noise 86 3.2l tough!

[sleepdoc]

The 1986 3.2l in my 914/6 conversion has a chronic tapping noise that I can't figure out. It is loudest when the engine is warm.

It sounds like an exhaust leak, and is certainly heard with the stethoscope over one header, although not completely limited to one outlet pipe, but nothing like heard with your ear while looking into the engine bay.

It synchs with rpm, gets less noticable at higher RPM.

Careful examination with stethoscope fails to localize the noise well. Valves, tensioners, cams, intake runners, block, cylinders, fan all with reasonable smooth machine noises. This is really strange, it is quite loud like an exhaust leak and easily heard at idle from five feet, and yet is not really transmitted through the block, cylinders, heads as metallic vibration or tap.

Noise heard well from below and above. No increased sound with the oil filler off.

Valve covers off reveal no broken studs, no blowback soot.. Compression 170/175/170/170/170/160 cold.

Exhaust is headers no heat exchangers to stock early 911 two in one out banana. All exhaust connections are easily accessable to see, feel and listen to, and all seem tight with no leaks. Listening with stetho around connections unrevealing.

The engine starts, and runs well, leaps to redline, idles pretty well with some minor hunting, ( no O2 sensor yet).

Does anyone think this could be a combustion gas leak at the cylinder/block, or cylinder/head union on the top under the cooling shroud? I certainly could not appreciate leaking gas sounds with the compression test which I might of expected to reveal a leak at the head/cylinder.

Please offer your thoughts.

best Mark

[Rot 911]

If you are using the DME to run the 3.2 with no O2 sensor then the DME defaults to a "limp home" setting which results in an overly rich fuel mixture. I suspect what is happening is that not all the gas is being burned up in the combustion chamber and the excess is going into your exhaust and is probably igniting in your headers, probably in the collector portion of the header.

[sleepdoc]

Thanks Kurt

Good thought. I would expect this type of detonation to occur
on both sides and pretty symetrically though. Any other ideas out there?

best mark

[Early_S_Man]

How about a loose baffle in the muffler?