engine rebuild

[ds475]

when doing an engine rebuild, is it possible to just get new rings and have the cylinders honed out, but still use the old pistons? as long as you don't bore it out, it should be fine, correct?

i've been contemplating an engine rebuild, mainly so i could have a fresh start... but depending on how much the rings are, plus getting the cylinders honed...

also, while doing this rebuild, could i somehow convert my engine to be able to withstand a turbo? what other modifications does the engine need to accept a turbo?

[Scott R]

You can't hone the 944 engine, it's a lapped aluminum cylinder. Usually you can get away with new rings if you don't have any bad grooves.

Their are of course companines that can cut and lap the cylinders again for a hefty sum.

[todwic]

When I took apart the core engine I bought, it obviously had a lot of miles on it, and there was no perceptable ring groove. I put new rings on it and it ran excellently.

[ds475]

is it possible to put on new rings, without removing the engine from the car? that would be my biggest problem, because i don't have an engine hoist, jackstands, or a quality jack... not to mention, it seems like a real b!tch unhooking the WHOLE engine...

[Verruckt]

It can be done, however most on this board will tell you it is better just to pull the whole engine out. You need to remove the intake manifold, the cam housing, the cylinder head, then go under the car and while using jacks, support the engine so you can remove the lower cross member and then the oil pan. You can remove the connecting rod end caps and put the connecting rod and piston up and out of the block. Doing it this way is still a real pain. You will need two quaility jacks. There is a way to hold the engine from the top after removing the head. There is a factory part, however you can build your own with some lumber and a chain. If you want more details let me know.

[AFJuvat]

Yes, it is possible to remove the pistons and put new rings in provided that

1. Piston meets tolerance.
2. Cylinder meets tolerance.

Do not, under any circumstances, hone the cylinders. The cylinders are aluminum, coated with alusil. The Alusil coating requires a special machining process to replace. This process normaly costs somewhere in the neighborhood of $500.

Before deciding to make the leap into a rebuild, I have to ask why? Unless the engine has been abused or damaged, rebuilding the block is not normally necessary. Due to the labor involved, I would NOT recommend a rebuild unless a leakdown showed it was necessary.

Further, you could buy a known good engine for less than what you would pay for parts invilved with a rebuild.

Normally, you can bring an engine "back to life" with a top end job, replacing\repairing vacuum components\hoses, and a reseal (front end) (or a combination of all three)

AFJuvat

[todwic]

Originally posted by AFJuvat



Further, you could buy a known good engine for less than what you would pay for parts invilved with a rebuild.

Normally, you can bring an engine "back to life" with a top end job, replacing\repairing vacuum components\hoses, and a reseal (front end) (or a combination of all three)

AFJuvat

Forsooth.

[ds475]

i wasn't planning on a rebuild tomorrow, just some knowledge for the future...

[todwic]

"Reconditioning Aluminum Cylinder Bores
Most of the engine blocks you will work on will be either cast iron or aluminum with cast-in or pressed-in iron sleeves or liners. However, some lightweight engine blocks use no liners at all — the pistons bear against a specially prepared aluminum cylinder wall. These are often referred to as "linerless" engines. Most linerless alloy engine blocks use a special hypereutectic casting process that distributes small particles of very hard, pure silicon throughout the alu-minum. During production machining, the manufac-turers use an acid etching process to dissolve away the soft aluminum from the surface layer of the cylinder bores. This leaves only the exposed silicon particles to support the piston and to keep it from wearing the aluminum away, figure 11-56. The piston skirts are generally plated with a thin layer of iron to protect them from the abrasive silicon particles. "



"Machining limitations
Aluminum cylinder blocks cannot be machined in the same way that cast iron can. Hypereutectic castings have to be reconditioned so that the silicon particles stand away from the cylinder walls to prevent the alu-minum from contacting the piston skirts and rings. After you open up the bore, you perform a lapping process to scrub the aluminum away from between the silicon particles.

An alternative method is to fit the block with iron sleeves rather than trying to duplicate a factory bore. If you choose to recondition to stock specifications, be sure to check with both the engine and the machine equipment manufacturers for specific recommenda-tions. Although you can open up the bores using a boring bar, most manufacturers recommend performing the entire resizing job using an automatic honing machine. If a boring bar is used, it is essential that the cutting bit is extremely sharp and freshly lapped. If the bit is dull, it will gouge chunks of silicon from the bores instead of clipping them off cleanly. If this hap-pens, the cylinder wall is destroyed and the block must be sleeved or scrapped.

Following is the procedure Porsche recommends for reconditioning cylinders in their hypereutectic engine blocks. The entire operation is performed using a Sunnen CK-10 honing machine. Keep in mind that this is a brief summary of a detailed procedure. "

All description and picture courtesy of Chek-Chart Publications

[todwic]

thanks again, auntie wilk.