Identify This Noise
 

I am hoping that someone can help me identify the knocking/thumping sound heard in the video. I had my finger on mic initially and when I took the camera under the car - sorry!

The sound is more pronounced when the engine is cold. After warm up, the sound exists but is diminished.

I rebuilt the engine nearly two years ago and it now has 10k miles on it. Runs like a champ from crank to finish.

Engine specs: 9.5 JEs, 964 Cams, SSIs, Dansk Exhaust, CIS

I have an idea of what it might be but I don't want to skew any opinions at this time. Please let me know your thoughts.

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Pay particular attention to :09 through :11 seconds in the video.

Rocker on the right bank?

hey craig, go by tims and let him listen.

did you go by stans?

my ears are shot, and cant hear, playing drums. take the belt off to eliminate alt.

Could be. I just did a valve adjust about 2500 miles ago. All rockers were in proper position - no leaks either.

The sound seems very centralized though.

I have two ideas:

1) Alternator bearings - discovered recent fan housing scrapes. Spinning fan (without belt) results in a subtle grumble. I can't detect any movement / wobble of the alternator shaft. No cracks in housing. Fan is new as is outer pulley half.

2) Piston slap - I didn't measure pistons when I got them from EBS via JE. They were custom made to EBS's specs. Could be that one or two are off. Slapping when cold and less so when warm due to expansion?

I was going to do that next - pull belt and see what happens. I've had issues with fan scraping in the past.

I should probably pull the alternator and have it rebuilt anyhow. It is really the last "unknown" piece on the engine. Everything else has been replaced.

Man, I haven't seen or spoken to Tim / Stan / Kevin in months. I need to get in touch with those guys soon. Waiting for cooler weather!

BTW ... might have a mountain house for us up near Asheville, NC. I think I'll have access to it as often as I like throughout the fall. Might be a good road trip!

get yourself a mechanics stethoscope and go to town.

i thought about the piston slap being a possible probelm. just did not want to scare you just yet. if it is still there after taking the belt off, run by tims, he is good with noises.

i was down in charleston a while back and saw you. car looked good. i am thinking of selling mine. i want something i can take to a track. even though my car is not perfect, i think it is still too nice and in too good a shape to convert to a track car. i bought this BMW 325is a while back. man, i love ths car. fun to drive and cheap for parts. you can buy engines, tranny's, LSD rear ends for $300. plus, i would rather have a coupe, not a targa, and the porsche is just too expensive right now. i am thinking i could pick up an older motorhome and a car that is already ready for the track.
i would really love something like stan has, and old long hood that is stripped with a 3.0. but the BMW is a blast to drive too.

hey Craig. Really old thread, but what was the source of this noise, if you ever found out.

The answer might help a lot of other folks with the same symptom.

Thanks

I'm honestly not sure of the source. One theory is that it is play in the Intermediate Shaft which is more apparent at low RPMs (and was told it was nothing to worry about). I keep my idle RPM around 1k and the sound isn't as noticeable. However, sometimes my idle RPM will be at 850 or 900 (CIS seasonality and sensitive nature) and it is pretty pronounced - and sometimes I don't hear it at all!

Another theory is that it is piston slap from the JE Pistons. I don't think this is the case since the noise seems to be more pronounced with a warm engine. If it was piston slap, the noise would diminish with a warm engine - JE pistons would expand and close the gap with the cylinders.

Since my original post nearly 3 years ago I have put a ton of miles on it (including 4200 a month ago when I drove it across the country) and haven't had any problems. Runs great, uses virtually zero oil (1/2 quart in 4200 miles), no smoking, no leaking, solid running throughout RPM range, etc.

About 6 months ago I replaced both cam seals b/c they decided to leak. This required timing the cams and all that good stuff. I didn't find anything unusual or alarming.

I suppose there could be some internal stuff going on that I can't see, but I haven't found anything suspicious in my oil so I'm not terribly worried. I wish I could help more!

Thanks Craig. Very helpful info. It sounds exactly like my engine, and my shop told me it was piston slap, and they recommended an engine rebuild. Very expensive.

Nice to hear that you are still driving it without problems. Good luck, and happy driving.

I'd certainly get a second opinion. I don't believe that piston slap alone is enough reason to tear down an engine. You'll even read that some piston slap is good b/c it means less friction! It is more of an annoyance than it is an actual problem.

How much history do you have on your car? Any idea if the engine has been rebuilt already? Does your car make the noise throughout the rev range or just at idle?

Mine had a similar noise, it turned out to be a rod bearing. Hope that is not the case for you...
http://forums.pelicanparts.com/911-engine-rebuilding-forum/739457-rebuild-2-a.html

Full story here. I had just posted when I read your post when searching for "piston slap"

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/748496-full-rebuild-result-piston-slap.html#post7426597

Ya that would suck. I'm not about to tear down my engine to find out. So many noises sound the same but are a result of varying components.

So you heard the noise initially, then starved the engine of oil, and then heard a loud bang? Was the problem there before the oil starvation?

No, that is the other way around. Oil starvation first, then a noise that sounded like it was located in the heads, then got really loud when piston hit valve.

Ooof. Man I am so sorry about that! Glad to see that you are working on version 2!

I vividly remember reading your first rebuild thread as I was preparing for mine. I'm nearing the 5 year mark as well. Seems like yesterday though. Crazy how time flies.

Best wishes!

Same Noise Exactly...??
 

mca,

My noise sounds exactly like yours? A bit harder to hear over my exhaust but its the same... Anymore info on your noise? Is the car still running good?

Thanks!
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BEFOREFULLWARM-UP_zps108925e9.mp4 Video by supersport911 | Photobucket
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AFTERFULLWARM-UP_zps0fc07968.mp4 Video by supersport911 | Photobucket
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Original Post:
http://forums.pelicanparts.com/porsche-911-technical-forum/764385-930-3-4-oil-pressure-relief-valve-wtf-videos.html

+1
Harbor Freight has them for a reasonable price.

I had a rod knock once, and with a stethoscope held to the bottom of the motor you could hear it. If it were me, I would want to eliminate a rod knock as a possibility or I would tear the motor down. A loose rod bearing will ruin your motor if you let it go.

DSM-

Yep still running great. Super smooth and powerful, no leaks, no smoke, no oil consumption, no glitches, no high temps, great gas mileage, pulls like mad all the way ...

My noise only seems to occur at a specific RPM near idle. Sometimes it is more prevalent and other times it can't be heard at all. I really have no clue what it could be. I'm not concerned in least and would take my 911 across the country again in a heartbeat!