Stripped spark plug hole - Honda TRX Forum
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post #1 of 29 Old 07-12-2018, 10:46 PM Thread Starter
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Stripped spark plug hole

I got a 04 Foreman 450. I've heard of repair kits for the plug holes. I've never used one, tho. I see quite a few kits on ebay, but, I don't really know which one I need. I guess first I need to know the thread size and pitch. Anyone know what that is offhand?
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post #2 of 29 Old 07-13-2018, 02:20 AM
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12mm dia - 3/4 reach
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post #3 of 29 Old 07-14-2018, 01:28 PM Thread Starter
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Originally Posted by Here 2 help View Post
12mm dia - 3/4 reach
Thank you. Is the thread pitch standard of spark plugs? Any recommendations on a repair kit? I found this one. Right in my price range.

https://www.ebay.com/itm/Spark-Plug-...ug+thread.TRS0
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post #4 of 29 Old 07-14-2018, 02:02 PM
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Yes, the thread pitch is standard on spark plugs - 1.25 on 12 and 14mm plugs, 1.0 on 10mm plugs and 1.5 on 16mm plugs

There's a reason the kit you found on Ebay is cheap - it's a cheap fix that's not very good quality wise. I've seen those inserts come out with the spark plug.

A better fix is a Helicoil thread insert - more permanent and correctly installed will never come out unless the spark is grossly over tightened. The Helicoil provides a stronger thread than the original hole, but unless you want to take the head off, it's best to take it to an experienced mechanic to have it done right. In my shop, I set the engine about 90 degrees before TDC of the exhaust stroke with the exhaust valve open - I then connect the shop compressed air supply to the exhaust outlet of the muffler - with shop air flowing through the engine and out the spark plug hole, I use a special combination piloted reamer tap to cut the hole to an oversize and thread it for the insert in a single pass. The airflow blows the chips from the reaming and threading out of the cylinder via the flutes in the tap. That was the easy part. Now you use a special tool to pre-wind the Helicoil to insert it into the spark plug hole. When the Helicoil is nearly all the way in, you remove the pre-winder and set the Helicoil about 1/2 thread below the surface of the head. Now the hard part; there's a tang that the insertion tool hooks on to screw the Helicoil insert into the hole that has to be broken off and removed from the cylinder. You have to ensure the tang is removed or engine damage can result. If the head is removed, then it's a simpler job to remove the tang.

You can attempt the repair yourself, or bite the bullet and have it repaired by an experienced mechanic. It might be cheaper initially to repair it yourself, but I might be cheaper in the long run to have it professionally repaired. It's your machine and your call, but a cheap fix is usually not good and a good fix is not cheap.
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post #5 of 29 Old 07-14-2018, 02:10 PM Thread Starter
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Quote:
Originally Posted by Here 2 help View Post
Yes, the thread pitch is standard on spark plugs - 1.25 on 12 and 14mm plugs, 1.0 on 10mm plugs and 1.5 on 16mm plugs

There's a reason the kit you found on Ebay is cheap - it's a cheap fix that's not very good quality wise. I've seen those inserts come out with the spark plug.

A better fix is a Helicoil thread insert - more permanent and correctly installed will never come out unless the spark is grossly over tightened. The Helicoil provides a stronger thread than the original hole, but unless you want to take the head off, it's best to take it to an experienced mechanic to have it done right. In my shop, I set the engine about 90 degrees before TDC of the exhaust stroke with the exhaust valve open - I then connect the shop compressed air supply to the exhaust outlet of the muffler - with shop air flowing through the engine and out the spark plug hole, I use a special combination piloted reamer tap to cut the hole to an oversize and thread it for the insert in a single pass. The airflow blows the chips from the reaming and threading out of the cylinder via the flutes in the tap. That was the easy part. Now you use a special tool to pre-wind the Helicoil to insert it into the spark plug hole. When the Helicoil is nearly all the way in, you remove the pre-winder and set the Helicoil about 1/2 thread below the surface of the head. Now the hard part; there's a tang that the insertion tool hooks on to screw the Helicoil insert into the hole that has to be broken off and removed from the cylinder. You have to ensure the tang is removed or engine damage can result. If the head is removed, then it's a simpler job to remove the tang.

You can attempt the repair yourself, or bite the bullet and have it repaired by an experienced mechanic. It might be cheaper initially to repair it yourself, but I might be cheaper in the long run to have it professionally repaired. It's your machine and your call, but a cheap fix is usually not good and a good fix is not cheap.

Alright. I watched a youtube vid on the repair. It had some kind of grease to keep the chips from falling inside. I like the air in the pipe idea. I'm pretty mechanically inclined. I'm sure I can do this. I just never done it and I wanna get the right kit. I may just take the head off. That's pretty easy. Then I don't have to worry
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post #6 of 29 Old 07-14-2018, 03:13 PM
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Taking the head off is assuredly the best option. I hate installing a Helicoil in any engine with the head on and there some that are just damn near impossible. A TRX400EX is one of those and a CRF250 is best having the head replaced because the spark plug is a 10mm and has an unthreaded shoulder and sits in a well about 6 inches deep.

I have tried the "grease" idea and adopted the compressed air method because the grease is messy, can fall into the cylinder, lubricates the threads and can cause the repair to fail. If you opt to grease the tap, you have to remove all the grease from the threads before installing the Helicoil or insert and if an insert is used, it has to be locktite-ed in to assist in inadvertent removal when replacing the spark plug. One thing I didn't mention - the first time I saw an insert repair - a guy came to me with an old Triumph 500 Daytona and said his spark plug came out while he was riding. I was trying to figure out what kind of spark plug he had in it because the threads were different on the plug that came out than on the replacement plug. That's when I figured out the old plug had a threaded sleeve on it. I used vice grips to get the sleeve off the plug. The insert had to be put on the new plug and installed into the head with the spark plug. The vice grips deformed the threads on the insert just enough the insert never came out again, but that cylinder lost a tiny bit of compression due to leakage past the insert. Just became dirty around the plug while running due to the leakage.

I'm not a fan of insert type repairs.
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post #7 of 29 Old 07-15-2018, 12:15 AM Thread Starter
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Originally Posted by Here 2 help View Post
Taking the head off is assuredly the best option. I hate installing a Helicoil in any engine with the head on and there some that are just damn near impossible. A TRX400EX is one of those and a CRF250 is best having the head replaced because the spark plug is a 10mm and has an unthreaded shoulder and sits in a well about 6 inches deep.

I have tried the "grease" idea and adopted the compressed air method because the grease is messy, can fall into the cylinder, lubricates the threads and can cause the repair to fail. If you opt to grease the tap, you have to remove all the grease from the threads before installing the Helicoil or insert and if an insert is used, it has to be locktite-ed in to assist in inadvertent removal when replacing the spark plug. One thing I didn't mention - the first time I saw an insert repair - a guy came to me with an old Triumph 500 Daytona and said his spark plug came out while he was riding. I was trying to figure out what kind of spark plug he had in it because the threads were different on the plug that came out than on the replacement plug. That's when I figured out the old plug had a threaded sleeve on it. I used vice grips to get the sleeve off the plug. The insert had to be put on the new plug and installed into the head with the spark plug. The vice grips deformed the threads on the insert just enough the insert never came out again, but that cylinder lost a tiny bit of compression due to leakage past the insert. Just became dirty around the plug while running due to the leakage.

I'm not a fan of insert type repairs.
Thanks so much for your help. My buddy that lives up in the hills has a kit that I'm going to get tomorrow. However I have another issue. This is with an 06 trx 500 4x4. I got these quads in a trade. The 500 needed a carb clean due to sitting a while. So, I got it to run, but there is a lot of noise coming from what seems to me the top part of the engine. It's a tinny, rattling type sound. Idk how many hours are this quad. It doesn't have hour meter on it. Btw the 450 has, IIRC, ( I took the battery out to put in the 500, else I could double check it) about 4,000 hours on it! So, what do you think about the noise? Cam chain/tensioner? Valves out of adjustment? Probably wouldn't run, if that was the case? Oh, and the spark plug broke(bkr5e) when I took it out, and it's too late in the day to get another, so I put a ngk br8e in it just to see if it would run. That can't be the source of the noise could it?
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post #8 of 29 Old 07-15-2018, 12:59 PM
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It's highly unlikely the spark plug is the source of the noise - it's more likely spark knock caused by stale fuel or it might end up being something else, but cyber diagnosis is difficult. It is a push rod motor, so it might be valve adjustment. Let me know what you figure out.
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post #9 of 29 Old 07-15-2018, 01:55 PM Thread Starter
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It's highly unlikely the spark plug is the source of the noise - it's more likely spark knock caused by stale fuel or it might end up being something else, but cyber diagnosis is difficult. It is a push rod motor, so it might be valve adjustment. Let me know what you figure out.
Ya, I noticed while looking at a diagram of the cylinder head that it had pushrods. I will let you know. I'm gonna tear into it today.
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post #10 of 29 Old 07-15-2018, 08:00 PM Thread Starter
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So I watched this video. Same sound that mine makes. The valves were way way out. Like they probably a good .062 instead of .006! I adjusted them and it still makes a loud sound. Not as much noise, I think that the adjustment quieted it down some. This quad has been sitting for a long period. I thought maybe a stuck/collapsed ring(s). I did a compression test and it came up to 50 psi. I put a teaspoon or so of oil down the plug hole, cranked it over a bit and checked again and it came up to 90 psi.

Oh and to get T.D.C I put a small rod in the plug hole after I saw the intake valve open, and the piston is on it's way down. When it comes back up that would be compression stroke, right? Same as t.d.c?

I think my next step is to take the valve cover off and see what's going on. It sounds like the cam/rocker arm area is not getting oil. The valve adjusters seem awfully dry.


https://youtu.be/GAcgWc4THsA
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