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exhaust channel pics - after removing tubes

 
Old 12-11-2018, 06:47 PM
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pold9000
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Default exhaust channel pics - after removing tubes

I want to change my exhaust and befor reinstalling i shot this pics of the exhaust channel - what do you say, are the channels ok? i see there breaks out some pices?
please let me know
engine is 3.6 year 90 or so (built in my 80´s SC)





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Old 12-12-2018, 12:21 AM
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Goughary
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That isn't uncommon to see. It's not as big an issue as it looks. That ceramic tends to do that over time. So if it were mine, and i wasn't interested in an engine rebuild...I'd close my eyes, install the exhaust and pretend i never saw that...



In all seriousness- at the point when you are rebuilding for another reason, you can think to address it then. You may choose to never do anything abt it.
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Old 12-12-2018, 09:58 AM
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If you think you may rebuild in the future it might be worth looking for good used parts while they are still somewhat affordable. I am going through a 993 engine build and finding good used parts is next to impossible and prohibitively expensive. What should have been a few weeks has turned into months waiting on a single part worth reconditioning. 964 parts are still available for the time being thanks to all the Singers. I am assuming the engine is original and never had the TSB addressed?
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Old 12-12-2018, 02:22 PM
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Some of my ceramic liners were in almost-as-bad shape when I did my top end. Unfortunately, the only repair is to replace the head. Not great engineering from Porsche on this one. The number of used heads with completely intact liners is dwindling fast. I don’t know what the price is for a new head, but likely expensive enough to make billet 9m heads a consideration.

Anyway, around 15k hard red-lining miles since I discovered my cracked liners. Besides finding some small ceramic bits in the bottom of the cat pipe, no issues to speak of. Missing chunks in the exhaust port can’t be great for flow though.

On the bright side, your exhaust valve stems appear clean. A sign that your valve guides are in good shape.
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Old 12-12-2018, 03:03 PM
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JasonAndreas
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Originally Posted by -nick View Post
Some of my ceramic liners were in almost-as-bad shape when I did my top end. Unfortunately, the only repair is to replace the head.
Advancements in full barrier ceramic coatings have come a long way in the 33+ years since Porsche originally spec'ed those liners. I can't imagine not sending them out to be coated rather than replace the head if that was the only issue?
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Old 12-12-2018, 04:07 PM
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pold9000
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Originally Posted by cobalt View Post
If you think you may rebuild in the future it might be worth looking for good used parts while they are still somewhat affordable. I am going through a 993 engine build and finding good used parts is next to impossible and prohibitively expensive. What should have been a few weeks has turned into months waiting on a single part worth reconditioning. 964 parts are still available for the time being thanks to all the Singers. I am assuming the engine is original and never had the TSB addressed?
its original, some years ago i changed the rubber-gaskets and adjusted the valves every 10k km - i think the engine has done only about 30k km until now.
what is TSB?
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Old 12-12-2018, 04:49 PM
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my heads look the same. when I rebuild the engine I will be replacing the heads. when I talked to Steve he told be the ceramic is important for cooling and flow. my did this because when I got my car on one side of the engine was a big mouse nest and that side over heated. and the ceramic is put in when the pour the head. it's not something you can repair.
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Old 12-13-2018, 11:31 AM
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Originally Posted by pold9000 View Post
its original, some years ago i changed the rubber-gaskets and adjusted the valves every 10k km - i think the engine has done only about 30k km until now.
what is TSB?
The early engines came without head gaskets machined into the cylinders. The Technical Service bulletin #9404 IIRC explains the changes made to the cylinders to a newer design incorporating these rings and heads. Over time these had a tendency to leak from the heads. I will see if I can find a pdf of the TSB unless Jason has one handy.
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