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Neil Harvey Neil Harvey is offline
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Join Date: May 2004
Posts: 218
Originally Posted by irrational_e View Post
Just an update after fetching the car and driving it for about 40 miles.
The mechanic said there is a possibly play on a rod (I forgot now which exactly it was). HE also explained how it could be the piston too but it is not something to be concerned about.
After warming up the car it is indeed much quieter and smooth with great power delivery and sound. And bringing a smile as only a well tuned 911 engine can.
He said the sound is definitely due to the old parts that were not replaced, but that it is not a problem at all. Just, as always, remember to not race the engine hard while cold. Which is normal behaviour.
So it looks like I am just a bit too paranoid for now.

Thanks for the pointers though. I will still monitor and have a healthier knowledge to go with it.

It's unfair to challenge an opinion as there are always another side to every explanation.

However, there should never be any rod noises coming from an engine. The rods in these engines are bottom guided so the clearances between the crank and the rods BE is around 0.005" max. The bearing clearances should be around 0.0008"- 0.0025" or so, and the difference is taken up with oil. The pin to pin bushing clearances are approx. 0.0008" to 0.002' also, with an oil film. So no noise should be heard. Clearances of these sizes will not make any noise that can be heard.

The use of existing old parts is Ok if the sizes are in spec, their condition is good, and the expected use after rebuilding is within a time period those parts can last. If you have any piston noise there is a chance the clearances are beyond those that will not make a noise.

Best to ask the builder the clearances measured on assembly, and the piston manufacturer. Some pistons made from 2618 require more clearance than those pistons made from 4032 aluminum.

Any noise has to be investigated. It could be the pistons hitting the head, valves just touching pistons, all sort of reasons some also suggested in other posts. The devil is always in the details and the builders build sheets with all measured dimensions will tell. Or remove any doubts.
Old 04-09-2018, 02:13 PM
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