Cleaning out bolt threads

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RJJ

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Hello

I bought an after-market exhaust elbow for Penta D2 55. Seems a decent bit of kit, however I am struggling to fit the (original) water inlet using the two (original) machine screws. The screws still work fine in the original corroded elbow.

It looks as though the makers were a bit enthusiastic with the primer, and there's paint in the threads. They swear it's the same M8 thread...and it appears to be as far as I can tell.

Recommendations please to clean the threads of excess paint? Chemical or mechanical methods? I already have a heat gun, HCl and caustic soda to hand if those are any good.

Many thanks indeed.
 
What about running a m8 tap through it?
Another option would be a pick and slowly clean the thread.
Get a m8 bolt, cut a slot on both sides, wind it in a little, remove, repeat until paint removed
 
You should really run a M8 tap down the threads but in the absence of a tap you can make one from an old M8 bolt. Just cut vertical slots, 4 with a hacksaw starting deep at the end and tapering off to nil about an inch from the end. Just work it back and forward gently and the paint in the threads will go into the slots cut. Take it out clean off the thread paint and continue until the bolt goes right down.
 
The proper tool for this job is a thread restorer, not a tap. Here's a metric set on Amazon:

81Ev9fmXaAL._AC_SL1500_.jpg


When I rebuilt my Triumph Herald I bought a set of UNF/UNC thread restorers and they were without doubt among the most useful tools I had.
 
There are three types of thread tap ...

1. Non bottoming that can exit other side and usually has a longer taper at start ..
2. Bottoming tap that has very short start taper - to allow the thread cutting to go as deep as possible
3. Thread restorers

No 2 or 3 are the ones for this job.

If you have a Thread set - you often have the bolt thread cutter die as well ... so run that down the bolt as well - this not only cleans the bolt but also tells you - the exact thread.
 
Refueler said:
1. Non bottoming that can exit other side and usually has a longer taper at start ..[/qupte]

That's a "taper" or a "plug" depending on the length of taper - 8 to 10 or 3 to 5. A taper is definitely not suitable, as you say, because it tends to cut a new thread rather than pick up and clean the old one. A plug can be used, with care, but bottoming or restorer are, again as you say, better.
Click to expand...
 
If you don't have any paint remover, brake fluid is often effective.
Picking the paint out with an improvised single point tool initially might avoid the risk of cross-threading a tap?
 

There are three types of tap; taper, second and plug. Plug tap has no taper.

Not sure why you have problems with a taper tap Jumble Duck? On a really bad thread that would be my first choice.
 
Refueler said:
There are three types of thread tap ...

1. Non bottoming that can exit other side and usually has a longer taper at start ..
2. Bottoming tap that has very short start taper - to allow the thread cutting to go as deep as possible
3. Thread restorers

No 2 or 3 are the ones for this job.

If you have a Thread set - you often have the bolt thread cutter die as well ... so run that down the bolt as well - this not only cleans the bolt but also tells you - the exact thread.
Click to expand...

There are three types of tap, but they are Taper, Second and Bottoming taps

The "second" tap has a shorter taper and the "bottoming" tap has pretty much no taper, used for tapping blind holes.

Thread restorers are different beasts altogether. These are used to clean and re-profile threads, without cutting extra material away.

Taper or second taps are not best suited to the job of cleaning paint from threads (as you say). A bottoming tap isn't much better. Best thing is the thread restorer. In the absence of a thread restorer, a bolt with hacksaw cut along the sides makes a decent job. Just look closely at the set JD posted.
 
penberth3 said:
There are three types of tap; taper, second and plug. Plug tap has no taper.
Click to expand...
I've heard those terms too.

Not sure why you have problems with a taper tap Jumble Duck? On a really bad thread that would be my first choice.
Click to expand...
The problem is that a taper tap is - more or less by definition - designed to get a very gentle grip on the material and then cut its way in to a proper thread. Try it on a damaged thread and it is far more likely to start cutting a new one than to "find" the old one and clean it out. I've used second cut taps to clean out threads and though they work, a proper well-made thread repair tool is a revelation in comparison.

As with all cutting tools, though, it's important to have good ones. Lots of cheap rubbish around. My UNF set are Britool and were not cheap.
 
RJJ said:
Hello

I bought an after-market exhaust elbow for Penta D2 55. Seems a decent bit of kit, however I am struggling to fit the (original) water inlet using the two (original) machine screws. The screws still work fine in the original corroded elbow.

It looks as though the makers were a bit enthusiastic with the primer, and there's paint in the threads. They swear it's the same M8 thread...and it appears to be as far as I can tell.

Recommendations please to clean the threads of excess paint? Chemical or mechanical methods? I already have a heat gun, HCl and caustic soda to hand if those are any good.

Many thanks indeed.
Click to expand...

I had exactly this problem with a stainless aftermarket elbow for a Volvo a few months back.

Caused me no end of grief trying to fit - exactly as you described. It turned out that in manufacture, the mating face had warped, and the bolt holes had turned inwards accordingly. As a result I could only get it part way over the bolts.

When I contacted them it turned out there were similar elbows in the stainless batch.

I returned it and fitted a genuine Volvo instead. I would have preferred stainless but I'd already paid to have the face milled flat before I realised it wouldn't go over the bolts, so had had enough by then.
 
johnalison said:
You overlook the fascination that engineering talk has for the ignorant. To me, it is a bit like Latin verse - I know that it is a thing of beauty but I can't understand a word of it.
Click to expand...
Bit like the comment from our wives when we three brothers start talking... Is that code????? for something
 
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