My son requested/completed his first spark plug change and satisfying test drive! Playing with camera really visualizes for the boy too.Tip..do not use wing bolts to hold heat shields in, they were nubs getting out after deformation of vice grips. Also tought corvette words..
we shot a few pics of 6/8 cylinders and plugs, some same cylinder. The camera is not 4k and casts some shadows that may trick my eye so open for thoughts. I can be completely wrong but
- runs great, even better , smoother after plugs
- my history is ~ 7 years ago 29000 area, ngk ur4 when I changed plugs wires.about 46000 now mobil 1 15-50 zinc, always non ethanol 89 octane, lars carb, lars timing, no smog, burns a quart a year about 3000 miles, duals.
- one pic i thought goofy valve seat so ran compression check on that one , and one other 140 psi both.
- sometimes hard to start after sitting days until fuel catches..maybe weak plugs i shall try again and see if catches faster, is that fuel washing in one pic? What is ring wash and cause?
- plugs to me look ok..one has more brown .
- is that a crack between valves? Maybe just carbon.
- i thought L82 was flat top piston?
Runs fantastic and gets driven some, always fully warming up and driven.
thanks for thoughts!

 

To me those cylinders look in pretty good shape. Definitely a crack between valves, but if it isn't causing issues....don't make it an issue. That one pic where you can see the crack, the follow along the lower valve seat, and looks like a chunk missing....I'm thinking that's just a carbon chunk that's departed the fix. The piston is an L82 flattop with a valve relief all the way across.....unlike the L48 which is a "dished" flatop, with individual valve cutouts.
Looks like valve seals could be leaking, as a couple of those piston tops look pretty oily, and plugs should be cleaner without the oily residue might need to go to a hotter plug or as it's running slightly rich, adjust for a leaner mixture.

My .05

 

I'm about to switch to those plugs, a little hotter. I would say you have a tad of oil usage on those plugs, you are running 20/50 so it's thicker than stock, I'll wager10/30 would use a little more. If you are worried about that crack, run some Gumout through it and then mist some water over the carb while it running, higher revs than idle...that breaks up some of the carbon and you might see that crack picture change for the better, or not. Either way if you are running 3K miles a year then just enjoy it, it's not going anywhere...

60

 

What quality-level of fuel is going through the car? I'd like to see the plugs looking a bit cleaner from the orangy-reddish looking deposits, so would probably try a few tanks of top-tier fuel if not already running that. (Chevron gets good 3rd-party reviews for its Techron additive.)

You're already running a hot plug with the UR4 (AC Delco 45/46 equivalent), so I'm not sure trying to find and use an NGK 3 is going to serve you well.

It does seem to have some pretty heavy carbon deposits going on. Look into what 1860army mentioned about water down the carb to steam clean the valves and chambers. I did it decades ago before the innernet and all the google-able info out there, so a little research would be in order.

 

The good news is the cylinders look great. I'd be interested in seeing the results of a compression test or a leakdown test. I don't like the looks of the valve seats but the images aren't that great so it may be artifact. As for the plugs, I agree it's time for new ones, but I don't see anything about them that concerns me.
If it's running well, I wouldn't do anything except drive it. It's a small block Chevy. They go forever.
Aren't borescopes awesome?