Stripped thread

[Shifty]

Hi guys

I have a (completely) stripped thread in an alloy timing case.

This bolt is critical as it also goes through the water pump.

Can this be easily repaired?

[kingmick]

Yes, look in the phone book for someone near you that does helicoils, a engineering shop etc close by will will prob tell you who the local mobile helicoiler is. its not hard to fix.

[RWDboy]

What he said 'Helicoils' are your saviour in this case.

[Starfire]

You can also get a tap and cut the thread out to a slightly larger one and put in a bigger bolt.

A helicoil is probably a better idea though.

[stradlater]

what engine?

[Shifty]

Cool, I'll see what I can amange. I was planning to buy a tap for a bigger thread so I'll try that first, I can at least do that without pulling it all apart. I've already done that about 5 times due to a bunch of snapped bolts - not through being ham-fisted but because the last person who worked on it overtightened everything, so now when I'm trying to nip things up I keep shearing the heads off - and in this case they've chewed out the thread

Engine is a 22RE...

[LeeRoy]

Helicoils aren't the best for hi-torque bolts. Another option is they drill your hold out then tap it bigger and put a sleeve in there so you can use the original bolt or its equivalent.

- LeeRoy

[Shifty]

Now I'm an expert on the topic, I thought I'd share

I went to the Nut & Bolt Factory at Buranda. They were able to supply a drill bit in the appropriate size to redrill a blank hole, a stainless bolt in the next size up (and if you have an extra few bucks get a spare, as you will read below), and a thread tap to suit the new, larger bolt. I suggest you replace as many other bolts as you can at the same time, and if the bolts that came out were a bit ordinary looking, get an appropriate size tap to clean out the holes in case they are damaged at all. This saves you fixing the problem you've got and then having the same problem with the next bolt!

Just a matter of:

1. Carefully drill out the exiting thread with a suitably sized drill bit. The correct size will be exactly the same size as the raised part of the thread on the ORIGINAL bolt (or a poofteenth larger if you can't get it exactly). Good bolt/tool shops will have a chart detailing which is the appropriate size for your situation - otherwise you can measure it and work it out yourself. It is important to drill the hole deep enough, but not too far in a situation where there is something behind it (in my case the water outlet). This may pose a problem in some cases where you can't drill the hole deep enough, due to the "point" on the end of the drill bit making the hole that extra few mm longer in the middle. In my case there was enough meat left.

2. Use the tap to create a new thread. Be patient, do it by hand, and don't force it! Wind it in a bit, then out again, over and over, to clean the shavings out. A touch of compressed air can be handy to blow out the hole, but watch those metal shavings as they won't do much for your eyes.

3. Wind in the new bolt gently, doing it a bit at a time in the same way as you did with the tap. Once it's in all the way but not tight, wind it back out again. Inspect the bolt for damage, if it's damaged at all then use another new bolt as some of the shavings may have damaged the thread a little.

4. Tighten up the bolt and everyone's happy!

[Starfire]

You should always use a cutting lube with a tap. Using one dry is asking for trouble.

[BrianRA23]

If cutting a tap into aluminium brake fluid is a good substitute for the cutting lube.

Some motorbike shops can fit various sizes of helicoils as well (since all engine casings are alloy) if a specialised fitter is not available. Buying a kit to DYI is an expensive way to do it if you only have one bad thread, so opt for somelse to do it for you .

[74ROLLA]

Helicoils if fitted correctly can end up as strong, if not stronger, than the original thread. The trick is to "lock" the helicoil into its new thread by inserting a bolt into the helicoil for the first time, and "tighten" the helicoil into its new thread (tighten the bolt up very tight!). Remove said bolt, and re-install the bolt you want to use and torque to correct specification.

Helicoils only fail if not tapped or fitted correctly.

[RPM016T]

Go to CBC Bearings. They stock helicoils in smaller quantities.