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Opinion: damaged exhaust valve seat
I got during the last two weeks two intermittent CEL ... with a generic code reader twice got P1120 (throttle plate) and P1121 (throttle position). Symptoms where with WOT throttle would not accelerate. Switched of car and did E-gas reset. Car ran fine after that. Then some days ago the car stalled upon coming to a stop when pressing the clutch. I tried twice to restart. Engine turned but nog ignition. Pushed it to the side of the road. Had my code reader with me. Again P1120 and P1121 but now also P0102 (MAF Hot film) and P0300, P0302 and P0303 (misfires cilinders 2 and 3). Upon opening the engine compartiment I noticed dusty engine compartment and still some dust coming out of the intake snorkel. What triggered me to believe some air was pushed back by the engine into the intake. Flatbedded the car to my Indy. Diagnosis, no compression in cilinder 3. First guess of my Indy was a problem with intake valve, a broken valve spring or a valve seat. After the head came off this was the result. https://cimg8.ibsrv.net/gimg/rennlis...1bb2f1894.jpeg Valves on cilinder 3 https://cimg9.ibsrv.net/gimg/rennlis...768849e39.jpeg Piston cilinder 3 A broken Intake valve seat on cilinder 3. Removing the valve revealed the crakced seat, with the piece still in place. Piston hardly damaged.. Everything looks further fine, cilinder walls clean and unscratched. Head is now out for repair. My indy says it is no problem to repair and reassemble since no scattered metal parts. The piece that broke off from the valve seat is a nice clean fracture. What is the experts opinion here on this? Any extra precautionary measures that should be taken? I expect some will say to reassemble like that is heresy? Car has now around 115k miles, 30k miles ago it was rebuild and fitted with 6 new cilinder liners (Hartech), running spin on oil filter adapter |
Call me skeptical, but how does a valve seat break like that? What is the chipping around the outer edge of the seat? Looks to me like someone jammed something in there while trying to remove the valve or the seat... The seat doesn't otherwise look damaged or worn. :corn:
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The chips are from the seat that came loose and was pushed back. That is probably also how it broke. To correct the story, the valve itself took some hits too and needs to be replaced. |
My indy is a reputable and renowned shop around here and only does MY96/97 engines and rebuilds. He told me he has seen a few cases were the valve seat came loose. Question that remains is where did the chipped of pieces of the head go. |
Valve seat failure can happen on any engine, although I haven’t read much about that here on the M96. You probably want Jake or other engine builders to weigh in. |
Yes, from what I was told it is not so common. After the compression test and troubleshooting with the engine still in the car his first diagnose was a loose valve seat or a broken valve spring. It seemed he was not far off at all. Will have the knock sensors replaced now with the engine out. And the intake verified. Drop the oil pan etc. |
The chips r probably (hopefully) making there way through your exhaust.
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Does your mechanic have any concern about crank, rod or bearing damage? Will it get a new piston?
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I have a set of 3.4 heads from my 2000 911 with less than 55K miles on them from my engine that lost a crank bearing. I went with a 997 engine so I harvested the parts of the 996. Let me know if you are interested.
https://cimg6.ibsrv.net/gimg/rennlis...f53f6e87fa.jpg https://cimg7.ibsrv.net/gimg/rennlis...4a22002f42.jpg |
If you Google 996 valve seat you will get a few hits that look like yours. One with good pictures is from renntech.org in 2010.
https://www.renntech.org/forums/topi...at-ring-broke/ My 03 996 has had a major failure and I thought I'd ask if anyone has seen anything like this happen before. Under very low idle and speed I heard a metallic "clang" noise from the motor and then it died and would not restart. Had it towed to the shop where they had to drop the motor and pull off the 1-3 head to find the problem. One of the valve seat rings on the #3 cylinder popped out and caused damage to the head and top of the piston. Here you can see the missing valve seat ring and the damage done to the head when it came out. I had him remove the other valve for comparison. http://tinypic.com/r/2hf47pv/7 Different angle... http://tinypic.com/view.php?pic=2cdg4qr&s=7 Top View... http://tinypic.com/view.php?pic=vcxmk6&s=7 Other side of the head. Cylinder 3 is on the right. No issue there. http://tinypic.com/view.php?pic=2j1va09&s=7 |
Thanks for the offer! The scuffs on the piston are really marginal. Mainly the Carbon deposit that was touched. Any collateral damage is at this point not visible but it could however be there. That is why I want some input. Off course the best is to open it up clean and verify the condition. |
Originally Posted by Silk
(Post 15056991)
My indy is a reputable and renowned shop around here and only does MY96/97 engines and rebuilds. He told me he has seen a few cases were the valve seat came loose. Question that remains is where did the chipped of pieces of the head go. |
Yes he confirmed ... very rare, but it happens. |
Originally Posted by dporto
(Post 15057981)
I'll take his/your word for it - especially after seeing the photo's of the other one from Renntech. Hopefully it's a rare phenomenon...I wonder if it's included in Jake's "101 ways for an M96 to eat itself" (the book he never published) ?
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I agree, the valve seat coming loose is a rare failure that can happen to any engine, usually happens if an engine has experienced higher than normal operating temps. The aluminum expands more than the steel seats and the interference press fit becomes insufficient to hold the seat in place.
You are extremely lucky to have had minimal collateral damage , usually a dropped valve seat causes the valve head to break off, piston damage, block damage, and catastrophic engine failure to occur. The piston doesn't appear to have any structural damage.Given your lucky streak I would put all my chips back into the pot and roll the dice again, fix the heads and reassemble. But after reinstall I would look closely at any potential for higher than normal operating temps ( water pump, cooling fans radiator debris ect.) |
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