I am disgusted, I just finished the installation........

[Don in Redondo]

of a top end rebuild, got the engine running o.k., no leaks, no smoke after 10 minutes, good oil pressure.......but a loud knocking sound like a bad rod bearing, which was not there when the engine was pulled. This has been a long hard rebuild with small setbacks along the way, and this latest snafu is the straw that has just about broke the camels back. The thought of having to pull the engine and start all over is chilling.

I checked the rods manually by push/pulling on them when I had the piston/barrels off, and could not feel any bearing looseness. Now I wonder if I should have taken the extra time to actually remove the rods in order to make exact measurements instead of just the cursorary manual check.

My only hope is that the knocking sound is from a large rocker gap but I have my doubts as I was very carefull in the initial adjustment when the engine was out.

Any suggestions?

[Thomas Owen]

Well that is not good news. I can only imagine how you must feel after just completing a complete rebuild.
A couple of thoughts- If the rod bearings were ok when you pulled the engine, it is hard to imagine, although possible, that something could have been introduced into the oil that could damage a bearing that quickly upon restart. There is a check you can make to determine rod or main bearing problems. One knocks on accel, the other on decel - maybe John Walker will chime in here. You say the oil pressure was good...what about cam timing? Valve hitting a piston? Are you sure your cam timing was right? What about wrist pins? You notice I am mentioning things you *did* remove, where there may be a chance something went wrong. Hopefully someone else can tell you some other things to look at before you pull the engine again.
Good luck.
Tom

[RoninLB]

What eng., any mods., how many miles, what year. Are you sure it's not chains. Did you use a probe to find area of noise. "Salin' 'round the world in a dirty gondola. Oh, to be back in the world of Porsches"..............Ron

[Doug Zielke]

Did you interchange any pistons with different cylinders? Are any of the pistons installed upside down (and contacting a valve head)? Are all the wristpin circlips properly seated in their grooves?


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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

[stlrj]

Could a rocker arm have come loose?

Joe

[john walker's workshop]

turn it over slowly by hand with the plugs out, and see if you feel any binding in one spot. it wouldn't be the first washer that went down an intake port.

[This message has been edited by john walker's workshop (edited 07-29-2001).]

[Don in Redondo]

Towen, of the items that you suggested, the one that might be a possibility is the wrist pin to rod bearing assembly. I have always felt uncomfortable that I had to tap the lubed pins through the pistons and bearing bores with a plastic mallet and wood dowel, I did this with the barrels in place in order to provide some side support, but any time you have to apply force in a direction that the parts are not designed to be used in makes me feel uncomfortable, although I have used this method in several other pin installations with no problems. Actually, at the time I considered it a good sign, in that it indicated that the pin to bore fits were tight. The pins seemed to go in easily with just a few light taps but would not go in with just finger pressure.



RoninLB and Doug, yes I did try to probe for the noise location using both a solid rod and hose tube on this older, stock, 67 911S, with 90,000 miles......... nothing specific jumped out, possibly the #4 cylinder area sounded louder but not conclusive. This is a fairly loud matallic knocking cadence that is easily heard at idle in 1000 rpm range. Knocks about once every revolution.

Can a chain or chain tensioner cause a loud knocking sound? My tensioners are the second generation style with collars and seemed to tension and hold the chains in a very tight manner during the valve timing procedure. I am sure that the timing is correct because the valve openning/closing specs. were right to the manual figures. These were new pistons that were installed and I double checked the orientation and clips, they seemed correct.

Well, I am out to the shop this fine Sunday morning to double check the rocker/valve clearance, will keep you posted.

[Doug Zielke]

On any engines I've worked on that had tight interference-fits on the wrist pins, I heat the piston with an electric heat gun, until the pin pushes in with finger pressure. I also freeze the wrist pin in a deep freeze before installing. This step prevents the need to stress the rod and bearings from tapping the pin into place.
Good luck Don!

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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

[BRAINIAC]

Don. Bad rod bearings don't usually make noise at idle. (unless they are REALLY bad) What you described in the second post sounds like valve train. (Loose rocker or tappet, etc.) Rod bearings usually make noise at the crescendo of acceleration. Kind of a "rrrrrrrrevvvvvv-knock-knock-knock.....rrrrrrrevvvvv-knock-knock-knock. Hope that translates. John may have something there with the "foreign material in the cylinder" theory, but for your sake I hope not.

------------------
Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[Don in Redondo]

John, Joe, Doug and Tyson.........I completed the valve adjustment re-check this Sunday and the valves and rockers appeared correct.

Per Johns suggestion I manually turned the engine over without plugs looking for tight spots but did not feel anything unusual, although this was somewhat less than definitive since compressing the valve springs gives somewhat of a resistent feeling when a cam lobe comes around. During almost all of the rebuild I kept paper towels stuffed in the intake ports so that foreign objects could not enter, but you never know, maybe something could have slipped by.

I also ran a compression test of all cylinders, while I had the plugs out, to possibly help identify the possibility of a misplaced washer/nut items.......but all cylinders showed appx. 140 psi.

Something that puzzles me, is why the knocking sound cannot be heard when turning the engine over using the starter motor and with the ignition off? For such a loud knocking sound, I would think that the rpms generated by the starter would be enough to make some sound.

I ran the engine again after the valve lash re-check, and was able to run another sound check which resulted in possibly locating the general area of the sound source which seems to be somewhere around the #4 cylinder or the passenger side chain housing.

Are there any other tests that I should run while the engine is in the car, before removal and more disassembly?

Thanks for all your help and support,

Don Jackson in Redondo Beach, Ca.

[Wayne 962]

Hi neighbor Don! Hey, here's an idea. I just moved to the area (exactly one month ago). You're more than welcome to bring the car by, and we can take a listen to it. I have a similar noise in my recently rebuilt 911SC motor that I've been trying to diagnose. Mine only occurs stone cold though, and lasts about a minute. Just about everyone that I've taken the motor too (people who are tens of years older and have built many more motors) have told me that it's nothing to worry about, and that it's normal for the 911 engine to make all sorts of odd noises when warming up.

Email me, and we can set up a time when I'm home working on my 911 (in my new 4+ car garage!)

-Wayne

[Thomas Owen]

Something that puzzles me, is why the knocking sound cannot be heard when turning the engine over using the starter motor and with the ignition off? For such a loud knocking sound, I would think that the rpms generated by the starter would be enough to make some sound.

This may be a clue. Remember, the only difference is that during the cranking you do not have the detonation driving the piston/rod back toward the crankshaft. Something else I thought of - what about proper cam alignment - put all the correct shims back in? Chain on both sets of spockets? I remember in Anderson's book he mentioned seeing an engine that had the chain installed on the outer set of sprockets only.
Keep pressing - you'll find it.
Good luck.
Tom
p.s. That is a very generous offer that Wayne extended.

[964Cab]

My theory is that the clutch/flywheel is not balanced and your getting torsional vibration that mimics a bad engine. I assume the crankshaft was not reground ? I assume the crankshaft bores were lined-bored ? I assume the pulley/damper was installed balanced ? I assume you didn't have the old flywheel skimmed ?

Hope this helps,

Patrick

[Leland Pate]

Do you realize that you now have me absolutely scared to death? Just what I need... now i'll be pissing blood for a month. Sure hope you figure it out though, and keep us posted on the results.

This is the worst feeling of paranoia I have ever experienced. The thought of reassembling my motor only to have it explode when it starts up...I honestly have nightmares about it.

[Don in Redondo]

Wayne and Tom, thanks for help with this problem.

Wayne, I have sent an email to your personal address.

Tom, I believe that the spacers, sprocket, and chains are installed properly, as I returned them exactly as I removed them (pre-knocking condition), I didnt go thru the end play adjustment since I hadnt changed anything and this part of the engine seemed fine prior to removal........wish maybe I had made the measurements, now.

One part, in this area, that I did have problems with during the re-assembly was the Woodriff key that the gear slid over. The gear would continually grab the half-moon shaped key and rotate it out of its seat, thereby pinning the key against spacers and the cam plate in an up-cocked position. I was able to eventually file the key to a less tight fit so the gear would not catch it during the gear installation on the camshaft end. Problem is, is that it is a blind installation and one cannot see what happens to the key once the gear starts to ride over the top of it. Hope it didnt catch and rotate again, to the point where it might be making contact with the cam holding plate or its securing bolts.......I dont think this would be the case because I would think that I would hear some grinding or knocking, or feel some interference when manually rotating the engine during the cam timing adjustments.

Still scratching my head and wringing my hands,

Don Jackson in Redondo Beach, Ca




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[Don in Redondo]

Hi Patrick and Leland.

Patrick, since this was a top end rebuild only, in order refresh worn valve guides, pistons, rings, and cylinders........and the rest of the engine seemed fine, I did not change any of the items that you mentioned, so hopefully they are not a factor in this knocking problem.

Leland, you are absolutely right, I am having nightmares over this, and to make matters worse, this is a spare engine that is replacing the original engine belonging to this car because the original was just beginning to develope a similar knocking sound but with much less noise and intensity.......I did not want to take any chances in creating extensive and expensive damage to the original so I rebuilt the spare and made the swap. Now I have 2 near identical engines with near identical problems and no concrete solutions in sight. Biggest decision now is which to tackle.

[Kurt B]

Could you please submit an audio file? I know it's a lot of work, but I'd really like to hear this sound...I have my own engine tapping problems, and I'd like to compare them.

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Kurt B
1984 Carrera Cabriolet
911 Page
carrera_cabriolet@yahoo.com

[Doug Zielke]

Leland,
Since when are you afraid of things that explode?

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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

[rstoll]

Since both spare and original motors are making the same noise, is it possible the noise is further down the driveline? I think there was a thread way back about starter solenoid not retracting, causing a knock. Warren??

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Robert Stoll
83 SC
83 944

[BRAINIAC]

I don't mean to alarm you but I seem to remember that #4 is the first rod bearing to get oil. This means it is going to get the brunt of foreign material. What I'm getting at is that debris from your old motor's bad rod bearing may have not gotten cleaned out of the oil tank, oil cooler, etc. Then when you started your new engine, this debris was pumped into #4 and destroyed that bearing.

Please tell me you removed everything in the oiling system and thoroughly cleaned it! If not, I think it's mystery solved.

------------------
Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet