NO Compression on Number 3

jatt · 05:27 PM

I'm looking at #3 head there is severe pitting on the large surface area in compression chamber. I will attach pics. Additionally there groove lines running vertical in cylinder holes mostly at the top on two opposing sides.

Could this be from pieces of the rings that got up in there where did this pitting come from ?

Can it be ground out ? There is no compression in this cylinder.

Noob.

Thanks.

dgcantrell · dgcantrell's Garage

Could be.. Since you're going to have to pull the piston, you'll know shortly there after. I think they only make one oversized piston that measures 100.50mm (standard is 100mm). There may be some aftermarket pistons in several oversized dimensions. I don't know, I've never really looked. The cylinders will all need to be bored and treated with the Silicone coating that is used on these blocks. It could be an expensive operation though.

Arizona_928 · 06-04-2016, 02:21 AM

hmm should have done a leak down.
clean it up with hone and green scotch pads, and special compound. new rings, maybe piston as it's likely the coating is flaking. Run it. It won't be a 100%, but these engines are not exactly your bore and run pistons. You will need to nikasil plating after bore. or you can always sleeve that cylinder, and run a JE piston...

hmmm time to search for a new block imho.

jatt · 06-04-2016, 01:22 PM

Thank you for the replies. The rings on #3 were broken into pieces....I pulled all the pistons out the others look ok. Also there is some fairly deep indentions on the cylinder walls of #3 I'm not sure honing could take care of this ?

Do the sleeves come out ?

Thanks,

John

dgcantrell · dgcantrell's Garage

Sleeves generally have to be cut out on a boring bar... I'm not exactly sure how Porsche has done the cylinders on the blocks. I've never had to machine one just yet.

Techno Duck · Techno Duck's Garage

These blocks are not sleeved. Depending how deep those gouges are you can bore for oversize rings, but you need a place that knows how to do nikalsil.

It would probably be cheaper to find a good used block.

DannoXYZ · 12:26 AM

Couple tidbits of info:

1. Block does not have separate sleeves

2. Block and cylinders are all one-piece

3. Block and cylinders are made of Alusil, a hypereutectic aluminium alloy

4. After final boring, an etching/lapping process is used to remove only the aluminium from between the silicone crystals on the cylinder walls. This leaves a hard and durable surface.

5. Nikasil is an additional coating that is applied ON TOP of steel or aluminium bores. It is NOT used on the 944, on some 911s.

Many possibilities to fix this engine, all costing thousands in parts and machine-shop expense. Quickest and cheapest is to buy a used engine from a junkyard. I bring a LiFePO4 motorcycle battery with me to pick-n-pull yards to do compression test. Last month, I pulled a nice engine from a 944na to build a hybrid-stroker. Cost me all of $149 and a couple hours.

DannoXYZ · 06-05-2016, 12:31 AM

The other thing is to find out WHY the #3 cylinder had cracked rings or else you'll be cracking the rings on your replacement engine. It could be overheating because #3's coolant passages are clogged in the head. Could be clogged injector on #3. Could be fraying/shorting wiring or connector on #3 injector. Could be wrong plug heat-range on #3 plug... Etc. etc.

Repairing/replacing the engine is just dealing with the symptoms, not the actual cause of the problem. Without fixing the cause, the symptoms will just happen over and over again.