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On a scale of 1 to 4th of July BBQ, how cooked are these pistons?

I've got my 3.2 completely torn down. Now as I'm starting to clean and prep for the rebuild, I need to get to the bottom of what happened to my pistons. Here are a bunch of pictures of the tops and undersides. They have not been cleaned at all, so they look exactly like they did in the engine.

Here are the side skirts where you can see the discoloration along the edges of the skirts




This is the piston with the most build up


And this is the piston with least build up


This is an overhead look into the under side of the pistons




This is the least discolored piston


This is about the worst discoloration. I'd say 2 look like this and 2 look slightly better.



One of the local shops I was talking to mentioned that the discoloration on the edge of the skirts is a sign of too much heat on top of the piston (in his words something is wrong with the tune). He said he usually sees that when someone puts a brand new carb on an engine without setting it properly. He also said that if the discoloration was starting from the center of the piston skirts, then that is probably on oiling problem. Can anyone else confirm that, or offer competing interpretations on what these pistons show? I've checked the DME, and it still has the stock chip in it and it doesn't look like the previous owner has fiddled with it at all. I'll be upgrading to new injectors, so I haven't checked those.

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'79 Copper 911 SC
'88 White 911 Carrera- 98mm p/c with JE 8:1, Turbkraft EFI-T cam, Carrillo rods, Injector Dynamics 1050x, twin COP, AEM Infinity, twin Garrett GT2860rs's
Old 05-09-2019, 01:00 PM
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Looks like most engines on teardown. Oil from valve guides usually.
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Old 05-09-2019, 02:01 PM
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John - he sounds like he is worried unnecessarily about all the carbon on the crowns (which he can just remove and be happy, and doubtless he will get to the valve guides as part of the rebuild).

But I think he is also wondering why some of the pistons are brown, and the coloration on some of the skirts is uneven. Need to measure the skirts?
Old 05-09-2019, 02:26 PM
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john walker works on Porsches for a living. Walt has always been very helpful.

The pistons can be measured to determine if in spec.
Old 05-09-2019, 02:33 PM
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Squirters plugged? The clean one looks more washed than the other one.
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Old 05-09-2019, 02:35 PM
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My real concern is about the discoloration. Is it just oil staining or did the piston get too hot? I'm not too worried about the carbon build up, but included it in case it could help clear things up. The build up did make its way into the bottom ring as well. I'm not reusing the pistons, but wanted to make sure there wasn't an indication of some problem that I wasn't aware of. The heads are off with Craig Garrett, so the guides won't be a problem.
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Jonathan

'79 Copper 911 SC
'88 White 911 Carrera- 98mm p/c with JE 8:1, Turbkraft EFI-T cam, Carrillo rods, Injector Dynamics 1050x, twin COP, AEM Infinity, twin Garrett GT2860rs's
Old 05-09-2019, 02:38 PM
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The piston squirters were next on my list. I haven't tested them yet, but if they test good, then does it seem that there really shouldn't be anything out of the ordinary?
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Jonathan

'79 Copper 911 SC
'88 White 911 Carrera- 98mm p/c with JE 8:1, Turbkraft EFI-T cam, Carrillo rods, Injector Dynamics 1050x, twin COP, AEM Infinity, twin Garrett GT2860rs's
Old 05-09-2019, 02:44 PM
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Is there any way to test the piston squirters without splitting the case . My heads are off currently .
Old 05-09-2019, 06:40 PM
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Here is a good read on checking pistons. If you are concerned there are a number of checks that can be carried out.
Evaluating UsedÂ* Pistons:Â*How to Determine if Your Pistons Are Still Good

The real question is: what do your cylinders look like? Are they Mahles, and in spec?
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Old 05-10-2019, 08:14 AM
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You will be shocked how they look once cleaned up. Measurement is the key way to determine if they are reusable. If you have the money, replacement them and have the piece of mine.
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Old 05-10-2019, 09:21 AM
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Pictures are after how many miles?
My '73 looked like these after 89,000 miles - and they were fine after rehab.
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Old 05-10-2019, 09:38 AM
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but you use conventional oil.

Chris
Old 05-10-2019, 11:00 AM
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I didn't clean the pistons in case there was something to be gleaned from their in use condition. I'll clean them up after I finish the case. I got the drivers side mostly clean and tested the piston squirters. At least two of the three work and the third may, but I was having trouble getting a seal with air tool. From the article above, I need to clean the pistons before judging their color, but the wrist pins came out with just some taps from a hammer as Wayne describes in the rebuild book. I don't have feeler gauges down to 1 and 2 thou, but looking at the rings, the gaps look nice and tight and the rings appear to be in good condition. I'm waiting on my other micrometers in the mail, and then I'll measure the piston diameter to see if it's in spec. As for age, the odometer shows just shy of 32k. I'm not sure if that's quite believable, but the crank was in great shape, and the bearings all looked brand new except for the intermediate shaft.

I'd say, given the above input, it was mostly a bit of panic on my part. I'm putting in new pistons and freshly bored and plated cylinders, so being able to reuse the current set isn't a huge concern. It was mostly just trying to figure out if there was some hidden problem that wouldn't get found along the way.
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Old 05-11-2019, 04:46 PM
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I'm back with a conclusion. I washed one of the pistons in my parts washer and a lot of the brown to black discoloration washed out with some scrubbing. This leads me to believe that it was mostly oil staining. There was a faint darker gray left behind, but I don't think it's of concern. A bit surprisingly though, the build up on the top of the piston did not really come off, even with heavy scrubbing from a brass brush.

As for the piston squirters, I just wasn't getting a definitive result, so I ordered the Stomski tool. I then faced the realization that the squirters were just done. It was probably three days of soaking and trying to blow them out with compressed air and they wouldn't give. I now have a new set of Taormina Racing rebuildable squirters on order. That also allowed me to upgrade to a larger opening for hopefully better cooling with all the extra boost.
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Jonathan

'79 Copper 911 SC
'88 White 911 Carrera- 98mm p/c with JE 8:1, Turbkraft EFI-T cam, Carrillo rods, Injector Dynamics 1050x, twin COP, AEM Infinity, twin Garrett GT2860rs's
Old 05-22-2019, 01:41 PM
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heat the piston up in the stove or a grill a little and spray them with oven cleaner. let it sit for about 5-10 mins and wipe off... works great!
Old 05-22-2019, 03:15 PM
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On a scale of 1 to 4th of July BBQ, how cooked are these pistons?

It is possible that the “tune” was inconsistent from cylinder to cylinder, thus the temps were also different. An overly lean condition will cause higher temps. A stock 3.2 does not have individual o2 sensors at each cylinder, nor any way to adjust mixture individually, so it “averages” based on the sensor which is well down the exhaust chain. If it will put your mind at ease have the injectors flow tested before servicing and see what that brings to light. As said, what I see is fairly normal carbon from oil, which you’ll address with confirming that pistons and cylinders are within spec, fresh rings, valve guides and valve guide seals.


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Old 05-22-2019, 03:28 PM
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I find that old brake fluid will clean off the carbon on pistons.
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Old 05-22-2019, 03:41 PM
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First, how many miles? They actually look pretty good. Next, a competent machine shop needs to clean and inspect them, usually the pass or fail is due to the ring lands (grooves) being worn and beyond spec. Next the cylinders need to be checked. Porsche has 2 different coatings, Alusil and nicasil. Alusil' are usually worn out, Nicasil' last a very long time.
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Old 05-22-2019, 04:48 PM
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Quote:
Originally Posted by john walker's workshop View Post
Looks like most engines on teardown. Oil from valve guides usually.
Quote:
Originally Posted by john walker's workshop View Post
Squirters plugged? The clean one looks more washed than the other one.
Listen to John.

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Originally Posted by Trackrash View Post
I find that old brake fluid will clean off the carbon on pistons.
A little wax and grease remover (or any solvent, for that matter), then just let them sit. Most of that carbon will just flake off. Those pistons look normal. Measure, of course. And send the rods/pistons to the machine shop. That's the part I skipped. The engine works great, but I wish the rods had been reconditioned.
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Old 05-22-2019, 05:04 PM
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I didn't expect this thread to keep going. At the start, the discoloration of the pistons worried me because I didn't have any experience to know what they should look like. As the title suggests, I thought they had been burned, or at least been running too hot. Based on a few comments above, I concluded that it was normal oil staining which a short stint in the parts washer confirmed. This did remind me to check my piston squirters, of which at least three were no good. I upgraded to Taormina Racing's rebuildable squirters which also allowed me to go up in orifice size.

As stated above, the engine has 32k, but I'm no longer concerned with the pistons, cylinders, and rods as I have all new components to drop in. I'm also switching to running an AEM Infinity, so the stock chip is a non issue as well. I'll worry about what kind of shape the old stuff is in when I go to sell it, or in the case of the cylinders, get ready to send them out to millenium.

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Old 05-26-2019, 04:31 PM
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