Metty

See if this works.

Weazer

Metty, just to be clear, on your 1999 996 5 chain engine there are three chain tensioners: one for each engine bank cam chain, and one for the crankshaft to Intermediate shaft chain. These are screwed into and out of the engine externally. Each of these chain tensioners has an oil pressurized plunger which acts upon an internal chain guide rail and pad which actually contacts the chain creating the required operating tension. Your rattle is most likely caused by the chain tensioners failing to hold hydraulic pressure after engine shutdown and being noisy upon engine start up until they pressurize. The chain tensioners are cheaper and easier to fix, if I recall correctly they were about $125 each or thereabouts. Your engine's internal chain guide rails may also be the source of your rattle, typically when the pads made of dark brown plastic material wear down from chain contact to the point that the chain is contacting the guide rail itself. or the guide rail has failed and is banging around inside the engine. The internal chain guide rails are much more costly to repair as the engine needs to be opened up to get at them. If you have been doing your own oil changes and dissecting your oil filters and have not found good amounts of bits and pieces of dark brown plastic type material, then I would suggest the rattle is more likely your external chain tensioners. If you have been finding good amounts of dark brown plastic type material in your oil filter at each recent oil change, then its most likely your internal guide rail pads. Me, personally, I would try the external tensioners first as they're cheaper and easier. If that doesn't remedy the problem, then you know its the guide rail pads. BTW, listened to the audio/YouTube clip several times, kinda tough to distinguish a particular sound from the rev on start up with the muffler delete, however, when the engine gets down to idle I hear a distinct rhythmic tap which may or may not be bore scoring, you may want to have your engine bore scoped to inspect for cylinder wall damage. Is this the "rattle" of which you speak because, if so, then that's a whole other kettle of fish (entirely different issue).

Metty

Weaver, thank you so much for your reply. It’s the loud rattle upon start up. That secondary tap disappears after a few seconds.

rockhouse66

At the extreme risk of turning this into an oil thread, changing brands of oil might influence your startup rattle. I believe mine got better when I switched to Motul.

808Bill

That does not sound good!

DBJoe996

I agree...that does not sound good. But, it appears to happen when you hit the starter. It actually sounds like your stater bendix gear is getting stuck in the flywheel gear. Perhaps time for a new starter?

Alpina68

[QUOTE=Noz1974;16483002] On the 99 it's ok to just lock the crank at TDC and then remove the tensioners , QUOTE]

You don't have to lock the cams?

Mike Murphy

The shop that did my tensioner pads on both sides used Motul for the refill. I was using Mobil1 for the last 3 years prior. It is quieter.

SoCal911t

Unlike you, Motul got my vote when I bought my 996 three years ago tomorrow.

islaTurbine

It seems to me that there should be an easy way to discern between bore scoring and lazy tensioners:

The bore scoring noise would remain for the entire time that the engine is running, whereas lazy tensioner noise should go away after a minute or so once they get fully pressurized. No?

Mike Murphy

Right.

Mike Murphy

Too popular of a name

Weazer

Yes, lazy tensioner noise typically goes away after the tensioners re-pressurize and sound like a diesel engine idling (just like my 1999 Boxster), whereas bore scoring is a consistent clacking sound best heard at idle. Often when you rev a car with bore scoring, the clacking goes away, but returns at idle. I have personally never heard a failed guide rail/pad but I would imagine that noise would not go away and even increase with engine revs.

Byprodriver

The sound of chain flapping is caused by the IMS tensioner at the bottom of the engine. The updated tensioner (2002 I think) has a preload spring to minimize slack & flap before the tensioner is fully pressurized with oil.
There is a update bulliten on this that a good search would reveal .

Byprodriver

The 1st sound you hear when a guide rail completely fails is the chain coming off the rails,sometimes thru the Cam cover.