Cleaning crank threads?

[julianf]

Doing the timing belt on my 300tdi.

Odd experience - normally when you undo a bolt, after the initial crack, things get progressively easier.

This one was really tough, and stayed really tough. You can see in the photo above that I'd got 10 mm or so of thread exposed when it bound up again entirely.

This was with a 3 foot breaker. It got to the point where the deflection on the bar was fearful and the whole engine was just rocking on its mounts.

The only torch I have is a full size mapp, but I had to resort to that, very cautiously, as the damper is part rubber, and it came out.

The thread looks fine, but there's clearly some sort of thread lock on it, which was probably the issue.


The belt was last changed by me, about 12 years ago (engine has been stored for a lot of that time) and I was 250 miles from home, using whatever tools I could scrape up.

I reckon I put some thread lock on that was whatever I had access to, and it was a bit too extreme.



Anyway, what now?

I can easily clean up the male side, but the effort that I needed to get this undone will exceed the tightening torque, assuming it's the same on the way back in.

Will it be? I don't know. Id need to reposition the locking tool to test, which I plan to do, but what's my best plan?


I'm concerned that a tap may take off metal and loosen the bolt on an area that is already problematic on the design.

 

[voipio]

Run a die over it, and a tap through the nut. Or use a thread file. I've used a carborundum tipped scriber on occasions.

 

[Kram]

Thead lock is usually brittle and can be peeled out with a stanley blade or triangular needle file, or carbide lathe tip. Using a tap to clean male threads works well, you wont damage it easily - where as a die might cut some clearance.

Or did you mean to clean the nut? A tap of same pitch but smaller size is good for cleaning.

Soak in acetone may soften or disolve it.

 

[julianf]

To clarify -

The male thread (the bolt) can be cleaned by hand easily enough, but the female thread (the crank) is what I'm concerned about.

 

[Kram]

Acetone + smaller tap of same pitch

Keep acetone away from any seals, dont use if seals are near by.

 

[Agroshield]

You can make a poor man's tap out of a standard bolt by cutting some grooves in it with a dremel. Angle them in a little to give a bit of a hook (positive rake).

The advantage of this is that the bolt is softer than a tap would be. A bolt will also be slightly smaller than the corresponding tap. The tap proper cuts a thread that gives correct clearance on a bolt inserted into the tapped thread.

Once the 'tap' has been in and out, if you still see any gunk on the female threads, jam some wood into one of the grooves you have ground in the bolt. That will push it slightly off centre and cause it to cut a little deeper.

 

[Seadog]

It's probably a non-standard thread, I expect.

 

[julianf]

I've sorted it now.

Cleaned the bolt by hand. Pick or razor blade.

Attempted to scrape about in the crank end with a pick for a while, and then used the bolt a few times, re-cleaning the thread on it each time.

I can now hand tighten / loosen the bolt, by hand, to further than it needs to go on final tightening.

It means that my torque reading on reassembly will not be influenced by old thread lock.


(I've got the damper off too now, so that should be all the hard bits done... should be...)

 

[Ian X]

Picks and patience followed by a blow gun or can of air duster. On a male thread if there is enough access a small brass wire wheel (real brass) normally lifts Loctite 263. Glad you sorted it, I detest dealing with fasteners stuck by aged high strength thread lock, swinging on a long bar or even a cheater pipe and you think, well you think the part might give way at any moment or follow the path of least resistance and distort either part of the fastener. Even the rattle gun causes fear if you have to resort to the 1" drive one on a 10mm fastener, spark erosion seems to be an expensive option when it gives way.

 

[Morrisman]

When you were unscrewing the tight bolt did you back it up every so often, not just unscrew continuously in one direction? That can make a massive different with a really tight bolt, much the same way you reverse regularly when tapping a thread.

 

[julianf]

When you were unscrewing the tight bolt did you back it up every so often, not just unscrew continuously in one direction? That can make a massive different with a really tight bolt, much the same way you reverse regularly when tapping a thread.

No. As mentioned, you have to lock the rotation with a tool. To then change the direction of rotation, it's needed to undo all the tool and rotate it. Which becomes near impossible anyway, as it binds itself to another part.

I 100% agree with what you are saying. Just in this specific example, it's not even slightly easy to do.

I think that the moderate heat was the solution. I should have done that earlier. One of those inductive heating coils would have been the best thing for the job.

 

[Morrisman]

When I had my Mondeo timing belt done the mechanic pointed out that it had already been done at some stage, but there was nothing in the very comprehensive paperwork to state that.
It wasn’t actually due for it another 5k miles, so why someone would do it prematurely is beyond me.

The mechanic said it had a cheap aftermarket belt on, and the centre bolt had been re-used, and drowned in thread locker. The correct bolt is a one time use, with a thread locker coating already on it.