'98 3.4 Engine Tapping Noise

Hi guys, ever since ive had my car the engine has made a tapping noise at idle. it doesn't smoke or use any fluids and runs great I ust wondered if anyone could identify it and if it's anything unusual

https://1drv.ms/u/s!Aq4JZepsh1G4hAdrymr5Y7aZkiUl

cheers
chris

(for some reason you need to copy and paste the whole link, it only picks up half of it if you click on it)

the timing chains on early cars have always been considered "noisy"
- excessively noisy could suggest the hydraulic chain tensioners (and probably guides) should be replaced

big end bearings also don't last for ever....


what is the scale of the mileage and the service history of the car?

Mileage is 137k with decent service history. It's not a big end knock I've heard them before it's just a rythmic tapping

Hope you get it sorted mate, they are a sod to identify I am having the same at the moment with my 997.2 we have gone from Duel mass flywheel to big end to sticky tappets and still no clear idea yet , Have you done things like compresion test , pull the oil filter and inspect it for debris, oil pressure, scope the bores etc. Seems to be just a case of working through a list until you see a clue and follow that . good luck :thumb: :thumb:

Sound like tappet noise, you get a similar sound when you put and engine back together and have tappet noise until the pump up with oil.

Could also be a blowing manifold, this can sometimes sound like an internal metallic part, can be checked easily.

Does it do it with the engine hot and cold?

Mine is a 1998 3.4 and it makes the same noise when cold and it goes away after it's been driven. I'm totally convinced it's a tappet that it slow to fill with oil. On your's, if it's doing it all the time then it's probably a tappet that won't fill up becuase it's seized/jammed by a flake. It's not a big deal and won't do any damage.
See mistercorn's thread on his engine strip-down for how to access them. Not simple or easy, but feasible for an ambitious DIYer. New tappets can apparently be had pretty cheaply too.

All that said, if it were mine, I would leave it until I had another reason to open up the engine. It's not serious enough on its own.

Agreed, that sounds like a sticky tappet, one of the buyers guides (I think by RPM) mentioned that the early 3.4s were prone to it, not a big deal. It can sometimes be cured with an engine flush although you'll get a lot of mixed opinions on flushing.

996 ticking noises can be signs of a problem or just a feature of the engine and its management system. If it has a tick after a rebuild it is almost certainly nothing to be concerned about.

If it is a tiptronic and at tickover the noise goes away or reduces if you engage 'D" or if you switch on the air-con and it goes away or reduces and your tail pipes are equally sooty - you probably do not have a serious problem (boroscope to check).

The model has several reasons for a tick and several cures and sometimes it cannot be cured. It is usually from the bank 2 area half way from the crank to the camshaft, back of engine cylinder 4 area.

All engines speed up and slow down between each firing stroke and this causes a shake to the various chains, cams and tensioners. This engine has more chains than later ones.

A few decades ago - when tickover was adjusted by a screw - you raised it until any 'ticking stopped" (hence the term tickover). An engine would then normally speed up at tickover when the oil is hotter and thinner but to reduce emissions (checked at tickover) and fix that problem more modern cars are made so the management system makes the tickover speed drop as the engine warms up (to compensate).

But older engines that are very free running and with lower oil pressure, weaker leaking tappets and cam timing systems - can lower the revs too far for an older engine when hot (especially if you leave it running to listen for a tick as heat soak initially raises oil temperatures and lowers viscosity even further).

Tickover revs can be increased when re-mapping – there are 8 or 10 settings at different temperatures gradually reducing the tickover revs as things warm up and ambient conditions affect the engine – sometimes raising these individual settings sorts the problem although the slightly higher tickover can change the drivers familiarity with the right throttle position for smooth driving off in first gear and can take a while to get used to and it is not an easy job (as the engine is sitting ticking over and changing various temperatures while the operative is trying to find the setting that reduces or fixes the issue) and it is not free either.

The main chain tensioners are a very poor design indeed. No reservoirs and not even a sprung loaded ball non-return valve. Furthermore the feed is after all the other drains on oil pressure and flow to the tappets, variocam systems, camshaft bearing areas etc. The tensioner has a tiny flat plate that is supposed to seal the return stroke if the chains flap.

The bank 1 tensioner allows the tiny sealing plate to fall onto the sealing face so when you strip it you usually find it full of oil still and with some resistance. The bank 2 one is upside down (so the sealing plate is always unsealed unless there is good oil pressure available) and is always empty when you strip it and has no resistance at all. There is not even a seal on the piston. This shows that at relatively low oil pressure and delivery this tensioner probably does nothing much to stabilise the cam chain snatch.

The oil that feeds the tensioner is delivered to the head via a gallery that also feeds the tappets, variable cam timing unit (that also incorporates a tensioner) and the camshaft bearing journals. The oil pump design is poor on oil delivery at low revs and it is entirely possible that minute wear everywhere results in the oil being pumped into the head barely filling these components and by the time the oil in the gallery reaches the main chain tensioner from the IMS it just shunts back and forth in the gallery and fails to make the tensioner do its job.

We have over the years gone through changing just about everything you could think of to eliminate the noises. This includes heads, tappets, tappet housings, injectors, chains sprockets, tensioners, cams, pistons etc. Sometimes a sticky tappet is the cause but it is expensive to change them and find it made no difference. We even tried making tensioners with different springs and a ball valve which sometimes worked but often didn't and finally concluded that at tickover the tensioner piston just flaps back and forth and the oil flow from the head isn't sufficient to keep it pressured but just experiences the movement of the tensioner creating a pressure wave in the oil feed gallery leading to it but insufficient oil flow to maintain the tensioner blade position– hence the tick.

Because there are three firing stokes/engine rev – anything that causes one cylinder to produce a slightly different push on the piston (like a sticky injector) can result in the management system reading a pulse that it over corrects for setting up a cyclic speeding up and down of the tickover revs that also encourages ticking noises.

Rebuilding an engine can make it worse because the original standard cylinders had quite variable piston clearances and bore shapes and produce less tickover compression and therefore less of a tickover pulse from each power stroke than a rebuilt engine with tighter more powerful piston clearances and overhauled cylinder heads etc – that it was not designed to manage.

Different exhaust systems can also work better at higher revs than at tickover leading to rougher tickover performance - again moving the control parameters away from their designed areas – so really any uneven running between cylinders makes things worse and rebuilds with better than standard compression or bigger pistons can create a slight tickover problem (especially with lighter flywheels).

We only find this problem with the 996 3.4 engines and they also have off-set gudgeon pin alignment that works out different for one bank of the engine than the other (which doesn't help). The Cayman S, 3.6 and 3.8 engines put that right but I guess it was found not to be an issue because the Gen 2 has gone back again to the original variance in off-set between banks.

Other reasons already previously listed by other contributors are probably all valid since almost anything can influence the tickover running between individual cylinders and it is therefore always possible to find someone who found a solution to their problem that they are trying to help by revealing – but that turned out didn't work for anyone else.

Because the flywheel speed sensor reads the speed every 3 power strokes any imbalance can only be adjusted by the ECU on the third stroke and as cylinder 4 is next and the bank 2 cam chain on the end of the IMS shaft feels any adjustment next, that chain receives the biggest jerk.

Having spent hours and hours (and a not inconsiderable amount of money) trying to eliminate this problem - unless you have other problems or signs of imminent failure – it is probably just a noise that many have wasted hours trying to fix and usually eventually give up on after absolutely everything has been changed and the tick is still there.

You could get lucky and identify and change the component causing your problem first time but the odds are very much against it and you would be more likely to spend time and money getting frustrated and more annoyed with the engine and whoever you paid to try and fix it –all to no avail – as more often than not it is better just to live with it.

If the noise is not in the area I have descibed above it may be worthwhile investigating further but if it fits the descriptions most people provide and there is nothing else wrong with the car I suggest it is best to ignore it.

Sorry there is not an easy answer.

Baz

Not an easy answer, but once again Baz, a fascinating and informative insight into the fundamental design of the M96 engine.

I noticed my cable throttle M96 has a throttle position stop screw. Might give it a tweek to see if the revs rise. I imagine that it will just be counteracted by the idle control valve though....

Superb, Baz.

Very interesting, thanks!

:thumb:

Interestingly, my 3.4 996.1 had a tapping at idle ( which went away if you put the aircon on , raising the revs by about 200 ) when I bought her, she was running on 5W30 Mobil 1, so I carried on with that regime, but topped up the oil with 10W40 as it was used ( she does use about 500ml per 1000 miles, no smoke, no sooty tailpipes on either side and within Porsche oil usage parameters even after 108,000 miles )

She doesn`t tap now :?:

What oil are you running OP :?:

I`ll be switching to Millers Nanodrive 5W40 shortly, shockingly expensive, but opinions are that this is the oil to be using on these fragile engines :thumb:

...I have Miller's Nano 5w40 in my 3.6 can't say that I have noticed any difference to performance or engine noise (mine has been described as a 'quiet one' by an Indy )but it's meant to be very good,if rather expensive so I will stick with it...