heli-coil sizes

Kajun37

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Feb 17, 2006
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348
well i broke off 3 bolts on the force 125 exhaust cover, which needed to be taken off to clean out the corrosion.....i got all 3 of them drilled out and i was going to try to go back with the same thread size...but i still have some steel threads left in the housing threads which makes going back with original size almost impossible with breaking some taps off in it....so i decided i need to put heli-coils in them...is there a chart or something that can tell me what is size bit/tap and heli-coil to use? i've installed some heli-coils at work a very long time ago just cant remember the specifics on them.
 

MWBROWN

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Feb 7, 2006
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231
Re: heli-coil sizes

Hi,

Go to helicoil.com and you should find the information you need.
You can also get them online at McMaster Carr.

Did you try to use a plug tap, 2 fluted to clean out the holes? They are much stronger, and the plug type have a nice lead on them. Then follow up with a bottom tap if needed. Most hardware type stores don't sell that type. You may have to go to a tool supply. Don't forget to use some oil when tapping the holes. Wd 40 is not good enough for that. Light greas works well too.

Good luck,

Mike
 

Bigprairie1

Commander
Joined
Jun 13, 2007
Messages
2,568
Re: heli-coil sizes

Hi,

Go to helicoil.com and you should find the information you need.
You can also get them online at McMaster Carr.

Did you try to use a plug tap, 2 fluted to clean out the holes? They are much stronger, and the plug type have a nice lead on them. Then follow up with a bottom tap if needed. Most hardware type stores don't sell that type. You may have to go to a tool supply. Don't forget to use some oil when tapping the holes. Wd 40 is not good enough for that. Light greas works well too.

Good luck,

Mike

...ditto, and right on. Follow this Kajun and you'll be done in time for dinner.
ps: McMaster Carr are known for quick delivery...so if you order something on line often by/before noon...you'll have it the next day, not 2 weeks later. Have it sent to your work address if you can.
 

Kajun37

Petty Officer 1st Class
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Feb 17, 2006
Messages
348
Re: heli-coil sizes

Hi,



Did you try to use a plug tap, 2 fluted to clean out the holes? They are much stronger, and the plug type have a nice lead on them. Then follow up with a bottom tap if needed.


not following you on this ...i tried to use a regular tap...it is flat on the end of it, which i believe is a bottoming tap....2 fluted?....also where is the charts that tell you the size drill bit and tap that i need to step the hole up too..i cant find it on helicoil.com...
 

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Re: heli-coil sizes

Because Heli-Coils are 1/4 X 20 internal threads, the external threads are also 20 tpi. therefore they are not standard and you must buy the kit containing the proper drill and tap. A kit with 6 Heli-coil inserts, the drill and tap costs about 20 bucks. And, There is not much meat on the exhaust cover bolt hole bosses. It is MUCH easier to just drill the hole deeper, tap 1/4 X20 deeper, and use a longer bolt.
 

Scaaty

Vice Admiral
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May 31, 2004
Messages
5,180
Re: heli-coil sizes

HeliCoils use a special drill size, and a purpose built tap, AND insert tool.... get the kit...(21 years Machinist)
 

Kajun37

Petty Officer 1st Class
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Feb 17, 2006
Messages
348
Re: heli-coil sizes

i have a kit at work....but i dont know which size to use.
 

MWBROWN

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Feb 7, 2006
Messages
231
Re: heli-coil sizes

Ok, I will explain.

Most home taps are 4 flutes. Flutes being the cutting edges.
A good hardware store may have a two flute plug tap. Plug tap is tappered on the end, thus cuts easier. Take a bolt with you if you don't know the size and pitch. Guessing from Franks post that they are 1/4 x 20.
If you drill them deeper you will need a .201 to .205 diameter drill.
13/64 diameter drill will work.

The kit will say 14/ x 20 repair kit. The drill and tap will be bigger of course than a standard drill.

Sorry, I thought Mcmaster would have that info.

Good luck,

Mike (37 years making chips)
 

Kajun37

Petty Officer 1st Class
Joined
Feb 17, 2006
Messages
348
Re: heli-coil sizes

thanks for the help folks and mike thanks for the explanation on that...

i ended up not having to put a heli-coil in it..i stepped up to a 7/32 drill bit and it took out all the steel threads left over from the broken bolt..and ran my 1/4-20 tap and was able to make some good threads with it.....all 3 holes are ready to go!....now i got to get that old gasket off......anyone have a good way to get that black exhaust cover gasket off? its hard as a brick and ain't coming off by scraping it....i really dont want to sand it off cuz it looks like asbestos.
 

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Re: heli-coil sizes

Tough it out with a single edged razor blade, lots of time, and lots of sore fingers.

When you go to replace the gaskets be sure to tighten all bolts securely starting from the center and working out--in steps, just like the head pattern. And use PLENTY of anti-sieze. The water tends to wick into the bolt holes and corrode the aluminum. Then after running, re check tightness. Good and tight but be careful not to strip them. I know--I know--factory says to install gaskets dry. I'm not a big fan of Permatex, but a light coat here may help to stop corrosion.

When replacing the gaskets, be doubly careful especially at the lower front. The gasket is only about 1/8 inch wide here and easily kinked, leading to water leaking into the bottom cylinder. If the engine is run frequently, no harm will come but once it is layed up, the bottom cylinder will rust, jamming the piston tight.
 
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