Tapping noise on idle

Hi guys Recently purchased a 996 c4 3.4, I've noticed it tapping on hot idle. Never when cold, and does away when increasing revs No loss of performance, it's been run on millers 10-50 nanodrive It had a Full Hartech rebuild 12k ago https://youtu.be/X3qjfb9vKcs Anything to worry about? Thanks Marc

You should have posted that before midday...

Did it have a top end rebuild?

Not to sure, it's had a closed deck rebuild, I've attached the works below

I'd be talking to Hartech. They'll soon have you sorted

I would email the question and link to hartech. Sounds like the tappets to me, used to get same noise in the 993 when it was on thicker oil until oil got hot. Changed to thinner oil and was not a problem any more. Different though as yours is noisy when hot. Noise is same though. Try this renlist link, seems to be same symptoms as yours in a 996 https://rennlist.com/forums/996-for...lve-noise-fixed-my-findings-and-solution.html

Not much help but I have heard exactly the same on a couple of 3.4's when hot and at Idle, I think it was RPM also that mentioned this in one of their buyers guides as not uncommon on 3.4's. To me it sounds like a hydraulic tappet/lifter not holding oil pressure, does the noise stop if left idling for a while?

I've had 3 different 3.4 996"s all have ticked on hot idle, all ran fine with no issues. Posted before by someone else, but. The term "Tickover" was apparently coined by the engine speed that the ticking noise from a reciprocating engine ceases to tick at. Increasing the low idle speed on these engines tends to stop the ticking noise. Just a characteristic of these motors that sometimes happens. Think there is a member on here with a full rebuild which does it. If you don't have A/C on, try it and see if noise goes away or decreased Could be piston slap but I'd hazard that this is unlikely unless it's a heavier knocking sound? Ultimately I imagine you will get lots of answers and suggestions on here but you may decide to go to a good independent garage to give you a definitive. Hope this helps

Mine had an extensive rebuild and taps like a bastard on hot idle . its very annoying although apparently not damaging. Not what you want after a 10k rebuild but that's life.

Mines sounds the same as that and from bank 2 also. I've got a Hartech rebuild also and they said that was nowt to worry about and is a trait of the M96. I was going to change the tappets at some point.

Thanks for all the replies, Point to note, it quietens down when the a/c is on and also disappears when 'd' in engaged. I should also note that the car hasn't been started for 2 weeks so I think the oil must of drained from the tappets etc Hopefully nothing to worry about. Thanks again Marc

Thanks for all the replies, Point to note, it quietens down when the a/c is on and also disappears when 'd' in engaged. I should also note that the car hasn't been started for 2 weeks so I think the oil must of drained from the tappets etc Hopefully nothing to worry about. Thanks again Marc

Ah your invoice says "basic cylinder head overhaul". The car had 1x new cylinder liner and the restraining rings on all. I wonder if it had D chunked the cylinder or something, though there is no new piston listed. Good it had new main bearings and chains and tensioners. So my internet expert diagnosis agrees with the others, probably tappets. Shame they didn't stick new ones in at the time, though you can do them with the engine in I think, I heard they are an INA part much cheaper from a BMW source. But they all do it with a few miles on them. Mine are little noisy for a few seconds on cold start (137k). Try a thicker oil it might hang around a bit longer, but worth dropping in to Hartech as they built the engine not too long ago for some advice.

I am sorry to say I don't have a simple answer to this problem. Unfortunately after extensive research we concluded that this is a feature of the engines up to and including the 996 3.4. We tried hard to eliminate the cause because engines can tick after bore scoring or big end failure and it was difficult to explain when it could be still present after a rebuild - but most 996 3.4's have ferrous coated pistons and don't score bores anyway.The confirmation that this is not that problem is that it goes quiet if you engage the air con or drive (which it would not otherwise do if it was any of the other faults causing it). Many replies gave good clues that it is innocent and is caused by the basic original tickover being too slow for the design of the engine after running in and becoming very free running some years later combined with gradual imbalance caused by natural wear and tear that the system on tickover cannot adapt to resolve. The tickover in the ECU actually has 10 speed settings that slow it down as the oil and coolant get hotter (although you don't see this on your rev-counter) and this is partly to try and reduce emissions on tickover. What happens is that the speed sensor only reads the crankshaft speed once/rev (and there are 3 firing stokes/rev). Crankshafts actually speed up and slow down several times/revolution and each firing stoke has a slightly different pulse strength than the next one. Heavier crankshafts damp down the amount and lighter ones (like in these engines) fluctuate. When the sensor reads the revs and finds on that the one cylinder it measures - that the engine is running too slow it opens the throttle bye pass to speed it up and because the crankshaft is so relatively light it snatches at the camshaft chains as it momentarily speeds the crankshaft up - creating a jerk in the camshaft chain, tensioner blade and hydraulic tensioner that sounds like a tick. The crankshaft is relatively light because a flat 6 has excellent balance and can tickover quite slow without a heavy flywheel (which in turn provides faster acceleration due to lower flywheel mass). The engine tickover is basically unstable and replacing one cylinder and fitting support rings to the rest will not result in identical compression pressures or perfectly smooth fining of all 6 cylinders at tickover when so little fuel is pumped to each injector and they have slightly different flow rates at such low speeds and short opening times and spray patterns with slightly variable tickover compressions. Even the design of the exhaust manifolds and inlet system slightly imbalance tickover pulses. When the throttle is opened for driving the crankshaft speed is higher and it is pushing against the inertia of the various auxiliaries and the car, the jerks are many more/minute and it all happens to fast for the chains to jerk before the next pulse is due. When the oil is thick and the car is cold – or if the air con is on or torque converter are engaged (in 'D") the extra mass (or resistance) damps the crankshaft so it slows the rate of it speeding up and down and so can eliminate or reduce the jerk. It is possible to speed up the tickover settings in the ECU and this can reduce or even sometimes eliminate the tick but then with a tiptronic car this can cause drive to partially pull the car forward on tickover and is not recommended. Trying to balance the firing power in each cylinder would require 6 new cylinders, full valve overhaul, replacing all injectors, new pistons and rings etc etc but even then the basic design simply is not sophisticated enough to always eliminate it even after all that additional cost and effort that may otherwise be unneccssary. The hydraulic tensioners for the camshaft chains don't help. They are crude and don't have a proper sprung loaded ball valve – but a loose flap valve instead (relying on the oil flow to move the small plate and blank off the piston on the pressured return stroke). On one side of the engine this is the other way up to the other side. One way up the flap valve falls through gravity to shut off the return but the other one does not - it stays open. If you strip an engine (or remove both tensioners) you will find one holding oil still and the other completely empty (as it has drained out under gravity). Oil pressure is anyway relatively low on tickover and with tappets and variocam solenoids to deliver pressure to as well as the crankshaft etc – the delivery rate can be too slow to keep the chain tensioners full – in fact we suspect that at tickover the oil simply shunts back and forth as the tensioner blade pressurises the piston especially as the tensioner is after all the tappets and variocam delivery and down a long hole being the last in the system to receive delivery. To try and influence this – despite the lack of space - we designed and made several tensioners with sprung loaded ball valves which worked in some engines but not others. Some tensioners also has metal to metal contact with the tensioner in some versions and although they are made with a curved face – over time they knock flat and this increases the noise if they flap. We changed the metal end to a plastic one with some good results but in others it made no difference. Original air cooled 911 hydraulic tensioners incorporated sprung loaded ball valves and a reservoir to hold oil under pressure which there simply is not enough room to replicate in these engines. Not only that – there are no seals around the tensioner piston and it has a flat most of the way down one side and easily leaks. The slower the tickover the slower the oil is flowed around the system and the longer the valves and crankshaft bearings are exposed to pressure and this increases their leak rates which at higher speeds there is less time to do and anyway oil pressure and flow rate is very much higher at higher revs (and the 9A1 Gen 2 has an oil pressure biasing system to increase oil pressure at tickover beyond that possible by the crude double gear oil pump on these models). on our test engines we tried changing in sequence, heads, camshafts, tensioners, cylinders, valves and springs, pistons and rings even the gearbox etc etc but found that on engines that ticked badly when they came in it often made no difference. Frequently the engine came in as non-runners so we could not even determine if they were tickers or not before rebuilding them. We didn't think we could justify recommending changing so many parts (at huge cost) when we knew it didn't always fix the problem (especially when the car was running when it came in and already exhibited the problem) and particularly as it is not damaging – just irritating. So with it only afflicting a small number of engines - after spending hours on the issue and thousands of pounds – we simply could not find a viable answer that would be reliable enough to justify the cost during a rebuild and so (very reluctantly) we advise customers of the possibility before we start work on their engines instead. If anyone has found a reliable cost effective solution we would be delighted to hear about it – but in circumstances where the tick is not there cold and goes away on engaging the air con – or drive – it is in our experience - always nothing to do with the parts others have mentioned in reply but very likely to still be there afterwards and due entirely to the influences mentioned here. Baz

Thanks for the reply baz, I can sleep easier now! Cheers :thumbs: