Rod Knock? Distributor?

spooldup · 08-19-2007, 02:10 PM

Looking for some ideas on my 82SC with 103k. Hot or cold, I have a knock that sounds like its coming from the fan area. I replaced the alternator which had badly worn bearings so I thought I had it, no such luck. The oil pressure hot or cold is great and the car runs fantastic. I did a lot of searches including distributor because their was a post that if brass looking particles were in the oil (which I did have but very little) it may be the distributor. I just want to finish the driving season which will be about 2000 miles before I go tearing into the motor this winter if needed. If its a rod bearing, what type of oil do you guys think would be best to limp this baby along til late fall? If its the distributor, is their something I can do in an evening and what am I looking for (the post on distributor was not very detailed). I pulled the lower valve covers and did a valve adjustment even though its not a tick, its a knock. The car has been driven about 1000 miles like this and has not changed for the better or worse, I wish something would happen like low oil pressure so I could at least have a target point. As for the oil type mentioned above, what I ment was dino oil or Mobil 1 to lighten the load on the bearings. Lastly, this is just my driver so it wont be subjected to high revs, just normal rides in the country with my 5 yr old son. Thanks in advance for any input on this.

jmz · jmz's Garage

I had an engine that did this. A very reputable shop told me that 3.0 litres tended to be noisy. It was the exact same sound you are describing. I always figured it was a little piston slap.

I'd be interested to see what others have to say.

BURN-BROS · 08-19-2007, 08:16 PM

I have heard the same thing about the SC, At Idle the SC can have this condition. The remedy was to increase the idle a bit and the sound would go away. Is the knock your experiencing at idle or thru the whole rev range?

NY65912 · 08-20-2007, 02:25 AM

Same here.

+1 on what Burn Bros said.

spooldup · 08-20-2007, 03:13 AM

Yes, idle is the only time you hear it. I will turn up the idle and drive it. I know their are a million threads but what type of oil are you running?

stlrj · 08-20-2007, 03:36 AM

It could be a bad tensioner.

BURN-BROS · 08-20-2007, 04:29 AM

I like Delo or Rotella. I doubt this will fix the sound though...It is what it is. Good news is that it isn't fatal.

anthony 911 · 08-20-2007, 08:18 AM

yes 30ltrs are prone to make noise at idle but what i did was turn idle down and i use 20/50 royle purple oil now its quiet

Superman · 08-20-2007, 08:37 AM

I use 20/50 also.

Rod knocks are deep, and they don't just happen at idle. Have you held your hand on the distributor while the knocking occurs? If you do, you might want to touch the distributor body without placing your hands on or near the ignition wires. That can be EXCITING.

Also, a stick or long screwdriver can be used as a listening device. Place on end firmly against your ear and the other end on various engine components.

YTNUKLR · YTNUKLR's Garage

Intermediate shaft end-play. only happens at <1000rpm, then it finds its happy place at higher rpm.

Chevron Delo 400LE (Diesel mineral oil) is a good one for 911s: 15W-40 so fairly viscous. The newer CJ-4 formulation (instead of CI-4) has very appropriate amounts (.012-.014%) of zinc, phosphorous (and much lower sulfur and ash content) and other minerals to protect gasoline engines well, especially regarding the camshafts/rocker arms. A lot of newer oils formulated for gasoline engines often do not have sufficient amounts of zinc and phosphorous, and increased cam wear has been the result within the past year.

enjoy the car.

RoninLB · 08-20-2007, 09:17 PM

my experience with diagnosing Detroit Iron bad rod bearings is to quickly rev from idle and the knock will sound like it's lagging behind the revs and needs a couple of seconds to catch up.

i would think an experienced 911 wrench pro would know all the nuances of the 911 engine knocks.

also... I use 1/2 rubber hose to probe around. And your auto parts store may have a $15 stethoscope?

spooldup · 08-21-2007, 03:37 AM

Thanks for the replies, I have stethascope and did check it and had it to two good techs yesterday that were left scratching their heads too. They both suggested to turn up the idle, put good oil in it and drive it. If it gets worse or ? I will open this thread for an update. Thanks again for the suggestions.

spooldup · 07-22-2008, 10:16 AM

Update: I do not get to drive this one much but now with over 1000 miles, the intermediate shaft noise must have been the case. I turned up the idle, put in Brad Penn this spring and everything is great. Only knock is when the motor is stone cold, faint when hot and only at idle. I figured it would not have been a rod because the oil pressure when hot, even this summer when its been really hot here is very good. Thanks for the tip on the intermediate shaft and to turn up the idle a bit, all is good now. Thanks again