Number 1 Spark Plug Hole - Stripped! 1975 Bus

[BellePlaine]

While preparing the bus for winter storage, I noticed that the #1 spark plug was all sooty, foreshadowing a bad problem.



When I tried to replace the plug, of course it would kinda tighten and then get looser before it got sort of tight again. Even though there was no metal shavings on the threads, nor do I recall ever over-torturing the plug I have to face facts and consider my options to rethread this spark plug port. The good news is that I’ve never done this before and now I get to learn something new. So, what is the very best method to perform this task? I expect to remove the engine and remove the head(s); but then should I Heli-Coil it, or something else? While I’m at it, I will rethread one of the intake manifold bolt holes (on the same head) as it is also kind of weak.

[sped372]

I don't have any experience with doing the spark plug holes, but in other cases I always liked the kind with the little keys you drive into place to prevent them from backing out later on:

See "Thread Locking" with the four little sticky-uppy things here:
http://www.mcmaster.com/#threaded-inserts/=9qeuuo

We used to put them into aluminum fixtures right off the bat to prevent thread issues later on.

[chitwnvw]

Time cert.

[hambone]

Does he have to pull the engine/head? Mebbe.

[BellePlaine]

Does he have to pull the engine/head? Mebbe.

The way that I understand it is that I probably don't have to pull the engine/head, but I will anyway. I hate to deny myself the pleasure.

Would now be a good time to tap the galley plugs, or does that require splitting the case?

[sped372]

How could you do it without pulling the head? I'd be nervous of stray chips in the cylinder no matter how careful I was.

[BellePlaine]

How could you do it without pulling the head? I'd be nervous of stray chips in the cylinder no matter how careful I was.

Me too, but technically, I think that it's possible. I believe what you would do is oil the tap in order to catch as much of the shavings as possible then open the exhaust valve and blow compressed air in through the spark plug hole.

[chitwnvw]

You don't need to split the case to pull the galley plugs, but it is tapping and dieing and metal shavings galore.

[Amskeptic]

You don't need to split the case to pull the galley plugs, but it is tapping and dieing and metal shavings galore.

I could not sleep at night if I tapped gallery plugs without the case being apart.

Repairing a spark plug in situe, I could live with.
Colin

[vdubyah73]

grease on the tap, not oil.

[dtrumbo]

Repairing a spark plug in situe, I could live with.

grease on the tap, not oil.

Fortunately, I'm not in this predicament, but thinking about it brings up a question. Grease on the tap is good for collecting shavings when tapping new threads for your time-sert, helicoil, whathaveyou, but what about when you have to drill out the original stripped threads? Seems like grease on the drill bit would just fling off. Along that line of caution, should you have the piston-in-question at TDC so that there is less "room" for shavings to fall into the cylinder which might then be removed easier with a thorough vacuuming with a shop vac via your newly threaded spark plug hole? How's that for a big ol' run-on sentence? I suppose the downside is the piston crown is right cozy with all the machinin' and would be easily damaged if something slipped or went too far.

[Amskeptic]

Grease on the tap is good for collecting shavings when tapping new threads for your time-sert, helicoil, whathaveyou, but what about when you have to drill out the original stripped threads?

Paradox here. If drilling, I would prefer dry dry dry. Then you can vacuum. Grease would allow big damaging chunks to glue themselves all inside. Dry would fall down, vacuum up. High pressure air would be dangerous, blow chips down around the piston crown and ring land.

After a thorough vacuum, I would then drench the area with oil and spin the engine with no plugs installed to assist the remaining particles to get knocked out of the way where they may without operational speeds or pressures acting upon them.
Colin

[sped372]

Ok, thinking way out in left field, could you:

1. Ensure that the engine's rotational position is such that the exhaust valve for the cylinder in question is open.

2. Hook the exhaust side of a shop vacuum up to the tailpipe.

3. Perform all drilling and tapping exercises with the shop vac on, creating positive pressure inside the cylinder to help keep shavings out.

Seems plausible...?

[dtrumbo]

Seems plausible...?

I like it!

[zblair]

Phred's a 1971 but J is having a problem with one of the spark plugs like this. J got the helicoil and "retreaded" the hole which we thought fixed it. I think he may have replaced that spark plug also. this was probably last month. Two days ago Phred spit out the plug again.

I could be leaving out more information that is needed for this, but I just wanted to post this before I forgot. I think it is also the #1 plug. I will ask him to post on this thread.