Helicoil Help Needed

I am hoping that someone can give me some advice.....

I have acquired an engine which has four cylinder holding down bolts, one of which has been helicoiled. When I dismantled the cylinder I noticed that the helicoiled one was binding and damaging the thread, and on closer inspection, the bottom of the helicoil is raised and bites into the thread on the bolt, damaging the thread and making it difficult to remove the bolt; it also looks like the helicoil is gradually working its way down into the hole.

I am guessing that when the helicoil tang was broken off it pulled the bottom of the insert out, which is acting like a spring. So, is there any remedy other than using a helicoil removal tool to extract the wire and starting again?

Thanks,

Colin

just wind the old coil out and fit a new one this why the military use them for quick on site repairs.

Thank you! But do I need a special tool to do it?

You will need to get hold of the outer end of the helicoil with a pair of grips, and then wind it out. It may take some ingenuity to bend the free end radially inward, so as to get hold of it.

It will not be easy, the top of the helicoil is about a quarter of an inch down into the hole........Grrrrrrrrr.

You can grind up a piece of flat steel about 1/3 the diameter of the bore of the coil thick. The steel should be just slightly narrower than the tapped hole and tapered slightly. The end profile should be trapezoidal, so that the acute angle is in the direction of unscrewing the coil.

Edited By old mart on 11/08/2022 17:51:23

Make or buy a small diamond point chisel, or use a 1/8" punch ground off at about 45*and go down the back of the helicoil to bend the start in. point nosed pliers to unscrew ! Then buy or borrow a helicoil kit and fit a new coil. RETAP the hole ! You WILL damage the start of the thread but this will be of no consequence ! Noel.

A cheap set of dental tools such as these may be your friend
https://www.ebay.co.uk/p/1388586914?iid=133286229112
Perhaps with a pair of artery forceps depending on the hole size.

Thanks for the suggestions, I have an idea of what to do now.

Colin

Could you get a small Dremel grinding point in to grind back the bit that is catching

But do I need a special tool to do it?

Suitablly dimensioned file tang tapped into the insert & used to wind it out.

Inserts are available in different lengths as multiples of insert diameter. Kits typically include 1 x D inserts, but 1.5 x D, 2 x D etc are also available to suit different materials. Maybe use one closer to the depth of the hole to bottom the insert & stop any further creepage ?

Last inserts I fitted were into a BMW motorcycle aluminium crankcase & were 2 x D long to be the same length as the original tapped hole. Tapped holes into aluminium are typically threaded 2 x D deep.

Nigel B.

It is out! I tapped a tiny flat punch under the top and then eased a small screwdriver under the insert and bent the end in, was then able to unwind it with needle nosed pliers. The reason why the thread was binding was that the tang had not broken off, it was simply bent in and was holding the bottom turn of the thread off of its seat. Next step is to buy a kit and redo the job.

Thank you to all those who offered advice, you guys are the best!

Cheers,

Colin

What kind of engine is it? Not a BMW motorbike is it? Helicoils on their oft-stripped cylinder stud holes can sometimes block off a tiny oilway drilling that supplies the rocker feed oil if not installed very carefully.

No, not BMW - it is an old Ducati Single.

Old Mart has shown what the manufacturers sell as the 'Special' tool to remove them. Drive tang break off can be a problem when fitting.

200cc Cat?

Regards Ian.

Edited By Circlip on 12/08/2022 10:25:00

350!

Oooh luvly!

We will see!