or this one? http://www.grainger.com/Grainger/items/2XUC7

 

heli-coiled the holes in my pump and a buddys pump. as long as you are careful about drilling it you will be fine. if you are going to be pulling the afc on and off you will be better off with the heli-coil than taping the holes bigger and having them strip again

 

Both the taps you found will work, should be an easy task, Happy tapping!

 

This one will work best. You should be able to get one at a local hardware store

The other tap is a thread forming and they require a clean hole to work proper.

¼-28 is 1/4" fastener with 28 threads per inch or pitch and also identifed with NF or UNF for fine thread. NC or UNC is coarse thread or ¼-20

Helicoils are great if you want to keep the same size fastener. They are often used to give more strength to soft materials. They are also used for hardware meant for periodic disassembly.
Helicoils are bad if you make a mistake which is easy unless you have some experience.

edit
Added more details

 

thanks for all the help. as for the helicoils i don't plan on getting in and out of the housing. and now that i know how easy it strips i will keep that in mind when working on it in the future. also if i strip it out again then i will just get it helicoiled.

Again Thanks everyone for the help. will try to get it tapped within the next two days before i have to go back to work.

 

ok, so today i went and picked up everything i needed to tap it to 1/4-28 only to find that it had already been tapped tp 1/4-20 so now i was thinking about just Helicoiling it so that a 1/4-28 bolt will fit. now i looked at a kit to day that had like a 17-16 something tap in it and the helicoils now. if do i have to drill then tap for the helicoil or can i just tap it using the tap in the kit and then put the coil in and be done with it? or do i have to drill it out and then tap it? i talked to the same shop today and to have him do the helicoil without removing the pump from the truck was like $200 but he told me that shavings could get into the pump. and to take off the pump and helicoil it that would be $400 but he said that no metal shavings would get in the pump and if they did he would fix it.

Now if i just have to tap it with the tap in the kit and not drill first then i think i can handle that. i would pay the shop the 200 to do it but i don't want any shavings getting in the pump. and if i'm the one doing the work then i can make sure none get in there but with them doing it i have no way of knowing if they are doing everything they can to keep the shavings out.

Anyways Thanks for everyones input and help and i will be done with this soon so i will stop bugging yall.

Thanks,
Eric

 

Hi Fire Rescue,
We had lunch in Liberty Hill today... The mexican food restaurant Jardin Corona or something like that.

I hate the slippery slope of having a twice screwed up thread in a soft housing. The answers you had were all based on experiences with only once screwed up threads. I am a machinists and threads are a big part of what I do every day.

How do you know that it had already been tapped 1/4 -20 if the threads are currently stripped out? Is the hole approximately 1/4 inch in diameter and basically clean since it has no threads in it?

My assesment of why it stripped is this...
The outside diameter of a 6mm bolt is .236 dia in inches.
a 1/4 bolt is .250 leaving only .014 of thread engagement.
If done properly a 1/4-20 thread should require a pre-drill diameter of .201 leaving almost .050 of thread engagement. So you simply had almost no thread engagement and there is no wonder why the thread pulled out. Did I read a response correctly to say that an 8mm fastener will fit where the 6mm fastener was?

An 8mm fastener is .315 in diameter... a little bit bigger then 5/16 (.312) So if this next size will fit then it would still be simpler to tap the hole bigger and install a larger bolt. But the risk would be that if you messed up an even bigger bolt then you may or may not be able to helicoil at that point.
If you went with an M8 or a 5/16 you could simply buy a tap and tap your soft material. Then buy a larger bolt and your done.

If you go the helicoil route you can still choose the 1/4-28 or 1/4-20 at this point and the helicoil will completely fix the problem and the fastener would be closer to the original size.

I buy a lot of supplies from the Fastenal store in Marble Falls. Their taps are well made unlike the taps you get from most home depots. They also have individual sized helicoil kits. You get a tap and an inserting tool along with about 10 helicoils, but they aren't cheap, but way cheaper then a whole set. They will have all your standard SAE thread taps such as 1/4-20 or 1/4-28 and a bolt to fit. If you go to Austin then Austin Bolt on Rundberg is going to have an even better selection of the same stuff.

If indeed an M8 bolt will go. Then I personally would probably spring for a 5/16-18 tap, do no pre-drill and then pick up a socket head cap screw to replace your bolt. This could potentially cost you less then $10.

I would get a tap handle that has the "t" shaped cross bar that can slide freely so you can get a 1/2 turn then slide the handle over, kinda like a ratchet. I got one that goes up to 1/4" at home depot in Marble Falls just last week.

You need to line up fairly square to the hole. We often use a block of aluminum with a slightly larger hole in it then the tap. Drill it nice and square on a drill press then when you hold the block over your hole to be tapped you can slip your tap in the hole and it will square it up as it starts. After a few turns back the tap out and remove the block now that your thread is started square.

This is alot of typing to convey such little information. How about we will let this digest and if you have questions or others chime in I will be glad to expand on what I have missed. Take care.
-Greg

 

Ok the way i know that it was tapped 1/4-20 is i took the bolt out and took it into ace hardware and checked it, it fit into the 1/4-20. also all the other info really messed me up i was lost at Hi. lol anyways thanks for the info and i will try to reread it and try to under stand better.

Thanks,
ps Jardin Corona is the best around these parts. it is about 2miles from my house so we eat thers way too much.

 

It very well could be the previous owner didn't even bother tapping out the striped hole to 1/4".
Probably just screwed a 1/4" bolt in.
Makes for a weak connection.

 

Big decision point. You can heli-coil at this point, but with the limited access and no prior experience, it is a somewhat risky choice. If you go to an 8mm or 5/16" fastener then you are stuck with that choice as the hole is too large to go back and helicoil for 6mm.

Sounds as if you have a very experienced neighbor that could stop over and do the job for less money than the local shop?

 

i was thinking about helicoiling it so that a 1/4-28 will fit. but like you said i have no experience and not sure if i can do it and can't afford to mess it up. And yes if i could talk Chevummins into helping out that would be great, if not then the truck goes into the shop tuesday morning when i get off shift. now like i said before they want 200 or 400 and i think i am going to do the 400 which they will pull the pump off the truck and helicoil it so no metal gets in the pump. they want 200 to leave the pump on the truck but, i don't want them to get metal inside. anyways this mess up is going to cost me good chunk of money.

 

took the truck to the shop and they just tapped it out one size. everything works great and it only cost me $150. got lucky.