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Purchased a Mazdaspeed3 with misfiring engine due to low compression. Cylinder 3 had 20 psi wet and dry compression.
Only 1 of the exhaust valves and seat is severely damaged. According to owner, the engine was running high rpm low load when started misfiring - then would misfire at idle the following day. Guy drove it for a couple more weeks on mis-fire. Thats when I bought it.
Any idea what could cause the valve to fail like that?
looks like something has gone through it to me
Hi Chris, thanks for the reply. looks like the valve seat is damaged as well but the cylinder/piston is not.
Looks like I posted this in the wrong section, if someone can move this thread, it would be appreciated.
#2 picture Looks like its been cut with an oxy acetalene torch.
The valve was burned or cut.
I find it common on high mileage Hondas and found they typically burned oil and had a lot of carbon build up. When I pull the pistons the rings are typically completely stuck with carbon as well.
I have speculated as to the cause, but am curious to hear others input.
Thanks for the replies everyone. I have done some more research on this and I believe this can be classified as a torched valve. There was either build up or the valve was starting to deteriorate, allowing some hot gasses through, eventually making it look like it was cut in multiple places.
I don't know how the valve seat got damaged. Could it be from the valve fragments that fell apart?
The valve seat could be damaged at the same time as the valve. The combustion is leaking out through the closed valve and will cut the valve and seat at the site of the leak just like a torch.
The seats are not as bad either because of the material they are made from, or the extra mass of the head pulling heat away, this im not sure and is just speculation.
This is a classic burnt valve. While there are a number of reasons for this, generally though it is a result of the valve not seating properly and hence the valve is unable to transfer heat back out of the valve into the valve seat. This results in the valve overheating and melting.