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#59650 - 02/24/08 4:34 pm Helicoil blind hole?  
Joined: Sep 2007
Posts: 103
gory Offline
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gory  Offline
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Rocky Mount VA
Any help appreciated.
I removed the oil feed lines from the tank to the cases on my 66 Atlas, and upon trying to reassemble stripped the threads in the cases. Aluminum actually stripped before I tightened (bi-metallic corrosion maybe?) This leaves me with a problem. I cannot tap for a bigger thread as this would require me to drill out the casting which the bolt runs through.
All I can think of is a helicoil, but I can't find any info on how to tap a helicoil into a blind hole.
Anybody with any suggestions? I really don't want to pull the motor and would like to do this 'in-situ'.
Thanks, Greg

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#59651 - 02/24/08 6:54 pm Re: Helicoil blind hole?  
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t120mike Offline
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t120mike  Offline
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hampshire, england
You are in luck! It is perfectly possible to helicoil a blind hole. The kit comes with a clearance drill, a tap and coils and insertion device. Needs a steady hand to drill out the remnants of the old thread, but there is little or no resistance in alloy where the thread is already stripped. What is vitally important is that the tap goes in straight, and all your attention is required for this. Once the hole is tapped and ready, a spot of lubricant and screw in the coil, break off the tang with the tool provided. Bingo! Better than new!
You can get inserts of different lengths, BTW.


mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))
#59652 - 02/25/08 2:22 am Re: Helicoil blind hole?  
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gory Offline
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gory  Offline
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Rocky Mount VA
thanks Mike, I thought the tap was tapered, like regular taps, where there are different ones for blind holes.

#59653 - 02/25/08 4:50 am Re: Helicoil blind hole?  
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Posts: 3,348
BONZO R.I.P. Offline
In Remembrance
BONZO R.I.P.  Offline
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Posts: 3,348
Michigan, USA
Gory , If you are married to the idea of a heli coil , as T-120 Mike mentions, this should be a non issue ...but if I were in your situation I would look into a keensert . It has been my experinece that these are quite a bit more reliable than the helicoil inserts , being a one piece insert with peened stakes , but it may require more clearance for the clearance drill ... I dont know the Norton engines enough to say this is an option , just that it is possibly worth a look if you want a more permannet repair .

FWIW-BONZO

#59654 - 02/25/08 12:27 pm Re: Helicoil blind hole?  
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Dennis B Offline
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Dennis B  Offline
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Annapolis, MD
Gory,
I won't sugar coat it, your in trouble.
The bolt in question is #03-0448 or 06-2763 5/16x18 7/8 long & thin head
“ I cannot tap for a bigger thread as this would require me to drill out the casting which the bolt runs through”
If I understand this correctly, you want to hellicoil the hole and use a smaller (1/4”) bolt? If so, I doubt there is enough meat in there to hold the coil. 5/16x?
Some things to consider; even with the inner tranny cover off you won't have a very good shot with a drill. Even using a tap handle here will be difficult.
If you have never done a hellicoil repair then you sure picked a doozie of a job to learn on.
I can only think of 2 possible solutions if you must do this in-situ
Buy a 5/16x18,2” long stud (or just make one from a long enough bolt)
Clean the hole real good, shove some JB weld in there, and using double nuts install the stud as far as it will go and leave it alone for 24 hours. Don't remove the nuts, just walk away!

Or get a stepped stud, 3/8x16 big end and 5/16x18 small end
Use a guide block and 3/8x16 tap to re-thread the hole
I would not try to pre drill the hole, the taper on the tap will do this.
Once the tap has gone as far as it can, grind the taper off the tap and thread as far down as you can. I would install this stud with JB also.

Then a washer and lock nut, don't over tighten it!

Good luck with it, hope this helps

Cheers
Dennis B


Member # 182
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#59655 - 02/25/08 12:44 pm Re: Helicoil blind hole?  
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Bob S Offline
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, Lower -Lower michigan
BE very, very careful, with the drill and don`t go any further in with it; than necessary. mo, i think i`d do the heli-coil. i`ve done a number over the years and never looked back. The aluminum is definitely the.trick here.

And they are the easiest, of the three ideas jmo
bob s smile


Bob S
Street Rods, Kustom Kars,A BSA,Cushmans,H.Shadow ACE, Now a 2004 triumph america . "More than enough!!!!
#59656 - 02/25/08 4:49 pm Re: Helicoil blind hole?  
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Alex Offline
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Seattle
Gory,

All you have to do is buy a second helicoil tap and grind the taper off it to make a bottoming tap. Mcmaster-carr sells helicoil bits separately.


A smattering:
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#59657 - 02/26/08 12:42 am Re: Helicoil blind hole?  
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t120mike Offline
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t120mike  Offline
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hampshire, england
Just looked at my UniThread 1/4" BSF thread insert likt and it has TWO taps, one taper and one final (especially for a blind hole).
HTH


mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))
#59658 - 02/26/08 11:47 am Re: Helicoil blind hole?  
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gory Offline
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gory  Offline
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Rocky Mount VA
Thank you all.
The plan was based on my assumption the thread would be unavailable as a tap (whitworth or suchlike). as Dennis says, it's a 1/4" 18, so my first shot will be to run a tap down there to clean up any remaining threads, then try a 1 1/2" bolt.
if this doesn't work I'll move on to the helicoil or JB weld options, probably helicoil first.
Will keep you all updated.
Thanks again for all the suggestions and advice,
Greg

#59659 - 02/26/08 4:24 pm Re: Helicoil blind hole?  
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Alex Offline
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Seattle
1/4-18? What threadform is that?


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
#59660 - 02/26/08 4:31 pm Re: Helicoil blind hole?  
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Posts: 1,654
Dick Harris Online content
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East Bethany New York
Real course!!!! Used mostly on old BSA racing bikes. :rolleyes:

#59661 - 02/26/08 5:04 pm Re: Helicoil blind hole?  
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norbsa48503 Offline
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Flint,Mich
He may be thinking about a 1/4-22 or a 5/16-22 Norton used the 5/16-22 in the head at the banjo bolts. BSA uses the 5/16-22 on the gas tank brackets in the tank and the bolt that holds the oil spigot on the motor case. BSA use the 1/4-22 for the tapped hole in the head for the balance spigots. It seems like a favorite thread form in castings.


norbsa
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#59662 - 02/27/08 12:57 am Re: Helicoil blind hole?  
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gory Offline
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gory  Offline
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Rocky Mount VA
meant 5/16 18, mistyped, brain was elsewhere, not too uncommon - unfortunately

#59663 - 02/27/08 5:20 pm Re: Helicoil blind hole?  
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gory Offline
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gory  Offline
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Rocky Mount VA
Thanks to everyone who assisted, the 1 1/2" long 5/16 18 did the job, there was plenty 'unused' thread in the hole.

#59664 - 02/28/08 12:13 am Re: Helicoil blind hole?  
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t120mike Offline
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t120mike  Offline
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hampshire, england
Makes me wonder gory if the bolt you were using in the first place was a tad short. I have had the odd bad trip with stripped threads so now with alloy castings, if I am worried about stripping the thread, I test the depth of the threaded hole with a long set screw and then choose the bolt length to maximise the thread contact. Gotta be careful not to overrun the hole and if it is a blind hole not to get hydraulic bursting from stuff like grease or LocTite. FWIW


mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))
#59665 - 03/01/08 4:23 pm Re: Helicoil blind hole?  
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gory Offline
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gory  Offline
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Rocky Mount VA
Bolt in there was the original, but I agree, too short, barely 1/2" was in the threads, which are approx 1" deep


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