how much should it cost to have a camshaft pulley fitted and supplied

This is interesting. You go to shop telling them you have loud tapping noise, and they want to replace cam pulley. Makes no sense. Only thing I can even fathom is the pulley has a broken cog, and has jumped time. But that would make it run very badly. Here is DOHC...1.8

Now SOHC

I don't get it. But I am by NO MEANS knowledgeable about Vauxhall Matter of fact I would like to learn. We have repair estimate resources but that particular one is not available. Anything you can add?

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at first it was a low tapping noise which was only noticeable when i first turned the ignition, within a couple of days it was so loud and it was still making the tapping noise whilst i was driving there was a slight reduction in performance so i checked the oil and that was fine albeit a little low. i was beginning to think it may be my tappits as the noise was definetely from the top of the engine and a lot of the people i asked thought the same. i used to have a really good mechanic who i trusted so im a little wary of the diagnosis and cost

As you should be- a bit cautious of that diagnosis. Usually a 'tapping' or ' 'clicking' sound is indicative of tappets, followers, or lifters. Can be from overdue oil change, the oil can get less effective lubricating the cam and the lifters. Or a low-quality filter. An oil filter is one of the most misunderstood and overlooked things that can cause problems, especially on the top-end.. valve tappets. I have very little knowledge about the Vauxhall and what that engine uses, bucket lifters....a 'Bucket lifter'' is just what it sounds like. It's a bucket-type thing that fits over the valve spring, and with high-mileage the cam lobe(s) begin to wear, with the bucket that fits over the valve spring...or hydraulic lifters. Now Lilly, I can and will be as much assistance as possible. But please change your avatar. This is not facebook, where that is Ok for conversation and fooling around. We are a reputable Q&A site, and that is not the sort of thing we want here. Thank You