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Piston/Cyl/Cam Identification? - Now with borescope pics
Sooo, I have a 75 911 that has a rebuilt 2.7L in it. The previous owner said it had "Euro Pistons and S cams" in it but I have no clue if that is true.
The car does have 40mm webers on it. All of this was done back in the 80s. The carbs and engine were recently rebuilt by a local shop, but no mention of what pistons or cams were in the car. The case has been restamped "2.8" beside the 911/43. Any way I can determine what cams or pistons are in the car without really tearing into it? Compression test shows about 165psi across all cylinders, not that it matters for this question. Here are some borescope images of the pistons. They look like they are flat or just slightly domed on top with relief cuts for the valves. Anybody have any input? Maybe euro pistons?   I found casting numbers on the cylinders - 911.104.342.2R Not sure where the date code is. Any help and input is appreciated!
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'12 Cayman R 77 C3, 85 Carrera, 75 911S, 88 Carrera, 96 Carrera, '65 912, '06 Cayman S - Gone Last edited by awdbandito; 11-21-2012 at 07:49 AM.. |
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11-19-2012, 09:23 AM
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Get a borescope and look at the pistons. If they have valve pockets they will not be stock CIS pistons. The dome shape will help tell you what is in there for compression.
RE cams: You should be able to remove a valve cover and measure the cam lift. This can be easily done by measuring a base circle diameter and the full cam lobe height. compare the lift specs to known cams. An Early "S" cam will be very different than a CIS "S" cam.
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11-19-2012, 09:27 AM
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You can also look @ what is stamped on the end of the cam. 'S' cams typically have an 'S' or part number stamped on the end. If they are unmarked, the only way to confirm the lobe profile by measuring lift as Jamie said above.
You can see the Mahle part number cast into the base of the cylinder by peaking behind your fan/alternator under the shroud. You may be able to see this number from the underside of the engine also.
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11-19-2012, 09:32 AM
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165, i doubt that is stock.
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11-19-2012, 02:57 PM
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Bump for added pics and casting numbers.
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'12 Cayman R 77 C3, 85 Carrera, 75 911S, 88 Carrera, 96 Carrera, '65 912, '06 Cayman S - Gone |
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11-21-2012, 06:42 AM
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Anybody?
I started looking at pictures and they resemble 2.7RS pistons. What I also found was that the 2.7RS pistons were only 8.5 to 1 compression. Anybody want to chime in?
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'12 Cayman R 77 C3, 85 Carrera, 75 911S, 88 Carrera, 96 Carrera, '65 912, '06 Cayman S - Gone |
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11-21-2012, 01:30 PM
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Nobody?
Any help would be great. Thanks,
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'12 Cayman R 77 C3, 85 Carrera, 75 911S, 88 Carrera, 96 Carrera, '65 912, '06 Cayman S - Gone |
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11-22-2012, 06:20 PM
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What kind of help are you looking for? Have you found the Mahle numbers?
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11-22-2012, 06:26 PM
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I am wondering if anybody recognizes these pistons.
The casting number on my cylinders is: 911.104.342.2R Not sure where the date code is. Would there be a part number as well? The last time I had the valve covers off I saw part of a part number on the cam, but just the first two digits starting with 91. I am going to get the bore scope out and see if it will allow me to see anymore of the casting number on the cam.
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'12 Cayman R 77 C3, 85 Carrera, 75 911S, 88 Carrera, 96 Carrera, '65 912, '06 Cayman S - Gone |
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11-22-2012, 07:08 PM
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The number you posted is the casting number for a 2.7 head, not the cylinder. Heads are easily confused for cylinders as they are also finned. The number you're looking for will be at the base of the cylinder next to the case.
Good luck. |
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11-22-2012, 07:13 PM
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You should be looking for a number something like 90ZN2 at the base.
You can see where the number is in this post: Mahle 2.7liter Pistons & Cylinders
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11-22-2012, 07:44 PM
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Thanks,
I found this - H..90ZN2W6 Also had a 5 inside a triangle. The pistons are shown above. Any ideas on what these are?
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'12 Cayman R 77 C3, 85 Carrera, 75 911S, 88 Carrera, 96 Carrera, '65 912, '06 Cayman S - Gone |
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11-26-2012, 05:08 AM
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The search tool is your friend.
Quoting Tom1394racing from this thread: 911 piston casting numbers "90ZN2... These are most likely 90mm (2.7 liter) Mahle Alusils. Check to see if the inner bore is slightly magnetic. If the wall do not attract a magnet (like the KS cylinders), they are Alusil. If they attract a magnet, they are Nikasil." You've got 90mm 2.7 cylinders. |
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11-26-2012, 06:02 AM
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I am wondering if anybody recognizes these pistons.
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11-26-2012, 06:15 AM
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Thanks for the help on this.
So it looks like I have 8.5 to 1 compression ratio using 2.7RS pistons.
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'12 Cayman R 77 C3, 85 Carrera, 75 911S, 88 Carrera, 96 Carrera, '65 912, '06 Cayman S - Gone |
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11-26-2012, 06:24 AM
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Sounds like you've figured it out. Should be a nice strong motor. Congrats.
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11-26-2012, 06:35 AM
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I just got a borescope and discovered the same thing! Next step is to see if ive got a cw crank too . engine came out of 2.2t ,hopefully its not a bore increase only. S
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11-28-2012, 02:26 PM
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