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irrational_e irrational_e is offline
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Join Date: Jan 2012
Posts: 18
Freshly rebuilt piston slap


I had a rebuild on my 1980 911SC engine recently due to a broken head stud.
I kept the same pistons and rods as they were great but had all studs, bearings, valve guides and rings replaced.

I have done about 2000km since the rebuild and sometimes I would hear an uncharacteristic knocking. Mostly when cold. That knocking seems to be more the usual than the exception now.

I returned the car for a general checkup, new oil etc and asked that they investigate the noise.
The dealer (They are very good Porsche specialists and have been in operation since the 1970s) told me that the noise is some piston slap and that I shouldn't worry as it doesn't matter.

Now I generally trust the guy as he is a real expert, but this was a $10 000 job and I need to be damn sure that this is not going to cause problems later. I am not going to pay for even bigger work if something is wrong and I don't own a Porsche to drive it like a Volkswagen. So I am going to drive it properly and sometimes hard.

So the question is. Is it unacceptable to have some piston slap on a rebuilt engine with new rings but original pistons/sleeves? It did not have this before.
If there is some piston slap, is it something that needs to be looked at immediately or is it indeed not something to be unduly worried about?
Is it something that I should monitor and deal with if it doesn't go quiet when warmed up? Obviously it shouldn't get worse.

Its not terrible, I have sensitive ears, but it is a definite knocking on a specific cylinder. Power feels great after the rebuild at low speeds. High speed still feels a bit tight and I struggle to go over 128-ish mph where I should be easily doing 135.

Any comments?
1980 911 SC Weinrot Metallic - All Original 179 000km
1955 Triumph TR2 - Unrestored and mostly complete original.
2007 BMW F650GS motorcycle.
2014 BMW R NineT motorcycle.
Old 04-03-2018, 06:17 AM
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