Need new bore specification: M96.03

I hope the RennList community can bail me out before we have to wing-it. The $5k Targa rebuild is moving along and I need to find two data points for the finish work at the machinist before we go back to assemble the engine. a) M96.03 bore specification and wear limit (new engine) b) If published piston to bore clearance specification. (stock bore / stock piston) I know in general terms it's a 96mm bore. But for final honing I am looking for the spec akin to what i would have for an Audi I-5 3B/AAN engine which is an 81mm bore specifically: 81.01mm w/max deviation +0.08mm Thanks in Advance.

I do not have the dimensions/tolerances you ask for. I have not come across this info in the factory manuals. Porsche techs I've talked to suggest they have access to this info but have not given it to me when I casually asked for it. Jake Raby may have this info and may be willing to share it. (However, he may consider it company confidential information and thus not be willing to share.) I can't speak for him though you'll have to contact him directly. From memory, these engines and their cylinder bores (assuming the bores have not been sleeved and are made of different material) are a bit tricky to deal with. The bore material is Lokasil and this needs special machining/finishing to bring about the desired cylinder size, geometry and finish. Briefly, the cylinder bore is machined and left a bit undersized. The machining creates a shallow but intolerable zone of damage at the surface. This is removed via finish honing which also brings the bore to its final size. At the same time this finish honing also removes aluminum from between the grains of silicon leaving the grains standing free (a tiny tiny) bit of the aluminum. This creates depressions to hold oil which helps lubricate the rings/piston in the cylinder. Special (diamond) hone stones are used. The wrong type of abrasive stone or stone matrix can damage the silicon grains. You might be better off boxing the block and shipping it to a shop that specializes in these engines and can do the finish machining for you and do it properly. Oh, last but not least, if you are using aftermarket pistons and rings, and I guess a bit (used to be oversized. (0.030" was considered standard oversize but these engines may not tolerate that much material removal.) the piston/ring manufacturer might have some info on what the clearance should be between the cylinder wall and piston. Added: To give you some idea of the special effort these bores need here's a link to some info you may find interesting: http://www.sunnen.com/NewsDetails.aspx?NewsID=11

Thanks Macster- your pursuit turned up the same results as me. It's bizarre to have such a void of information on such a basic attribute. I appealed to Bentley Publishers as well - their factory manual has naught to say about the core of the engine between the heads - the section just isn't there.

My impression was also these are trade secrets.

Once you determine your bore diameter and tolerance, this is what you are up against: LOKASIL LINERS. One new part of the design (with both early and late engines) is that the cylinders do not have cast iron liners, plating on the bore or a hard material cast into the alloy - but have a “cast in” composite liner that is then bored and honed (rather like more traditional cast in iron liners). However it is a new technology and with that comes some new technical challenges to overcome. The liners are not as strong or accurate as older cast iron liners and sometimes the liner moves during casting and then when it is bored out the thickness and corresponding strength varies around the circumference (some even seem to be marked with an X to identify the best side for the thrust face as if they were recognised as imperfect with the less than perfect areas being selectively located). Another problem is achieving the right surface finish to that composite bore that is technically challenging and requires expensive test and production equipment. The bores have to be machined 1st with a diamond cutter in such a way that the tool does not dislodge the silicon crystals from the matrix but cuts them instead. Too fine a cut and you cut each crystal several times – thus making its bond weaker in the Matrix (and it may loosen and fall out later). After that (and leaving the exact right final bore thickness) a solid diamond honing head hones it with precise speed, feed and lift angles (in both directions) to an exact surface finish (with a machines usually costing a 5 figure sum see following photo of our machine).

NONE of the internal clearances have ever been released. I have had to gather my own data and create my own tolerances and specifications. Let me guess, your bores are out of round and have a taper?

Jake - I assumed you have developed proprietary specs; I did not feel it was right/prudent to ask you for yours given the intellectual capital involved in finding those specs. Hence the more generalistic approach for any BTDT experience that might be available. I would naturally be delighted if via PM you were willing to point me between the ranges we are discussing; if doing so did not compromise your intellectual capital. a) 0.0010" - 0.0015" b) 0.0015" - 0.0020" c) 0.0020" - 0.0025" Situation: No, my freshly LASleeved bores need finish honed, now that the machinist has completed the sleeve insertion. The sleeving was cdue to #2 and #4 being scored and therefore I had the whole thing done. The thread is documented int he $5k Targa thread. The new sleeves (and old bores) are straight and true - and with stock the pistons having been treated to the PolyDyne service I would assume that we need to run somewhere in the 0.0012in-0.0015in bore clearance spec based on each given piston. All others - These are Chrome-Moly bores sleeves so we can drop all the discussion about Lokasil and the methods by which you can increase the bore & refinish with the correct degree of roughness - I too have read the Sunnen articles etc. And no, the lead-times for LN Sleeves are what d drove me to the LASleeve solution; I would have preferred a known-good solution that is well respected in the community. LASleeve is known-good to me in many other applications and they support the M96.03 motor with two different sleeve styles and multiple engines out there running them. Goetze had no issues with the ring material creating a good seal on the Chrome-Moly sleeves - so we're going forward. Note: I would request that we don't turn this into a discussion about LASleeve vs. LN Eng - both have their places and are fine products in their own rights.

If there are multiple engines out there with this LASleeve sleeve solution I would think LASleeve would have the info you seek. How did it arrive at this before for known-good solutions in the field? LASleeve should know the coefficient of expansion for the sleeves vs. the pistons and come up with a clearance and other cylinder topology (like on purpose taper even out cylinder out of roundness) call outs that are suitable and deliver suitable service life from its sleeves. If not LASleeve, then the piston/ring maker I would think would be able to offer you or the sleeve company the ideal clearance, bore topology and finish to result in an ideal fit and ring/cylinder sealing.

Considering that you have altered the cylinder material and used iron, it is very far removed from what we have developed and work with routinely. I tend to only speak from first hand experience, and since I don't have first hand experience with iron sleeves, my values won't help you at all. Changing cylinder materials vastly alters optimum running clearances. It took us years of development to perfect these properties with the LN Engineering Nickies sleeves and I would believe that whomever developed the LA Sleeve technology would be the only person who would have the true answer to this.

Almost took the words right out of my mouth. I wanted to add to my previous post that given the OP was using LASleeve chrome-moly cylinder sleeve material and who knows what piston and metal composition (even if aluminum different allows have different behavior under temperature) even if he could get the numbers he seeks from Porsche they might not be ideal, let alone right, for this hybrid engine.

Thanks all - I've gone back to them, since there's no available spec from the factory that can be used as a reference point. I appreciate the inputs.

Quotes source post: 11296018

Wise decision. The same questions should be addressed concering the roughnes averages of the cylinders and ensure that was also specified with the ring selection, along with what type of playeau finish may be applied. Ring gaps will also change with the material changes, so get those values as well.

Did you ever get the piston to cylinder tolerances from LA Sleeve ?