• Ciao Guest - You’ve landed at the ultimate Guzzi site. NEW FORUM REGISTRATIONS REQUIRE EMAIL ACTIVATION - CHECK YOUR SPAM FOLDER - Use the CONTACT above if you need help. New to the forum? For all new members, we require ONE post in the Introductions section at the bottom, in order to post in most of the other sections. ALWAYS TRY A SEARCH BEFORE STARTING A NEW TOPIC - Most questions you may have, have likely been already answered. DON'T BE A DRIVE-BY POSTER: As a common courtesy, check back in and reply within 24 hours, or your post will be deleted. Note there's decades of heavily experienced Guzzi professionals on this site, all whom happily give endless amounts of their VALUABLE time for free; BE COURTEOUS AND RESPECTFUL!
  • Be sure to see the GTM STORE link also above for our 700+ product inventory, including OEM parts and many of our 100% Made-in-SoCal-USA GTM products and engine kits. In SoCal? Click the SERVICE tab above for the best in service, tires, tuning and installation of our products or custom work, and don't miss our GT MotoCycles® (not) art on the BUILDS tab above. WE'RE HERE ONLINE ONLY - NO PHONE CALLS MADE OR RECEIVED - DO NOT EMAIL AND ASK QUESTIONS OR ASK TO CALL YOU.
  • There is ZERO tolerance on personal attacks and ANY HYPERLINKS to PRODUCT(S) or other competing website(s), including personal pages, social media or other Forums. This ALSO INCLUDES ECU DIAGnostic software, questions and mapping. We work very hard to offer commercially supported products and to keep info relevant here. First offense is a note, second is a warning, third time will get you banned from the site. We don't have the time to chase repeat (and ignorant) offenders. This is NOT a social media platform; It's an ad-free, privately funded website, in small help with user donations. Be sure to see the GTM STORE link above; ALL product purchases help support the site, or you can upgrade your Forum profile or DONATE via the link above.

Spark Plug Thread Stripped on Removal

C

countryguz

Tuned and Synch'ed
GT Contributor
Joined
Oct 1, 2023
Messages
51
Location
virginia
I was removing a spark plug from the engine and the last 1/4” or so of the unscrewing was extremely tight. It finally came out and I noticed the mucked up threads. Initially, it was coming out just fine, the first 1” of threads are clean and (in tact) but the last 1/4” was stripped or almost no threads - somewhat smooth. The upper threads were just fine, but the last threads bit the dust.

Background: I bought the bike last year in Sept. It had 2000 miles on it and it is a 2014 CA1400. It was barely used so I have been doing tires, fluids, and I decided it was time to check the timing as it was a little running a little rough. I now have 9600 miles on it. So, the first three plugs came out real easy with no real effort. When I removed both of the head covers the bolts were tight, but not sure if they had ever come off before I took them off. Cud have been, I don’t know. So, I have ordered new spark plugs and I am unsure how to go about inserting new plugs. Do I need to clean the threads of the odd plug hole or use something like a back tap (I think that’s it)? I don’t understand this thread damage to the spark plug. I wud have thought that all the threads would have been damaged and not just the last 1/4” of the threads. I wanted to get some advise on my next move.
 
These are the two from the Left Cylinder. The tape signifies the bottom plug. The mucked up plug comes from the center. I took images from several sides of the mucked up plug. It started coming out fine and easy then there was resistance then I turned it in and out and finally it came out under resistance. These are all NGK-LMAR8F-9 plugs and do not know if these are original from factory or were installed before I bought it. Don't know if this plug version "-9" is new or old.
 

Attachments

  • IMG_2269 small.jpg
    IMG_2269 small.jpg
    73.5 KB · Views: 19
  • IMG_2267 small.jpg
    IMG_2267 small.jpg
    73.4 KB · Views: 18
  • IMG_2268 small.jpg
    IMG_2268 small.jpg
    82.8 KB · Views: 19
  • IMG_2266 small.jpg
    IMG_2266 small.jpg
    75.8 KB · Views: 18
  • IMG_2265 small.jpg
    IMG_2265 small.jpg
    73.7 KB · Views: 17
  • IMG_2264 small.jpg
    IMG_2264 small.jpg
    71.2 KB · Views: 18
Wow! That is unbelievable thread galling.

How somebody could be so dumb as to use a wrench to apply so much force to turn in a spark plug, in order to gall those threads that bad is staggering. 🤦‍♂️

I would get a spark plug tap, slather it with Vaseline to catch any cut metal and run it into your spark hole to clean up the threads.

The next spark plug that is installed should be seated fully with nothing but fingers until it goes all the way in, and then only tightened just enough. You do not over tighten spark plugs.
 
Last edited:
What happens, how much resistance do you get if you try and hand thread an old/new plug into the hole that mess came out of ?
I would imagine you won’t be able to even start the plug.
For the last threads of the plug to be fouled like that it had to happed at the top/exit of the hole ?
That’s all my brain can imagine, but why / how ??
 
MotoGuzziFan said:
Wow! That is unbelievable thread galling.

How somebody could be so dumb as to use a wrench to apply so much force to turn in a spark plug, in order to gall those threads that bad is staggering. 🤦‍♂️

I would get a spark plug tap, slather it with Vaseline to catch any cut metal and run it into your spark hole to clean up the threads.

The next spark plug that is installed should be seated fully with nothing but fingers until it goes all the way in, and then only tightened just enough. You do not over tighten spark plugs.
Click to expand...
Can you give me examples of the correct tool needed? I understand there are differences in thread tools. Some are for cleaning and some are for deburring and some are for re-cutting?
 
DeadEye said:
What happens, how much resistance do you get if you try and hand thread an old/new plug into the hole that mess came out of ?
I would imagine you won’t be able to even start the plug.
For the last threads of the plug to be fouled like that it had to happed at the top/exit of the hole ?
That’s all my brain can imagine, but why / how ??
Click to expand...
I have not tried to re-insert any new plugs or even an old plug just yet. But I assume that there is or was something in the threads that mucked up this plug so I need to clean first and not push anything into the cylinder. I cannot visibly see anything without good light, just yet. I have new plugs en-route and do not want to hurry anything until I learn the correct remediation process and get the right tools. If you have a good tool recommendation I am all ears.
 
Similar thing happened on my car's spark plug hole. Ended up needing to Helicoil it. It's been great ever since which has been maybe 70k miles. Like the prior post said make sure no metal flakes go into the hole which may be the hardest part. Looks like you have 2/3 of the thread left. Not sure how viable it would be just to clean the threads off the spark plug and just put it or a new one back in. Not sure if 2/3 thread is mechanically good enough to hold a spark plug in place with the engine doing it's thing.
 
FWIW: that huge galled area has most certainly mucked up the entire threads in the head when you backed it out. They may be ruined. You absolutely need to chase the threads completely. This tool will get you where you need to be.
 
The tool you are referring to is the power built noted above? The threads are M10-1 (10mm with pitch 1) on the spark plug. I double checked those today. Power built does not make anything smaller than 12mm from what I have seen so far, maybe, unsure as of now??? Will check other vendors.

Quite possible have to use helicoil. Not my favorite choice right now. I did one in a Honda car once, but I removed the head for that. I am not sure about removing the head on this bike unless it is straight forward with four bolts?

Possibly chase the threads while on the bike with chase tool in leiu of the power built if I cannot find one size that works in my case. I’ll check on other sources.
 
I did some looking at other vendors for the back tap option and I found something from DPTOOL that might just work. For those who have done this before, do I have enough work space to be able to back tap this properly? Will I be able to get my fingers and tools in the right area so that I do this correctly?

The hole is 4.5" and the tool is right at 4.5" in length. I don't want to fumble around and muck the job, but do I need a longer tool? Screen Shot 2024-08-22 at 17.53.53.png Image-12.png
 
I did check all the spark plugs and they all match as per the Maint book. I am just curious if these were the originals from the factory or someone replaced them before me. I am replacing the air filter as well and it is the original from the factory. Anyway, I was not familiar with this backtap device until now so I have looked around and found a few tools to order. Also, I did see a few video's already and it seems straight forward and now I understand the procedure. I'll take it slow and I should try it next week when all parts are in hand.
 
I do remember reading that there were phoney Chinese NGK plugs being sold on fleabay that were very hard to detect. The bad ones you have could possibly be some of these. A slightly imperfect thread or coating could cause gauling.
 
But the strangest part is that it was “Ok” when initially coming out and only “had the problem “ during / With that last 1/4 “
The threads are engaged for the entire plug are they not ?
 
Last edited:
That's why I asked about it possibly being the wrong plug for the bike. If it was too long, the threads sticking into the cylinder would distort from the heat. Although, I'd also expect it to hit the piston.
 
All the plugs were the same size and make as required for the bike. The plug boot was all the way inserted as were all the boots/plugs. I am guessing at some point the plugs were changed after delivery - its only as assumption. I was curious to know what the actual markings would have been for the factory plugs. The plugs I pulled out are labeled "NGK-LMAR8F-9" but were the plugs from the factory labeled "NGK-LMAR8F" without the "-9"? The new plugs I ordered are "NGK-LMAR8F-9" as well from a reputable source.
 
It's a 2014 bike bought with 2k miles on it, so those plugs may well have been in there from the factory. That's 10 years ago. I like to replace my plugs every few years max just so a) they don't fail me and b) they don't seize. I don't use anti seize as I prefer to follow NGK advice.
 
You must log in or register to reply here.
Back
Top