help - new 911 owner - engine noise

[313green]

just got my 72 911t back from an inspection. good overall report. it has several oil leaks, but they are very very minor.

i drove the car today at high speeds (70mph) for the first time. when i got home, i heard a ticking/thumping in the motor at idle. it was random. sometimes it got loud, almost like there was something rattling around in there.

i've read about chain tensioners. mine is the old one. never upgraded.

any suggestions?

thank you!

[steely]

Welcome to the club!
Suggestions:
alternator bearing or fan hitting the housing? Alt/belt nut tight? or is it more of an internal engine noise? L or R side

BTW, post a pic of your car (it's a rite of passage).

[Oh Haha]

Welcome to Pelican.

How knowledgeable are you on cars?

Can you tell a ticking lifter versus a rod knock?


As steely posted, it could be a simple problem like a nut not torqued correctly(a problem yes but not as bad as a rod knock) or it could be internal.

Tensioner failure sounds like nails in a tin can. It's rather distinctive.

A video would be very helpful, if you can do it. Try to replicate the noise and capture it with the microphone as best you can.

[BoxsterGT]

Tensioner noise comes in at about 1200 rpm & goes away at about 1800 + up.

If you still have the original type, check it out carefully before you trash one side of the motor.

Len

[313green]

thanks for the quick responses. i don't know a lot about motors. i listened to the engine again. it's not as loud since the car has cooled. i opened up the big air filter cover and found the sound. it appears to be inside of the air pipes (I know that's not what it's called). the sound is actually the sound of wind or air "puffing". like when you blow into a bottle.

[Oh Haha]

So it isn't a metal on metal sound?


What engine do you have? Carbs or fuel injection?

If the shop that did the inspection knows Porsche cars and gave it a good review, hopefully it is a minor issue.

Nice looking 911, BTW. I like the understated color.

[313green]

2.4l. no upgrades. factory motor.

here is a link to a video. you can hear it clearly near the end, when I remove the air filter cover

YouTube - 911t motor sound

[nineball]

you have one angry car. i have never seen one that tries to spit at you

(that's what it sounds like to me)

[steely]

Beautiful looking car.

I'll have to "disqualify" myself now because my intake/fuel setup is different - I am only guessing that it's intake related - perhaps someone else will zero in on the cause - nice big clue in that vid.

Is it that tick/tock puffing sound? Very interesting.

[313green]

Yes, tick/tock, sound but it's clearly a puff of air.

[313green]

Could it be the mfi?

[Oh Haha]

I'm out. Sorry. FWIW, it does not sound internal so that is good.

(Great video, though. It captures the sound perfectly.)

Be patient. There are some real MFI gurus here that will chime in.

Good luck and please tell us what the problem and solution is so that the next guy can be informed.

[bgyglfr]

I can't help but that is a nice car. Congrats!

[jason2guy]

after nearly 20 yrs of pcar ownership i have experienced my first tensioner failure. mine sounded much deeper than nails in a can or chain dragging. i heard it and thought, im in BIG trouble. granted i never had to diagnose a rod knock or anything major like that, so my experience in bad noises is somewhat limited. nevertheless it SOUNDED like big money. so in your video what i hear some loose valve clearances and that puff is either a backfire or i bet ull find ur heat exchanger to head connection in need of attention

[313green]

I will post the problem/solution asap. Mike

[jpnovak]

Does your 72 have carbs? If so, you have a lean pop through the intake. The cause is a clogged idle jet or passage way. time to disassemble and clean the carbs.

FYI, MFI can do the same thing with worn butterfly shafts.

MMM sephia Brown. Great car.

[313green]

I have mfi pump

[Flieger]

You have worn throttle bodies, most likely where the shafts pass through the magnesium throttle bores, if not it is the butterflies have worn a groove in the bore. If the butterflies are not adjusted correctly (so that they are not fully closed and rest on the stop screws), the intake reversion from the camshaft overlap will cause them to bounce and wear into the softer Magnesium. The only fix for either shaft wear or bore wear is to take the whole MFI off and send the parts to someone like Eurometrix for re-bushing and possibly porting smooth. This is not cheap but it will run great when you get it back, especially if you have your pump done with the other parts.

The good news is that all this means is that you tune the MFI pump to have the proper air/fuel ratio at wide open throttle and high rpms, when it matters. The worn throttle bodies have no effect in this realm. You will suffer from too much air leaking in at low rpms, causing poor manners when puttering around town. Possible stalling, high idle, or just lumpy idle.

Even with good throttle bodies, a motor with S cams which have more overlap will have those ticks through the intake at low RPM. that is just the overlap of the intake and exhaust events. When you rev it, it will get smoother.

You do not need to worry about anything. My 2.7 RS spec (and most all MFI engines) does the same stuff but pulls strong in the canyons at high RPMs and full throttle, so I am happy. You can decide when poor idle bugs you enough to rebuild.

Welcome to the MFI club.

[313green]

Thank you for such a thorough response. I alsoown a 1982 23' oday sailboat and it's known to have a great forum....but this one blows away anything I've ever experienced. Cheers.

[313green]

Haven't received a definitive answer, but it could be a bent cam.