Cylinder Head Heli-Coil - 950 - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 21 (permalink) Old 06-18-2019, 07:23 AM Thread Starter
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Cylinder Head Heli-Coil - 950

So I took my bike in for its first service since buying it, and was informed that the previous service cross-threaded the rear cylinder spark plug. They were able to get the new plug to torque to spec, and applied a bit of LocTite to make sure it held (the temporary stuff, not the chemical weld stuff). Has anyone had success using a heli-coil thread repair kit in this kind of application, or am I just going to have to replace the head? Seems that given the soft material heads are made from, this isn't that uncommon of a problem and there has to be a solution that doesn't involve a new head.
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post #2 of 21 (permalink) Old 06-18-2019, 07:28 AM
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Short answer is yes, heli-coil is exactly what you need for a stripped spark plug hole.

A previous owner must have been tightening the plugs without a torque wrench - its very easy to mess up the threads in alum in you dont use a torque wrench, and then the next time its easy to cross thread it.
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post #3 of 21 (permalink) Old 06-18-2019, 07:33 AM Thread Starter
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Thanks - my only concern was I was told there wasn't enough material to drill out the bigger hole required. I'm wondering if he was just trying to upsell a head replacement.

Yeah, I have learned the hard way myself that tight is tight, and too tight is broke. On the bright side, bike is running fine for now. Hate to have it in the shop this time of year!
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post #4 of 21 (permalink) Old 06-18-2019, 07:46 AM
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If Lesblank does not pick up on this when its morning in Houston, maybe send him a PM and ask for his input.

Im not sure if the threadlock will keep the plug in place. I would not take any road trips till you find out for sure. There is an incredible amount of pressure in the cylinder when the mixture burns, I have heard of people having spark plugs blow out of their heads in cars (because they were stripped out).

To fix it the hole is normally drilled out larger and tapped, and this is exactly what they are for, so unless someone really got in there and buggered it up a heli-coil should fix it properly.
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post #5 of 21 (permalink) Old 06-18-2019, 07:55 AM Thread Starter
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Thanks for the info. Yeah, I don't think having a rear cylinder plug blow out into my crotch would make for a very pleasant ride.
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post #6 of 21 (permalink) Old 06-18-2019, 08:29 AM
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Good morning, a little busy at work and just jump on site at break. My first try would be thread chaser. With any luck there are enough threads to clean. Make sure and put some grease in side grooves to catch metal shavings from going into cylinder. Lots of utube videos out there.



Second option would be a make a thread kit. I've used these on aluminum race heads and work pretty good.



Last option would be heli coil. The heli coil is actually the best solution but more labor intensive. They make thin wall heli coil so should be plenty of material to drill insert. Good luck and keep us informed.

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post #7 of 21 (permalink) Old 06-18-2019, 08:51 AM Thread Starter
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Thanks for the info lesbank. I'll let you guys know what I end up doing. Guess if I ever buy another used bike, I'll remove the damn spark plugs to make sure the previous owner didn't bugger them up!
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post #8 of 21 (permalink) Old 06-18-2019, 08:59 AM
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It can be hard to tell - its best to talk to the previous owner, ask him who did the maintenance on the bike, what kind of experience and tools he had

when I got Ursa it was running rough. When I decided to change the plugs I discovered they were only finger tight, which did no harm, but yeah... yikes!

Finding a used bike with low miles that is completely stock is gold - the less a person did to the bike, the less chances for them to mess things up.

Last edited by KCW; 06-18-2019 at 09:02 AM.
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post #9 of 21 (permalink) Old 06-18-2019, 10:02 AM Thread Starter
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post #10 of 21 (permalink) Old 06-18-2019, 10:07 AM
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I have successfully used them before. Good product.

2001 Vstar 1100 Classic (sold), Cobra Slash Cut full exhaust, Dropped 1 inch with lowering links, ORK, 4.5 inch handlebar risers, Ultimate passenger seat, Passenger pegs moved forward 4 inches, Handlebar clock, KN air filter, Viking saddlebags, Additional rear lighting
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