Those damn Helicoils...

[sirhrmechanic]

Thought I would post this method of repairing stripped out threads in cast iron (and aluminum). The need to do this is pretty common on old bikes and very common on our car work where water jacket covers are generally a mess.

In our experience, heli-coils can be used on temporary fixes. But they are definitely not an ideal long-term repair technique in many applications.

Instead of Helicoils we use Irontite tapered plugs. These replace the metal and then can be properly re-machined/tapped for a homogenous, permenent solution. Plugs are available in cast iron, aluminum, steel, etc.

Installation requires special tapered taps and, for larger sizes, a tapered reamer to prepare the hole. Here are some pictures of the process.


First, the old Helicoils have to come out. You can see they have been driven in too far in this case. These cylinder blocks were leaking at the water jackets both because of weeping around the threads and because several of the Helicoils were loose and so the cover plate didn't seal properly.

heli1b.jpg

One of these helicoils is too deep and the other is proud. Both are loose. Not good

heli1c.jpg

This one is uncoiling as the screw came out.

heli1.jpg

Removing Helicoils can be a royal pain, especially the small ones. We use a small bottoming tap to 'hook' the edge of the Helicoil and lever it up.

heli2.jpg

[sirhrmechanic]

Once you pry up an edge of the old Helicoil, you can twist it out with a pair of pliers.

heli3.jpg

The old helicoil is just like a spring.

heli1d.jpg

These are the repair plugs and the special tapered tap used to fit them. The advantage of these is that the threaded taper lets the insert lock very tightly into the tapered hole. Unlike a helicoil that is pressed in by the fastener, these are locked by their taper. One risk is that if you turn it in too hard (especially in cast iron) you risk breaking the casting around it. Tighter is NOT better. Use solid pressure, not a 2 foot breaker bar.

heli4.jpg

This shows the taper reamer and taper tap used for some of the larger taper plugs. Plugs larger than 1 inch are available, with their matching taps. Some very large holes/threads can be repaired using this system.

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Using a regular tap handle, turn the taper tap in until the rusted/oversized edge of the old hole is removed and you have a clean, oversized hole with sharp threads all the way along its length. You may want to cut the tip of the plug off before installing it (so it is flush at the back). This can be done by threading it in and marking it, then cutting off with a hacksaw. You also want a plug large enough so that when you drill it, you don't cut into the tapered threads and weaken the repair. These plugs are for 2BA (British) machine screws which are about a 10-32. These are 1/4+ plugs -- 1/4inch at the tip and about .300 at the shoulder.

heli6.jpg

[sirhrmechanic]

Once tapped, the repair plug is put in using some Red Loctite. As mentioned above, the plug should be firmly screwed in, but don't go overboard on the cast iron plugs, especially in areas like this where a flange has no support on one side. Cast iron does not like to be in tension and you can very easily crack the original iron casting. Note that these are not bike parts but antique car blocks (water jacket side) which I used to show the process because I didn't have any bike repairs underway.

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Use a hacksaw to cut the protruding end off the plug.

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Use a mill (or a file) to smooth the plug off and ensure that the machined surfaces are smooth and gasket ready.

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This shows several holes repaired and ready to re-drill and then tap for 2BA machine screws. Using 'like' materials prevents any issues with expansion under heat and by locking the repair pieces using the taper, they are far, far stronger than helicoils. After re-drilling and tapping, we install the plates with gaskets and pressure check the casting with compressed air and soap/water before final machining and painting. It's no fun to get a block all done and find a leak!

heli9a.jpg

The plugs, taps, etc. are all available from Irontite out in California. I think they have been bought out, but last time I ordered plugs, the customer service people were just fantastic. Plugs vary in price, but a box of 100 .250 plugs is about $40. The bigger plugs range up to several dollars a piece. I don't know what they get for tap/reamer sets these days as we've been using these for years. But this system is worth it.

This set of car blocks had some 80 holes that had to be repaired. Earlier in the year I did a Bentley 3L block that had over 300 holes that needed to be repaired around the water jacket. Hey, if the hole is rusted and thread stripped... just drill another hole next to it, right?

These plugs can also be used to make 'stitch' type repairs by overlapping plugs. Cracks or thin casting areas can be reclaimed in some cases.

FYI, I don't work for Irontite... or sell their products... I just like to see things done right and I HATE having to spend my time picking helicoils out of holes...

Hope this helps someone somewhere along the line.

Cheers,

Sirhr

[c.o.]

Sirhr! Very good info to know. Thanks for taking the time to give the run down.

[T. Cotten]

Helicoils are great!

Any problems are invariably a result of a botched installation.

....Cotten

[indianut]

I have been using these lately and I like them. They seem pretty strong and I could not see how one could fail.
http://www.newmantools.com/kee.htm

[exeric]

I don't think Sirhr was condeming Heli-coils; but was demonstrating an alternative cast iron repair. I've used the Irontite repair system in cast iron and think for certain applications, it has no equal.

[sirhrmechanic]

I have been using these lately and I like them. They seem pretty strong and I could not see how one could fail.
http://www.newmantools.com/kee.htm

Indianut: I visited that site. Those are very interesting. I'll have to see if they have British (BA/BSF) sizes... Thanks. Those are a great find!

Cheers,

Sirhr

[sirhrmechanic]

@ Cotten. There are lots of good uses for HeliCoils, especially in-situ repairs and plug holes. But I see them mis-used a lot and, yes, installed badly. That is why I posted some pictures/info on an alternative.

One thing that I can say for sure... Heli Coils work well for a time. But for very long term repairs, HeliCoils don't hold up. The Helicoils in the above application were about 10 years old. And were completely deteriorated. The coils were fine -- they are stainless. The cast iron around them was kaput and so the repairs were moot. We've had engines back in the shop for service that were repaired w. the Irontite plugs in the 1970's, and there are no issues with the repairs at all.

So by all means, use Helicoils where appropriate. But between the Indianut reference and the Irontite products... hopefully folks learned at least two new methods of repair.

Cheers,

Sirhr

[kg993]

I have been using these lately and I like them. They seem pretty strong and I could not see how one could fail.
http://www.newmantools.com/kee.htm

I like the Timesert inserts, similar to Keensert but is locked in by expanding during instalation instead of staking the threads, also has a flange top to set deapth.
The Irontite looks good (similar to some other inserts I use which have straight OD's) especially for the really screwed up holes. Also apparently if you have the right tap you can make any thread needed.
Kerry

[fillibuster]

I like the Timesert inserts, similar to Keensert but is locked in by expanding during instalation instead of staking the threads, also has a flange top to set deapth.
The Irontite looks good (similar to some other inserts I use which have straight OD's) especially for the really screwed up holes. Also apparently if you have the right tap you can make any thread needed.
Kerry

I've done pipe plugs on tractors, very similar, tapered, w/loctite. available at the hardware store.
gimme a caution flag.