How do I repair strip threads on O.S. VF 40 ?

[Larry Wong]

What’s the best way to get it fix on one lug rear exhaust

[Brett Buck]

What’s the best way to get it fix on one lug rear exhaust

   I have one that way (that someone had stripped it, tapped out to 6-32 - then stripped again!), and I put Heli-coils in both holes.

    Brett

[RandySmith]

   I have one that way (that someone had stripped it, tapped out to 6-32 - then stripped again!), and I put Heli-coils in both holes.

    Brett

3.5mm  heli coils??   Where  did you find those, or did you just use  4-40 s

Randy

[Tim Wescott]

3.5mm  heli coils??   Where  did you find those, or did you just use  4-40 s

Randy

I can't remember if OS likes fine or coarse, but McMaster has M3.5 0.6 (coarse) helicoils.  I was too scared to look at their price, though.  Because -- McMaster.

[Dave Hull]

Randy,

You can try here:   

https://www.mscdirect.com/browse/tnpla/00069039?cid=ppc-bing-New%20-%20Catchall%20Campaign%20-%20PLA_xjKRiRVs__be_73529890243102_c_&mkwid=xjKRiRVs|dc&pcrid=73529890243102&msclkid=176e24f8a2f01fc7997f78d5f9d4f068&utm_source=bing&utm_medium=cpc&utm_campaign=New%20-%20Catchall%20Campaign%20-%20PLA&utm_term=4577129467923006&utm_content=Catchall#navid=12106045+4288055496

Dave

[Brett Buck]

3.5mm  heli coils??   Where  did you find those, or did you just use  4-40 s

   I got them at the local (now defunct) hardware store (Orchard Supply Hardware).

     Brett

p.s. I don't think a 4-40 would have worked, I think someone hacking it out to 6-32 and then stripping that removed too much metal for a 4-40 helicoil (which are usually 2 steps over, in this case, 6-40). I could have used a 5-40, but I wanted it to be the same as the others. That was a long time ago. Now, I it would have been compatible because the Jett uses  5-40s, too.

  If I can find my kit, Larry can just use mine, since I have 8 of them left. The problem is I haven't seen the kit in about 25 years.

    Brett

[944_Jim]

I'm just thinking, and drawing on my auto-repair experience, with no familiarity with your engine:

Option 1:
Is there any meat deeper into the casting? Maybe you could drill/tap same-size, but deeper and then JBWeld a stud into the hole, and finish off with a nut on the outside of the muffler. An acorn nut may be attractive enough.

Option 2:
I stripped out a bolt hole on a motorcycle sidecover one time. Permatex Thread Repair kit to the rescue...but it was one of eight side cover bolts. The kit comes with a two-part "epoxy," and a non-stick dip for the screw. The "epoxy" fills what is left of the OEM threads, and the "non-stick" coated screw forms new threads in the "epoxy." The material was strong enough to clean out with a tap, and holds pretty well. The bolt never rattled out, yet comes out and goes back in years later.

Good luck, and come back and brag on the fix please!

[Larry Wong]

What’s the best way to get it fix on one lug rear exhaust

.   Jim 944   I have used iJB Weld on my 914 at the track before but I think on the O.S. a coil would be better but thanks

[Brett Buck]

Larry -  I checked my box of Heli-Coils and found everything but the metric set for the OS. I would suggest that your options are to:

 

• find the correct, non-bastard, metric heli-coil kit (which looks to be up around $40 from the $15 I paid in 1990 or so)
• just use a 6-32 heli-coil which is easily available almost anywhere but is a bastard
• get someone with very special aluminum TIG or Heli-Arc welding skills to weld it up, then drill/tap
• use the Eutectic  "welding" rods to fill up the hole, then drill/tap that
• find a replacement case, new or from a parts engine
• accept an indefinite loan from someone who has 40VFs in abundance, the only proviso that you give it back in a functional state

I have a 4-40 and 6-32 Heli-Coil kit, I have the Eutectic welding rod, but I would expect a high likelyhood that the heat required might distort the case. I also have a parts engine with a good case, and I also have complete 40VFs that I am not likely to use in the foreseeable future. I do not have the necessary aluminum welding skills (ask Scott Dinger) for such a delicate operation.

     I measured it, and if you stripped out the hole with an M3.5 screw (with a nominal diameter across the peaks of 3.45mm/.136"), you can't use a 4-40 heli-coil, because it requires a 1/8" drill bit. A 5-40 Heli-coil (which I don't have right now) takes a #29 drill, which is exactly .136, so you can probably make that work given that it's liable to give you a .1365-.1370 hole - close enough for hand-tapping. A 6-32 takes a pretty darn big hole (5/32/.156+) but there appears to be more than enough meat on the case to do it.

    If you are going to sell it, you can use my 6-32 Helicoil kit, sell it, and move on with your life. If you are planning on running it, same thing works, but you can use my good case center section as long as you return it when you are done at some indefinite point in the future, or just take one of my many engines and run it, and return that when you are done.

    Brett


p.s. I think the stripped hole wlll be too big for a 6-32 to be directly tapped into it, minimum for a strip is .136 and you need a .1065 hole (or very slightly smaller), and th eoutside diameter for a 6-32 is only .138, and will just strip again almost immediately. You could tap directly with an *8-32*, which is probably the same as the 6-32 helicoil, but that is more likely to strip again than a 6-32 insert, at which point you are screwed.

   

[Dan McEntee]

    As Brett mentioned, if you know some one with a good hand at the TIG welder, they can be welded up and you can retap to original. Strip the engine down, and I usually grind away a section so I know I am reaching all the way to the bottom of the hole. You can heat the case for as long as it takes to boil out the oil in it, and there will be oil, but I usually just preheat the case, and with a patient foot on the pedal, heat the area with the TIG torch and let the hi frequency help scrub the area. You may have to stop from time to time to re grind the garbage away, but when the oil is gone you will just suddenly see a nice, clean aluminum puddle, then just add until you get what you need. You can't rush this process, just do what needs to be done. Practice on an old case if need be.
   In machine repair at work, some times welding wasn't an option either. And if I didn't have a Keen-cert or heli-coil the correct size, I would make one by picking the appropriate bolt or screw size, and then drill the center out for the tap size I needed. Get a length of bolt all drilled and tapped, and then dril and tap the part for the bolt outside diameter threads. Cut off the length you need, grind a slot on one end for a screw driver to catch it, then apply loc-tite to the threads and install. I have had this work very well on many occasions, you just need the appropriate machinery and tools.
  Good luck with it,
    Dan McEntee

[Brett Buck]

I know that this is a paleo-thread, but, for Larry and others (Randy...), here is thread replacement kit, $30 for 10 M3.5-6 inserts, which I think are the correct size:

    https://www.mscdirect.com/product/details/56353923?fromRR=Y

   Brett

[RandySmith]

I know that this is a paleo-thread, but, for Larry and others (Randy...), here is thread replacement kit, $30 for 10 M3.5-6 inserts, which I think are the correct size:

    https://www.mscdirect.com/product/details/56353923?fromRR=Y

   Brett

I have bought and  used  inserts before for these repairs, They were  not  heli coils  but  were  steel inserts, that  were  8/32  or  10/32 outside   with  4-40  inside threads, They also make them in  3mm  inside thread, I liked these  better than helicoils, You may also want to look at  these   
https://www.mscdirect.com/product/details/97644090
Randy

[RandySmith]

https://www.mscdirect.com/product/details/63790828

Above are  the  3mm  inserts,   The outside  is  6mm  that maybe pushing  it too far, You would  need to do a careful measurement

Randy

[Brett Buck]

https://www.mscdirect.com/product/details/63790828

Above are  the  3mm  inserts,   The outside  is  6mm  that maybe pushing  it too far, You would  need to do a careful measurement

    There's a decent amount of meat on there, but it depends on how many previous "repair" attempts have failed. I have one case where they first stripped the regular screws, tapped it 6-32, then stripped those, too. I think this engine was previously owned by Lancelot Link.

     Brett

[RandySmith]

    There's a decent amount of meat on there, but it depends on how many previous "repair" attempts have failed. I have one case where they first stripped the regular screws, tapped it 6-32, then stripped those, too. I think this engine was previously owned by Lancelot Link.

     Brett

The  4-40 inserts  I  posted are  steel and  they are   smaller  outside than 6mm  so  I would go that route to fix ones, in the future  I will still  use these, they are pretty bulletproof

Randy

[David Ebers]

[quote  I think this engine was previously owned by Lancelot Link.

     Brett
[/quote]

Awesome reference!

[Brett Buck]

[quote  I think this engine was previously owned by Lancelot Link.

     Brett


Awesome reference!

Glad someone appreciates these gems I toss out there!

    Brett