Spark Plug Threads Goobered

[b7labelle]

Aaaaalrighty, someone who shall not be named has made a rookie mistake.


Current situation:
https://i.imgur.com/RVzBB5e.jpg (LARGE IMAGE!!)


Lawnmower threads are fuckered about 3-4 threads in, the remainder are likely okay or untouched. It appears there is a sleeve inside the aluminum casting.

The spark plug hole is accessible. The head could probably be pulled in half an hour.

Options I am considering:

1. Soldier on!!
2. Thread Chaser (think tap would not be best choice, could start new thread paths and they may not align with existing threads after cutting through first few damaged threads)
3. Pull head and perform Helicoil insert. Not sure how this would play out while drilling into another insert
4. Buy a new mower
5. Run on 1 cylinder

Thoughts??? Any other suggestions?

 

[Jlbc212]

Is there already an insert in there?

I would pull the head try a tap from the undamaged side. If that doesn't work, either a Helicoil or a Time-Sert.

 

[b7labelle]

The only insert in there is the one from the factory, the brass looking one

Oooh tapping team the undamaged side - great idea!

 

[Kevkx125]

Try a spark plug thread chaser

 

[Stuart in MN]

They make a chaser tap specifically for spark plugs.

 

[James-W]

You can try a thread chaser, but those threads look pretty well screwed up so I have some serious doubts it will work all that well. I tend to think a Helicoil will be your best option but I would try the thread chaser first.

 

[Mick56]

Thread chaser from the back side to get it started straight.

 

[SGKent]

Spark plug thread chaser. They are usually tapered a little to help with the issue. Do not use a regular tap. Take the plug with you so you get the correct size. Worst case if the engine has a head is get a good used head from a mower bone yard, and replace it. Use anti-seize next time and go back and forth a tiny amount if it starts to bind, until it comes free. Drip a little atf or penetrating oil in if it binds because of being dry or carboned up.

example from aircraft spruce co:

 

[mfewtrail]

Another option is to place another insert without removing the head. Helicoil, Timesert, and others have various kits to do this. You can probably see most of them in action on yt. They work fine and if you're careful, you're not going to hurt anything. I've used them before on car engines that are still in service years later. I forget what the price of those are, but if it's a lot, and that head actually only takes 30 mins to remove, I would go that route if you need to save some cash.

 

[ghost68]

What about a back-tap? I've never used one but learned about them on this site. You insert the tap and expand it internally. Then turn the tap out. It drags the gunk out with it.

 

[b7labelle]

I did look at the back taps and the thread chasers. Back taps seem to be kinda pricy. If I need to tap it, I can pull the head fairly quickly and just run a tap through it on the back end like Jlbc212 suggested. I would probably need to pull it anyways to ensure the threads are fully cleaned out of chippings.

SGKent - I have not seen thread chasers like that, just cylindrical ones (basically bolts). I'll check them out first.

Helicoil will be the last option, but I wouldn't mind having that hardware on hand if there ever is a next.

I will post an update in a few days, hopefully one that doesn't involve a trip to a boneyard...

 

[ScottsGT]

Backtaps are $40 at Jegs. Seems to be a bargain compared to pulling the head, buying new gaskets and possibly head bolts (my Kohler required new head bolts) and the time involved.

 

[firebirdparts]

Pulling the head on a lawnmower is trivial. I never replace the gaskets. There's no water jacket, so there's no place for anything to go.

 

[SGKent]

SGKent - I have not seen thread chasers like that, just cylindrical ones (basically bolts). I'll check them out first.

funny - we have never seen any other kind. Any quality flaps should have one - might have to visit a NAPA or air cooled VW shop etc. The head you have looks to have enough threads at the top to start one and enough mass to save the threads. I think you will be Ok. Also look for plugs that have rolled threads like a NGK plug.Champion is good too.

 

[sberry]

I would chase it first. Might even oil or anti seize an old plug and work it back and forth in as a chaser.

 

[SGKent]

I would chase it first. Might even oil or anti seize an old plug and work it back and forth in as a chaser.

fyi - a plug tool like I posted is a chaser.

 

[PartsGuy]

Those expanding back-taps are the cat's ****, especially the 18mm for O2 sensor ports (where you CAN'T access the inside of the pipe or worse, converter...)
The Heli-coils aren't that bad for small engines and such. Used Wisconsin VG4D air-cooled heads are hard to find without stripped plug threads, and most of the ones I have found had already been Heli-coiled once and lasted a good long while after I got 'em secondhand.

 

[b7labelle]

Went with the chaser, should show up tomorrow. I’ll pull the head and drive it in with some lube from the back side ifyaknowwhatimean

 

[TractorJeff]

Yeah, Service Truck box has a chaser like that in one of the drawers.

 

[fsae0607]

I think you might be ok with the chaser, seeing as you have about 4 good threads.

If I recall correctly, didn't the Ford 3V heads only have like 2 threads?

Go nice and slow on the torque when you install the plug after you chase it. Good luck dude!

 

[SGKent]

I'd try chasing it before I went thru a head pull. If you pull the head replace it.

Time-Serts are better for spark plugs than heli-coils.

Time-Sert

Heli_Coil

 

[scdealer]

I would chase it first. Might even oil or anti seize an old plug and work it back and forth in as a chaser.

You can cut a slot through the threads of an old spark plug to use it as a chaser.

 

[jeff lary]

Yes this

 

[b7labelle]

If I pull the head replace it? The head was 5 bolts and a gasket. Ended up chasing it from the inside, worked out great. Took it off and reassembled last night.

https://imgur.com/a/UO3D3XQ

 

[b7labelle]

Put the mower back together last night, fired it up - its works!