yelcab

I have never prefilled oil filters.... ever.

Jagtem

Well... Now I know something new.

The builder did not send any pictures of the bearigs and never even mentioned pre-filling of the oil filter as a potential culprit.

They did however send me the following pictures of the bores/ pistons themselves. Nasty:

Charles Navarro

Part of the issue I see here is they reused the stock pistons. The pistons have an iron clad coating. You can't run that on an iron bore. That's a recipe for disaster. I wonder what they did for end gaps and for piston to cylinder clearance too.

The reason I ask is that I see this all the time. I'd say at this point about 1/4 of all the blocks we are getting in have been steel sleeved.

yelcab

No effing way? Who would do that on a rebuild? You buy new pistons, new rings, to go with the new bores....

De Jeeper

They may have been new but should not have been the stock pistons according to cn's experience.

Charles Navarro

Considering the cost of new factory pistons, I highly doubt they put new ones in. :-)

We see this all the time. People don't know what they don't know.

Mike Murphy

Those pistons look super dry

Charles Navarro

My guess is that between the iron clad skirt coat and incorrect piston to cylinder clearance, those two factors contributed to this failure. I don't think this was caused by pre-filling the oil filter (I'd expect the main and rod bearings to show damage if this was the case) nor from an air pocket in the cooling system.

De Jeeper

I have a feeling the op is getting f'd in this one. I would deff trust cn's anyalysis over a builder that thinks iron sleeves r a good idea for these motors.

I also find it hard to believe there is no "overheat" tab on one of the heads so the builder can prove it got hot.

Not sure u could prove either theory and its probably what this builder is counting on. Be nice to know who did the work.

silver_tt

The engine builders with the best track records moved past using iron/steel liners in this engine a long time ago save for possibly Jarno at Werksmotor in Germany. It is a cheaper path but presents several challenges including considerations due to different thermal expansion rates and inferior heat transfer properties. It also has poor wear properties compared to Nikasil.

silver_tt

According to this post, "piston clearance ... 0,06 on all cylinders."

https://rennlist.com/forums/996-foru...l#post18939525

Charles Navarro

That's roughly what we run with a forged piston with our aluminum sleeves (varies on brand of piston, alloy, and cam skirt profile). I can't comment if that's appropriate for a steel cylinder, but with a JE Piston on an aircooled engine, you typically have to run .0015" to .002" more clearance with the same 2618 forged piston on a steel cylinder vs an aluminum one.

Piston alloy also is a variable. A 4032 high silicon piston can run about .0005" less clearance than you would otherwise run with a 2618 forged piston.

I am also curious where they measured that 0.06mm clearance as piston skirts are cammed and the gauge point can vary depending on the piston. Lastly, unless they match honed each cylinder to each piston, I highly doubt those used pistons all measured the same. Hell, even in new aftermarket sets we can see up to a .0005" variation between the smallest and largest pistons, so who is to say some of the bores were tight, especially if all those used pistons did not come out of the same engine.

pdxmotorhead

Just based on random exposure to race setups. (not specifically any Porsche engine) Steel sleeves in a AL block with forged Pistons need about .008+ REALLY depends on teh piston builder.

The pistons pictured look like a classic "stuck piston" from a motorcycle.. They needed plenty of clearance due to piston expansion. Going to lean or too rich was a fatal mistake ...

Porschetech3

Op another thing to consider is the "break-in process" ......

During break-in the pistons will usually run much hotter than " after break-in is completed"...

The pistons transfer their heat to the cylinders through the rings to the cylinder walls, when the engine is not yet broken-in, the rings are not sealing well to the cylinders and much less heat is transferred to the cylinder walls therefore the pistons will run much hotter ( and grow larger) during break-in with mostly oil splash/squirt to cool them...

This is one reason the "break-in process" is so critical. Did you get a specific break-in regimen from the builder?

What exactly was your break-in regimen??

pdxmotorhead

Mine for comparison (Short version i had a specific list but this is off the top of my head.. )
was nothing over 3500 for the first five hundred miles on Breakin oil,
dump the oil then nothing over 4500 for 1500 more miles (non synthetic)
dump the oil then drive normal with no hard pulls to redline, for 1500 dump the oil again...
switched to lubrimoly.. Drive it.. At this point, part of the tuning logging I was pulling 3 full power pulls to 7K in 3rd for each log to the tuner.

Cut the filter each time (I have a LN solution)
Check the magnetic drain plug.
OVERNIGHT drain on each oil change nets almost another quart especially if you have the plug out and the Oil filter off.