Help! Tappet rattle!!

Hi, My 850i has developed a tappet rattle. The normally silent engine has now started to rattled loudly on start up (timing chain tensioner rattle) this quietens down as soon as the oil light goes off (2 seconds) but there remains a noisy tappet on the RHS bank (regular tap consistent with engine RPM) Occasionally the tappet sound will stop. I checked the oil level and all is OK and it's not due a service yet.

I am thinking it is due to low oil pressure to the hydraulic tappets (maybe the RHS bank, as the timing chain rattle at startup arrived at the same time as the tappet noise).

Does anyone have any ideas? Could this be a symptom of the banjo bolts coming loose? I have never dug that far into the engine to look at them but I do have a 1991 model. Any help will be greatly appreciated

thanks Les! I think it's worse then that though. This morning, I started it and it's like there's almost no oil pressure to the top end at all, tappets rattling on both banks plus the timing chain as well. The rattle is real bad at initial startup but decreases just after the oil light goes off.

This whole issue has developed over the course of 1 day, so it's like something's failed in there. I won't run the engine as the noise scares me too much and I don't want to damage it.

I have a good repairer who I'll get it towed to tomorrow

and it only gets worse... the repairer cannot look at it until 10 March, they are fully booked!

Anyway, I have been having a think about the problem...

With the initial symptom being that there was timing chain rattle at start up, it was almost like the reservoir that supports the chain tensioner was draining when the engine was stopped, hence requiring the oil pump to refill it when the engine started. (Same thing happens when you remove the tensioner to replace the O ring and start the enging 1st time afterwards) I have no external oil leaks, so it's not an O ring failure there but... could there be an internal leak of some magnitude? Depending upon the oil supply route to the tensioner, the leak could cause the pressure to be very low at this point even when the engine is running. If the tensioner supply was the same as the feed to the hydraulic tappets then this would account for the ongoing tappet rattle...?

I have yet to put a presure guage on the oil pump but the light goes out almost immediately (as it always has, sorry if I over estimated this as 2 seconds) so I don't think it lack of overall oil pressure.

Yeah I may be clutching at straws here.

Does anyone know what route the oil takes to get to the tensioner and the hydraulic tappets?

Are there any internal seals or otherwise which if they failed would cause the tensioner to drain?

From a servicing history, I'm religious and always change the oil and filter when it's necessary, plus I use fully synthetic oil (sam eoil for the 5 years I've owned the car) It uses virtually no oil between changes and it's never been overheated. This fault started yesterday with the initial rattle at startup and now today it rattles continously!

All help and advise very much appreciated

Cheers, Richard.

Drained the oil and dropped the sump today however all looks 100% down there, nothing loose and nothing nasty in the oil or the bottom of the sump that might be a clue to the problem. The chain tensioner looks OK too (not that I know what it should look like but it doesn't look damaged).

Seeing I've been reading all about banjo bolts lately, I'm now digging into it from above. Hopefully this will give me a chance to inspect the tensioner from above too plus putting my mind at rest by loctiting the banjos. I'm hoping I'll find something obviously causing the rattle and be able to fix it without going bankrupt... still can't fathom how this could be banjos.... would they be capable of dropping the oil pressure to the lifters on both banks?

Head bolt replacement procedure

Well I've got down to the valve gear (who said 2 hours to remove the inlet manifolds? They mustn't have meant earth time!) 6 hours later... Banjo's beautiful (no way could they effect oil pressure anyway, they are miniscule) anyway, I removed them and reinstalled with Loctite, so no future problems with banjos. Luckily I did take a peek in the top end cos there was 1 broken head bolt. I was able to remove the stump, at it was broken off right at the head. The engine has never overheated or lost water, so I think the gasket is still sealed OK.

Does anyone know the procedure for replacing the head bolts and the torque settings I'm hopeful that I can do this without disturbing the head or gasket (like 1 bolt at a time) but I'm uncertain of the torque setting. Any help out there much appreciated.

Anyway, this is not related to the rattling (bolt head tucked safely away and looking at the condition of the washer, it had been broken off for a long time)... but in thinking about it further, I've been unable to dismiss the thoughts of it being related to low oil pressure, so I removed and stripped the oil pump... all looked good until I got to the relief valve, which was stuck tight (stuck closed but basically could have been stuck in any position, it was solid). When I finally got it apart, there was a huge buildup of fairly solid gunk in the end of it. I have now cleaned it and it works freely and fortunately I've not caused any damange to the valve itself or the bore where it fits. The pump is now reinstalled and awaiting a test (fingers crossed!) More news once I'm back together...

An interesting observation is that the way BMW have designed the pump is ingenious but also prone to this type of failure. Unlike normal oil pumps, the pressure is not monitored at the pump outlet, it is in fact monitored somewhere further downstream (maybe the outlet of the filter). Pressure at this point is fed back to the pump via a tiny tube and this pressure is used to open the relief valve. This is clever, as it compensates for filter losses, etc. The bad point about this is that as the relief valve operates, the small amounts of aluminium that abrade off the bore remain in the area on top of the piston, there is no means to flush these away. It is likely that this build up could effect all pumps of this type, so I'd suggest that folks inspect the oil pump if they ever have the sump pan off.

It is an easy procedure, the relief valve can be removed without removing the pump from the engine. Be careful, as the spring is strong and will fly out once the circlip is removed, so take precautions. If it's good, the relief valve should fall right out after the spring (together with any debris) If it's stuck, I'd say you'll need to remove the pump to strip it and clean it.

Well back together and still rattling so stripped again... 1.5 hours to get down to the camshafts this time... really helps when you know what you're doing!!

The lifters that I thought would pump up once I had oil pressure look to be dead, as they are compressed. 3 in total, 2 RHS bank and 1 LHS bank. I'm guessing that the reduced oil pressure put additional load on the lifters and caused them to fail.

It would have been helpful if BMW had fitted an oil pressure guage, as I'd have had advanced warning that something had gone astray and may have been able to attend to it before it caused any damage. Warning lights typically come on at around 7psi, which is way too low IMHO.

All sorted - tappet replacement completed.

I spent some time testing each tappet and found 3 that didn't seem up to the mark. 2 were obviously stuffed, as they were totally colapsed. I attempted the "approved" process which is to push down on each tappet while the engine is hot and if it compresses then replace it but it takes so long to strip both heads that the engine was no longer hot by the time I'd got there.

So what I did do was to rotate the engine to a point where certain valves were open, leave it 15 minutes to allow the valve spring force to act on the tappet, then rotate it so those valves were now closed. I then tested each to see if there was any play in the tappet. Those that weren't tight I replaced. Note some could be moved sideways but there was no actual gap between the back of the lobe and the rocker, I didn't replace these ones.

The approved process to remove the tappets is to use a special tool to compress the valves to remove load from the rocker, so it can be slipped out from under the cam. I don't have the tool but I was able to remove the rockers by loosening the camshaft bearing caps to allow the cam to rise up sufficiently to remove the rockers from beneath. What was helpful was the the faulty tappets were in the rear half of the engine, not the front.

How this worked was that I rotated the engine so that the open valves were at the rear of the engine and there was no load on the cam at the front end of the engine. (ie no valves were open) It's also necessary to ensure that there is no load on the valves whose tappet needs replacing. From this point do not rotate the engine at all. Put some rag over the drain holes to the sump, so no tiny parts can fall down there. Then progressively loosen the bearing caps, ensuring that any valve spring load was always taken by the cap closest to the open valves. No need to remove the spray bar unless you plan to clean it or loctite it. It's only necessary to loosen the caps to till the top of the stud is just below the top of the nut. At that point, there is enough room to remove the tiny actuator on the head of the valve. This then gives enough room to slip the rocker arm out and then the tappet can be removed.

Replacement is a reversal of the removal process. I filled each tappet housing with oil prior to inserting the new tappet and lubed the top of each new tappet, where the rocker acts on it. Tightening down the cam needs to be progressive across all bearing caps to ensure the cam is not subject to any forces which may cause it to bend. Once it's all done, pour a good quantity of oil on each cam lobe to ensure it's well lubed before reinstalling the rocker covers.

On restarting the engine after final assembly, there was still a tapping from one tappet on the LH bank. This was not too loud and cleared after a 10 minutes of running at idle. It did reappear next time I started the engine and cleared after another 15 minutes. I then drove the car for a good 40 minutes before switching off, I think this is necessary to ensure any air in the tappets is bled out. Since then there's been no noise, so my V12 is again running silently