more on strange engine knock.

[bigyagi]

after my rebuild, engine sounds nice and tight. still, i can detect the knocking, but faint.
anyhoo, friend at work tells me that as i pull away, black smoke pouring out exhaust. the plugs always seemed black and sooty, for the last 6months. so, after reading a couple posts about adjusting mixture at the afm, i decide to back it out a tad, and see what transpires.
anti clockwise, 1 turn. car runs terrible, no power! so i re-adjust it back to around the same place. hmm, i cannot hear any knock now at all!!
sooo, i did notice that the adjusting screw seemed kinda loose. i'm now wondering, if it has been moving, and i have lost the proper fuel/air mixture?
and of course, how precise does this adjustment have to be? can all this have a bearing on the noise i have been experiencing?
i have no knowledge of fuel systems, so any experts out there, care to give me their thoughts on this matter.
i'm now thinking that i should try another afm, and see how things go.
anyways, i seem to be going in the right direction{i think}.
bob.

[SoCal Driver]

Adjusting screw on the AFS is only for the idle mix. Once the flap starts moving the bypass is moot.

Running rich is more likely the fuel pressure system. Either the regulator or the dampener. Could also be the engine temp sensor for the DME. Could be a leaking injector.

Problems with the AFS usually results in a lean condition.

[bigyagi]

ok, so i'm going to replace the fuel regulater, and dampener. now, the engine temp sensor. not sure where this is located, but will replace too.{when i find it} is this the same item, that is inside the afm??
will this never end?lol.
i have to say that this has me totally beat. only knocking about 1800rpm, not below, and not above. smooth as silk, and revs freely. not present at start up, only comes after engine is stinking hot, and even then, sometimes there is no knock, but it is a distinct knock!
has anyone experienced anything like this b4?
oh yes, oil pressure when really hot at idle {700 rpm!}3 bar. yes i know the idle is low, but its been like that years.
anyone got a lengh of rope!!
bob.

[ae1969]

How about recording a sound clip .... and show us with a pic where you think the noise is coming from.

[bigyagi]

hmm. i dont have a digital camera,but will try and get one.
honestly, the knock sounds just like rod-knock! what is confusing me,is that i dont hear it at all, hot or cold, below 1600rpm, and above 2000rpm. its not there at all at start up, and only begins after the engine is good and hot, usually after the fans have cycled. strangely, when hot, i dont always hear it??? but when i do, its quite noticeable. if i hold the throttle cam open, at 1600rpm, i can feel the knock coming thru the cam!!!
i will tape the noise, and put it on here. not sure how to do this, but will fumble thru i guess.
i took the old bearings{rod} to a mechanic, and he reckoned that they were in good, used condition, with quite a bit of life in them!
just to confuse me totally, now with 400 miles after my rebuild,i have tried giving the engine a bit of "welly", and it is so smooth, and mechanically quiet at high rpm, its beyond belief.
i'm reaching the point where i'm spending more time listening to the engine, instead of enjoying driving it!
i will change the items so-cal mentioned, but think i will have to bite the bullet, and go see a dealer.
maybe look on 944 parts for a spare engine, just in case.
thanks, bob.

[Mrmerlin]

Hi it sounds like you may have a loose pulley or camshaft bolt.
Try removing the timing belt cover and check all of the balance shaft,pulley/idler securing bolts and dont forget to tighten the camshaft securing bolt. also the camshaft rotor
Also check that you dont have a loose timing belt or balance shaft belt, it may hitting another part of its run, also check the water pump to see if the shaft is tight IE doesnt move side to side on its shaft axis. Also you never mentioned what your oil pressure is when its hot? at speed and and idle.
Is there any metal in the oil ?
To see get a dark piece of card board and pull the dip stick and let the oil drip onto the cardboard use sunlight to look at the oil stain, if there is metal it will be easy to see if so then it is prolly the #2 rod going bad, Goodluck ,Stan

[bigyagi]

hi stan. oil pressure at start up =5 bar. stinking hot at idle (700rpm} is exactly 3 bar.
holding throttle at 1k rpm, its almost 4bar, stinking hot.
you know, listening to the noise, i'm beginning to think that it is maybe a bearing, but omg, it must be in terrible shape. if i hold rpm steady, it will make the knocking noise, but its not consistent, ie: it comes and goes, gets louder, then quieter???? if i hold rpms steady, then blip the throttle, then it really does sound like rod-knock??
i dont know, its got me beat!
i drove to chicago over the long weekend, and i did not hold back! no problems what so ever!
anyhoo, i will check the mentioned items, and see whats up. btw, i retensioned the belts 2 weeks ago, and checked the rollers etc. thanks for the input!
bob.

[JRMock]

From FR Wilk...

"Get your idle up to 9,500 rpm..."

(I suspect you'll need his chip to do that.)


sorry, couldn't resist.

[bigyagi]

ha ha, thats too funny, and yes, i do have his chip!! seriously though, i've never bothered about the idle. when i bought the car from my friend, that was how it was set, and i have left it there ever since. it is very smooth, and never cuts out! i have held the rpms steady at about 900, and it sounds fast?.
hey FR, going to work the other day, right behind 2.5 boxster, we were indulging in some spirited driving{ahem}, seems like we were matched in the handling department, or maybe i mean we had the same trust in our machines, right?anyhoo, turn onto the straight part of private roadthat leads to work, and here we go, both hitting the loud pedal! i see the boxster squat down at the back,under hard accelleration and we are doing some serious damage to current oil supplies, i'm very surprised to see he has only pulled about 1 car lengh away from me, as i change up into 3rd, at 65mph, but not as surprised as he looks, and we both exchange a wave, as he turns off. i know he would have left me for dead above 75/80, but from low speed to around 70, who would have believed it! the chip sure makes the engine pull like a train, and rev its head off. if i had been in standard position , no doubt waiting for engine to hit its sweet spot at 3500k, he would have left me dead in the water!! great stuff FR.

[fast924S]

Sounds like rod knock to me. I have heard rod knock before and it can be a funny thing kinda like a phantom noise some times it does it sometimes it wont but it sounds to me like your #2 rod is on the way out. Also I dont understand, when you did your rebuild you didnt change your bearings?????? If you want I have a spare 85.5 944 engine for sale $800 + shipping and its yours

[bigyagi]

hi fast 924s. no, i did change the bearings. i took a plasti-gauge reading with the old bearings, and on #1 and 4, it was0.0025". on #2 and 3 it was between 0.003, and 0.004 ". hmmm. i measured the crankshaft with a micrometer,across 4 points, and it was round, and totally on spec.
wrist pins/bushings all ok, and using plasti again, checked new bearings, which came in at exactly 0.0015". no particles in oil, or any copper color to it. i'm totally stumped. i have considered everything to be honest. i'm thinking could it be the balance shaft bearings?? the water pump bearing?? i have no idea, but it is a definate knock. it does not sound the same at constant revs, it is always changing in fluctuation of noise, and volume???
at start up, nothing at all, but when stinking hot, thats when it starts!
anyways, i got an address for a local garage from a guy on the 928 forum who lives close by, so next week, i'm taking it over to a local garage, and get an expert to give it the once over. i refuse to believe that its rod-knock, after inspecting the crank journals, seeing the old bearings, and after putting in the new bearings, with right on the money readings. i know plasti gauge is not totally accurate, but its a great indicater. my old bearings were not worn, that would cause the knock described.
well, we'll see next week.
thanks for your input.
bob.