helicoils advice

[Meatball]

Ive dropped a bk over the weekend, ive managed to cross thread the first 2 threads of my crank (i know what an idiot or words to that effect) , is it possible to get a helicoil in straight with it in situ? as you can guess i really dont want to strip the engine or lift it out.
ive tried to get a matching tap in to see if i can clean the threads but after closer inspection the first two are as good as flat

Any ideas

[Justin S]

are you totally sure you cannot get the thread sorted with a tap? There should be enough threads beyond to take up any loss of the first 2 you have made a mess of. I am guessing at the crankshaft pulley bolt, which is pretty meaty into the crankshaft.

[Meatball]

The problems getting it on straight and not messing the remaining threads,
Another way could be drilling out the first 2 threads and try and pick up from there

[stevieturbo]

If you cant run a simple tap into it straight, which is a very easy task. I'd hate to see what damage you'd do trying to stick a drill in there !!!

And to helicoil requires drilling larger, tapping then inserting the helicoil.

[Meatball]

I didnt say i was going to do it

[Mr2Mike]

stevieturbo said:

If you cant run a simple tap into it straight, which is a very easy task.

That's a bit harsh; if the first couple of turns are really mangled then it could be difficult to get the tap to start cutting in the right place. The last thing you want to do it start cutting across the remaining good threads.

[Pumaracing]

Restoring a blind thread where the top threads are damaged is not easy at the best of times. Firstly you need what's called a 1st tap or taper tap rather than a 2nd or bottoming tap. A 1st tap has a long tapered nose for creating new threads in raw drilled material and will pick up better on undamaged lower threads than a blunter ended 2nd or bottoming tap.

However even with one it's no guarantee of success. What would be nice would be an expanding tap with say just 4 or 5 threads on it that you could push down the hole, expand out on a central mandrel until it had picked up on the good threads lower down and then wind back out to restore the damaged top threads. I've never seen such a thing though. Maybe I should invent one.

Hah!!! Just done a bit of googling and bugger me someone's actually thought of it.

http://www.icscuttingtools.com/catalog/page_359A.p...

A two handled expanding tool that you can lock to size inside a thread and wind back out. It says only for holes bigger than 3/4" I/D though so whether this would go down your crank thread I can't say.

[Steve_D]

If you were to give the task to someone else i'm pretty sure he would want it on the bench as it will not be an easy job even on the bench.

The job will involve drilling out the hole to about the same size as the existing thread so your best bet is to continue working with a 1st tap to try and clean out the thread. If you fail and end up stripping out the remainder of the thread the hole will be about the size needed to start tapping for the helicoil so nothing will be lost.

Before resorting to a helicoil I would look at just tapping out for a larger thread and fitting a larger bolt.

Steve

[cinquecento]

Could you not get a thread file.. insert it well into the hole then carefully file the 2 outside threads to clean them up?

Edited by cinquecento on Tuesday 7th September 11:59

[Meatball]

Thanks for the advice, ive got a local engineer looking at it on wednesday - he has a tool which should remove the first 2 threads..so fingers crossed.

[stevieturbo]

Pumaracing said:

Restoring a blind thread where the top threads are damaged is not easy at the best of times. Firstly you need what's called a 1st tap or taper tap rather than a 2nd or bottoming tap. A 1st tap has a long tapered nose for creating new threads in raw drilled material and will pick up better on undamaged lower threads than a blunter ended 2nd or bottoming tap.

However even with one it's no guarantee of success. What would be nice would be an expanding tap with say just 4 or 5 threads on it that you could push down the hole, expand out on a central mandrel until it had picked up on the good threads lower down and then wind back out to restore the damaged top threads. I've never seen such a thing though. Maybe I should invent one.

Hah!!! Just done a bit of googling and bugger me someone's actually thought of it.

http://www.icscuttingtools.com/catalog/page_359A.p...

A two handled expanding tool that you can lock to size inside a thread and wind back out. It says only for holes bigger than 3/4" I/D though so whether this would go down your crank thread I can't say.

You can get such tools for spark plug threads. pretty cool.

[Meatball]

That was a close one i managed to re tap the thread in the end thank god

[The Black Flash]

Good to hear

[Simon says]

Top banana now go and buy a lottery ticket