Noisy tick­over

Car Mechanics (UK) - - Help! -

Q I have a 2002 Citroën C5 2.0-litre diesel with a noise prob­lem when the en­gine is tick­ing over, al­though it sounds OK when the en­gine is at a higher RPM. The noise is com­ing from the al­ter­na­tor drive­belt – which dis­ap­pears for a few min­utes when you put a squirt of en­gine oil on it.

I have put a new drive­belt on the en­gine, but it made no dif­fer­ence. I can see the belt whip­ping be­tween the crank­shaft pul­ley and the air-con­di­tion­ing unit pul­ley. My thoughts are that there is some­thing wrong with the air­con pump and this is caus­ing a drag on the belt. I have ten­sioned the belt at all sorts of pres­sures, from slack to pretty tight, and there are a va­ri­ety of noises, but no silent run­ning un­less one ap­plies the squirt of oil. I haven’t ap­plied oil to the new drive­belt as I be­lieve it would not do a new belt any good. In any case, when I tried it with the old belt it was only silent for a few min­utes and didn’t re­ally re­solve the prob­lem.

If the prob­lem was caused by the air­con pump, how fea­si­ble would it be to dis­con­nect the air­con unit? Would this in­cur other prob­lems? I don’t think we have ever used the air­con, so we don’t need it. John Ash­ley

A The rea­son that the noise ceases when a squirt of oil is put on the belt is be­cause the belt will then slip. This is not an ideal sit­u­a­tion and oil should not be ap­plied to the belt.

The first check to make is that the air-con­di­tion­ing pump pul­ley is spin­ning freely when the air­con is dis­en­gaged. If this is the case then the air-con­di­tion­ing is prob­a­bly not the cause of the prob­lem. Un­for­tu­nately, if the air-con­di­tion­ing pump pul­ley is not run­ning freely, this will need to be rec­ti­fied. Given the route the aux­il­iary belt takes, it does re­quire the pump to be in the cir­cuit.

The most prob­a­ble cause of the whip­ping belt is the al­ter­na­tor clutch pul­ley. The pul­ley is de­signed to re­duce the pos­si­bil­ity of belt snatch when sud­denly re­duc­ing speed. Th­ese pul­leys do fail on a reg­u­lar ba­sis and give the symp­toms you are ex­pe­ri­enc­ing. How­ever, it is not easy to test the pul­ley and nor­mally noth­ing can be felt when spin­ning by hand.

An­other pos­si­bil­ity is that the tor­sional vi­bra­tion damper built into the crank­shaft pul­ley may have failed. This is far eas­ier to test. With the aux­il­iary belt dis­con­nected, the crank­shaft pul­ley should be in­spected for any move­ment or any signs that the outer sec­tion has been spin­ning and is not fully bonded to the cen­tre of the pul­ley.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.