much to do about it, except to replace your valve lifters; perhaps using a slightly heavier weight engine oil may reduce the amount of leak-down.
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  #3  
Old 11-03-2013, 05:48 AM
ou18 ou18 is offline
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Sounds like podmore hit it dead on. Meeknet has a write up on the procedure to get rid of noisy tappets...

Give it a read

http://www.meeknet.co.uk/e38/BMW_E38...sy_Tappets.htm


maybe will help solve the issue...
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  #4  
Old 11-03-2013, 08:52 AM
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ebida3 ebida3 is offline
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Quote:
Originally Posted by Podmore View Post
My car has exactly the same rattle on start-up. Sounds awful - however I think it's a hydraulic cam-follower (valve lifter) rattle rather than either VANOS or chain tensioner. Mine never does it on a warm start-up, only on cold. If it was timing chain or VANOS, it would be every time, I would have thought. VANOS rattle generally does not occur at start-up, but only when the engine is warm, and it's more like a gentle knock-knock-knock at idle.

The valve lifters are pressurised by engine oil and automatically adjust to maintain proper valve clearance; when they wear, they leak down and do not retain oil pressure, so on start-up, there is excessive valve lash which causes that dreadful rattle. As soon as the valve lifter(s) re-pressurise, the rattle stops. I don't think there is much to do about it, except to replace your valve lifters; perhaps using a slightly heavier weight engine oil may reduce the amount of leak-down.
Mine is exactly opposite only makes noise at initial cold start ups. Sounds like a can of marbles being shaken for 2-3 secs.
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  #5  
Old 11-03-2013, 09:04 AM
ou18 ou18 is offline
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Ebida,

+1 on the valve lifters. It can sound like that. Take a look at the link i sent you on bleeding that out.

One day after my car was sitting for a while, granted we dont have cold days down here, i started her up and heard a nasty rattle. I thought the same thing you did about the it being TIMING related. Then read that article by Meeknet. Performed it and the noise went away.

Its worth a shot...
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  #6  
Old 11-03-2013, 08:48 PM
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ebida3 ebida3 is offline
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Timm @ meeknet refers to a constant tapping noise that may last 3 minutes or longer. I don't have that. Just the initial rattle upon cold, sitting for two days, start ups.
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  #7  
Old 11-04-2013, 02:58 AM
Jonjo Jonjo is offline
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Cam followers

Quote:
Originally Posted by Podmore View Post
My car has exactly the same rattle on start-up. Sounds awful - however I think it's a hydraulic cam-follower (valve lifter) rattle rather than either VANOS or chain tensioner. Mine never does it on a warm start-up, only on cold. If it was timing chain or VANOS, it would be every time, I would have thought. VANOS rattle generally does not occur at start-up, but only when the engine is warm, and it's more like a gentle knock-knock-knock at idle.

The valve lifters are pressurised by engine oil and automatically adjust to maintain proper valve clearance; when they wear, they leak down and do not retain oil pressure, so on start-up, there is excessive valve lash which causes that dreadful rattle. As soon as the valve lifter(s) re-pressurise, the rattle stops. I don't think there is much to do about it, except to replace your valve lifters; perhaps using a slightly heavier weight engine oil may reduce the amount of leak-down.
Hi guys I agree with you both mine has the same on start up from cold and more so when not been running for a few days but once warm she's mint
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  #8  
Old 11-04-2013, 07:48 PM
Podmore Podmore is offline
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I hadn't previously seen Timm's solution (otherwise know as an 'Italian tune-up') to noisy tappets. I'm a bit sceptical about the merits of the 'air in the oil' theory, and I wouldn't have thought the process described would achieve anything that a good fast drive on the motorway in 3rd gear wouldn't achieve. Given the oil pressure inside the lifter / tappet, I should think that any air would be expelled pretty swiftly; having achieved this, and having got the oil good and hot, there should be no reason or mechanism for air to return to the oil inside the tappet. Why then, on the next cold start-up, does the noise return?

Also Timm's theory (although I note he refers to it as an 'official' reason) that a heavier / more viscous oil would prevent the expulsion of air from the tappet ("The oil in the HVA cavity contracts as the engine cools after a journey and in this way air finds its way into the system, if the oil is too viscous it will not immediately replenish the cavity.") is not sustainable because all oil becomes less viscous as it heats up, and in suggesting that the oil would not displace air, he implies that the oil would be too thick to be able to be forced into the tappet cavity at all for some time - which would mean that the tappet(s) would keep rattling for many minutes until the oil got hot enough and thin enough to work its way into the tappet (which is not the case, in our case). However if the tappet piston is sticking in the bore due to a build-up of gunk, meaning it would not naturally contract into the bore as the oil cooled then possibly the air theory has some substance - however oil viscosity would have little to do with it.

A hydraulic lifter comprises a little piston inside a cylinder; the piston is forced out of the cylinder by engine oil pressure until it contacts the cam lobe. Tolerances between the tappet piston and tappet cylinder walls are such that in a good lifter, the oil inside the cylinder does not leak out to any significant extent once the engine is switched off, and the lifter essentially remains in contact with the cam lobe; once the engine is started again, oil pressure inside the lifter is immediately restored and there is no discernible (or audible) valve lash.

I stand by my diagnosis that the noise on start-up is due to excessive leak-down in some of the lifters.

Last edited by Podmore; 11-04-2013 at 08:05 PM.
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