Jake Raby

No problem... Thats what differentiates what we do from the other modifications.

Closing the deck has some merit for strength, the Honda guys do it when they are making 800-1,000 HP from their drag engines, but they aren't concerned with cooling characteristics as they run 1320' and shut it down.

In a Porsche application where the car needs to maintain the best cooling capability retaining the open deck is essential to cylinder life and thermal conductivity. This is especially true for those who will see track time at elevated temperatures and loads.

Not to discount what anyone else has done, because their approach obviously works as well.. Different strokes for different folks!

Macster

Just so it is clear, my impression from seeing pics of a sleeved engine is there were still passages -- gaps -- between the sleeve tops that allows coolant to flow from the head down or over I guess past the cylinders and out of the block. I guess that is the path the coolant takes or does it enter the block and flow into the heads? I would think the former.

Your post suggests that some sleeve solutions block the flow of coolant from head to block?

If so I can certainly understand your avoidance of a sleeve solution that would result in this.

Sincerely,

Macster.

nick49

Generally a sleeved motor will look no different, except under close inspection one may be able to detect a difference in the color of the sleeve material from that of the case.

For Jake: Having seen many motors disassembled, those that have been sleeved from the factory to salvage porous castings, are all 6 holes sleeved, or just the ones where porosity was an issue? Also are the liners cast iron? If not what material? Are sleeved motors cylinders wearing at the same rate and degree of ovality as the Lokasil? Thanks

Macster

Yes, generally, but the pics I saw of the AutoFarm sleeve clearly showed the tops of the sleeves.

http://www.autofarm.co.uk/engines/wa...silsleeve_tech

Sincerely,

Macster.

Jake Raby

There are some members of the industry who are repairing just one sleeve when they make block repairs, the factory also does this as mentioned in the quote above. Generally a ductile iron sleeve is used by the other companies to fix just one bore or individual bores, which generally makes no sense to me, especially considering the differentials in ring capability with the ductile iron Vs. lokisil in the same engine.

Lots of these are not working out very well due to the differentials in expansion between the ductile iron sleeve and the parent material, but it is a cheap way to patch up a block for further use.

We never do this, LN will not do this even if you request it.. No matter the situation, cause of failure or etc ALL SIX cylinders are upgraded with aluminum billet sleeves and then Nikisil plated. All the way or not at all is the only proper approach, yes it does cost more money, but its a Porsche engine, not a Honda and cost is simply required.

Macster,
Yes, closing the deck does impeded the ability for coolant to transfer between the crankcase and the cylinder heads as well as between the cylinders themselves. The cylinder arrangement was designed to be open deck, when closed a good portion of the cylinder sees less volume of coolant, especially the outboard portions of the outermost cylinders on each bank. if you look at the closed deck approach you'll see that the hottest portion of the cylinder (top) has the majority of coolant flow severely restricted around most portions of the cylinder. Doing this is similar to machining the fins from an aircooled cylinder as the water must pass over and around as much of the cylinder as possible to stabilize cylinder temperatures throughout the engine. Without clearance between cylinders the coolant simply cannot flow freely enough or at a high enough volume to evenly cool the cylinder.

I've attached some photos of one of my 3.6 based 3.8 Big Bore engines with the open deck sleeving arrangement. Its hard to see that the bores have even been sleeved until you look at the back side of the cylinder to see where the parent material meets the sleeve.

nick49

Thanks for the pix. Is your 3.8 big bore conversion using iron liners? Just wondering as the color looks different to me than aluminum and I wouldn't think a plated bore would be honed. Just guessing as I haven't worked with plated bores. Also I assume the sleeve at the deck is flanged to eliminate potential movement?

One last question, are all cylinder failures or most that you have seen due to a factory re-sleeve issue, or does the cracking, breaking also happen with virgin as cast and finished bores?

Thanks

Jake Raby

NO! Those are aluminum liners constructed of billet extrusion. We do not (and will not) use an iron liner.

.
The color difference is the Nikisil plating... Those liners are honed, the resolution of the camera and lighting do not allow for the super fine finished hone to be pictured very well. You can see some cross hatch patterns, but not very much.

No flange is utilized. The method utilized to fix the sleeve to the parent material is proprietary to LN Engineering and took at least two years to perfect. Honestly as their partner in development not even I know the exact method utilized.

These days we seldom see OE engines with cracked sleeves/ cylinders. Most of these that were going to fail, have already failed. The biggest issues were with the '99 MY engines that were "repaired" from the factory as new.

rb101

Jake,

I was going to ask how are the sleeves retained, but you answered it. What is the biggest the 3.4's can go to (3.6/3.8)?

Thanks

Rick
99 996C4
87 944S

Jake Raby

3.6 with bore alone, or 3.8 with a crank swap.

ohdavey6286

What else would be required to turn a 3.4 into a 3.8 when I rebuild? I would assume a tune and cams at least?

Regards,
David

logray

Found this interesting read the other day from Hartech. They claim to be able to overbore Lokasil (and replace/weight match pistons) instead of reboring/resleeve with Nikasil liners (or cast iron).

http://www.911uk.com/viewtopic.php?p=633086

"We have matched weights etc so it is possible just to fit one piston if the others are still OK - then with the extra cooling mods we do the others should run OK in the future. Our solution of just overboring the existing Lokasil and fitting securing rings while lowering the running temperature in the cylinders by reorganising the coolant flow and fitting a lower temperature thermostat - is the best way to go long term and also the least expensive - so I cannot see what advantage iron liners have (except they are less expensive than the Nikasli alloy liners we used to fit before we developed this overboring solution). " - Hartech

03996

Apparently, there aren't any liners in the engine. This was called out in "the book" as a misnomer. The apparent misunderstanding came about due to poor translation from the German to the English.

I'm just stating what "the book" says!

logray

From the link I posted above yours:

"The water coooled Carrera's have NO liners. They have impregnated Lokasil, the hybrid cooled GT3 and Turbo (+ derivs GT2 etc) have aluminium sleeves coated with Nikasil.

The Lokasil is a silicon hardening process for the aluminium castings. Porous cylindrical shells of silicon are aligned in the cast where the cylinder walls will be and when the molten aluminum is poured in it reacts with this LOCAlised SILicon matrix. The silicon "bleeds" into the local surrounding aluminium. The cooled cast is machined and acid etched to create smooth and hard cylinder walls.

Because the Lokasil is part of the cast it cannot "slip".

As the GT3, Turbo (GT2) are hybrid cooled (water cooled heads, air cooled bottom ends and cases), they have a different design so the air, oil and water stay separate. The case has a sealing liner coated with Nikasil.

(NICkel-SILicon carbide).

The incredibly hard Nikasil was first used by Porsche in 1970 for the 917 aircooled engines to allow smaller engineering tolerances, allowing greater pressures and bigger power.

One problem the Lokasil engine design can have is catastrophic edge failure.

The casting of the tube (cylinder wall) is squared off at the end. By this I mean the tube just ends perfectly straight. This means a very sharp right-angle edge with the associated point stresses and aerodynamic/hydrodynamic vortices.

The edge can get fatigued and break off, this in itself is not ideal as piston sealing may be jeopardised, the real issue is where the broken cylinder wall fragments end up next in a fast moving engine. The debris will destroy the pistons, conn rods, crank shafts etc and complete engine destruction ensues.

Fortunately it is pretty rare.

A more common failure of the casting is not related to any liners or lokasil etc, it is the thin walls associated with cross-flowed water cooling and large bore. According to Hartech, eventually ALL water cooled Porsche flat sixes will become ovalised over time (warped). Including Boxster.

For both, the solution is a re-bore with liners.

Replacement Hybrid Nikasil liners have with rounded/tapered edges to prevent the edge stress."