OutNSpace

I'm hoping some folks that have done this before can help me with some questions.

I have a '04 996 C4S with 103K miles in superb condition. My engine is a 996/03. The IMS and RMS, AOS replaced, sparks, plugs all done around 78K and the car just runs great.

What is absolutely driving me crazy though is a tapping sound at idle after the engine has warmed up. This comes from the passenger side of the engine. After a lot of research I'm fairly certain it's one or more stuck lifters. I've worked on engines before and want to do the replacement myself, but have some questions:

1. Are the exhaust and intake lifters the same or are they different?
I have this part #: Porsche: 996 105 041 72 (and alternate BMW: 11 32 1 748 884)
Can someone confirm that those are the correct lifters for both intake and exhaust?

2. To get the lifters out the cams need removing. Will I need to adjust the timing when I put them back in? The guide on Pelican says I can just line up the timing marks on the chain and gears, but I'm not sure about it.

3. I'm considering doing this without removing the engine. I know it would be easier with the engine out but I don't really have the room to do that and although I'm sure it will be a bit cramped, it looks possible. I'm thinking the biggest pain in the *** will be when I break the header bolts removing the exhaust and I'll have to buy a stomski tool to address that. Any comments on doing on on-chassis lifter replacement?

Thanks in advance!

Ahsai

Does it sound like this? The intake and exhaust lifters are different. The intake lifters are much more expensive.

OutNSpace

It does sound very similar to that but it's difficult to differentiate that sound from noisy lifters. I forgot to mention that I brought it to my porsche mechanic and he told me it was definitely not cylinder slap, and was very likely a stuck lifter.

AWDGuy

The "porsche mechanic " who did the ppi on my car said it wasn't piston slap either. "No way the cylinders are scored, try a different oil"

My cylinder 4 & 6 were completely scored.

post a video of your car idling here. People have done lifters to only start that car back up and realized it wasn't the problem at all. Hate to see you waste that money and effort.

Ahsai

The video teaches you how to tell this sound is from the cylinders. You just need someone doing the same to confirm.

The intake and exhaust valves are #5&6 here

http://www.autoatlanta.com/porsche-p...section=103-11

strathconaman

What if you didn't replace the stuck lifter? What are the consequences?

Porschetech3

Being a Porsche mechanic also, I feel the need to take up for the trade a little bit. These M96 engines suffer from bore scoring more than any engine type I have ever seen in my 40 years of being a mechanic. And the symptoms are not typical of other engines that have bore scoring. Any mechanic who does not know how unique and widespread this problem is will find it hard to believe.

I remember back about 15 years ago while attending Porsche special training class W10 ( water-cooled engines), the Porsche instructor mentioning that the pistons of the m96 had an offset piston pin that helped reduce side loading after combustion on bank 1, but unfortunately they they used the same piston on bank 2 which would increase side loading. I haven't actually measured the pistons to see which variations of m96 had this off-set or if they all have this off-set, but obviously (if true) is a cause of bore scoring that could not be fixed, since there is no other option for factory pistons.

OutNSpace

Thanks for the replies. I'll wait until the spring when I take the car back out of my garage and will get a second opinion at the dealer or other Porsche expert shop.

beetleything

Really ??

Porschetech3

Yes, really. The only engine type I can think of that comes close is the Chevy Vega 140 of the early 70's.

beetleything

Interesting.

I guess the issues with hot spots and cooling are a factor & oil change intervals etc.

Porschetech3

They are, the hot spots, cylinder cooling, oil quality, and piston pin offset on bank 2 are all contributing factors.

Ahsai

Yes, 0.5mm offset on my '02 996 engine. See post #564 here https://rennlist.com/forums/996-foru...l#post13253105

Warehouse33.net

The intake and exhaust lifters are different.

Exhaust
https://www.warehouse33auto.com/INA/...996-105-041-72

Intake
https://www.warehouse33auto.com/GENU...996-105-255-25

-Jason

Porschetech3

Thanks Ahsai, I actually had thought the piston pin offset hadn't been discussed in Rennlist forums, I should have know it would have been discussed in your detailed engine build thread ! So it looks like the offset pin was in the ALL m96 and m97 engines, when I first heard about it, the m97 hadn't even been produced, shame.