Next to do on the 996
Discussion
just got the 996 back after having the engine thoroughly checked over, clutch replaced, RMS done, new IMS fitted, rear end polybushed and new engine mounts fitted.
I recently refreshed all the front end rubber bits too and just need to get some new tyres on it before getting the geo done properly.
With a clean bill of health on the engine despite the annoying tappet noise I'm very happy and it feels like a new car, question is what to do next? I've been toying with an exhaust upgrade, I have sports boxes on at the moment which I presume was something factory optional as it looks OEM but is not the PSE. Is it really worth doing a whole system upgrade from manifolds right though or is there something else I should spend my cash on?
I know people will say just enjoy it as is but I really want it to be as good as humanly possible and completely futureproofed.
I recently refreshed all the front end rubber bits too and just need to get some new tyres on it before getting the geo done properly.
With a clean bill of health on the engine despite the annoying tappet noise I'm very happy and it feels like a new car, question is what to do next? I've been toying with an exhaust upgrade, I have sports boxes on at the moment which I presume was something factory optional as it looks OEM but is not the PSE. Is it really worth doing a whole system upgrade from manifolds right though or is there something else I should spend my cash on?
I know people will say just enjoy it as is but I really want it to be as good as humanly possible and completely futureproofed.
I've had that annoying tappet noise on mine for about 18 months now - comes and goes. Mine is a Hartech car, and they reckon it could be a sticky lifter - if it happens to be under compression when you stop the engine, it might take a while to "pump" back up when you restart. Mine tends to be less noticeable if the car has been driven for a good distance and given a bit of a work out last time it was out. If yours is a permanent noise and it is a lifter, perhaps its collapsed permanently - might be full of gunk?
Hartech tell me its difficult to diagnose which side its coming from so they generally do the lot, at about £30 each (x12) plus some gaskets, oil, bits and pieces and a lot of labour. Ouch.
Hartech tell me its difficult to diagnose which side its coming from so they generally do the lot, at about £30 each (x12) plus some gaskets, oil, bits and pieces and a lot of labour. Ouch.
Seagoon, I've had the same diagnosis as you. It's a real pain as the car has been thoroughly checked over and given a clean bill of health apart from the noise. It is on the list of things to do next for general maintenance but it is a lot of labour, the thought was to leave it until the next big bit of work and do the lot at the same time.
Might go with the larger throttle body, manifold and tubi combo as the next mods for the car and then do the CSF ally rad upgrade if I can find them in the UK.
Might go with the larger throttle body, manifold and tubi combo as the next mods for the car and then do the CSF ally rad upgrade if I can find them in the UK.
There are several potential causes of a metallic tapping noise - most of which can be recognised and fixed.
Typical are actual tappet failure, an exhaust manifold leak (yes it sounds unlikely but can happen especially when the manifold bolt heads corrode away), scored pistons and bores tipping over TDC and the top tilting and tapping the cylinder head, crank bearings failing and what everyone has referred to as "piston slap" when a bore is scored. Then there is another noise that sounds very like the rest but for which none of the above are the cause - that has plagued engineering specialists like us for some years while we have all tried to isolate and find it - changing countless other parts along the way to no effect.
It seems more prevalent of tiptronics (but not exclusively) and often changes the note if auxiliary equipment is engaged or nor - or "D" is engaged or the clutch engaged (in a manual). We have previously changed all auxiliaries in sequence, gearboxes, torque converters etc etc without finding the source - until recently.
I always thought it was connected to some cyclic engine snatch on tickover resulting from the firing sequence, the flat layout with long chains on both sides of the engine and the fact that on tickover an engine speeds up and slows down between each firing stroke and a flywheel is designed to damp it down. But the heavier the flywheel the better it does that job but the slower the car accelerates and the more fuel it uses - so designers limit the flywheel size as much as possible. Racing engines fitted with lightweight flywheels (or undamped flywheel/clutch plate combinations) will shake more than with their original heavier flywheels and if this is not felt through the engine (as the design is less prone to clattery noises) it is often heard at low revs as gearbox jingle (often heard on a standard 3.2 Carerra in low gears and revs).
If you have an engine with adjustable tickover (rare these days) you will find that if you slow down any engine it eventually shakes like mad and the more chains etc in the engine the more noises start to emerge.
The better the layout of an engine is naturally balanced the lighter the flywheel it needs and the 911 flat six is one of the best layouts for smooth natural balanced running that you can get and hence runs with a very light flywheel and this improves performance but increases the tickover speed differential between firing strokes.
As the engine ages some things get a minute amount out of perfect balanced setting (fuel injectors, valve seating etc) while clearances wear a little - all nothing to worry about and perfectly normal but adding to the chance of the engine picking up a slightly bigger shake between firing impulses on tickover. Once the revs increase a little and the fuelling is larger - there is not enough time between firing strokes for the inertia of the cam-chain drive to generate a tick before the next firing stroke occurs but the slight change in internal component balance can still result in the engine snatch increasing slightly at tickover which the firing sequence makes worse at one particular point when the opposite ends of the crankshaft fire in sequence and generate a snatch between the two banks of drive chains.
It was wracking our brains to see where this would influence bank 2 and not bank 1 and why it was always bank 2 at the front of the engine (where the drive chain is) that eventually steered thoughts into a place where there was a different design of component each side and to then cut it open and see what was inside that found the source of the problem - a part that should have and could have been designed better to eliminate the problem - but wasn't.
It now seems possible that when an engine scores a bore - the reduced firing forces on that one piston increase this momentary speed difference that promotes the crankshaft/chain snatch and makes this noise and that it may not be "piston slap" at all although it sounds like it and does follows increased piston clearances. This can also be generated when not all the cylinders are replaced resulting in some having a slightly stronger tickover pulse strength than others. This smooths out once the engine is running under load and at speed.
Once this new source was discovered a simple solution evolved that when tested stopped the noise and proved we had finally found the source. We now need to test this out on engines with what we (and others) assumed was piston slap to see if it is or is caused by this other issue.
Once it was proven other things fell into place (as usual) - explaining other odd observations when rebuilding engines and even why it could only be on that bank that it occurs.
When our testing is complete and we have tested the present solution for long enough - we will manufacture an inexpensive cure and explain in more detail.
The good news is that not all ticking noises are tappets, bore scoring or piston slap and if this new found source is the cause - are of no concern mechanically or technically - but are just a little irritating and will soon be able to be eliminated permanently.
Baz
Typical are actual tappet failure, an exhaust manifold leak (yes it sounds unlikely but can happen especially when the manifold bolt heads corrode away), scored pistons and bores tipping over TDC and the top tilting and tapping the cylinder head, crank bearings failing and what everyone has referred to as "piston slap" when a bore is scored. Then there is another noise that sounds very like the rest but for which none of the above are the cause - that has plagued engineering specialists like us for some years while we have all tried to isolate and find it - changing countless other parts along the way to no effect.
It seems more prevalent of tiptronics (but not exclusively) and often changes the note if auxiliary equipment is engaged or nor - or "D" is engaged or the clutch engaged (in a manual). We have previously changed all auxiliaries in sequence, gearboxes, torque converters etc etc without finding the source - until recently.
I always thought it was connected to some cyclic engine snatch on tickover resulting from the firing sequence, the flat layout with long chains on both sides of the engine and the fact that on tickover an engine speeds up and slows down between each firing stroke and a flywheel is designed to damp it down. But the heavier the flywheel the better it does that job but the slower the car accelerates and the more fuel it uses - so designers limit the flywheel size as much as possible. Racing engines fitted with lightweight flywheels (or undamped flywheel/clutch plate combinations) will shake more than with their original heavier flywheels and if this is not felt through the engine (as the design is less prone to clattery noises) it is often heard at low revs as gearbox jingle (often heard on a standard 3.2 Carerra in low gears and revs).
If you have an engine with adjustable tickover (rare these days) you will find that if you slow down any engine it eventually shakes like mad and the more chains etc in the engine the more noises start to emerge.
The better the layout of an engine is naturally balanced the lighter the flywheel it needs and the 911 flat six is one of the best layouts for smooth natural balanced running that you can get and hence runs with a very light flywheel and this improves performance but increases the tickover speed differential between firing strokes.
As the engine ages some things get a minute amount out of perfect balanced setting (fuel injectors, valve seating etc) while clearances wear a little - all nothing to worry about and perfectly normal but adding to the chance of the engine picking up a slightly bigger shake between firing impulses on tickover. Once the revs increase a little and the fuelling is larger - there is not enough time between firing strokes for the inertia of the cam-chain drive to generate a tick before the next firing stroke occurs but the slight change in internal component balance can still result in the engine snatch increasing slightly at tickover which the firing sequence makes worse at one particular point when the opposite ends of the crankshaft fire in sequence and generate a snatch between the two banks of drive chains.
It was wracking our brains to see where this would influence bank 2 and not bank 1 and why it was always bank 2 at the front of the engine (where the drive chain is) that eventually steered thoughts into a place where there was a different design of component each side and to then cut it open and see what was inside that found the source of the problem - a part that should have and could have been designed better to eliminate the problem - but wasn't.
It now seems possible that when an engine scores a bore - the reduced firing forces on that one piston increase this momentary speed difference that promotes the crankshaft/chain snatch and makes this noise and that it may not be "piston slap" at all although it sounds like it and does follows increased piston clearances. This can also be generated when not all the cylinders are replaced resulting in some having a slightly stronger tickover pulse strength than others. This smooths out once the engine is running under load and at speed.
Once this new source was discovered a simple solution evolved that when tested stopped the noise and proved we had finally found the source. We now need to test this out on engines with what we (and others) assumed was piston slap to see if it is or is caused by this other issue.
Once it was proven other things fell into place (as usual) - explaining other odd observations when rebuilding engines and even why it could only be on that bank that it occurs.
When our testing is complete and we have tested the present solution for long enough - we will manufacture an inexpensive cure and explain in more detail.
The good news is that not all ticking noises are tappets, bore scoring or piston slap and if this new found source is the cause - are of no concern mechanically or technically - but are just a little irritating and will soon be able to be eliminated permanently.
Baz
Edited by hartech on Wednesday 13th November 10:56
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