Noise resonance

zaph · 31st December 2019, 19:36

I have been trying to track down a resonance on my 75 diesel and after fitting a new alternator, I used a torch to check the best when it was running.

At relatively regular intervals the belts between the crank pulley and the alternator vibrates up down like a guitar string. That is what is making the noise.

The crank pulley is a new discount rover spares item, as is the drive belt. Has anyone got any idea what could be causing this?

Comfortably Numb · 1st January 2020, 18:23

Did you replace the tensioner(s)?

Mike Noc · 1st January 2020, 19:45

Could be play in the water pump bearings. Whip the serpentine belt off and check all the pulleys for play and roughness.

zaph · 2nd January 2020, 08:30

Quote:

Originally Posted by Mike Noc

Could be play in the water pump bearings. Whip the serpentine belt off and check all the pulleys for play and roughness.

I checked all the pulleys when I switched the belt, couldn't find any roughness or play.

zaph · 2nd January 2020, 08:32

Quote:

Originally Posted by Comfortably Numb

Did you replace the tensioner(s)?

Nope, the bearing is fine, it could be a weak spring but there doesn't seem to be excessive play in the belt.

Neither is the tensioner bouncing when the engine is running.

If I hadn't changed the crank pulley, this would be my best guess based on where the belt flutter is.

Mike Noc · 2nd January 2020, 08:58

Do you know anyone with a T4 locally? If so worth checking the injector balance at idle and the compensation figures just to rule out a faulty injector.

31st December 2019, 19:36	#1
zaph Avid contributor Rover 75 Join Date: May 2015 Location: Leeds Posts: 135 Thanks: 0 Thanked 17 Times in 11 Posts	Noise resonance I have been trying to track down a resonance on my 75 diesel and after fitting a new alternator, I used a torch to check the best when it was running. At relatively regular intervals the belts between the crank pulley and the alternator vibrates up down like a guitar string. That is what is making the noise. The crank pulley is a new discount rover spares item, as is the drive belt. Has anyone got any idea what could be causing this?

1st January 2020, 18:23	#2
Comfortably Numb Posted a thing or two Rover 75 Saloon Join Date: Dec 2017 Location: Penrith Posts: 1,336 Thanks: 165 Thanked 303 Times in 241 Posts	Did you replace the tensioner(s)?

1st January 2020, 19:45	#3
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,553 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	Could be play in the water pump bearings. Whip the serpentine belt off and check all the pulleys for play and roughness.

2nd January 2020, 08:58	#6
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,553 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	Do you know anyone with a T4 locally? If so worth checking the injector balance at idle and the compensation figures just to rule out a faulty injector.