How to prevent cross-threading fasteners


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How to prevent cross-threading fasteners

Post by WingAdmin » Thu Jan 31, 2013 9:09 pm



Cross-threading is more than just an annoyance - cross-threading a fastener can cause serious, expensive damage to your motorcycle! Cross thread something like a spark plug into the soft aluminum head (very easy to do!) and you will be in for a world of hurt trying to fix it. Even cross-threading everyday fasteners like ordinary nuts and bolts can do damage.

What is cross-threading? It means the threads on the male part of a rotating fastener aren't correctly lined up with the female part of the fastener. It's usually caused when one of the parts of the fastener is slightly tilted when it is tightened. Instead of the lands and grooves of the threads lining up and sliding along one another, the threads cut across one another, causing damage. The more it's forced, the more damage occurs, to the point where the fastener becomes "stripped" - the threads are so damaged, that the fastener will no longer tighten correctly.

(Stripping a fastener can also occur when it is tightened beyond design limits, causing the threads to break - this is why you should use a torque wrench!)

Spark plugs are infamous for cross-threading. The fork tube covers (wide, thin threads) are also easily cross-threaded. The larger in diameter the fastener, and the finer the threads, the more susceptible the fastener is to cross-threading. Not to say that coarse (wide, more distant) threaded fasteners can't be cross-threaded! You can even cross-thread the lid on a peanut butter jar if you try hard enough!

Crossthreaded spark plug hole in engine block
Crossthreaded spark plug hole in engine block

You can detect a cross-threaded fastener usually because it "binds" as you turn it. Normally fasteners should rotate freely until they are fully tight. If the fastener starts to bind, or give resistance when it is only partway in, gently back it out, adjust the angle, and try again.

If the bolt is torqued in even though you feel resistance, meaning it is crossthreaded, it will shave away metal on both the male and female parts of the fastener, weakening the threads:

Crossthreaded bolt
Crossthreaded bolt

If the fastener is torqued very tight while crossthreaded, the threads can fail completely, destroying the bolt, the nut, or both:

Crossthreaded shock bolt
Crossthreaded shock bolt

How to prevent cross-threading

So...how do you prevent this? Diligence and attention is always a good way. However, there is a very simple technique which I have used for many, many years. I don't know that anyone taught it to me, I suspect I just figured it out on my own. However, it works on every threaded fastener, and I use it every single time I screw any fastener into place, even bottle caps and jar lids! It works every time.

The secret: Screw the fastener in place BACKWARD. That's right, turn the fastener backwards instead of forward. If you normally twist the bolt clockwise to tighten it, instead twist it counter-clockwise. Do this until you hear/feel it click. This is the end of the male thread going past the end of the female thread. Once you feel this, you know the threads are perfectly aligned, and you can tighten the fastener normally.

I know it sounds a bit odd, so I made a short video demonstrating the technique:





How to repair cross-threaded fasteners

So...it's too late, and you already cross-threaded the fastener? As long as you haven't wrenched it so tight that you've completely destroyed the threads, most of the time it can be rescued. What you need is a tap and die set, available at any hardware store:

Tap and Die set
Tap and Die set

Taps (the long thin pieces) are used to cut threads in holes, and dies (the roundish pieces) are used to cut threads on rods. They are made of very hard, high-strength carbon steel.

Normally taps and dies are used to cut threads in things that aren't already threaded - i.e. you can drill a hole in some metal, then use a tap to create threads in the hole. Or you can take a metal rod, and use a die to make it into a threaded rod. However, they are also good for repairing damaged threads.

You will need:

- Tap and die of the correct size and thread pitch (this is important! Using the wrong size or pitch will destroy your fastener even more!)
- Tapping lubricant

Use the lubricant to lubricate the tap, die, bolt, hole, everything. Not using lubricant is a good way to destroy your tap/die and quickly destroy the threads in the piece you are trying to repair.

Gently insert the tap into the hole or the nut, and make sure the threads are lined up correctly. This is not the time to cross-thread again, because the tap will very easily cut across the existing threads! Gently twist the tap in and let the threads guide it. As it encounters damaged threads, you will feel a very gentle resistance. It's ok to keep pushing through.

Using a tap
Using a tap

For the other end, you want to thread the die onto the end of the bolt, again being very careful not to cross-thread it as you twist it on. The same procedure goes as for the tap - let the threads guide it into place, and push it through gentle resistance to repair the threads.

Using a die
Using a die

When you've moved past the damage, gently turn it backwards until it comes free.

A quick warning: It's entirely possible that you will cut damaged metal threads away from the fastener with the tap or die as you twist it. Particularly on spark plug holes, you don't want this metal falling into the engine! Use plenty of tapping lubricant, and every time you push through any resistance, back the tap out and clean any metal off before reapplying lubricant and starting again.



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Re: How to prevent cross-threading fasteners

Post by ghostvet » Fri Feb 01, 2013 8:35 am

"male part of a rotating fastener aren't correctly lined up with the female part of the fastener. It's usually caused when one of the parts of the fastener is slightly tilted when it is tightened. Instead of the lands and grooves of the threads lining up and sliding along one another"

I really hate when my male parts don't line up with female parts and they cannot slide along. Have you tried lubricant?

:lol:

:oops:

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Re: How to prevent cross-threading fasteners

Post by captaindan » Fri Feb 01, 2013 9:41 am

This technique has been used on the our farm for several generations. It becomes habitual. Good of you to bring it up. Much of what we do that seems to be a "no-brainer", is a brand new idea for many others.

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Re: How to prevent cross-threading fasteners

Post by ghostvet » Fri Feb 01, 2013 10:23 am

captaindan wrote:This technique has been used on the our farm for several generations. It becomes habitual. Good of you to bring it up. Much of what we do that seems to be a "no-brainer", is a brand new idea for many others.
Agreed... I have done this since I first put bolt to nut. To us it seems instinctual, but to others, not so much. But, I am always afraid of explaining things that are too simple because I don't know who will read it and think, "What, does this guy think I am an idiot?"... lol

Maybe we should have a real basic How-To section for people that are new to this or are not-so-mechanically-inclined... Seriously!

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Re: How to prevent cross-threading fasteners

Post by WingAdmin » Fri Feb 01, 2013 1:10 pm

ghostvet wrote:Agreed... I have done this since I first put bolt to nut. To us it seems instinctual, but to others, not so much. But, I am always afraid of explaining things that are too simple because I don't know who will read it and think, "What, does this guy think I am an idiot?"... lol

Maybe we should have a real basic How-To section for people that are new to this or are not-so-mechanically-inclined... Seriously!
I always thought this was instinctual, until I talked to a few people who had never heard of the method - and thus this article was born. :)

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Re: How to prevent cross-threading fasteners

Post by ChasK » Sat Feb 02, 2013 9:38 am

Your article is missing the second installment where you have severely messed up female threads and you resort to the Helicoil, thread repair kit. These have saved my bacon many times.
Chas

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Re: How to prevent cross-threading fasteners

Post by themainviking » Sat Feb 02, 2013 10:42 am

WingAdmin wrote:So...it's too late, and you already cross-threaded the fastener? As long as you haven't wrenched it so tight that you've completely destroyed the threads, most of the time it can be rescued. What you need is a tap and die set, available at any hardware store:
And if you have totally ruined the threads, and do not wish to go to a larger size bolt - Helicoil it. This is a system where you re-cut the threads to a larger size, but then install a thread coil inside the hole to bring it back to the original bolt size. All kinds of info on Helicoils may be found here:

http://www.helicoil.in/pdf/HeliCoil%20Catalogue.pdf


Excellent thread by the way, WingAdmin.
It ain't about the destination - it's all about the journey

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Re: How to prevent cross-threading fasteners

Post by WingAdmin » Sun Feb 03, 2013 10:50 pm

themainviking wrote:
WingAdmin wrote:So...it's too late, and you already cross-threaded the fastener? As long as you haven't wrenched it so tight that you've completely destroyed the threads, most of the time it can be rescued. What you need is a tap and die set, available at any hardware store:
And if you have totally ruined the threads, and do not wish to go to a larger size bolt - Helicoil it. This is a system where you re-cut the threads to a larger size, but then install a thread coil inside the hole to bring it back to the original bolt size. All kinds of info on Helicoils may be found here:

http://www.helicoil.in/pdf/HeliCoil%20Catalogue.pdf


Excellent thread by the way, WingAdmin.
Yup, Helicoils have saved my bacon more than a few times.

That said, many years ago, I had a 1991 MR2 Turbo, and I went to change the oil. I unscrewed the oil drain bolt, let the oil drain out, the tried to put it back in - and it wouldn't go in, it just spun. Huh? It turned out that a previous owner had stripped it out, and put a helicoil in. When I took it out, the helicoil came out with it, and dropped onto the ground, unbeknownst to me. Of course the bolt wouldn't fasten back in place without it.

The helicoil was useless, and it was a very long 5-mile walk to the nearest store (and back) to buy a replacement.

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Re: How to prevent cross-threading fasteners

Post by gravygrabber » Fri Apr 12, 2013 6:07 pm

This article is pretty good except if you are trying to fix cross threaded or damaged threads/holes you should use chasing taps/dies. It's like a regular tap and die but it's not going to remove material it just reforms the threads. The tap and die will work but it tends to remove metal and sometimes makes the parts fit loose or sometimes they will not tighten at all just spin around.

Also Heli-coils are good but Timeserts are the latest and greatest thread repair setups. The time sert is like a heli coil but it's one piece. It's much stronger by design. Almost all auto manufacturers have switched from heli-coils to timeserts. Even Honda.

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Re: How to prevent cross-threading fasteners

Post by WingAdmin » Sat Apr 13, 2013 10:35 pm

gravygrabber wrote:This article is pretty good except if you are trying to fix cross threaded or damaged threads/holes you should use chasing taps/dies. It's like a regular tap and die but it's not going to remove material it just reforms the threads. The tap and die will work but it tends to remove metal and sometimes makes the parts fit loose or sometimes they will not tighten at all just spin around.

Also Heli-coils are good but Timeserts are the latest and greatest thread repair setups. The time sert is like a heli coil but it's one piece. It's much stronger by design. Almost all auto manufacturers have switched from heli-coils to timeserts. Even Honda.
Good points, but a lot of people may have a tap, but not a chasing tap. If it was a critical item, like an engine bolt, I would go buy the correct chasing tap. Just for a non-critical item, I'll just thread a regular tap in there and be gentle with it.

Also good point about the Timesert. I just put one in the head of my truck when it blew a plug out, taking all the threads in the head with it. NOT cheap however!!!

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Re: How to prevent cross-threading fasteners

Post by Fatwing Chris » Sun Apr 14, 2013 10:02 am

All very good info.I'd like to add a little trick I've used for spark plugs for years.Been wrenching for a living for more years than I care to talk about.When installing plugs I jamb the plug into a short piece of vacum line or fuel line.This serves two purposes.One it holds the plugs where the plug hole is recessed passed the point of holding it with your fingers and two you can start to thread it in by turning the hose.If it cross threads the hose will slip on the plug before it damages the threads.Back it off and try it again.I like to get a couple of turns on it before I put a socket on it.Personally I think that plug sockets with the rubber insert that holds the plug in them are the worst thing ever.I seen more cracked and cross threaded plugs from people useing these than enough.JMHO
I know that the plug manufacturers say you don't need anything on the threads,but I also use a good hi-temp anti-seize especially with alum heads.This not only keeps plugs from seizing in the heads,but it also stops binding when starting the plugs(by hand).
If I'da known it would last this long,I'da taken better care of it.
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Re: How to prevent cross-threading fasteners

Post by Mac_Musick » Wed May 01, 2013 11:01 am

I appreciate the information in this article. I have never methodically rotated a fastener backwards. I know that I times I turne back and forth but wasn't listening or looking for a click indicating the threads have matched up. From now on I'll use this method consciously. I appreciate the time you put into a good how to write up. Thanks.
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Re: How to prevent cross-threading fasteners

Post by hondageorge » Sun Feb 02, 2014 11:14 am

The use of a piece of vinyl tubing or hose that fits over the end of a spark plug is the cheapest trick for preventing cross threaded spark plugs when inserted as stated by others above. I bought a couple feet of it at one of the big box stores, taking an old spark plug with me for fitment eliminating any wrong size issues. The tubing slips before the plug can cross thread so it's easy to align properly without costly thread stripping out. The next cheapest way to keep out of trouble in conjunction with the vinyl tubing is hi-temp anti-seize. A little dab goes a long way and that aluminum head (and your wallet) will thank you each time you pull out the spark plugs. Speaking of aluminum heads, in my 65 yrs,of wrenching, I've always been pulling the plugs on a cold aluminum head engine for extra safety. Considering all the latest stronger aluminum alloys, I'm assuming this is still a good idea. Is there any Honda info regarding this?
Oh, the extra foot of vinyl tubing I bought is used to cover and protect the rat-tail file in my tool bag from wrenches being dropped on it. I have to agree also, that those well intended spark plug sockets with the plastic inserts promote more cross threading then they prevent. For me, I'll always use the vinyl tubing when inserting my spark plugs following with my torque wrench...and I'll start it backwards until it clicks. What a great thread. I appreciate all the input.

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Re: How to prevent cross-threading fasteners

Post by Mac_Musick » Sun Feb 02, 2014 8:00 pm

Thanks all, this is a good thread.


Mac from Durango CO
1985 Goldwing GL1200I project
1984 Nighthawk CB650SC daily rider
I have been riding Hondas since 1964. My first bike was. 1962 250 Scrambler CL72 I have owned two Valkyries, a VTX1800R, a Naked 1982 GL1100 and half a dozen non Hondas.

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