ddubois

Isn't the ceramic coating also inside the ports, and therefore it could be from the exhaust port and therefore never "passed through the exhaust valves"?
Besides, I can't imagine a 50 cent sized piece passing through the valves and remaining in one piece.

I've had this same metallic, clanking noise at startup and have discussed it in other threads. It would only last for a second or two at COLD startup. I checked everything including cleaning chain tensioners, pulling and checking the starter pinion movement. Using the hose stethoscope it seemed to come from the bell housing so I figured it was the DMF calling it quits and planned on dealing with it when I do the clutch this winter. I did also consider that something could be rattling around in the cat converter.

Anyway, after a few DE days of running up to redline, the noise has disappeared. So after reading this thread I'm wondering if I had something rattling around in the exhaust system that finally got blown out?

I also remember reading some threads about the ceramic coating coming off and it not being something to get overly concerned about.

JasonAndreas

The ceramic port liner exist only on the exhaust side so there is no possibility of any broken pieces damaging the cylinder walls or pistons. If you had a turbocharger the impeller could get damaged but that is about it.



I'll include the official word from Porsche but there really is no reason for you to do anything other than put the exhaust manifold back onto the engine and to forget about rebuilding anything.


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Cylinder Head Ceramic Liners - Cracks or Breaks

9222porsche01

June 8, 1990
Model
911C2/C4

Group
1

Number
9015

Part Identifier
1570

Subject:
Cylinder Head Ceramic Liners



ATTENTION:
Service Manager/Service Technician

Models Affected:
911 Carrera 2 and 911 Carrera 4

Concern:
Cracks or breaks in ceramic exhaust port liners.

Repair Information:
Small cracks and/or breaks in the ceramic port liners in the area of the valve guides are sometimes visible even on new cylinder heads (See Figure 1). They do not influence the function of the port liners.

Cylinder heads must not be replaced for the above mentioned symptoms unless 1) breaks go down to the base material of the cylinder head, 2) broken surface area is larger than 1 sq.cm (0.155 sq.in.) or 3) the cracks extend from valve guide to the edge of the ceramic liner (on the valve seat or exhaust flange area).

f11

Well, its good to know this isn't a killer event...

"Repair Information:
Small cracks and/or breaks in the ceramic port liners in the area of the valve guides are sometimes visible even on new cylinder heads (See Figure 1). They do not influence the function of the port liners.

Cylinder heads must not be replaced for the above mentioned symptoms unless 1) breaks go down to the base material of the cylinder head, 2) broken surface area is larger than 1 sq.cm (0.155 sq.in.) or 3) the cracks extend from valve guide to the edge of the ceramic liner (on the valve seat or exhaust flange area)."

I've deferred to the technicians comments at the service centre I go to (specializing in european imports and exotics) regarding what I do about this situation, and they're recommending liner replacement. They know my situation, so I doubt they'd sandbag me on this service, although I suppose stranger things have happened.

Relative to Jason's comment, I don't know yet which or how many of the 3 conditions for head replacement I meet. The large piece of ceramic I handled this morning looked like it exceeded the 1 sq cm 2nd condition (it was about 4 sq cm or larger), and its extreme edges appeared to be finished suggesting it met the 3rd condition as well.

Assuming none of the three conditions are met, but pieces have come loose and are falling out, the Porsche comment suggests nothing needs to be done. So what do you do about the remaining pieces still in place: remove them once and for all before they break free; or leave them in and remove them after they break free (sounds like a lot of work)?

Thanks for your reassuring comments, regardless of where this goes.

f11

Ceramic parts are usually used where you want to dissipate heat quickly and efficiently (I believe), which would make sense when used around exhaust components. Considering the violent environment around the exhaust ports, I can see why ceramic parts would be subject to shattering and breaking off from time to time.

But if you don't replace the broken liners as the pieces come loose, don't you risk the introduction of hot-spots around the exhaust port, perhaps accelerating the burning of the valve seat and ground face, not to mention prolonged heat saturation of the valve stem and lubricant?

Or am I worried about an insignificant heat transfer issue, here? If the liners are "expendable", why were they designed into the engine in the first place?

deep_uv

Dunno. But the same people who designed it are saying to leave it alone and put it back together.

Regards,

JasonAndreas

The only way to fix the ceramic liner is to replace the cylinder head.

The normal course is to remove any broken off pieces that have ended up in the exhaust (usually just before the catalytic converter) during a valve adjustment.

Obviously Porsche used the ceramic liners for a reason but they also went to the trouble of publishing a document that says not to bother with a top-end rebuild for a broken liner. So they provide some benefit but not that much... I don't think you will find even a single 964 with ceramic port liners that are still perfectly intact. And the fix that your shop is suggesting will cost you $3000-5000USD and likely provide almost no benefits!