Rebuilt Engine Run-In

[vm]

Originally Posted by Malekreza11

Do you have pictures of the new cross-hatching on the cylinder walls?

I just want to point out that elmariachi's engine was sleeved with iron liners so the cylinder walls are crosshatched but if the engine would have been bored oversize, which is BMW standard procedure, the Alusil block would not have been cross hatched but machined to an almost mirror finish and then honed with a chemical paste that removes aluminum and leave silicon crystals exposed as the hard surface that supports the pistons.

[satinghostrider]

Originally Posted by vm

I just want to point out that elmariachi's engine was sleeved with iron liners so the cylinder walls are crosshatched but if the engine would have been bored oversize, which is BMW standard procedure, the Alusil block would not have been cross hatched but machined to an almost mirror finish and then honed with a chemical paste that removes aluminum and leave silicon crystals exposed as the hard surface that supports the pistons.

Thats a more technical explanation of the process. Care to elaborate the pros and cons of what you have described. It would be most useful to me.

Thank in Advance.

[vm]

Originally Posted by elmariachi

Thats a more technical explanation of the process. Care to elaborate the pros and cons of what you have described. It would be most useful to me.

Quick explanation: The M3 block is made of Alusil ("hypereutectic aluminum-silicon alloy"). The advantage of this material is that it can be bored and honed and the pistons can run directly on the aluminum block withoud an iron sleeve. This have the advantage that the block will be lighter, the heat transfer of aluminum is better, there is only one machining operation and no sleeve installation operation. This material has been in development from the seventies and have been used by many high end German manufacturers and is now established technology. The disadvantages are that is more expensive (more difficult to cast and machine), that needs a different and higher precision honing process and (important for tuners) that needs pistons that are iron coated. When iron liners are used the main advantage is the conventional machining process and (for the aftermarket) more piston choices.
The crosshatching in iron bores is done for the crosshatch to hold the oil where the piston rings slide. Alusil blocks dont have these textures so they depend on silicon aluminum interface to do that job (see link). Now for your case, usually for a block to be sleeved the damage on the cylinder bores have to be greater than the highest oversize piston that is offered by the manufacturer (In this case 0.40 mm) so that could have been your problem or it could be that the machine shop was more comfortable using the sleeving technology. I really dont know. Although I would have tried to go BMW's way (using oversize pistons) there is no reason that the sleeving that you have will not be excellent. In fact, it might make for a more durable solution which can also stand more abuse.

You can find an explanation of machining Alusil at http://www.mmsonline.com/articles/ne...cylinder-bores

[Chill72]

So how much did this rebuild cost you?