Knocking in motor when cold!!
 

When I start the '70t in the morning and it idles a bit low while the oil is cold it makes a pronounced knocking sound. Sounds like a rodknock but I doubt it because it goes away once the car warms up at all. The engine is in great shape with Carrera tensoners and Webers.

Ideas??

Alex

This is not an answer to your question, and i know this isnt your problem, but it reminds me of a time in another car i have where i had the same knocking thing. It was only when the car was warming up. Turned out to be that an engine mount had come loose and since when the engine is cold it shook more, the warmer it got the less it rattled. Anyway, I know i am not any help but i just thought it was funny.

It could be a rod knock that goes away once the oil has a chance to fill the main bearings. How is your cold oil pressure?

Re: Knocking in motor when cold!!
 

wrist pin

Um...you don't want to hear this. I had the same problem in my '73E 2.4. It started one morning after an all day drive across Kansas and up to Denver in June. When I turned it on my skin crawled with the noise the engine made. I shut it off right away, and cheecked for a big oil puddle! None found, I started it back up, and it went away in about 20 very loooooong seconds. From then on, when I shut it down hot, the knock would return after a long rest (6+ hours).

I called a buddy, who was a Redline oil dealer and ordered a couple cases. Never heard the noise again. Even after 8 hour drives up the 5 from LA to SF in a heat wave.

Unfortunately, a valve keeper failed a year later, and that was that. Subsequent teardon revealed that #3 big end was a couple thou out of spec. Not much, but enough that the oil, when hot and thin, drained away. The Redline wsa superior in that aspect and it did the trick. Lower running temps to. Pricey but cheaper than a motor!

Thanks for the replys. I am running Mobil 1 and the car has very good oil pressure cold or hot. Is this the kind of thing one ignores till it finally lets go? If it is a wrist pin why does it go away once it warms up?

it's routine..
any shop mechanic should be able to know exactly what the "knocking sound" is once he hears it.. wrist pin is no big deal, usually.. don't have hard info on the 911 wrist pin knock.......Ron

Does it happen only aftre a "cold soak"???

If so, try another brand/weight of syn oil.

I can't imagine that the knock is doing anybody any good! If you can manage the problem with proper lubrication, I would say that while you should respect resonable rev limits, you will be ok indefinately. But if the knock continues, I'm afraid it will get worse.

I had good luck with Redline, which is about double the $ of Mobil 1, but I've heard good things about Amsoil as well. I can only refer you to my experiences with Redline though, which "cured" the same sounding problem.

let us know what happens!

As the engine warms up...everything expands and the oil becomes more fluid. Sometimes tolerances tighten up with the change in heat.

The knock could be caused by a piston with greater-than-spec cylinder clearance. As the engine/piston heats up, the clearance decreases and all is well (sound wise). This could be more typical with aftermarket pistons that need increased cold cylinder clearance due to heat expansion when warm or by a piston/cylinder that's worn.

Sherwood Lee
http://members.rennlist.org/911pcars

Thanks once again. I have a few local experts who are on the piston slap tip. I think they and you all are right. The big question is to worry or not. The car runs very well and it seems a shame to rip into a nice motor like this. Me thinks I'll leane it and if it get's worse then freak out later.

Alex

based on your reporting, I agree..

if your tense about the knock a DE will solve the mystery, or relax you.......Ron