928 S4 strange tapping from sump
04-05-2009, 05:38 PM
#1
Intermediate
Thread Starter
928 S4 strange tapping from sump
Dear experts
My beloved but ageing S4 has recently developed a tapping sound from the bottom of the engine. Two months ago it was a barely audible light tapping only heard when standing near the front left headlight. It has continued to get louder and although you cannot hear it from inside the cockpit it now sounds like a diesel tractor! The noise appears to be coming from the sump. I have posted a small video clip on YouTube. Please have a listen and tell me what you think it could be.
Cheers
Stuart Waite
http://www.youtube.com/watch?v=-SpL9RqyifI
My beloved but ageing S4 has recently developed a tapping sound from the bottom of the engine. Two months ago it was a barely audible light tapping only heard when standing near the front left headlight. It has continued to get louder and although you cannot hear it from inside the cockpit it now sounds like a diesel tractor! The noise appears to be coming from the sump. I have posted a small video clip on YouTube. Please have a listen and tell me what you think it could be.
Cheers
Stuart Waite
http://www.youtube.com/watch?v=-SpL9RqyifI
04-05-2009, 07:18 PM
#2
Welcome Stuart, what does it sound like when you rev-it-up? What is the oil pressure hot and cold? Is it louder when the engine is cold or hot? Check the oil for signs of metal. Sounds like an exhaust leak from what I can hear with crappy laptop speaker. Lay underneath the engine at night and look between the head and exhaust manifold for blue flame. I would get the Timing belt covers and inspect the belt/gears/rollers etc..
04-05-2009, 08:17 PM
#3
Intermediate
Thread Starter
Hi Soupcan, thanks for your reply. Oil pressure is 5bar, noise the same when the engine is hot or cold, tapping speeds up with rpm but does not get louder. I changed the water pump and t/b just before the noise started but I'm pretty sure it is not related. The tapping is quite metallic and I think you can actually feel the knocking if you touch the bottom of the oil pan. I've been underneath and listened to the manifolds and I will be amazed if it is them. Sounds to me like a big end or wrist pin or piston slap but disconnecting the plug leads in turn did not isolate it to one cylinder. What component in the belt/gear/roller department do you suspect could be the cause?
Cheers - Stuart
Cheers - Stuart
04-05-2009, 08:39 PM
#5
Rennlist Member
04-05-2009, 08:52 PM
#6
The fact the noise started shortly after the wp/tb work was done, I would go back inside for a good look. I would check the exhaust/accessories and wp/tb then drop the pan to look at the bearings.
04-05-2009, 08:57 PM
#7
Team Owner
a quick check on the oil would be to pull the dipstick drip some of the oil onto a black piece of cardboard go into the sun and look for very small metallic particles, a mag glass would help , if you find metal them you may have a rod bearing going bad. Have you ever had the flexplate tension checked.(if its an auto)
Please add more info about your car, year, model, mileage , stick or auto??and the last few things you fixed
Please add more info about your car, year, model, mileage , stick or auto??and the last few things you fixed
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04-06-2009, 04:55 AM
#8
Intermediate
Thread Starter
Hi Guys
The car is a stock UK Spec 1990 S4 5.0lt V8 Auto1990 model. The oil looks clean - it was changed 1000miles ago. When the T/B was replaced I just replaced the belt and rebuilt the tensioner. I checked the flexplate when I did the pump (I bolt a metal block to the flywheel using two of the flexplate bolts in order to lock the crank when undoing the front pully bolt) I checked it again yesterday, you can see the inspection cover on the floor in the video :-) My 1st plan was to disconnect the ancillaries but the noise definitely appears to be coming from inside the sump. Unfortunately I don't posess a stethoscope so I am just using a trusty long handled screwdriver. I am back to work right now but may get a chance to remove the ancillaries tonight. BTW is it a big job to drop the pan? do you have to remove the lower subframe crossmember 1st?
The car is a stock UK Spec 1990 S4 5.0lt V8 Auto1990 model. The oil looks clean - it was changed 1000miles ago. When the T/B was replaced I just replaced the belt and rebuilt the tensioner. I checked the flexplate when I did the pump (I bolt a metal block to the flywheel using two of the flexplate bolts in order to lock the crank when undoing the front pully bolt) I checked it again yesterday, you can see the inspection cover on the floor in the video :-) My 1st plan was to disconnect the ancillaries but the noise definitely appears to be coming from inside the sump. Unfortunately I don't posess a stethoscope so I am just using a trusty long handled screwdriver. I am back to work right now but may get a chance to remove the ancillaries tonight. BTW is it a big job to drop the pan? do you have to remove the lower subframe crossmember 1st?
04-06-2009, 05:12 AM
#9
Racer
Hi Stuart,
I recently had a similar problem on my S2.
Noise started quietly then progressively got worse until it sounded like a really loud metallic knocking noise.
Turned out it was the rearmost exhaust manifold gasket that had blown. New set of gaskets solved the problem.
I know you are convinced that it is a mechanical noise, but so was I at first. I would suggest checking out your exhaust manifold gaskets first.
I recently had a similar problem on my S2.
Noise started quietly then progressively got worse until it sounded like a really loud metallic knocking noise.
Turned out it was the rearmost exhaust manifold gasket that had blown. New set of gaskets solved the problem.
I know you are convinced that it is a mechanical noise, but so was I at first. I would suggest checking out your exhaust manifold gaskets first.
04-06-2009, 05:48 AM
#10
Addict
Rennlist Member
Rennlist Member
Take the blet off the air pump and see if that changes / eliminates the noise - air pump bearings / impellers going bad sound like a quiet/soft version of rod bearing failure
04-06-2009, 10:00 AM
#11
Team Owner
you can check for a damaged exhaust manifold /gasket by starting the car and sniffing around the sides of the engine if you smell exhaust then its a good bet you have a damaged gasket or cracked manifold.
There are places on the bottoms of the manifolds that will rub on the cross member supports, if the MM are/were bad and then can make holes. Look at the manifolds where they cross over the top of the rear side of the cross member.
Also check the manifold securing nuts try to put a wrench on every nut and see if its loose. If you have a engine pan in place it will have to come off to do a visual inspection .
The pan is held on with about 12 bolts
There are places on the bottoms of the manifolds that will rub on the cross member supports, if the MM are/were bad and then can make holes. Look at the manifolds where they cross over the top of the rear side of the cross member.
Also check the manifold securing nuts try to put a wrench on every nut and see if its loose. If you have a engine pan in place it will have to come off to do a visual inspection .
The pan is held on with about 12 bolts
04-12-2009, 06:48 PM
#12
Intermediate
Thread Starter
Hi Stuart,
I recently had a similar problem on my S2.
Noise started quietly then progressively got worse until it sounded like a really loud metallic knocking noise.
Turned out it was the rearmost exhaust manifold gasket that had blown. New set of gaskets solved the problem.
I know you are convinced that it is a mechanical noise, but so was I at first. I would suggest checking out your exhaust manifold gaskets first.
I recently had a similar problem on my S2.
Noise started quietly then progressively got worse until it sounded like a really loud metallic knocking noise.
Turned out it was the rearmost exhaust manifold gasket that had blown. New set of gaskets solved the problem.
I know you are convinced that it is a mechanical noise, but so was I at first. I would suggest checking out your exhaust manifold gaskets first.
Thanks for the heads up on the exhaust gaskets - have checked these and it is definitely not the cause. The tapping noise is at at least crank speed and is quite central when looking from the front. A leaking exhaust would have a much lower frequency and would be louder on one side. Also disconnecting each plug lead in turn should isolate the offending cylinder and this does not happen!
Cheers anyway - Stuart
04-12-2009, 06:56 PM
#13
Intermediate
Thread Starter
Thanks for your input :-)
I have now removed the belts, one by one, and have eliminated the alternator, the air pump, the power steering pump and the air-con compressor. The tapping noise is really loud and seems to be coming from the centre front of the engine even with all ancillaries disconnected.
Cheer stuart
PS, thays a funny looking hang glider on your roof-rack - it will never fly!
04-12-2009, 07:51 PM
#15
Intermediate
Thread Starter
Hi Guys
Well...... I've finaly had chance to do some further investigations.
I've systematically removed all the ancillaries, one by one, and the tapping is still there. I have removed the front timing covers and temporarily re-attached the top covers & dizzy caps so I could take a closer look & listen to the timing tensioner in motion. The tapping was louder and seemed to be coming from around the flywheel area.
I have dismantled and inspected all of the timing gear parts and have the following observations. There was a small amount of belt "fluff" built up on the timing pionter and in the very bottom of the lower cover; The belt appears to have been wearing on the metal guide plate that is positioned between the belt pully on the crank and the orange front flywheel. Inspection of the timing components themselves reveals the following. The large tensioner wheel is perfect, the smaller tensioner idler has a slight amount of play. The tensioner arm itself is supported on a single shaft with two nylon bushes, both of these exhibit slight wear evident by about 3mm lateral play at the tensioner roller. My 1990 MY S4 has an additional pair of belt guide idle rollers positioned below the crank pulley mounted on a small metal carrier. This carrier is itsef mounted on two projecting pins and is secured by circlips. Both of these rollers are a little bit worn but by biggest concern is the diameter of the carrier mounting pins and the associated holes on the carrier. The left hole is a nice sliding fit on the pin but the right hole is of a much larger diameter allowing the carrier to "ratlte". Does anybody have any knowledge of this arangement? is it normal?
I am planning to replace the two tension arm pivot bushes and have ordered replacement bearings to rebuild the idlers. I have pressed out the bearings from the rollers and am replacing them with SKF twin sealed deep roller bearings 62012RS and 69052RS costing about £20 for the set as opposed to about £100 from any of the UK's independant Porsche specialists and possibly a lot more from Porsche themselves!
It will be a few days before I get all the bits ready for re-assembly.....it is Easter after all. So watch this space to see if a small amount of play in a few bushes & bearings can cause such an alarmingly loud rattle. Whilst I am waiting for the postman if any of you can throw any light on my lower cam belt idler assembly then it would be much appreciated
Happy Easter
Regards
Stuart
Well...... I've finaly had chance to do some further investigations.
I've systematically removed all the ancillaries, one by one, and the tapping is still there. I have removed the front timing covers and temporarily re-attached the top covers & dizzy caps so I could take a closer look & listen to the timing tensioner in motion. The tapping was louder and seemed to be coming from around the flywheel area.
I have dismantled and inspected all of the timing gear parts and have the following observations. There was a small amount of belt "fluff" built up on the timing pionter and in the very bottom of the lower cover; The belt appears to have been wearing on the metal guide plate that is positioned between the belt pully on the crank and the orange front flywheel. Inspection of the timing components themselves reveals the following. The large tensioner wheel is perfect, the smaller tensioner idler has a slight amount of play. The tensioner arm itself is supported on a single shaft with two nylon bushes, both of these exhibit slight wear evident by about 3mm lateral play at the tensioner roller. My 1990 MY S4 has an additional pair of belt guide idle rollers positioned below the crank pulley mounted on a small metal carrier. This carrier is itsef mounted on two projecting pins and is secured by circlips. Both of these rollers are a little bit worn but by biggest concern is the diameter of the carrier mounting pins and the associated holes on the carrier. The left hole is a nice sliding fit on the pin but the right hole is of a much larger diameter allowing the carrier to "ratlte". Does anybody have any knowledge of this arangement? is it normal?
I am planning to replace the two tension arm pivot bushes and have ordered replacement bearings to rebuild the idlers. I have pressed out the bearings from the rollers and am replacing them with SKF twin sealed deep roller bearings 62012RS and 69052RS costing about £20 for the set as opposed to about £100 from any of the UK's independant Porsche specialists and possibly a lot more from Porsche themselves!
It will be a few days before I get all the bits ready for re-assembly.....it is Easter after all. So watch this space to see if a small amount of play in a few bushes & bearings can cause such an alarmingly loud rattle. Whilst I am waiting for the postman if any of you can throw any light on my lower cam belt idler assembly then it would be much appreciated
Happy Easter
Regards
Stuart