insurgent

Good to know, that's another cause eliminated!

So, its not big ends, not little ends, not main ends, not thrust bearings, not oil pump chain, not timing chain, not cam caps, not valve clearances, not piston slap, not injectors, and compression is good.

The thot plickens!

I'm wondering if I can mount the cam sensors somehow to allow me to run the engine with the cam cover off?

Gotpepsi

Sounds almost exactly like a bad idler pully.Take the serpentine belt off and run it no longer then a minute. Does your noise go away?

superchargedk20

Have u tried pulling each coil individually to see if the noise goes away. I know u said it's not rod knock but that's what it sounds like to me. Freakin noise is weird . At idle it sounds like knock but when u give it gas I think it's TCT noise

insurgent

I tried pulling each coil, no change. Dropped the sump yesterday and room the rod caps off, all the shells are fine. I was convinced it was a big end but seemingly not!
Under load when driving it becomes more of a clack clack sound and not a tap tap like tickover. Wondering if it might be as simple as a blown head gasket, they can sound weird and don't always show up on compression tests?
Will remove some belts tomorrow and see if it's the idler pulley.
Checked the tct and not that...

windhund116

Not the belt pulleys, either?

Billman250

Check compression. High comp in #4 = #4 cylinder failure.

If it gets louder as it warms, that also points to cylinder liner failure. That's what it sounds like to me.

insurgent

Hmm, sounds like that could be a culprit. It has now started making a pnuematic kind of hissing sound, like air leaking under high pressure, which probably indicates some kind of cylinder failure.

In what way does the liner usually fail?

insurgent

Think I'm going to have to take the head off to take a look regardless of what the problem is. If the liner has failed is it possible to replace the liner with the engine in situ? I.e. Remove the piston through the top and tap the liner out from below? Excuse my ignorance, I know engines very well but this is my first S2000

Slowcrash_101

No, not really, the engine must be disassembled to fix a bad cylinder liner.

You can only overbore the FRM liner .25 mm, a lot of times people just sleeve the bad cylinder(s) usually when a cylinder goes it takes the piston skirt with it requiring a new piston. You can usually re-use the rod as it's a forged unit, and possibly the pin. The FRM is cast into the block, and a machine shop would just bore to the edge of the liner and press fit a dry sleeve. There are better more expensive options.

insurgent

Well I found the problem, just a belt tensioner like was mentioned. Not before having dropped the sump and taken the head off to have a look though. What a pain the proverbial...

Found slight scoring to cylinder number two, more kind of vertical polish lines that scoring, I'm guessing that's nothing to be too concerned about though?