C8 vibration at tickover only!

[PeteC8]

Must be vibration query day!

C8 2.0Hdi 110bhp auto 2004 model, engine vibrates noticeably at tickover speed in neutral (around 850RPM). If I increase revs to 1000 it magically smooths right out. Always had a slight vibration there (owned car 4 months, done about 1000 miles myself, 80000 on clock), but has worsened in last 300 miles)

Can one of our enlightened Members give some clues what to look for? The crank damper is running out of true in line with the crank, but I wonder if that may be another problem, another day?

Many thanks,

[Rp0thejester]

I'm thinking an engine bush mount

[PeteC8]

I'm thinking an engine bush mount

Had a little rest under the car to get out of the sun, checked the lower right mount(s), they are okay. Some weird logic nags at me that if it is a mount, then vibrating at low frequency would suggest top mount but I really can't remember enough stuff about harmonics any more!

Many thanks for the input, Pete

[Rp0thejester]

If your on level ground, try parking uphill. The vibrations should be more noticeable as I found out today. Might help you locate the issue.

[jml]

Have a good look at the auxiliary drive belt. If it’s kicking about at tickover speed, but smooths out at 1000 rpm report back on here and I’ll give you a suggestion that I think will be about 90% certain to cure it !

[PeteC8]

Have a good look at the auxiliary drive belt. If it’s kicking about at tickover speed, but smooths out at 1000 rpm report back on here and I’ll give you a suggestion that I think will be about 90% certain to cure it !

The belt is running smoothly, only noticeable discrepancy is the crank damper not running true in line with the crank itself, probably in the order of 1mm, but no bouncing!
The resonance is particularly annoying as it causes something inside the DPF to jangle like the sound of loose washers rattling. I fear the ceramic structure may be damaged.....

Many thanks for your input!

[jml]

You’re welcome.

I had a problem which sounded similar and it turned out to be the alternator pulley (I thought pulleys were just pulleys - no longer so these days - on the C8, and many other modern cars, it’s an OAP , which is an overrunning alternator pulley)

However this definitely causes the belt to jump around - so not what you’ve got,

Good luck with sorting it Could it be the vibration damper built into the crankshaft pulley ?