Spark plugs binding

[WilCo]

Engine has been missing around 6500 rpm pretty consistently, so I decided to change the spark plugs even though they aren’t that old. I previously went with NGK LFR6 (not A) and gapped them myself. The 2 plugs at the rear of the boat came out easily, but both of the plugs towards front of the boat were really tough. I alternated loosening and tightening them to try to break them free, but ultimately had to spray some WD40 in there and hen loosen/tighten until free.
Now that I got them out, the new plugs (LFR6A) on front 2 cylinders appear to bind after just 1 turn or so. I have not installed them for fear of getting them stuck. Any suggestions? The back plugs went in fine.

thanks in advance!

 

[Gozills]

Unfortunately the most likely answer Is during prior installation of the problematic plugs the cylinder head threads were crossed and damaged.

 

[WilCo]

I was afraid of that. Is there a remedy?

 

[WilCo]

I see something called a thread chaser. How do I determine what size threads to do? And is there any major risk of attempting this on my own?

Performance Tool Spark Plug Hole Thread Chaser 14 and 18mm, Model# W80539 | Northern Tool

Quickly and easily cleans dirt, carbon and metal particles from spark plug hole.

www.northerntool.com

 

[WilCo]

They are 14 mm threads it seems per ngk.com
So now to figure out what are the do’s/donts of using a thread chaser. If anyone has experience, I’m all ears.

 

[tdonoughue]

I was going to say a plug tap (ugh)... But this thread chaser thing is intriguing. Following.

 

[Gozills]

I see something called a thread chaser. How do I determine what size threads to do? And is there any major risk of attempting this on my own?

Performance Tool Spark Plug Hole Thread Chaser 14 and 18mm, Model# W80539 | Northern Tool

Quickly and easily cleans dirt, carbon and metal particles from spark plug hole.

www.northerntool.com

this is just my opinion and is based on my experience only and with the caveat that without detailed inspection it’s only best guess. No offense meant but if your mechanical skills are that you cross threaded them initially, IMO you certainly don’t need to be attempting to repair them. if you use a thread tap there will be some aluminum shed down into the cylinder. Additionally these corrected threads will be inherently weaker and there is no reliable way to gauge their strength and eventual reliability. I would have a trusted mechanic verify this is in fact the issue before I jumped to any conclusions. If cross threaded I would have the head removed and a helicoil or timecert solution installed and then head reinstalled. Some people are comfortable installing either of these solutions with the head installed. I am not one of them.

 

[MidnightRider]

Yeah I'd second that, if they are indeed cross threaded and not just corroded, any repair I'd attempt would mean the removal of the heads. Seems to me that if they got progressively easier to remove with lubrication and movement I'd be taking a closer look at possible corrosion. What did the plug look like after removed?

 

[WilCo]

Plug was fine. I'll try to upload a picture later.
I'm a bit surprised at the recommendations to not do it yourself given this site typically prides itself on we can do anything. I guess that speaks to the risk versus reward of this particular repair. I'll watch a few more videos on the thread chaser as it seems pretty straightforward, but will likely take it to my trusted mechanic (hopefully he'll agree to work on the boat). The only Yamaha dealer in the area is not one I'm excited to have touch my boat again.

 

[Gozills]

Plugs are hard steel-head is soft aluminum. The head threads will show the damage if any.

 

[MidnightRider]

Plug was fine. I'll try to upload a picture later.
I'm a bit surprised at the recommendations to not do it yourself given this site typically prides itself on we can do anything. I guess that speaks to the risk versus reward of this particular repair. I'll watch a few more videos on the thread chaser as it seems pretty straightforward, but will likely take it to my trusted mechanic (hopefully he'll agree to work on the boat). The only Yamaha dealer in the area is not one I'm excited to have touch my boat again.

I actually do recommend you do it yourself, I would. But only caveat here is I personally would not try any type of thread repair (be it a thread chaser or some type of thread insert like heli-coil) without removing the head - getting metal in the cylinder could put you in a whole new can of trouble. So my only question would be how comfortable do feel about removing the head. Everyone has different mechanical skill levels so the recommendation to attempt repairs around here is based on that - you don't want to make it worse. But hell, its your boat and failure is sometimes the best instructor. I'd know.

 

[WilCo]

Most of the videos I’ve watched encourage coating the chaser with grease to catch any shavings.
doubt I’ll remove the head, but will look into it also.
Gonna call my mechanic in a little bit. Gotta finish up work calls first.

 

[WREKS]

Do you recall the previous plugs on Clys1&2 being harder to install than on Cyls3&4? Also, is it possible 1&2 were over-torqued?

 

[WilCo]

no - they all seemed to go in easy. Hand tightened and then put 1/4 turn with ratchet attached after that.

 

[WREKS]

I do not think they are cross-threaded. Perhaps, applying anti-seize and hand turning them in and out a few times to see if you make any progress.

 

[WilCo]

Just such a difference between the other 2. The other 2 go in simply. these cannot be tightened in by hand at all after initial threads grab

 

[Scottintexas]

you can read this one,

https://jetboaters.net/threads/spark-plug-hole-tap.13311/#post-231542

in that thread I used this on my lawn mower,
you insert it, expand it and then cut the threads as you back it out, so no shavings go down,

Amazon.com: Powerbuilt 14mm Back Tap Thread Repair Tool - 640811: Automotive

Buy Powerbuilt 14mm Back Tap Thread Repair Tool - 640811: Spark Plug Thread Repair Kits - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

.

 

[WilCo]

thanks @Scottintexas. That seems to be the other approach. I think I'm going to start with the threadchaser and then use the back tap thread repair tool next, if necessary.
My mechanic can look Monday/Tuesday next week, but it feels like pretty low risk honestly on the threadchaser from everything I'm seeing. (Stay tuned for the possible regret story).

 

[anmut]

Could you fashion some sort of temp gasket to prevent any shaving from falling in? The threadchaser is hollow, so what if you had a round piece of leather on fat head nail that you could push past the inlet, then hold up against the opening. If you could secure it you could at least see any pieces that fall as you come out and you'd have a chance to vac / pick them out.

 

[Weeb]

Put the grease on go in a little then back it out and clean it off, re apply grease and repeat going a little deeper each time.