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73 911t rattling (bad) only at 2000 rpm's


zebswiss

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1973 911t mechanical fuel injection, 85K miles, 5 speed, silver, whale tale, fuch's etc.

Any 2.4 liter experts out there... my 73t runs smooth and strong above or below 2000 rpm's and when it is cold.

It developed a buzzing rattle in the area of the distributor gear or cam chains and only when the engine is at or passing 2000 rpm's. It doesn't matter if the clutch is in or out or if it it in gear or not...it still occurs.

I was hoping that the new hydraulic cam chain tensioners I installed would fix it but they had no effect. I pulled the alternator out thinking it might be a really bad bearing... no change.

I can't pin point exactly where the noise is coming from with a stethascope but it seems to be the loudest on the distributor base and even lower where the gear is. It sounds like a gear hitting a bolt as it spins (kind of a metallic zzzzzz) and very noticeable rattle.

Any thoughts on this would be much appreciated... It's a beautiful silver little 911 with ony 85K on the odometer, it's in top condition I'm just afraid to drive it with the noise.

Thanks in advance for any thoughts.

Pics attached.

post-15839-1166475392_thumb.jpg

post-15839-1166475407_thumb.jpg

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I'm not really sure what could be making a noise from that part of the engine. Does the engine produce good oil pressure? Have you removed the dist. for inspection? Perhaps one of the advance weights spring has broken and it's rattling around at that RPM. Just a shot in the dark..... could you post a sound clip of the noise in question?

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Its sounds like(unfortunately) you might have imediate shaft bearings that are nearing the end of their life. Its worth checking the distributor and the cam chain rollers as well(doubt these will be it though) but its always somewhat difficult diagnosing these types of issues over the web. :cheers:

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I'm not really sure what could be making a noise from that part of the engine. Does the engine produce good oil pressure? Have you removed the dist. for inspection? Perhaps one of the advance weights spring has broken and it's rattling around at that RPM. Just a shot in the dark..... could you post a sound clip of the noise in question?

I had it out for the pertronix pointless upgrade... looked okay.

Oil pressure is High if anything... 90-100 on the gauge.

Thanks for the quick reply, any other thoughts you have are much appreciated.

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Its sounds like(unfortunately) you might have imediate shaft bearings that are nearing the end of their life. Its worth checking the distributor and the cam chain rollers as well(doubt these will be it though) but its always somewhat difficult diagnosing these types of issues over the web. :cheers:

Thank you for taking the time to reply,

Assuming it is the shaft bearings... I am mechanically inclined but not super familiar with the internals on this motor... What's the fix? (Please don't say a complete rebuild!). Can it be remedied without a complete overhaul?

If you wouldn't mind telling me what you know in some detail I would be grateful. Thanks again.

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Hi

I have had serveral 2.2 and 2.4 motors -every one had substantial wear to the intermediate shaft bearings. However , not a one exhibited the symptoms you describe - and all were fairly high mileage - around 100k.

When the chain tensioners were replaced , did you notice if the chains tensioned properly and were not worn excessively? Have the chains been replaced recently? Did you inspect the chain sprockets and the rails?

Hope this helps

Ed Huber

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