EW350-1926

[Michel H]

Hello everybody,
On my Douglas two of nine timing case threads are damaged. Just in case, I asked HeliCoil if they have one 3/16" x 27 tpi Thread Repair Kits. Of course they don't have.
If somebody else had this problem, which solution he finds?
Your opinion can help me.
Thanks.
Michel.

[oily bloke]

Hi Michel,
The purists won't like this one but I have tapped mine to 5mm and bought stainless cheesehead screws and machined them to resemble the originals. A 5mm tap goes straight in no problems. If yours are beyond a 5mm tap then a metric helicoil is easily obtainable. Be carefull on the corner holes as clearance is minimal and you will need a finishing tap for the blind holes.
Hope this helps
Andy

[Doug]

Michel,

Well you will not like to hear this, but I have run into the same problem on a DT crankcase and made 3/16-27 threaded inserts in order to maintain the original thread series. Just to be perverse I suppose. Since I did not have the tap, I single point thread cut the insert in the lathe. It is a small thread to cut this way, but it can be done, only just. This only works if you have sufficient material around the threaded hole to screw the oversize insert into, so in that regard you need even more radial space than a Helicoil.

On another project, not wishing to go through the same ordeal I purchased some thread repair compound from Loctite. But I have to say I was very disappointed in this product, as the material never seemed to set up proper. I even tried it twice, making sure to follow the directions the second time, but no improvement. I have also tried structural epoxies. These do set up, but I have not yet found one that is as hard as I would like to see for this type of application. O.k. for fixing a wobbly thread, but not for taking the primary load. I use a nylon screw as a core ( you will still need a release agent) so as to pick up the existing thread.

-Doug

[LATDOUGNUT]

Hello Michel, Group,

May I draw your attention to Techno-Weld  -- a low temperature (380 degree Centigrade) fusion welding material/process, developed by Cambridge Welding institute many years ago, that is a perfect means of restoring threads even in tight or thin areas. This material is still available in the UK and the USA under that name.

If, for example, you can machine a special bolt with thread and hexagon, preferably in tough titanium alloy with the required TPI on a lathe -- you can copy the thread by adding molten Techno- Weld to the enlarged thread hole and then inserting the special bolt. Titanium works better than steel because it is tougher and does not oxidize so much. When it cools you can remove the bolt by unscrewing with an air ratchet, but first soak in WD 40, so that it penetrates the thread. For better results coat the bolt with chalk -- it will keep Techno-Weld from sticking too tightly. Also if you have a proper tap handy -- make the bolt slightly smaller and a bit tapered. Then you can re-tap the hole afterwards. Techno-Weld, after application, has a Brinnell hardness of 100, like forged aluminium and most importantly it will work with old castings with high zinc content which are prone to cracking if TIG welding is attempted.

I have been working with Techno-Weld for 14 years and it is the best material for any stripped or broken threads in old aluminium and in modern car aluminium cylinder head injector or glow plug threads! Simply nothing comes near it in terms of hardness, application or centering simplicity, and last, but not least service life! This is also the only material that you can weld mazak or pot metal with by the way!

Go to  http://www.techno-weld.com/about.html  for more information.

Good luck with your threads!

[Edin]

Hej Michel
Your problem is recognizable to all of us.
Maybe Time-Sert tread insert  can help you,- it is an exelent solution,- easy to make,- very strong
and have been used by me in 15 years,- always with good result.
Have a look here - www.timesert.com/
Regards and good luck
Edin DK