View Full Version : Helicoil advice
Conquistador_del_mar
11-06-2009, 11:07 AM
Has anyone used a helicoil to repair the damaged threads on the 1/8" NPT threads of the high pressure drive trim (Mercruiser) or trim tab fittings (old K planes)? If so, is there a special tap and installer to prevent damaging the steel nipple inside the aluminum threads of the female fittings? Bill
joseph m. hahnl
11-06-2009, 04:46 PM
http://www.helicoil.com.sg/HeliCoil-Pipe-Thread-Inserts.htm
I am assuming the thread you are trying to repair is for a flared tube?
You can get tangles inserts that you don't have to strike the tang off. As far as the tap goes, you could have the center of the tap relieved to allow the nipple to fit into. the biggest obstacle is you have to drill it out larger to re-tap it for the helicoil .
I think you may end up having to drill and tap it for the next size NPT up and then use a brass reducer male to female with the nipple inside. This method would eliminate the need for any specialty tools for installing the thread insert and a special tap, as well the inserts them selves.
I also would like to point out that Helicoil is now just a brand name. There are other companies that make inserts. They have come to be known as STI's (standard thread inserts).
installation of a tang insert can be done by filing a flat half way of center on the end of a screw"in your case a fitting" to except the tang. With the insert on the screw, install 1 turn below the surface and then back the screw back out, you then use a punch to knock the tang off . you could probably use a wood dowel to knock the tang off that way the nipple wouldn't be damaged .
hope that gives you some ideas
HOWARD O
11-06-2009, 05:45 PM
I have been fighting a leaky fitting on my TRS, even a new line didn't cure it. It seems to thread in just fine but I think it bottoms out before the flare seals inside the female end. MOP guided me in using some thread seal and it seems to hold for a good, long while.
I know this isn't your specific problem, just wanted to wish you luck and hope you have a successful repair! These cylinders don't come cheap!
Also, I wish I had a machinist like Joe for a neighbor!!! :cool:
Conquistador_del_mar
11-06-2009, 08:07 PM
http://www.helicoil.com.sg/HeliCoil-Pipe-Thread-Inserts.htm
I am assuming the thread you are trying to repair is for a flared tube?
You can get tangles inserts that you don't have to strike the tang off. As far as the tap goes, you could have the center of the tap relieved to allow the nipple to fit into. the biggest obstacle is you have to drill it out larger to re-tap it for the helicoil .
I think you may end up having to drill and tap it for the next size NPT up and then use a brass reducer male to female with the nipple inside. This method would eliminate the need for any specialty tools for installing the thread insert and a special tap, as well the inserts them selves.
I also would like to point out that Helicoil is now just a brand name. There are other companies that make inserts. They have come to be known as STI's (standard thread inserts).
installation of a tang insert can be done by filing a flat half way of center on the end of a screw"in your case a fitting" to except the tang. With the insert on the screw, install 1 turn below the surface and then back the screw back out, you then use a punch to knock the tang off . you could probably use a wood dowel to knock the tang off that way the nipple wouldn't be damaged .
hope that gives you some ideas
Yep - it is the fittings that accept the flared tube high pressure lines. I considered the larger brass insert method, but in my case the aluminum casting is not very large around the fitting hole. No one locally has a kit, but one place said he could rebuild the hole with aluminum and retap it. I am surprised that it is not a common problem with an easy solution. One boat repair shop I called said he just throws out the bad part and gets the customer a new one instead of simply repairing the fitting hole. I can get a repair kit online, so I think I will follow your advice on installation. A tangless insert would be sweet, but I have not found them available. Bill
Conquistador_del_mar
11-06-2009, 08:09 PM
I have been fighting a leaky fitting on my TRS, even a new line didn't cure it. It seems to thread in just fine but I think it bottoms out before the flare seals inside the female end. MOP guided me in using some thread seal and it seems to hold for a good, long while.
I know this isn't your specific problem, just wanted to wish you luck and hope you have a successful repair! These cylinders don't come cheap!
Also, I wish I had a machinist like Joe for a neighbor!!! :cool:
Howard,
You could do the brass insert trick on your TRS. It will only raise the fitting level by about 3/8", I believe. Bill
You need to use S/S fittings the brass and the aluminum do not like each other in a marine app.
Phil
BigGrizzly
11-07-2009, 09:41 AM
Delmar, try MSC. they have several types
Conquistador_del_mar
11-07-2009, 10:35 AM
Delmar, try MSC. they have several types
Thanks, Randy. They are a good source of all kinds of hardware. Bill
joseph m. hahnl
11-07-2009, 04:53 PM
one place said he could rebuild the hole with aluminum and retap it. . Bill
I think that is your best bet,
But if you would rather still use the insert? I found this kit on line.
http://www.allfasteners.com/Recoil-Thread-Repair-Kit-NPT-18-27-4010pcs41-403602041_p_3177.html
Conquistador_del_mar
11-07-2009, 07:02 PM
I think that is your best bet,
But if you would rather still use the insert? I found this kit on line.
http://www.allfasteners.com/Recoil-Thread-Repair-Kit-NPT-18-27-4010pcs41-403602041_p_3177.html
Joseph,
Thanks for the lead. I almost bought the one you linked, but I ended up buying this one on Ebay. Thanks again, Bill
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370250279780&ssPageName=STRK:MEWNX:IT
Conquistador_del_mar
11-14-2009, 11:27 AM
As a followup on this thread, I bought a good helicoil kit and installed it yesterday. The 1/8"NPT kit calls for a 3/8" drill. I ground off the end of a 3/8" drill bit and ground the center back so that it could drill out the sides of the hole without touching the center nipple which makes the connection with the flared SS tube after marking the depth with a micrometer to make sure it didn't touch the nipple. The tap that comes with the kit is tapered. I again used the micrometer and measured exactly how far down it could cut before hitting the nipple. I loaded the helicoil in the preloader and screwed it in as far as the breakoff tab would allow and then broke off the tab with some very thin needle nosed pliers. I then had to break off almost one turn of the helicoil wire that remained above the surface so the fitting would screw down to make the flared fitting tight against the nipple. Bingo! It worked, but I had to really tighten the last turn with more force than it should have taken to stop the leaking fluid when under pressure. In hindsight, I think I should have ground about 1/8" or so off the tap in order to get the tap to enlarge the thread cuts a little wider by using the slightly larger portion of the tapered tap. The fitting I had to repair was on an old K plane ram cylinder on my 1978 36' Cigarette - a ram that would be hard to find. The 1/8"NPT fitting seems to be the standard for Merc drives - don't be scared to try doing this repair instead of believing you have to buy a new part. Anyway - success! Bill
So glad it worked out Ok, must admit though I have never strayed away from the nipples:hangum:
BigGrizzly
11-15-2009, 07:57 AM
Good Bill but I was not awhear it was pipe I thoufg it was a standard thread, either course or fine, It could be like most mercs that are what they call streigh NPT.
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