Engine Rattle when Hot

I have an '83 911 SC with an engine rattle when hot. I had the Carrera tensioners installed 2 years ago, and use 20W50 oil. The problem occurs when the engine is fully warm, under heavy acceleration and above 3000 RPM. The mechanic who did the tensioners (and whom I trust) assures me that the chain and guides are fine. Any ideas what I'm missing?

I think you would hear 'chain slap' or the dreaded 'gravel stirred in a bucket' sound at start-up if it were a tensioner problem! And I have heard it only once, in the spring of 1979, and there is no mistaking the gut feeling it gives you to turn the engine off IMMEDIATELY!

I tend to believe you have a lean mixture/ignition timing/sparkplug heat range problem ... engine knocking sometimes sounds like a 'rattle' ... although I have never heard it in a 911 engine under full throttle!!! I suggest you pull all of the sparkplugs, immediately, keeping track of which plug came from which cylinder, and inspect carefully, even take to an experienced mechanic you trust for evaluation, if you don't know what to look for!

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Warren Hall
1973 911S Targa

I agree with Early Man, knock or detonation can sound like a rattle, I had just that on my '82 euro SC. The cause of the problem on my car was a lean condition due to a faulty auxilary air valve (hung up in the open position). A common symptom of this can be an excessivly high idle under certain conditions, due not let this go on too long as a lean condition can cause damage to valves and pistons.

Thanks for the tips. The plugs look good. The problem has been thee both pre and post-tensioner upgrade. The aux air meter is relatively new, but it still has the standard SC high idle when cold. The local mechanic keeps insisting that it's normal noise when hot, but I'm going to go with your advice regarding the lean situation. Thanks again.

Your problem is most Probably to much ign. timing! I have seen engines knock with the timing set correctly. It is an issue of poor fuel. Try retarding your timing 2-3 degrees. Also check the vacuum advance on the dist. they freeze and will produce the same problem.

Good Luck,
Lee

This may seem alittle strange, but i had an ugly sounding rattle on hard acceleration also and of course i was prepared for the worst. i checked around the car for loose anything and found that the center cap on the driver's rear wheel was loose and the vibration on the wheel was the culprit. hope yours is this benign.

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ras911

i had the hydraulic tensioner upgrade done on my '68 911 about a year ago and i still get a slight inconsistant "rattle" below 3500rpm. though i am not mechanically inclined i questioned why my mechanic did not replace the relatively inexpensive chains while being 10 hrs total labor deep into the car ($1300 parts/labor total). we sort of had words and he is now my ex-mechanic. maybe i was wrong but i sure didn't feel good about him wanting to charge be an additional 10hrs to go back into the car. anyways, the car is going to my new mechanic for a tune up this month in which i will mention the EARLY S MAN'S comments re: the mixture, etc. should my former mechanic have replaced the chains during the carrera tensioner upgrade?

About chain replacement ... it is really a matter of engine mileage and how meticulous the oil change schedule has been over the years. If the engine has less than 180-200K miles, and is otherwise in good condition, I wouldn't even worry about the chains. From what I have read (and I did my own pressure-fed tensioner update) changing the chains at that kind of tear-down level is PRETTY TRICKY ... so that tells me your ex-machanic was hesitant or inexperienced doing that procedure, because he could have easily added $100 for the chains and another two hours shop time to your bill ...

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Warren Hall
1973 911S Targa

Sounds like folks are on to the right track with the timing/lean mixture course.. quick and easy check is to go buy some race gas or octane booster. if it stops rattling, definately detonation. If it doesn't though, you can't necc rule it out.

$1300 to put in the hyd chain tensioners?!? WOW! I'm in the wrong line of work . . .