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Tech Forum : Strange noises

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      - Strange noises
melloh   Posted Monday, Dec 8th 6:45am [Edit] [Quote] [IMS] [View car]
Post nr. 115
California, USA (San Jose)
1980 320is, 1991 318is
Well, I finally have my car back after one of my cylinders went out. Apparently it was a combo of things (bad wires, rotor, cap, clogged injectors, plugs, valves too tight....again, too lean). The car holds cold idle better now, but I hear this strange noise more consistently now (it was only very intermittent b4). If/when i rev it up and then let go of the gas (IE: for down shifting or even out of gear), there is this sound like a combo of bubbling or like something (a marble or nut) bobbling around in the engine. Is this what "knocking" is? Thanks for any help.

PS: I would take it to the mechanic, but I feel guilty. He spent 3 days troubleshooting and only charged me for parts and a couple hours for the tune-up (total 300 and bonus 12 of guiness & becks). Probably saved me 200-500 in labor costs.

Max   Posted Monday, Dec 8th 7:17am [Edit] [Quote] [IMS] [View car]
Post nr. 8
85 635CSi euro, 89 325iA
Check for loose muffler and/or metal heatshields or something like that. If it's from the tail pipe you might have mixture/timing set wrong and have the remaining fuel burning in the exhaust.
It's hard to diagnose things like that w/o seeing and hearing, if I were you I'd ask the mechanic who worked on it what it is.

Sorry, did not help much.
good luck!


melloh   Posted Monday, Dec 8th 7:51am [Edit] [Quote] [IMS] [View car]
Post nr. 117
California, USA (San Jose)
1980 320is, 1991 318is
Perhaps by coincidence, but you're right. My muffler hangers disappeared (again). But, the noise seems to be comming from the engine bay. I'll try and 'pinpoint' the noise. I know I didn't give much useful details. Still learning...

Tricord   Posted Monday, Dec 8th 2:23pm [Edit] [Quote] [IMS] [View car]
Post nr. 350
Belgium, Europe
323i Baur
Could indicate worn conrod bearings.

RDAvena   Posted Monday, Dec 8th 5:06pm [Edit] [Quote] [IMS] [View car]
Post nr. 288
SELECT * FROM users WHERE clue > 0
1981 323i, 1988 545is, 1997 528i
My thoughts exactly Tri. Sounds like a low knocking that keeps time with the engine? Might have starved one of your con rod bearings and caused it to wear prematurely. Catch in time with a new set of con rod bearings and fix it. The hardest part will be removing the oil pan.

melloh   Posted Tuesday, Dec 9th 5:08am [Edit] [Quote] [IMS] [View car]
Post nr. 118
California, USA (San Jose)
1980 320is, 1991 318is
Wow... i've never even heard of that part before. Thanks for replying. Also, just noticed today that it begins to be heard and around 3k rpm, and becomes louder & more frequent as it goes higher in rpms.

So, what is a conrod? Purpose? Thank you and sorry, I'm trying to learn!

Blauundweiss   Posted Tuesday, Dec 9th 5:26am [Edit] [Quote] [IMS] [View car]
Post nr. 35
Phoenix AZ, U.S.A.
1983 320i
You've got you're crank -[_]-[^]-[_]-[^]-
(crude I know) to which the pistons are attached, the con-rods stand for connecting rods ergo they attach the pistons to the crank and allow power from combustion to be transmitted to the crank and turned into useful energy such as twisting a transmission and wheels and such. very useful things that need well lubricated bearings in order to survive the force of gasoline burning in confined spaces. if they become starved for oil they wear and tolerances get sloppy. so you get a nice tock, tock, tock at increasing rate as the engine revs.sounds a little more severe, no scatch that a lot more severe than a sewwing machine. but they can and should be replaced before anything catasprophic (spell check?) happens like a rod being thrown off that rotating crankshaft at high velocity (much damage). anyway there's a crude crash course for ya, post any more ?'s you've got and everyone else make sure I haven't goofed up. -Chad

melloh   Posted Tuesday, Dec 9th 10:00am [Edit] [Quote] [IMS] [View car]
Post nr. 119
California, USA (San Jose)
1980 320is, 1991 318is
Thanks. Connecting rods sounds more familiar. obviously, ill need to do some serious studying if I want to understand/learn much more than what you told me. It's also pretty clear that I shouldn't try doing this on my own at this time.

Tricord   Posted Tuesday, Dec 9th 10:35am [Edit] [Quote] [IMS] [View car]
Post nr. 351
Belgium, Europe
323i Baur
Actually, it shouldn't be too hard for you to do it yourself. On the other hand, I suppose you don't want to pull the entire engine just to replace the connecting rods.

If you can jack up the car high enough so you can work underneath, you can remove the oil pan and you will have direct access to the crank and the conrods. You just turn the crank until there's a piston at BDC (bottom dead center, lowest point) after which you can unbolt the rod from the crank. Push the piston a little upwards and remove the cap. You can now remove the two shell bearings, and replace them with new ones. Oil everything properly, pull the piston a little back down, seat the rod back on the crank and retighten the cap to specifications, move to next cylinder.

Oh, and since you've an M10 engine, it's 1/3 less work for you than for us

M42powered   Posted Tuesday, Dec 9th 7:15pm [Edit] [Quote] [IMS] [View car]
Post nr. 228
Arizona, USA
1981 BMW 320i
Sticky wrist pin perhaps? Does the noise go away over time (ie after the engine warms up)? or is it there all the time?

melloh   Posted Wednesday, Dec 10th 5:11am [Edit] [Quote] [IMS] [View car]
Post nr. 120
California, USA (San Jose)
1980 320is, 1991 318is
It's there all the time. Can't tell if it gets worse or I just notice it more over time (other noises going away), but definitely does not get better over time.

Thanks Tri. Its tempting. I will just need to find a place to do the work, then! If i decide to do it, this will be revisited with inquiries for full instructions (so that a literate monkey could do it). First, I'll call the mechanic and see if he noticed it on test drives. Maybe he'll let me borrow/rent some garage space . I'll have to load em up w/ a ton of Guinness' !!

g323   Posted Wednesday, Jul 22nd 5:36pm [Edit] [Quote] [IMS] [View car]
Post nr. 337
323i 1982
Must I replace the conrod bolts when I change out the conrod bearings? Also, do i need any of the different sizes or should I buy standard?

Yety   Posted Tuesday, Aug 4th 2:38pm [Edit] [Quote] [IMS] [View car]
Post nr. 170
Europe, Romania
I had the same type of increasing noise (knocking) a few hundred miles before the bearings from the 1st piston slipped one over the other stalling the engine. In my case, before that "disaster" (crankshaft fitted already with +0.25 bearings was ruined) the knocking was distinct (the "tock, tock, tock" Chad mentioned) especially at startup just until the oil lamp went out and also over 3k rpm, especially at WOT.
IMHO that noise could be caused by the bearings from the piston that "went out" - they have been surely submitted to a high level of mechanical stress during the incident... so the sooner you change them, the higher are your chances to save your crankshaft (a micrometer would be very useful in order to mesaure the diameter of the crankshaft where the conrod bearings are fitted - specifications can be found in any E21 manual). Usually, the bearings wore out faster than the crankshaft, as they are made of a softer kind of metal than the crankshaft, meaning that if they are replaced as soon as they start knocking, the crankshaft can take the wear with another set - maybe even 100k miles if driven "softly".

g323   Posted Friday, Aug 7th 12:05am [Edit] [Quote] [IMS] [View car]
Post nr. 340
323i 1982

and see this video:

All help will eb useful for diagnosis - Im lost!

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