Vibration and intake noise issue?
01-11-2020, 01:48 PM
#1
Vibration and intake noise issue?
Hi all
I have a high mileage ((170,000 miles) but fully maintained 968 coupe.
Recently I had belts done and then a few thousand later a service (always at auto ahrens in Germany). Throughout that time though, I was lacking power high up until the service. They cleaned the Distributer cap but due to torrential rain, they couldn't test at full power on the road. They felt it was fine (in fact they say its very well looked after and in fine shape) but as mentioned, couldn't try it fully on the road and I hadn't specifically mentioned the vibration.
The engine seems to run fine (maybe a bit down) but there is a slight rough edge to the engine (it seems a touch louder in the intake department) and some vibration I feel when revving. I feel it through the pedals and gear lever and even when standing still, so not tyres. TBH, maybe this is somewhat normal, but I don't recall it being like that.
It had new engine mounts 10,000km ago and is in good condition.
Could this be Leads and distributer cap? It's damp here in Belgium, so perhaps they are past their best. Could it be fuel issues (I tend to use shell though)
Any other thoughts?
Cheers
David
I have a high mileage ((170,000 miles) but fully maintained 968 coupe.
Recently I had belts done and then a few thousand later a service (always at auto ahrens in Germany). Throughout that time though, I was lacking power high up until the service. They cleaned the Distributer cap but due to torrential rain, they couldn't test at full power on the road. They felt it was fine (in fact they say its very well looked after and in fine shape) but as mentioned, couldn't try it fully on the road and I hadn't specifically mentioned the vibration.
The engine seems to run fine (maybe a bit down) but there is a slight rough edge to the engine (it seems a touch louder in the intake department) and some vibration I feel when revving. I feel it through the pedals and gear lever and even when standing still, so not tyres. TBH, maybe this is somewhat normal, but I don't recall it being like that.
It had new engine mounts 10,000km ago and is in good condition.
Could this be Leads and distributer cap? It's damp here in Belgium, so perhaps they are past their best. Could it be fuel issues (I tend to use shell though)
Any other thoughts?
Cheers
David
01-12-2020, 10:54 AM
#2
With your description, the potential issues are not narrowed down much. The intake side doesn't have much I can think of that can cause a vibration. Most common causes of vibrations that occur when the car is stationary are:
1. having a balance shaft that isn't aligned properly sometimes because the belt jumped a tooth or more than a tooth. Balance shafts can be inspected by removing the cover, which is not difficult but takes a little time.
2. having one cylinder compromised with a bad ring or valve. Testing compression and leakdown is the first step for finding the health of your cylinders
3. Throwout bearing failure
4. Torque tube failure.
5. Motor mounts
6. Maybe others will add to this list.
Throwout Bearing and TT and mounts can be initially checked from the driver's seat. This procedure isn't intended to fully diagnose, but to give some good clues.
Think of the car in 3 sections: Engine at the front, Torque Tube in the middle and transmission at the rear. The engine and the torque tube are separated by the clutch. The transmission and torque tube are separated by putting the transmission in neutral. The engine and flywheel always rotate so if the vibration occurs all the time, then it is not the torque tube.
Start the car. With the car stationary, does the vibration change if you depress the clutch? Rev with the clutch depressed and if you get a vibration it is certainly in the engine or flywheel, but throwout bearing could create a TT problem. Then drive the car and also let the car roll in neutral both with the clutch depressed and not depressed - that allows you to rotate the torque tube from the transmission or not have the torque tube rotate at all. You can even shut off the engine while the car is rolling and the clutch is depressed and move the transmission from a gear to neutral which will only change the rotation of the torque tube.
Others will certainly chime in. What year is your car??
1. having a balance shaft that isn't aligned properly sometimes because the belt jumped a tooth or more than a tooth. Balance shafts can be inspected by removing the cover, which is not difficult but takes a little time.
2. having one cylinder compromised with a bad ring or valve. Testing compression and leakdown is the first step for finding the health of your cylinders
3. Throwout bearing failure
4. Torque tube failure.
5. Motor mounts
6. Maybe others will add to this list.
Throwout Bearing and TT and mounts can be initially checked from the driver's seat. This procedure isn't intended to fully diagnose, but to give some good clues.
Think of the car in 3 sections: Engine at the front, Torque Tube in the middle and transmission at the rear. The engine and the torque tube are separated by the clutch. The transmission and torque tube are separated by putting the transmission in neutral. The engine and flywheel always rotate so if the vibration occurs all the time, then it is not the torque tube.
Start the car. With the car stationary, does the vibration change if you depress the clutch? Rev with the clutch depressed and if you get a vibration it is certainly in the engine or flywheel, but throwout bearing could create a TT problem. Then drive the car and also let the car roll in neutral both with the clutch depressed and not depressed - that allows you to rotate the torque tube from the transmission or not have the torque tube rotate at all. You can even shut off the engine while the car is rolling and the clutch is depressed and move the transmission from a gear to neutral which will only change the rotation of the torque tube.
Others will certainly chime in. What year is your car??
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David Morley (01-13-2020)
01-13-2020, 02:19 PM
#4
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Rennlist Member
Rennlist Member
It sounds like they goofed up the balance belt. It's easy to get the lower BS sprocket on wrong. Thankfully it's also easy to take the covers off and check.
http://www.clarks-garage.com/shop-manual/eng-08.htm
It's perhaps not easy to tell if it's wrong as the lower sprocket 'O' can be hard to see and to verify if it's not in the wrong place.
You can also take the plug leads off one at a time and see if it runs "less worse" with any specific cylinder disconnected.
At this mileage it could also be the DMF (flywheel) falling apart.
http://www.clarks-garage.com/shop-manual/eng-08.htm
It's perhaps not easy to tell if it's wrong as the lower sprocket 'O' can be hard to see and to verify if it's not in the wrong place.
You can also take the plug leads off one at a time and see if it runs "less worse" with any specific cylinder disconnected.
At this mileage it could also be the DMF (flywheel) falling apart.
01-13-2020, 03:31 PM
#5
Thanks Jfrahm
I will try and find someone local who knows these to have a look.
The shop I had it done are specialists and it went back for a service where they would have checked tension, but I guess they may have mucked up.
Thx!
I will try and find someone local who knows these to have a look.
The shop I had it done are specialists and it went back for a service where they would have checked tension, but I guess they may have mucked up.
Thx!
01-13-2020, 06:36 PM
#6
Rennlist Member
With your description, the potential issues are not narrowed down much. The intake side doesn't have much I can think of that can cause a vibration. Most common causes of vibrations that occur when the car is stationary are:
1. having a balance shaft that isn't aligned properly sometimes because the belt jumped a tooth or more than a tooth. Balance shafts can be inspected by removing the cover, which is not difficult but takes a little time.
2. having one cylinder compromised with a bad ring or valve. Testing compression and leakdown is the first step for finding the health of your cylinders
3. Throwout bearing failure
4. Torque tube failure.
5. Motor mounts
6. Maybe others will add to this list.
Throwout Bearing and TT and mounts can be initially checked from the driver's seat. This procedure isn't intended to fully diagnose, but to give some good clues.
Think of the car in 3 sections: Engine at the front, Torque Tube in the middle and transmission at the rear. The engine and the torque tube are separated by the clutch. The transmission and torque tube are separated by putting the transmission in neutral. The engine and flywheel always rotate so if the vibration occurs all the time, then it is not the torque tube.
Start the car. With the car stationary, does the vibration change if you depress the clutch? Rev with the clutch depressed and if you get a vibration it is certainly in the engine or flywheel, but throwout bearing could create a TT problem. Then drive the car and also let the car roll in neutral both with the clutch depressed and not depressed - that allows you to rotate the torque tube from the transmission or not have the torque tube rotate at all. You can even shut off the engine while the car is rolling and the clutch is depressed and move the transmission from a gear to neutral which will only change the rotation of the torque tube.
Others will certainly chime in. What year is your car??
1. having a balance shaft that isn't aligned properly sometimes because the belt jumped a tooth or more than a tooth. Balance shafts can be inspected by removing the cover, which is not difficult but takes a little time.
2. having one cylinder compromised with a bad ring or valve. Testing compression and leakdown is the first step for finding the health of your cylinders
3. Throwout bearing failure
4. Torque tube failure.
5. Motor mounts
6. Maybe others will add to this list.
Throwout Bearing and TT and mounts can be initially checked from the driver's seat. This procedure isn't intended to fully diagnose, but to give some good clues.
Think of the car in 3 sections: Engine at the front, Torque Tube in the middle and transmission at the rear. The engine and the torque tube are separated by the clutch. The transmission and torque tube are separated by putting the transmission in neutral. The engine and flywheel always rotate so if the vibration occurs all the time, then it is not the torque tube.
Start the car. With the car stationary, does the vibration change if you depress the clutch? Rev with the clutch depressed and if you get a vibration it is certainly in the engine or flywheel, but throwout bearing could create a TT problem. Then drive the car and also let the car roll in neutral both with the clutch depressed and not depressed - that allows you to rotate the torque tube from the transmission or not have the torque tube rotate at all. You can even shut off the engine while the car is rolling and the clutch is depressed and move the transmission from a gear to neutral which will only change the rotation of the torque tube.
Others will certainly chime in. What year is your car??
-Yogii
AKA 968 Novice
