detonation damage?

[OttawaCharger]

Just poking around my engine with a borescope after having done a compression test. Motor build is in my signature. I'm not hearing any pinging but then again I've never had a good ear for that. I did have the vacuum advance hooked up after the cam install and found that the engine was missing badly at highway cruise speed from too much timing so I pulled that off soon afterwards planning to recurve things when I had a chance then bringing vacuum advance back to the party. I currently have 16 initial and 38 total and it seems happy. That being said, every now and then I feel a 'miss' in it while cruising along at highway speeds. I figured it was an ignition thing to be chased down. Anyway, my point is that I don't recall seeing that mossy looking finish on the pistons when I had the heads off last winter. Maybe I'm being paranoid but is that a sign of too much timing?

 

[Dart Frog]

I would say yes, you should be seeing signs also on your plugs. You can't always hear detonation. To me 38° is quite a bit of timing for just Hot rodding around. What kind of heads do you have? I would drop it down to around 35 total timing.

 

[NC Engine Builder]

I cant think of a small block mopar I have built that wanted more than 34° total

 

[Inertia]

Detonation pitting is generally on the perimeter of the piston head.
More-so on the side opposite the spark plug .
As above, 34* ish with good fuel.
As above, plug porcelain will have grey specks, from the piston material that is missing.

 

[318willrun]

Just me... but on low compression engines I've run 38* without issue. But your engine has to want it. I ran the low dollar 318 at 38-40* for 10 years, and beat the tar out of it at the track and out of town.. lol. Never an issue. I ran it there because the engine liked it best. Performed the best. But you have to read your plugs. And I keep my engines cool. By the way, I'm not sure that's detonation.

 

[jos51700]

I don't see any signs of detonation. I see oil wash rinsing the carbon off the pistons, and a fine layer of carbon across the surface. Looks like you might be running a little rich, which is ok with that much timing

 

[OttawaCharger]

Thanks guys. You've given me some things to think about. To Jos51700's point, she is burning a fair amount of oil on deceleration. Valve guides are worn. I do run it a bit rich. I'll be pulling the heads this winter so I'll be able to inspect things a bit better. In the meantime to be safe, I'll pull some timing out of it. My distributor isn't the easily recurved type so she'll have to live with less than ideal base timing until I get there.

 

[furrystump]

Your miss can be those plugs, been chewing on some oil. Look REALLY close at the grey plugs for small round deposits. I run a cheap plug and change them like underwear. Oh, is your valve cover leaking oil? I read on FBO website once that oil can wick through the spark plug threads. See how the oiled plug threads are darker that the others? I have no idea if it can happen, but funny that the threads are darker.

 

[OttawaCharger]

good observations FS. The valve covers arent leaking but she's definitely burning some oil. I'm guessing some of it is seeping into the threads over time. You're right about plugs being cheap enough to replace. I'm swapping in a clean set right now.