Spark plug gap closed fresh rebuild

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

C

Cdog_96

Member
Joined
Jan 15, 2022
Posts
45
Reaction score
31
Location
Aiken
First Name
Clay
Truck Year
1983
Truck Model
K10
Engine Size
454
Uh oh, fresh rebuilt tbi 350 just changing the plugs and noticed #2 plug gap closed. Engine also runs rough under load, bad timing maybe ? What am I in for ? Any help appreciated thanks !
You must be registered for see images attach
 
nvrenuf

nvrenuf

Full Access Member
Joined
Jul 30, 2010
Posts
1,940
Reaction score
2,424
Location
Mobile, Al.
First Name
John
Truck Year
1991
Truck Model
K5
Engine Size
454
Are you sure that’s the correct STYLE of plug for your heads?
 
Tonimus

Tonimus

Full Access Member
Joined
Sep 17, 2024
Posts
59
Reaction score
106
Location
Phoenix
First Name
Tony
Truck Year
1978
Truck Model
C10 Suburban
Engine Size
454
Dollars to doughnuts that either you aren't supposed to use extended reach plugs, or you have something riding around in the cylinder.
 
Snoots

Snoots

Full Access Member
Joined
Jan 23, 2013
Posts
8,709
Reaction score
17,994
Location
Georgia
First Name
Roger
Truck Year
1973
Truck Model
Jimmy Sierra
Engine Size
350 w/203
That should be about an R45TS with a gap of .045
 
R

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
5,385
Reaction score
8,588
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
Put in another plug,correct plug,of course,maybe someone dropped that one prior to installation and never even looked at it.. If a new plug does the same thing. Start it with that plug out,run it a minute,then put a plug in. If that plug closes too,that head needs to come off to see what's hitting the plug.Dont waste time trying to diagnose it through the plug hole the heads going to have to come off anyway to fix it. I've had plugs close up like that on other engines due to rod bearings. IDK if plug location on sbc will allow that or not. But that's one thing I'd be looking at. Incorrect rod bearing,wrong piston,wrong connecting rod letting one piston park to high in the hole.if it's doing this at cranking speed,as in never started,I wouldn't suspect a rod bearing,because there wouldn't be the momentum needed at cranking speed.
 
Last edited:
TotalyHucked

TotalyHucked

Full Access Member
Joined
Feb 24, 2020
Posts
3,638
Reaction score
11,672
Location
Auburn, Georgia
First Name
Zach
Truck Year
1985
Truck Model
Sierra 1500
Engine Size
5.3
Man that plug's F'd. Like @nvrenuf said, it bent the strap down hard enough to pull the porcelain to one side. I'd start with a cheap borescope, if you don't see anything, take all the other plugs out and put a fresh one in that hole. Put a bar on the crank bolt and turn the motor over by hand to see if it ever stops/gets stuck. If it does, take that plug out and then put the bore scope in that cylinder. It could be that that one got dropped before install but I find that hard to believe.

Who did the motor? Definitely need to figure out what happened with that plug first. If nothing is found, throw another plug in it and then check the timing before driving it again. Is it hard to start when hot? Could also be a combo of timing issues/advance issues and carb issues
 
Grit dog

Grit dog

Full Access Member
Joined
May 18, 2020
Posts
6,944
Reaction score
12,169
Location
Auburn, Washington
First Name
Todd
Truck Year
1986, 1977
Truck Model
K20, C10
Engine Size
454, 350
Well it would run rough because it was missing on the smushed plug cyl imo.
There’s been some speculation since OP didn’t say what “fresh built” means. Appears it wasn’t from hand cranking the engine over as the plug has been run for a bit (ceramic looks brown) which suggests it didn’t smash upon first roll over of fresh engine.
And the background in the pic looks like a fully assembled ready to drive engine.
OP also didn’t say if they’ve replaced the plug and tested again.
Before doing anything, I’d spend the $3 and slap a new plug in it and see.
Need better description from the OP. Did he install the plugs and/or build the engine or has he no knowledge of the condition of that plug previously and someone else closed up the motor.
 
C

Cdog_96

Member
Joined
Jan 15, 2022
Posts
45
Reaction score
31
Location
Aiken
First Name
Clay
Truck Year
1983
Truck Model
K10
Engine Size
454
Grit dog said:
Well it would run rough because it was missing on the smushed plug cyl imo.
There’s been some speculation since OP didn’t say what “fresh built” means. Appears it wasn’t from hand cranking the engine over as the plug has been run for a bit (ceramic looks brown) which suggests it didn’t smash upon first roll over of fresh engine.
And the background in the pic looks like a fully assembled ready to drive engine.
OP also didn’t say if they’ve replaced the plug and tested again.
Before doing anything, I’d spend the $3 and slap a new plug in it and see.
Need better description from the OP. Did he install the plugs and/or build the engine or has he no knowledge of the condition of that plug previously and someone else closed up the motor.
Click to expand...
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.
 
Grit dog

Grit dog

Full Access Member
Joined
May 18, 2020
Posts
6,944
Reaction score
12,169
Location
Auburn, Washington
First Name
Todd
Truck Year
1986, 1977
Truck Model
K20, C10
Engine Size
454, 350
So it’s possible (maybe not probable) that you smashed the plug on installation? Ran smooth, changed plugs, ran rough. And it didn’t smash the plug first time.
Gonna say slap a new plug in it and see what happens.
 
scrap--metal

scrap--metal

Full Access Member
Joined
Sep 15, 2021
Posts
691
Reaction score
1,314
Location
MN
First Name
Calvin
Truck Year
'85, '81
Truck Model
K10, K20
Engine Size
305, 350
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).

Rickf said:
Get one of those economical (cheep) scopes and take a look at the top of the piston.
Click to expand...
TotalyHucked said:
I'd start with a cheap borescope
Click to expand...
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.

You must be registered for see images attach
 
You must log in or register to reply here.

Similar threads

RanchWelder
4L80E fresh rebuild, no reverse.
Replies
4
Views
708
squaredeal91
squaredeal91
G
Rough Idle and Stalling
Replies
6
Views
1K
75gmck25
75gmck25
Rich77
No spark
2 3
Replies
35
Views
3K
Rich77
Rich77
B
Replacing 454 gaskets opinion
Replies
11
Views
603
Byard-HWJ
B
leotismumford
Reading Spark Plugs
Replies
8
Views
1K
Craig Nedrow
Craig Nedrow

Latest posts

Forum statistics

Threads
44,081
Posts
949,003
Members
36,158
Latest member
nobodyawesome
Top