Helicoil insert for a stripped spark plug hole: Difference between revisions

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The initial fix was to JB Weld a new plug into the head, in the hope that it would last for the rest of the life of the engine. Didn't work.

'''Before we go any further:''' This is not something for the faint of heart. ~~the~~ potential to mess up something really bad is very high. [https://www.ninja250.org/Dailyrider Dailyrider] has this advice for someone attempting this: "This is not a novice job. I've been a motorcycle mechanic for over 50 years and it wasn't an easy job for me. Modifying the tool and inserting the helicoils are both very intricate jobs. Take your time and think a lot about what you're doing."

'''Before we go any further:''' This is not something for the faint of heart. The potential to mess up something really bad is very high. [https://www.ninja250.org/Dailyrider Dailyrider] has this advice for someone attempting this: "This is not a novice job. I've been a motorcycle mechanic for over 50 years and it wasn't an easy job for me. Modifying the tool and inserting the helicoils are both very intricate jobs. Take your time and think a lot about what you're doing."

If you don't have a lot of mechanical experience, you may want to consider the alternatives:

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2. Find someone else to do it. It might be difficult, though. You'd have to find a good mechanic who is also a machinist, or a machinist who is also a good mechanic, and there are fewer people like that all the time. The cost of labor has gotten so high that it's no longer practical to make parts fit, as in the days before the Japanese started making bikes where every part made for a certain bike would fit every bike that the part was made for. People used to have to hand fit every part, but that generation is dying off now and it's harder to find someone like that.

Probably the best place to find someone to do the job would be a shop that specializes in old European bike repairs. Unless you can't find a good used head, it probably wouldn't ~~be would~~ be cost effective. At today's shop rates, both helicoils would likely run you over $500. The helicoil does make a stronger than stock hole though; the BMW factory used to helicoil all their plug threads.

Probably the best place to find someone to do the job would be a shop that specializes in old European bike repairs. Unless you can't find a good used head, it probably wouldn't be cost effective. At today's shop rates, both helicoils would likely run you over $500. The helicoil does make a stronger than stock hole, though; the BMW factory used to helicoil all their plug threads.

==What you need==

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[[image:CYLINDER HEAD.png|100px]]

The tower completes the plug cavity from the head to the valve cover. It's a part of the exhaust cam bearing. The two cam bearing bolts hold the bearing ~~wit~~ the tower to the head. There is an o-ring between the tower and the head, but it should be ok to reuse.

The tower completes the plug cavity from the head to the valve cover. It's a part of the exhaust cam bearing. The two cam bearing bolts hold the bearing with the tower to the head. There is an o-ring between the tower and the head, but it should be ok to reuse.

Because the tap has an extension on it that threads into the existing threads, the cylinder needs to be as close to bottom dead center as you can get it. When you're positioning the piston for the cylinder you're working on, turn the engine over until the intake valve rocker arm will just wiggle a little. That way both valves will be closed, but the piston will be well down in the bore, so it won't cause any interference with the Helicoil tap. Since the thread tap is a three-part tool (guide, reamer, and thread tap) there will be a good bit of it sticking down in the bore, and you don't want it running into anything.

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[[image: IMG_7358.jpg|150px]]

~~Now comes~~ the ~~fun~~ part~~. Take~~ the insertion tool ~~out and get~~ the ~~thread (string) into~~ the ~~cylinder. One way to do it~~ is ~~to ball up the thread and put~~ a ~~dab of grease on it to keep it bunched up, then put the guide into the~~ spark plug ~~well and use a piece of safety wire modified into~~ a ~~reverse~~ hook ~~to push it down~~. ~~You don't want any~~ of ~~the thread sticking up, because when you insert~~ the helicoil ~~it will cut the thread, and then all your hard work to get it in is gone~~.

The helicoil insert is screwed into the outer part of the insertion tool by the inner part of the insertion tool, which is like a very long spark plug thread with a very shallow hook on the bottom. This grabs the insertion tang on the bottom of the helicoil.

The ~~next step~~ is ~~to thread the insert~~ into the ~~newly cut threads. Hold the guide with a needlenose or some other similar means while turning~~ the insertion tool. ~~Once the insert is completely out of the guide tool~~, you ~~will be able to feel~~ the ~~tension release, so you know it is in. Take~~ the ~~guide and~~ insertion tool ~~out~~ and ~~find~~ the ~~top of~~ the ~~string and note~~ the ~~position. It should be right at~~ the ~~top~~ of the ~~threads, and~~ you ~~want it to be a half turn below so it doesn~~'~~t come unraveled. Once~~ you have the ~~position noted~~, ~~use the insertion tool~~ to ~~turn it another half turn, and verify that it is now at the other side of the hole~~.

The helicoil is screwed into the outer part of the insertion tool until it's at the very bottom thread. Next, you back out the center part of the insertion tool and use the reverse hook to poke the upholstery thread well down into the cylinder (while keeping the outer part of the insertion tool tight against the plug hole). When you're sure you have it well clear of getting trapped by the helicoil, you're ready to continue.

~~Next~~, ~~fish out~~ the ~~thread using~~ a piece of safety wire as a ~~hook~~, and ~~drape~~ it ~~over~~ the ~~side~~. ~~Using~~ a long, thin flathead screwdriver, knock the tang off while holding onto the string. If you're using a hemostat clamp instead, use that to hold onto the tang while breaking it off.

One way to do this is to ball up the thread and put a dab of grease on it to keep it bunched up, then put the guide into the spark plug well and use a piece of safety wire modified into a reverse hook to push it down. (To make a reverse hook, make a hook to pull with, then take 50% of it and bend it back the other way. This makes a hook to push with.) You don't want any of the thread sticking up, because when you insert the helicoil it will cut the thread, and then all your hard work to get it in is gone.

This next part is very, very critical: Screw the center part of the insertion tool in until it touches the insertion tang again, then you MUST hold the outer part of the insertion tool tight against the threads you cut in the head (in other words, make sure it isn't up on the shoulder of the plug recess). This is to keep it from skipping a thread. Use a needle nosed pliers to hold it down tight. Screw the helicoil in until tension is released on the outer part of the insertion tool; this indicates the coil is completely out of the outer part of the tool. The last coil of the helicoil should be level with the plug seat.

Once the helicoil is completely out of the outer part of the insertion tool and in the head, unscrew the center part of the insertion tool and remove the outer part of the insertion tool. Now look to see where the last thread of the helicoil ends. This is not easy to determine, as it's very hard to see down in that dark hole, even with a good flashlight. You want that end of the helicoil to be approximately 1/2 thread below the surface of the plug seat. This is very important. This will keep it from unscrewing with the plug. You also don't want to run it in too far, because you don't want the bottom thread of the helicoil to be clear of the threads in the head, which would tend to cause it to glow from combustion temperatures and cause pre-ignition.

Once you're sure you have the helicoil positioned correctly, fish out your upholstery thread with the hook (leave plenty of slack in it) then break off the insertion tang and retrieve it with your upholstery thread. To do this, use a long, thin, flathead screwdriver and knock the tang off while holding onto the string. If you're using a hemostat clamp instead, use that to hold onto the tang while breaking it off.

Once the tang is out, put the tower back on the spark plug hole, then do the other cylinder, if you need or want to. Once you are finished, reassemble everything with the [[Torque Values|proper torque]]. The torque on the cam bearing (tower) bolts is 104 inch-pounds (8.7 foot-pounds). Go for a test ride.

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 The initial fix was to JB Weld a new plug into the head, in the hope that it would last for the rest of the life of the engine. Didn't work.
-'''Before we go any further:''' This is not something for the faint of heart. the potential to mess up something really bad is very high. [https://www.ninja250.org/Dailyrider Dailyrider] has this advice for someone attempting this: "This is not a novice job. I've been a motorcycle mechanic for over 50 years and it wasn't an easy job for me. Modifying the tool and inserting the helicoils are both very intricate jobs. Take your time and think a lot about what you're doing."
+'''Before we go any further:''' This is not something for the faint of heart. The potential to mess up something really bad is very high. [https://www.ninja250.org/Dailyrider Dailyrider] has this advice for someone attempting this: "This is not a novice job. I've been a motorcycle mechanic for over 50 years and it wasn't an easy job for me. Modifying the tool and inserting the helicoils are both very intricate jobs. Take your time and think a lot about what you're doing."
 If you don't have a lot of mechanical experience, you may want to consider the alternatives:
@@ Line 13: / Line 13: @@
 . Find someone else to do it. It might be difficult, though. You'd have to find a good mechanic who is also a machinist, or a machinist who is also a good mechanic, and there are fewer people like that all the time. The cost of labor has gotten so high that it's no longer practical to make parts fit, as in the days before the Japanese started making bikes where every part made for a certain bike would fit every bike that the part was made for. People used to have to hand fit every part, but that generation is dying off now and it's harder to find someone like that.
-Probably the best place to find someone to do the job would be a shop that specializes in old European bike repairs. Unless you can't find a good used head, it probably wouldn't be would be cost effective. At today's shop rates, both helicoils would likely run you over $500. The helicoil does make a stronger than stock hole though; the BMW factory used to helicoil all their plug threads.
+Probably the best place to find someone to do the job would be a shop that specializes in old European bike repairs. Unless you can't find a good used head, it probably wouldn't be cost effective. At today's shop rates, both helicoils would likely run you over $500. The helicoil does make a stronger than stock hole, though; the BMW factory used to helicoil all their plug threads.
 ==What you need==
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 [[image:CYLINDER HEAD.png|100px]]
-The tower completes the plug cavity from the head to the valve cover. It's a part of the exhaust cam bearing. The two cam bearing bolts hold the bearing wit the tower to the head. There is an o-ring between the tower and the head, but it should be ok to reuse.
+The tower completes the plug cavity from the head to the valve cover. It's a part of the exhaust cam bearing. The two cam bearing bolts hold the bearing with the tower to the head. There is an o-ring between the tower and the head, but it should be ok to reuse.
 Because the tap has an extension on it that threads into the existing threads, the cylinder needs to be as close to bottom dead center as you can get it. When you're positioning the piston for the cylinder you're working on, turn the engine over until the intake valve rocker arm will just wiggle a little. That way both valves will be closed, but the piston will be well down in the bore, so it won't cause any interference with the Helicoil tap. Since the thread tap is a three-part tool (guide, reamer, and thread tap) there will be a good bit of it sticking down in the bore, and you don't want it running into anything.
@@ Line 81: / Line 81: @@
 [[image: IMG_7358.jpg|150px]]
-Now comes the fun part. Take the insertion tool out and get the thread (string) into the cylinder. One way to do it is to ball up the thread and put a dab of grease on it to keep it bunched up, then put the guide into the spark plug well and use a piece of safety wire modified into a reverse hook to push it down. You don't want any of the thread sticking up, because when you insert the helicoil it will cut the thread, and then all your hard work to get it in is gone.
+The helicoil insert is screwed into the outer part of the insertion tool by the inner part of the insertion tool, which is like a very long spark plug thread with a very shallow hook on the bottom. This grabs the insertion tang on the bottom of the helicoil.
-The next step is to thread the insert into the newly cut threads. Hold the guide with a needlenose or some other similar means while turning the insertion tool. Once the insert is completely out of the guide tool, you will be able to feel the tension release, so you know it is in. Take the guide and insertion tool out and find the top of the string and note the position. It should be right at the top of the threads, and you want it to be a half turn below so it doesn't come unraveled. Once you have the position noted, use the insertion tool to turn it another half turn, and verify that it is now at the other side of the hole.
+The helicoil is screwed into the outer part of the insertion tool until it's at the very bottom thread. Next, you back out the center part of the insertion tool and use the reverse hook to poke the upholstery thread well down into the cylinder (while keeping the outer part of the insertion tool tight against the plug hole). When you're sure you have it well clear of getting trapped by the helicoil, you're ready to continue.
-Next, fish out the thread using a piece of safety wire as a hook, and drape it over the side. Using a long, thin flathead screwdriver, knock the tang off while holding onto the string. If you're using a hemostat clamp instead, use that to hold onto the tang while breaking it off.
+One way to do this is to ball up the thread and put a dab of grease on it to keep it bunched up, then put the guide into the spark plug well and use a piece of safety wire modified into a reverse hook to push it down. (To make a reverse hook, make a hook to pull with, then take 50% of it and bend it back the other way. This makes a hook to push with.) You don't want any of the thread sticking up, because when you insert the helicoil it will cut the thread, and then all your hard work to get it in is gone.
+This next part is very, very critical: Screw the center part of the insertion tool in until it touches the insertion tang again, then you MUST hold the outer part of the insertion tool tight against the threads you cut in the head (in other words, make sure it isn't up on the shoulder of the plug recess). This is to keep it from skipping a thread. Use a needle nosed pliers to hold it down tight. Screw the helicoil in until tension is released on the outer part of the insertion tool; this indicates the coil is completely out of the outer part of the tool. The last coil of the helicoil should be level with the plug seat.
+Once the helicoil is completely out of the outer part of the insertion tool and in the head, unscrew the center part of the insertion tool and remove the outer part of the insertion tool. Now look to see where the last thread of the helicoil ends. This is not easy to determine, as it's very hard to see down in that dark hole, even with a good flashlight. You want that end of the helicoil to be approximately 1/2 thread below the surface of the plug seat. This is very important. This will keep it from unscrewing with the plug. You also don't want to run it in too far, because you don't want the bottom thread of the helicoil to be clear of the threads in the head, which would tend to cause it to glow from combustion temperatures and cause pre-ignition.
+Once you're sure you have the helicoil positioned correctly, fish out your upholstery thread with the hook (leave plenty of slack in it) then break off the insertion tang and retrieve it with your upholstery thread. To do this, use a long, thin, flathead screwdriver and knock the tang off while holding onto the string. If you're using a hemostat clamp instead, use that to hold onto the tang while breaking it off.
 Once the tang is out, put the tower back on the spark plug hole, then do the other cylinder, if you need or want to. Once you are finished, reassemble everything with the [[Torque Values|proper torque]]. The torque on the cam bearing (tower) bolts is 104 inch-pounds (8.7 foot-pounds). Go for a test ride.