Lifters. Replacement Methodology

[logray]

Hello all,

I'm tracing a persistent tick/slap/knock mainly noticeable on idle, but can randomly appear at other times. Other times it goes away completely, not on cold start, not warm, nor after warm restart. I am thinking wear in the variocam system somewhere or worn lifters (I've also noticed a reduction in MPG, used to get 26-28 on the highway, now I get 20-22. In town MPG is dismal in the 15'ish range, where it used to be closer to 18-20.

I'm planning to drop my 1999 996 M96 3.4L to replace the variocam pads and the minor chains. 72k on the original engine.

I'm also going to replace any collapsed or out of spec lifters. I understand replacing the tappet carrier is advised when it is out of spec, although at considerable expense.

I'm guessing this question probably warrants a religious answer, but I've read in some places people have had luck replacing just those lifters that are worn while others advise to replace all on one side (12 in this case, or 24 total), so you know they will all wear evenly.

Any schools of thought there and/or experiences to share?

Thanks!

[Dharn55]

Also do a visual check of the chain tensioners. The IMS to Crank and the 1-3 side are easy to get at. Lock the engine at TDC and take out one at a time. If they are scoured or worn then they will take some time to pump up and you can get some chain rattle on start-up. They are not expensive, and can be replaced with the engine in the car. The 4-6 side requires removing the AC compressor to get at it. You might want to check these first, it could be the source of the noise.

[logray]

Thanks again for the reply. Yes I plan to replace the tensioners When I did the LN IMS retrofit about 4k miles ago the 1-3 side was scored a little (and is the side with the noise). That side also reads -3 on cam deviation, and with the oil sump plate off I've seen some of the black/orange tiny shiny bits of cam pad stuck in the oil screen as well as in the bottom of the pan. Why Porsche would stick these plastic wear parts in that can clog up tiny oil passages is beyond my reasoning... sheesh.

I'm pretty sure though that I've got some lifter noise, either some are collapsed or out of spec. I guess the right thing to do is just open the wallet and replace all 24 (although reading elsewhere about replacing the lifter carriers at the same time means a much more costly R&R).

1-3 tensioner...