Spark plug gap closed fresh rebuild

[Bextreme04]

Sorry for lack of info, this was professionally rebuilt by local shop just a stock tbi 350, I changed all the plugs after break in and this didn't happen. I went to drive it and it ran like crap under load in gear, as changing plugs again this is what I found. I am hoping it is timing because I have had trouble timing this engine.

That gap doesn't close without a significant physical force. It isn't timing and it isn't detonation. Either you pushed really hard on that plug while putting it in and closed that up or something bounced around in that cylinder and did that.

 

[Snoots]

Note that it didn’t just close the gap, the porcelain is knocked off center.

Good eye John!

 

[scrap--metal]

The spark plugs from my engine look like they were smashed differently than yours... I still had these 2 riding in my truck.

If you're lucky, your plug was bent before installation.

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[Cdog_96]

The number 6 plug in my K10 has closed up like that on 3 occasions. Each time a peice of the piston bounces around and closes the spark plug gap causing the engine to run poorly (compared the baseline ). I replce the spark plug and it keeps going.

That's a high mileage 305, and not a fresh rebuild from a professional.

I bet something went down the intake, something was forgotten inside during the rebuild, or maybe detonation during break-in might've knocked part of the top ring land off the #2 cylinder (you mentioned trouble timing).



A borescope is definitely the proper tool to start with here.

Below is a borescope image of the problematic piston in my k10. Notice the missing edge on the left side.

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Does it go into spark plug hole ?

 

[Max Headroom]

Some thing to consider:
The plugs screw into the head at an angle to piston top travel. If the insulator on the plug is actually bent and the gap is closed, it is likely that the piston top has hit the plug. In a stock application with stock timing, the plug shouldn't come in contact with the piston. The cam timing should prevent this. If you replace the bent plug and the engine still runs rough it is entirely possible that you havee jumped time at the timing chain and could bend more stuff.
What ever the issue is, I wouldn't start that engine to run till I knew absolutely what went wrong and fixed it. You could take off a valve cover on the bent plug side, put a socket and breaker bar on the end of the crank and rotate the engine slowly in the correct direction.If the chain jumped a couple of teeth. The engine should refuse to rotate after some initial movement. Moving the distributor to "re-time" the engine will not tell you if you have a physical interference issue. If you have full movement turning with the crank end & socket, buy shorter plugs.

 

[Bextreme04]

Some thing to consider:
The plugs screw into the head at an angle to piston top travel. If the insulator on the plug is actually bent and the gap is closed, it is likely that the piston top has hit the plug. In a stock application with stock timing, the plug shouldn't come in contact with the piston. The cam timing should prevent this. If you replace the bent plug and the engine still runs rough it is entirely possible that you havee jumped time at the timing chain and could bend more stuff.
What ever the issue is, I wouldn't start that engine to run till I knew absolutely what went wrong and fixed it. You could take off a valve cover on the bent plug side, put a socket and breaker bar on the end of the crank and rotate the engine slowly in the correct direction.If the chain jumped a couple of teeth. The engine should refuse to rotate after some initial movement. Moving the distributor to "re-time" the engine will not tell you if you have a physical interference issue. If you have full movement turning with the crank end & socket, buy shorter plugs.

You are thinking of intake valve contact. The spark plug does not move and has nothing to do with timing. If the piston was going to make contact with the spark plug, it would do so at EVERY rotation of the crank, even with no cam installed at all.

I have never seen a stock truck SBC with a small enough quench area for there to be any concern that the spark plug is going to make contact with the piston.