Topic: Cleaning (chasing) threaded holes

[mystic_1]

So, this may be a common trick, and to be honest I don't even remember where I learned it, but I just used it today and I thought I'd post it here.

So I recently received a crankcase that needed cleaning, including cleaning out all the threaded holes.  I could have run a tap through them but sometimes that can result in a slightly looser fit for your bolts (different thread profiles, maybe?).  Also, a tap will not always reach the bottoms of blind holes, due to the tapered starting region of the tap.

So what you do is, take an old but good bolt of the same size as the hole you want to clean, and cut a couple of shallow slots down the length of it with your dremel or die grinder:



(click for larger images)

I cut two slots.  As you can see they don't necessarily have to be the prettiest things, but should be relatively clean cuts.  They should be slightly deeper than the threads in the bolt, and maybe three quarters to one inch long.





After using your chemical of choice to hose down the hole and removing most of the larger rocks, small animals, etc, you thread your new chasing tool into the hole.  The slots collect any garbage.  If the hole is very dirty, run the tool in a little then take it out and clean the slots.  Then turn it back in a bit further, and repeat as necessary.  If the hole is fairly clean you can just run it in all the way in one go.  I use a brass brush in between passes to remove the crud from the slots in the chaser.

I like to put a 1/4 inch socket drive adapter on my cordless screwdriver and use that to run the chasing tool in and out, just be careful when starting the tool into the hole that you don't bugger the threads.

Cheers

mystic_1

[troppo]

thats a great tip mystic
thanks mate
cheeers
troppo

[754]

That method will get stuff out of the holes.

However when assembling an engine torque values are on a clean hole, and the bolt wont pull all loctite and crap out, which can alter torque readings.

I prefer to use a bottoming tap or ground down tap with maybe a bit of grease to catch stuff as it comes off..

[mystic_1]

You're absolutely right that holes must be perfectly clean in order assure accurate torque values.  This form of cleaning is probably not sufficient for critical areas like conrod nuts, case studs, and the like, but should be fine for a majority of holes.  Many of my tips are geared towards accomplishing tasks in the lack of professional grade tools and a lot of people don't have bottoming taps in their garages.  If you DO have such things than this tip is obviously not for you lol

On the crankcase I'm working on, I'm visually inspecting each hole as I go in order to ensure the threads are 100% clean and undamaged.  So far I'm hugely impressed, not a single damaged thread anywhere on the case, just lots of junk in the holes.  I soaked the case in engine degreaser for several hours then pressure washed it to remove the bulk of the junk.  When cleaning the threaded holes I'm using degreaser with the thread chaser on the first pass, then carb cleaner on a second pass.  When done, the threads are bright and shiny all the way down.  After I'm done with my reconditioning, I'm going to have the case halves hot tanked.

I only pull out the taps for seriously munged holes that can't be effectively cleaned with this method.  Better safe than sorry IMO.  Because the threads of this 'tool' match the thread profile very closely, it will remove most foreign material, perhaps even better than a cheap Ace Hardware tap.

mystic_1

[BobbyR]

You cannot really get an accurate torque value on a used bolt. After torquing the bolt it has been stretched to 75 percent of its rating. With 4 percent tolerance on torque +/- the bolt may be at 83 percent of useful clamping. Therefore it will not have the same clamping strength as it did when it was first installed. I reuse bolts myself but I use  a mild Loctite which not only makes it more vibration resistant, it also retards galvanic action.