Name That Noise, opinions needed Options

[goose2]

Ok flat six gurus...let's play Name That Noise. The motor is a 2.4 six, has the chain tensioner upgrade, unknown mileage but good compression, normal oil consumption, runs very strong (except for some Zenith carb issues), minimal oil leakage, non-smoker. Sounds good, yes? I think so too, but something's not right. The first clue is a valve noise that comes and goes very quickly...a loud click-click-click that stands out above all the other nice mechanical music this motor plays. Two very careful valve adjustments have made no difference. This occurs hot or cold, but slightly more often hot. The noise is there maybe 50% of the time and can come and go in a couple seconds time. If I had to guess it's point of origin, I'd say # 4 or 5 exhaust but that's a tough guess. I've now put over 1000 miles on the critter hoping it would go away but it's not. I've searched message boards, talked to local Porsche mechanics, read all the books. Opinions range from "don't worry about it, when it gets worse it'll be obvious where it's coming from"...to"you'd better do a top end job on it now before it self destructs" Suggetions include sticking valve, bad swivel foot adjuster, worn valve guide, oiling problem, sloppy rocker shaft, and cam end thrust problem.

Second clue, not necessarily related. A strange noise noticable at idle to around 2k rpm. It may be present above that speed but other noises drown it out. It's a sort of muffled deep ka-bunk-a bunk-dunk....not a tapping like a bearing, or a clicking like valve train, or a rattle like timing chain. My mechanical experience would suggest crank end play, loose flywheel or something like that, but it does not change with the clutch in as one would expect if that were the case. This noise does not seem closely correlated with engine speed like valves or bearings. It could even be something other than the engine rattling against the body but I've checked for contact anywhere like engine shroud, exhaust system, etc. Does the dry sump oil system make noise maybe? It's almost a liquid sound like gurgling. Could this be related somehow to my valve noise?

I hope my noise descriptions make some sense...I realize it's pretty hard to diagnose sounds by a verbal description over the internet. I'm just trying to narrow things down as much as possible before deciding what to do about it. I know we have an incredible amout of talent, skill, and experience among our members. All opinions welcome, Thanks.
Randy

[ArtechnikA]

QUOTE (goose2 @ Jul 14 2005, 02:27 PM)

...a valve noise that comes and goes very quickly... a loud click-click-click ... bad swivel foot adjuster, worn valve guide, oiling problem, sloppy rocker shaft, and cam end thrust problem. ... Does the dry sump oil system make noise maybe? It's almost a liquid sound like gurgling.

second question first: yes. some combinations of oil, filter, and temperature moreso than others. the scavenge pump sucks up oil about twice as fast as the pressure pump reintroduces it into the engine. result: most of the time it's sucking air, or a big glob of oil and then air... anyway yeah - they do that. easier to hear in a 914 than a 911 because the oil tank is right there behind the driver.

as to clicking... when you say "the" chain tensioner upgrade, do you mean the Carrera "pressure-fed" tensioner upgrade? (there have been about 10 "updates" of various types through the years...)

donno. i'd be skeptical on cam endplay. adjusters and rocker shafts are easy enough to check. there is a spec for rocker axial play but 1) it's pretty big and 2) the only real fix is a new cam tower, so we won't spend much time going down that path...

if it happens as often as half the time, $10 invested in a mechanic's stethoscope, available at every FLAPS, can probably pinpoint the area of concern in a hurry. does the engine rev freely to redline? 'cause it almost sounds like a broken valve spring. these *can* be fixed with the engine in the car but it requires considerable patience - especially with a /6...

[sixnotfour]

QUOTE

second question first: yes. some combinations of oil, filter, and temperature moreso than others. the scavenge pump sucks up oil about twice as fast as the pressure pump reintroduces it into the engine. result: most of the time it's sucking air, or a big glob of oil and then air... anyway yeah - they do that. easier to hear in a 914 than a 911 because the oil tank is right there behind the driver.

(IMG:http://www.914world.com/bbs2/html/emoticons/agree.gif)

If it still has copper valve guides, they are shot.
If it has a Fram oil filter get a different one.

[goose2]

Rich and Jeff, I think you're right about the oil sump/tank noise...thanks for setting my mind as ease about that part anyway. Jeff, oil filter is Mahle...as to the guides, Dan told me they were bronze but not sure how he knows that. I've never had the intake off myself. Wouldn't bad guides cause a lot of smoking after decell overrun? Not seeing that. Rich, the valve spring is an interesting idea. I haven't often run it much over 5500 but I know it spins up to 6k ok....no evidence of valve floating. Redline's 6800 I think, it's a ROW 2.4 with Zeniths. I don't think it'll reach 6800 easily...seems to run out of stuff a little over 6, but it doesn't break up or miss like I'd expect from valve float. I suppose I could see a broken spring with the cover off, right? Might take a little poking around but it should be evident, I assume.
Thanks for your thoughts on this guys....any more?

[goose2]

Oops, forgot a couple things. It has the Carrera tensioners, done recently so I assume its the latest and greatest from the fatherland. Stethescope's a good idea...I'll try that.

[bd1308]

record the sound so i can add it to my library....


please?

[goose2]

Ya know...I have an old sony mini disc portable...I could record some cool sounds, as well as the ugly ones. I'll do that. Stay tuned....... (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

[goose2]

So it looks like I'll be tearing this motor down before long and we'll see which guess wins the prize...hey...maybe there should be a trophy or something? I just scored a 3 litre and the plan is to swap motors. I might have a nice 2.4 with a fresh top end to sell soon. Damn...I'm addicted to these cars big-time....gotta go rob a liquor store now.

[redshift]

Hmmm....

a 2.4 with a fresh topend.. Call me!

PM me when you go to sell it!


M