Author Topic: Blow By Coming From Spark Plug Holes? SOLVED!!!  (Read 1998 times)

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Offline Super CJ

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Blow By Coming From Spark Plug Holes? SOLVED!!!
« on: October 30, 2005, 09:48:18 pm »
Problem Solved!!! In no small part due to the advice of the forum members. I thank all of you for your input. So, here is how I fixed the problem.

I had serious blow by coming from 6 of the 8 spark plug holes. I took a blue dry erase marker and drew a line around the seat of each spark plug, then I installed the plug, torqued it tight, then removed the plug and inspected the blue dye mark. This told me that the plugs were not seating and where exactly on the plug seat the air was escaping from.

Next, I took an Autolite 45 plug and ground off the threads so now I can take the plug and spin it in the plug seat. I then made a contraption consisting of the modified plug, a peice of fuel line, a socket and a flexible 3/8 extension. I hooked that whole mess up to an electric drill . Then I took valve lapping compound and ran a bead around the seat of the new "plug tool".

I stuck this tool into the plug seat and slowly ground a new seat surface on each of the plug holes. I would grind, clean the seat and check the contact area using the aforementioned blue dye technique. I did this for each hole. Over and over again until they showed a good contact patch and I could crank the engine with no blow by. Then I would move on to the next plug.

As you all know, this is no easy task because there is NO room to work on these engines when they are installed in the car. I even pulled the motor mount bolts and jacked up each side as much as I could. This procedure took days to accomplish. But finally, I could crank the motor without hearing or feeling any blow by.

Obviously, the plug seats were damaged or corroded. The machine shop and I did not catch it before we put the motor together. I would have been alot easier doing this with the motor out of the car, but hindsight is always 20/20!

I any case, the problem is solved and I learned a valuable lesson about rushing your priority projects.

Thanks again for all of your help and input.
1970 Mach 1 428 SCJ, 4 Spd, 3.91 Gears
Red w/ Black Interior

2005 Mustang GT w/ Saleen Supercharger, 5 Spd, 3.55 Gears, Red w/ Blk Interior

1957 Chevy Bel Air, 350, Auto, 3.43 Gears
Red w/ Grey Interior

1977 Pontiac "Bandit" Trans Am

Offline hawkrod

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Re: Blow By Coming From Spark Plug Holes? SOLVED!!!
« Reply #1 on: October 31, 2005, 10:08:25 am »
That deserves a hearty congratulations! Hawkrod

Offline geraldt52

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Re: Blow By Coming From Spark Plug Holes? SOLVED!!!
« Reply #2 on: October 31, 2005, 01:42:45 pm »
Thanks for letting us know the outcome.  That had to be a heck of a job with the engine in the car.

Honestly, in 40+ years working on cars the only problematic plug seats I've ever seen on a cast iron head were those where someone had tried to rethread them, heli-coil them, or otherwise mess with them after they'd already been damaged.  I'm especially baffled as to how you managed to have the same problem on all 8 plugs with heads that were on an OK running engine beforehand...especially since you say the threads weren't touched in the rebuild.

Anyway, I'm sure it feels great to have that behind you!

Offline jmlay

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Re: Blow By Coming From Spark Plug Holes? SOLVED!!!
« Reply #3 on: October 31, 2005, 04:20:32 pm »
In the origional post I thought I read where the heads were sandblasted. If the seats were hit that could lead to the problem seen.

Mike

Offline Super CJ

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Re: Blow By Coming From Spark Plug Holes? SOLVED!!!
« Reply #4 on: November 02, 2005, 05:51:42 am »
Well, bead blasted is a more accurate description. But I still don't see how that effected the plug seats. I've bead blasted dozens of parts and the glass bead should not be enough to change the way the plug seats in the head. I also noticed alot of paint on the plugs the first time I tried to seat them. I think the engine assembler was a little too enthusiastic with the spray can!

I literally had to resurface the seats with the homemade tool and lapping compound. I've never seen or heard of anything like this before, but it is done and now I am on to the next challenge - getting this thing to fire and run!
1970 Mach 1 428 SCJ, 4 Spd, 3.91 Gears
Red w/ Black Interior

2005 Mustang GT w/ Saleen Supercharger, 5 Spd, 3.55 Gears, Red w/ Blk Interior

1957 Chevy Bel Air, 350, Auto, 3.43 Gears
Red w/ Grey Interior

1977 Pontiac "Bandit" Trans Am