Noticed a nice mark on my piston. The engine still runs but has no compression on the #3 cylinder. Am I the first person to achieve this feat? I'm going to put a new engine in, but I was just curious why a valve would hit a piston. Maybe a stuck lifter or valve spring, or dropped valve seat? Image Unavailable, Please Login
Rebuild the engine. Don’t replace it. Really, just a head job. Don’t buy an unknown as well as lose the originality. Just my 2 cents. Cheers. Sent from my iPhone using Tapatalk
The only way to put a "new" engine in it is to completely rebuild the current engine. And I don't care about originality--I do care about an engine that runs properly.
Can you post more images. That doesn't really look like a witness mark. Valves hit pistons on an angle because they aren't perpendicular to the piston top. They leave a crescent moon type impression, or an eyebrow, not a perfect circle like in your pic.
Yes, I wouldn't go running down a replacement engine just yet. I would continue to diagnose why you don't have any compression and see where that leads you. Heavy carbon on those valves could give you this problem and it would be a shame to replace the entire engine for a carbon issue.
For this car, I would always stick with the devil I know. Rebuild the head. You may need new liner and piston (1 set).
You are going to have to drop the engine. Once that's done, pull the head and see what the issue is. If needed do a valve job, clean the carbon, and then decide if you want to do the other head as well.
Thanks for the comments and guidance, everyone. My goal is also an engine that runs well. I was thinking about swapping in a spare motor to drive the car sooner. Then I could take my time rebuilding the original engine. You inspired me to get a better scope so I'll snap some better pics soon. Agreed, and I would be very happy if it's just carbon causing my problem. Definitely. I'm at 50k miles so it's probably worth inspecting both heads if I'm going to do one side. The motor needs a belt service at a minimum so I will be dropping it out soon. Image Unavailable, Please Login
That's legit. Now the question is, what caused the burned valve. (If I'm seeing the pic correctly, you have a chunk of valve missing -- or is that just carbon?)
To me, it looks like the valve hit the piston (impact mark seen on the pictures in posts #11 and #1) which caused part of the valve to brake-off. It does not look like a burned-off portion.
Correct, it's a chunk gone from the exhaust valve. I'm not sure if it broke off or eroded away. You can see a burn pattern in the port next to the hole, and I'm not sure where the any valve pieces went. They aren't in the exhaust.
Yea it has 50k but I think the oil seal and/or guide is just blown out on this cylinder. The other exhaust ports at least are not covered in oil like this one. Even with "running rich" all of the intake ports and valves look pristine. No carbon at all on those.
My late '95 also has 50k miles but the exhaust valves didn't look anywhere as dirty as that when I fitted Tubi headers. I would agree that oil must have made its way down there.
I have seen this multiple times on 355. The valve guide wears out, allows engine oil to slip past the stem causing thick deposits on the back side of the valve. The valve is no longer able to dissipate its heat from combustion and the valve burns off at the point of most heat retained. You need a valve job, all new guides, and replacement of all valves in that cylinder, and any other questionable valves. A proper repair includes replacement of the affected liner. Image Unavailable, Please Login Image Unavailable, Please Login
I'll have all the guides checked. I have paperwork that they were replaced back in '06 and they appear to be steel but that doesn't mean they aren't worn. The crack in my valve seems to be pointing toward the exhaust port (similar to your photo) so I wonder if it was an exhaust leak that contributed to the burning.
I had similar happen on my car, although the valve guides (including the one for the burnt valve) were fine. In my case it was caused many thousands of miles ago by a cracked exhaust manifold, so you may well be correct about an exhaust leak. The valve operated in its weakened state for many years before eventually letting go on the way to Le Mans, a long way from home! 2x new exhaust valves and a new liner later, all was good. See discussion here https://www.ferrarichat.com/forum/threads/no-compression-on-cylinder-2.679644/
