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If I were you, now is a good time to find a good engine machine shop near you, have them chase the thread for you, and build a little rapport with someone that can help you through the years. The old-timers are really good and know a lot of tricks with little jobs like this.
If it is just one spark plug that won't screw in it could be a nicked thread on THAT spark plug. It makes more sense the spark plug threads got damaged than the threads in the cylinder head.
I tried multiple spark plugs in that particular chamber; it's the chamber's threads that are off.
Wait wait wait even though advice here is generally good, you need to tell us more before proceeding!
Can you start a known good plug on the threads? Or is it sour right from the very beginning? I guess you can't get it to screw in any which way you position it? If it is screwed up right from the start, it might be wise to take that head off and see if just a little small file work will remove the damage! If you are getting a few threads with the chaser, then proceed! And test the chaser to get oriented to the correct position! If what you got is allowing you to run the thread chaser in a few turns, I really hope that is straight up and down to the hole!
If the file cleans up the problem, still chase the thread! Also usually any minute filings will blow out the exhaust, but you can stick a needle or something smaller than the hole attachment to air compressor and blow air into the cylinder forcing metal shavings out! For this should really be needed, but I am a perfectionist!
Last edited by TCracingCA; 12-27-2017 at 07:02 PM.
Wait wait wait even though advice here is generally good, you need to tell us more before proceeding!
Can you start a known good plug on the threads? Or is it sour right from the very beginning? I guess you can't get it to screw in any which way you position it? If it is screwed up right from the start, it might be wise to take that head off and see if just a little small file work will remove the damage!
The plugs start but only go 1/3 to 1/2 of the way in and then it starts to get tight enough that I don't want to force it further without running the thread chaser through. I had maybe 2 other spark plug holes that got a little bit tight and then quickly got nice with far less pressure than this one.
Just one spark plug hole in one head has this problem and it has it regardless of which spark plug goes in there. A spark plug that works fine in another hole still gets quite tight 1/3 to 1/2 way screwed in in this particular hole.
The plugs start but only go 1/3 to 1/2 of the way in and then it starts to get tight enough that I don't want to force it further without running the thread chaser through. I had maybe 2 other spark plug holes that got a little bit tight and then quickly got nice with far less pressure than this one.
Just one spark plug hole in one head has this problem and it has it regardless of which spark plug goes in there. A spark plug that works fine in another hole still gets quite tight 1/3 to 1/2 way screwed in in this particular hole.
Adam
Go slow and I actually would avoid oil! The oil can tend to also cause it to slip back up, jump threads! Not feeling it myself, It sounds like you have enough chance for success with the amount of threads you can engage! I would try to not put side forces on it with like a ratchet or wrench, but put like a socket on a t-bar. Go in a little and then turn it back out repeatly many many many times back it out after a slight advance! If you seem to think you are cutting through excess material, judgement but it sounds like they used a taper tap or something, and I if encountering something blatant would go get a square tap! My comments on the first post assumed just a section damaged! I would blow it out if you think excess material will get pushed into the cylinder, also you might take it completely back out and clean the thread chaser to ensure it is clean and not beaffevted by excess material getting and piling up on the threads! Whatever you do, you want to use smaller tools to have better sense of how you are doing! Most guys just grab the biggest socket wrench and go all gorilla on stuff like this! I work on my engines more like a surgeon! If I could rethread that by hand pressure Vice tools, I would try that first, but those tools don't give you enough to grab onto! So I am looking for the lightest tool that will allow that unit to cut threw. I want the tool cutting ability to be doing the work!
Last edited by TCracingCA; 12-27-2017 at 07:23 PM.
Just a thought. Call the head manufacturer or Jegs technical support and explain the problem. See what their suggestion would be. I dont think you want to risk damaging the head there at that spot. If you did i cant imagine how tough it would be to helicoil a spark plug hole. Maybe not bad but would not want to have to do it. I would vite for a machine shop since the head is off the motor.
As mentioned a thread chaser is different from a tap. It should not removed any material except for the part that is damaged which usually is not that much to cause what you are describing. Can you take a flash light and see into the threads to see exactly what is wrong?
I would use a little 3&1 oil just for kicks.
Run the tread chaser backwards (counterclockwise) to start it. You will feel the starter thread engage and then start moving it in. I do this with bolts too that I have a hard time getting started just because of the location or accessibility and I do this with all my spark plugs just to make sure I don't damage my head (which are aluminum).
My suggestion would be to call Jegs before you proceed and see if they will just warranty the head. If not let them give you suggestions on how to proceed, that way if their procedures damage the head you were following their direction. Make sure you get the name of the tech you talk to and record date and time of your call.
If they suggest to use a thread chaser purchase one they sell or recommend.
Then I would take the head to a good machine shop and let them do it. They are probably better equipped to do the job and won't just throw it up on a bench and wing it like you would, no offense.
Ask the machine shop to inspect the threads prior to chasing them, so if the threads in the head aren't right you can contact Jegs again and go from there.
You did right by stopping asking for advice and not just powering the plug in.
Good luck
It was mildly scary and I was kinda shocked with how much gunk came out of a couple of the spark plug holes but they go in nice and smooth now!I just used a bit of wd40 and my 4 year old followed behind me with qtips cleaning up behind me.Then I filled each chamber with water to check for leaks.Today I’ll remove any sharp spots around the chambers/ in the final threads.Thanks again, folks; I’ve never used a thread chaser and am not sure I could work up the nerve to try this stuff without the explanations and encouragement.Adam
Glad to hear all worked out.
I had a similar issue after cross threading a plug due to very confined space for my oversized hand to start the plug thread correctly.
I realised the thread was cross threaded, but try as I might I could not get the plug to start in the correct groove.
Using a tap or thread chaser wasn't going to solve the problem as it would cut a new thread and create a lot of swarth unless I removed the head and used the chaser from the chamber side out.
What was supposed to be a simple half hour changeover of spark plugs was becoming a tear down of the top end.
What I needed was a way to chase the thread from the inside outwards without having to remove the head.
That a very useful tool to know about. Although not useful for the issue that the OP had, I think it work really well for the more typical problem of cross threading the entry threads.
12-27-2017, 03:04 PM
