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Started to measure cylinder height groups...then found this

Getting organized for my 2.2 -2.4 build and noticed that of my six Mahle 2.2 S cylinders, four were height group 5 and two were height group 6. I bought them from a member here a while back and had not had an application till this build to look them over closely.
The height specs for the two groups are as follows, for the 5 group are 85.4-85.425 and for the 6 group are 85.425-85.45. Well mine all measured out 85.03-85.06. Then I noticed that the small flange/seat under the cooling fins looks to have been machined...it no longer exists.

Here is a stock 2.2 T cylinder for comparison.


Would this flange have disappeared when a PO machined all the cylinders to the same height? I checked the cylinder on a spare 2.2 case and it appears to seat ok. I'm wondering whether would someone do this to bump the compression ratio? As it is I am pushing the compression ratio by stroking the 2.2 to a 2.4 using a 70.4 crank which will push me to 10.3:1 with the 2.2 S pistons. I can't afford to increase the cr any further. I guess I can use base shims to get the cr down and height back up? But my options are .25mm and .5mm which will give me 85.28 or 85.53.
This started out with me being worried about mixing up two height groups...but I guess that doesn't matter now.

Looking for some guidance...thoughts?

Old 01-02-2020, 04:06 PM
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Speedo,
The height grouping will be a stamped number and not a cast number. The grouping is only determined after the cylinder is cast and machined, not before it's cast as it's the result of manufacturing tolerances.

With regard your other query about deck heights, squish clearances and compression ratios, do a search as there are lots of good threads on this issue.
Old 01-02-2020, 08:54 PM
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I have made custom base gaskets/spacers. I would do a mock up assembly, determine your CR and deck height and make adjustments to the base gasket accordingly.
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Old 01-03-2020, 12:19 PM
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I’m having the same issue with a set of new mahle cylinders for 3.2 to 3.4 conversion. Cylinders measure 85.07 +/- .01. I have an email into mahle awaiting a reply asking why that number. I too am unsure how to hit the right combination of CR, deck height given the usual gasket sizes.
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Old 01-03-2020, 12:31 PM
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First thought is that if the cylinder in the 1st picture is yours that is a 90mm 2.7 cylinder not a 2.2 / 2.4. You can tell because the early cylinders had open stud holes (like the 2.2T pictured) at the bottom and the later cylinders have fins that go around the studs (plus the casting number is 90mm cylinder). In any case it sounds like the cylinders have been machined. Maybe you are working with a set of 2.7RS P&C and someone was trying to get more than the 8.5 to 1 compression?
Second part is as you can see by the specifications if Is possible to have a mix of height 5 and 6 class cylinders that have less variance than the allowable for the class since the variance is .025. So a tall 5 and short 6 could be very close in height. If they have been machined you might need to get non standard thickness base gaskets to get the correct height. I thing there are several options for venders with non standard thickness base gaskets.

john
Old 01-03-2020, 01:18 PM
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cylinder height groups

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Originally Posted by targa72e View Post
First thought is that if the cylinder in the 1st picture is yours that is a 90mm 2.7 cylinder not a 2.2 / 2.4. You can tell because the early cylinders had open stud holes (like the 2.2T pictured) at the bottom and the later cylinders have fins that go around the studs (plus the casting number is 90mm cylinder). In any case it sounds like the cylinders have been machined. Maybe you are working with a set of 2.7RS P&C and someone was trying to get more than the 8.5 to 1 compression?
john
These are definitely 84mm p and Cs.


In addition, the jugs fit snuggly in the spigots on a clean 2.2 case I have on my shelf.
And I see no other indications of height groups other than the cast "5" and "6" on the base of the cylinders. It really doesn't matter now that they were all machined.


Can someone confirm from the part numbers inside the pistons that these are 2.2 S vs 2.4 S?
Old 01-03-2020, 04:58 PM
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The markings are very hard to make out after 45 years. Just below the cast numbers in the gray area. Very light etchings I think.
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Old 01-03-2020, 05:11 PM
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HI Speedo, you have some unique P&C there that do not appear to be stock items. You are going to have to take some time and figure out what they are. First from my data 2.2S 84mm Mahle pistons are 84p8 casting number, 2.4S 84p11. Your pistons look to be 86p3 casting that I dont show for any stock pistons. In general for stock pistons the first number matches the bore. Also stock factory E and S engines used Biral cylinders which are iron sleeve with Aluminum cast around for the cooling fins. On biral cylinders it is easy to see the cast iron vs aluminum. Yours look to be all aluminum. The 2.2 and 2.4 cylinders are open around the studs at the bottom as I mentioned earlier. The casting on the cylinders (90ZN2) are shared with a 2.7. So maybe these are something special with aluminum nickasil 84mm cylinders. You should be able to check with a magnet. Biral are highly magnetic nickasil very slightly magnetic. How about pics of piston tops.

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Old 01-03-2020, 10:34 PM
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I looked a little deeper and it looks like Mahle offers nikasil 84mm cylinders as current replacements.

https://www.ebay.com/itm/For-Porsche-911-S-2-2L-H6-1970-1971-Engine-Piston-Cylinder-w-Rings-OEM-Mahle/152591692163?epid=2154737882&hash=item23872c7183:g:GMcAAOSwm-pZun0O

these look to match what you have. So it looks like your set is newer. You should look at mods to case usually done for 2.7 motors with Aluminum cylinders.

john
Old 01-03-2020, 10:41 PM
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cylinder height groups

I see zero markings around the bases indicating height groups...maybe later Mahle cylinders didn't offer height groups? Here is a shot of the cylinder top and piston dome.

Years ago I tore down a 3.0 engine that was "not running well" and found that some "boat repair shop" had rebuilt the engine using aluminum pistons and aluminum cylinders and everything was horribly "galled"...very close to seizing. So my experience has been that one should not run aluminum pistons in aluminum cylinders? Is there an exception to this rule...or a situation in which this is acceptable?
Old 01-04-2020, 07:06 AM
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From what I hear, aluminum pistons will gall in aluminum cylinders, such as Alusil, specifically. I have Alusil cylinders with special coated JE pistons (a 2.7, BTW). JE says these will not gall, but it was 10 years ago that I bought them, so I don't recall the specifics of the discussion. I have not run it yet to provide first hand info.

Your jugs look pretty good...look like Nikasil. I suggest you put it together. and see how the heights all shake out.
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Old 01-04-2020, 07:17 AM
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HI Speedo, every 911 from the 2.7 to today run Aluminum pistons in Aluminium cylinders or bores. Typically the cylinders are plated with a hard substance like nikasil. Nikasil is very hard and does not wear, aluminum conducts heat better than iron which is a good thing on a aircooled engine. The cylinders you have would be a upgrade over biral. There are general two numbers stamped into the cylinders one is the height class. This is in a triangle the other is the piston class 0-3 this is the actual diameter of the bore. The attached picture show were they are usually found. They are often faint.



this piston is a height class 5, piston class 0. Since you have measured the height and the range is a little too large .03 with .025 spec. I would double check your measurements again. How are you measuring. I have found it difficult to measure cylinder heights with regular tools like calipers. I think you would need a very large micrometer to be accurate. I put the cylinders on a milling machine and use the Digital height readout to measure as it guaranties the cylinders are square to the measuring device and very accurate.

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Old 01-04-2020, 10:39 AM
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conclusion...

They absolutely do not have height or piston class. But with the help of my friends mill...they did measure out almost exactly the same for height group 5. The barrels are Nikasil, and they have an oil ring that is 4mm. My rod ends are all very much in spec with my piston pins too. I can go ahead and order my rebuild parts and spend some time with the parts washer. The case comes back from being faced and align bored this week. Thanks for all the help.
Old 01-04-2020, 03:25 PM
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Hi Speedo, did you have inserts put in the case? With the cylinders being Aluminum you would want that done. Now you have to read thru the infinite number of threads about mag cases and head studs and decide what you are comfortable with.

john
Old 01-04-2020, 10:07 PM
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Inserts

Quote:
Originally Posted by targa72e View Post
Hi Speedo, did you have inserts put in the case? With the cylinders being Aluminum you would want that done. Now you have to read thru the infinite number of threads about mag cases and head studs and decide what you are comfortable with.

john
Do you mean time serts? I will have the shop dealing with the case work make a suggestion on the head studs. I did the disassembly and had no issues whatsoever with the studs. Curious why aluminum cylinders would be of greater concern than Biral? Differences of heat expansion rates? Only ever had stud issues with 2.7 engines.
Old 01-06-2020, 11:51 AM
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Quote:
Originally Posted by speedo View Post
Do you mean time serts? I will have the shop dealing with the case work make a suggestion on the head studs. I did the disassembly and had no issues whatsoever with the studs. Curious why aluminum cylinders would be of greater concern than Biral? Differences of heat expansion rates? Only ever had stud issues with 2.7 engines.
Case savers are a must on any mag case motor. With the motor apart it is a no brainer.

Wow, 84mm nikasils. Cool.
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Old 01-06-2020, 12:47 PM
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Yes, but the preferred inset is a case saver. The factory biral cylinders were cast iron sleeve with cast aluminum fins (T motors had whole cylinder cast iron). The expansion rate of cylinders and studs were about the same so not much problems with stud pulling. When Porsche moved to the 2.7 motors they also moved to aluminum cylinders and Dilvar head studs. The difference in expansion between aluminum cylinders and steel studs put more stress on case and caused pulled studs(extra heat did not help). Dilvar was supposed to help with this (expansion rate closer to aluminum) but dilvar proved to make weak studs prone to corrosion that broke. Since you now have aluminum cylinders you have the same issue as 2.7 engines and should build accordingly. Almost no debate that all mag cases should have case savers inserts for the head studs. Lots of debate about what stud to use with Aluminum cylinders on a mag case. Opinions range from stock steel is fine after inserts, should use aftermarket, to must use latest 993 Dilvar studs and everything in between. When you seek advice on your 2.4 build you need to make it clear that you are using aluminum cylinders.

john

Old 01-06-2020, 01:00 PM
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