Ah s%$#. Broken bolt. - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 11 (permalink) Old 03-06-2020, 07:17 PM Thread Starter
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Thumbs down Ah s%$#. Broken bolt.

Hey all, I screwed up. I was halfway through coastering my reed valves on the cylinder when one of the bolts holding the valve on snapped at the head. I wasn't even going hard on it, maybe 15 pounds of force. All the other bolts came out bent so I'm thinking they just got weak after 30 years of sitting. Anyways, I tried vice grips but they just ate away at the metal. Before we go through the hassle of towing and welding a nut to it, does anyone have any ideas on how to get it out? Is a cover on the reed valve necessary?

Thanks.
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post #2 of 11 (permalink) Old 03-06-2020, 08:45 PM
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I've had good luck using an angle grinder to put flats on the sides of remaining threads sticking out, then using vice grips or wrench to back it out. Hit with penetrating oil and let it sit first.

You could try drilling out and using a bolt extractor, but risk damaging the engine casting. Might not matter much since it's not a real load bearing hole, so you could just clean up any damage by chasing with a tap once the bolt is out.

Some people swear by dissolving the steel out of the aluminum by using a heated alum solution, but I've not had good luck with that method.

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post #3 of 11 (permalink) Old 03-06-2020, 09:50 PM Thread Starter
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I've had good luck using an angle grinder to put flats on the sides of remaining threads sticking out, then using vice grips or wrench to back it out. Hit with penetrating oil and let it sit first.

You could try drilling out and using a bolt extractor, but risk damaging the engine casting. Might not matter much since it's not a real load bearing hole, so you could just clean up any damage by chasing with a tap once the bolt is out.

Some people swear by dissolving the steel out of the aluminum by using a heated alum solution, but I've not had good luck with that method.
Welp, we tried welding a nut on 6 different times, as well as cooking it with an acetylene torch. Of course, the bolt just kept breaking, and now I'm stuck with it being perfectly flush. I'll try an extractor.
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post #4 of 11 (permalink) Old 03-06-2020, 09:59 PM Thread Starter
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How important is an airtight seal on the cover?
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post #5 of 11 (permalink) Old 03-07-2020, 09:04 AM
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Is a cover on the reed valve necessary?

Thanks.
Not absolutely necessary if you find a way to block the port in the head. The right sized bolt would work, there's not a lot of pressure coming from that port.

If you can drill a straight hole through the bolt, the threads usually relax enough to let the bolt spin out. Reverse twist drill bits are perfect for this. Friction, heat, and force going to the left will often spin the bolt out with the drill bit.

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post #6 of 11 (permalink) Old 03-07-2020, 03:34 PM
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Yes it does need to be air tight. Not being air tight will result in an exhaust leak near the head, which will damage the valves. I suggest using a sharp punch (or scratch awl) to make a dimple right in the center of the broken bolt. Then use reverse drill bits in increasing sizes to slowly drill out a hole in the middle of the bolt. Don't get too close to the edge, and remember that even though it may be really close, the hole will not likely be in the exact center of the bolt. Try tapping in a small straight screwdriver into the hole drilled in the bolt and turning it out. I don't like easy outs, they tend to be very hard and brittle and break easily, and because they are made out of such hard metal, cannot be easily drilled out. If you wind up damaging the internal threads in the head, they can probably be repaired with a HeliCoil or TimeSert. Just be really careful not to let the drill go in at an angle and wallow out the hole to where it cannot be repaired.

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post #7 of 11 (permalink) Old 03-07-2020, 08:51 PM Thread Starter
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Not absolutely necessary if you find a way to block the port in the head. The right sized bolt would work, there's not a lot of pressure coming from that port.

If you can drill a straight hole through the bolt, the threads usually relax enough to let the bolt spin out. Reverse twist drill bits are perfect for this. Friction, heat, and force going to the left will often spin the bolt out with the drill bit.

https://www.amazon.com/Tools-Cobalt-.../dp/B0002NYBJG
What are your thoughts on using a self-tapping screw where the old bolt was?

And I've looked at the port a bit and don't quite understand how a bolt could block it off. Is the port you're talking about part of the head or part of the valve? Thanks.
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post #8 of 11 (permalink) Old 03-07-2020, 09:42 PM
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If you are talking about the reed valve cover bolts, it is not the bolt that plugs the exhaust. It is the rectangular cover with a hose fitting on it that plugs the exhaust. I didn't bother to remove the cover, I just removed the hose, and capped it with one of these https://shop.advanceautoparts.com/p/...100/22140619-P I just wanted those horrible hoses off my bike.

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post #9 of 11 (permalink) Old 03-07-2020, 09:46 PM
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What are your thoughts on using a self-tapping screw where the old bolt was?

And I've looked at the port a bit and don't quite understand how a bolt could block it off. Is the port you're talking about part of the head or part of the valve? Thanks.
The port is just a hole, inside the pocket in the head, behind where the reed box bolts on. Look around the bottom of the inside of the pocket. Been a while, but I think the hole may be around 1/8".

Yes I think a self-tapping bolt/screw of the right size would work. You don't want to force something that's too large. There's a thread here where we discussed different ways to plug this hole, don't know if it can be found. You can make a self-tapping bolt by simply cutting a diagonal slash on one side. Red Loctite on the threads would make it more permanent.

I started mine with the reed box removed and it just spits a tiny bit of hot air, I could seal it off with my finger, wearing a glove.

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post #10 of 11 (permalink) Old 03-08-2020, 12:00 PM Thread Starter
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Quote:
Originally Posted by Spockster View Post
Quote:
Originally Posted by rerb View Post
What are your thoughts on using a self-tapping screw where the old bolt was?

And I've looked at the port a bit and don't quite understand how a bolt could block it off. Is the port you're talking about part of the head or part of the valve? Thanks.
The port is just a hole, inside the pocket in the head, behind where the reed box bolts on. Look around the bottom of the inside of the pocket. Been a while, but I think the hole may be around 1/8".

Yes I think a self-tapping bolt/screw of the right size would work. You don't want to force something that's too large. There's a thread here where we discussed different ways to plug this hole, don't know if it can be found. You can make a self-tapping bolt by simply cutting a diagonal slash on one side. Red Loctite on the threads would make it more permanent.

I started mine with the reed box removed and it just spits a tiny bit of hot air, I could seal it off with my finger, wearing a glove.
Found it. That will be my plan B if what I just did doesn't work. I drilled out the old bolt with (I think) a 5/32 bit, and then tapped it with an 8-32 NC tap. I'm just hoping the smaller size will still allow enough torque to create an airtight seal. Thanks everyone for your help!
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