engine knock/tap

[cheeryble]

Hi there I've got a Vitara about 7 years old with perhaps 100,000 km or so on it. Regular 4 cylinder petrol.
A week or two ago a tap or knock started. It sounds a bit like a london taxi (diesel) idling!
It is most noticeable at idle and has got a bit louder. The car performs perfectly and i can't really hear anything at any speed although I'm not saying it's not there.
It is difficult to locate exactly but sure it's the engine. (Perhaps I should put a screwdriver to my ear)
Is it possible for there to be slack in the valve/cam system with an overhead camshaft?
Any other possibilities?
(If this is a clue the tickover speed has become slightly erratic, and I've had to slow it with the adjuster it went up over 1500.....is anything like preignition possible?......although it kind off sounds like one cylinder....)

thanx from Chiangmai
John

[posaunemeister]

You might want to try running a full tank of the highest octane fuel your country has to offer. That might alleviate some of the pings and knocking occurring in your engine. That'll be the cheaper and quickest option at this point, but if it worsens and persists, then you might want to take it in to a mechanic.

[XL7Limited]

if its doing this at idle its surely not the gas.. Sounds like a lifter or broken rocker arm??

[cheeryble]

I though OHC didn't have rocker arms???

[cheeryble]

FYI
Just went to Suzuki. I have to say the tickover tap was much quieter which may have had something to do with the engine being properly hot. They said the valves are adjustable, it's not dangerous, and it's an hour job.
Let's hope they're right.

thanx again
John