Sump plug thread

MikeG

MikeG

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what is the size of the sump plug used on my 71 Commando engine? Its the larger plug with the screen, replaced with one of Comstocks sump breathers, but I can't seem to find a tap or thread chaser the proper size. It measures 1 3/16 OD on the plug thread and is 20 TPI. I've seen it listed as 7/8 (whitworth?) but nothing I find is that TPI count.
 
You should be able to chase up a thread file for the size thread you need, thread files come in handy and usually have 8 difference threads on each file, my set fits every thread on my Norton from fine to course threads, have used them to clean the exhaust threads and may other threads on my Norton as well a few mates, saved a lot of threads over the years.

Ashley
 
I need to clean up internal threads, and it's a bit far gone for just a thread file.
 
You be surprised in what a thread file can do and save, be easy to use one on that big drain plug thread.
 
It's not the plug, it's the threads in the case.
 
MikeG said:
It's not the plug, it's the threads in the case.
Click to expand...
A thread file will clean the thread in the large gauze/drain in the case, using the end threads on the file and not using the file part, you can run the end of the file around.
 
baz said:
You may be able to use an old sump plug as a chaser by cutting some hacksaw cuts into it
But it all depends just how bad your thread is
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A small cut off wheel and dremel works well to make those cuts too. Don't make the cut(s) too close to the thread lead or it will be difficult to get the chaser started
 
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Its l 3/16-20 thread. One image is test piece to make sure before i ran the tap in
Sump plug thread
Sump plug thread
 
When I changed my oil today, I found out that someone tapped out the hole and installed a metric oil plug with the magnet on the end. I had changed the oil previously and don't remember the plug being metric, but in between I sent the bike out for a rebuild .
 
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Reactions: TBW
Another approach to cleaning up a compromised internal thread is to use a smaller size tap as a scraper.
According to MikeG, the sump plug is a l 3/16-20 thread. Most people don't have a thread that size!
A 1/4 x 20 tap is very common. The tap can be used as a scraping tool, not that different from a thread file.
Assuming there are still some decent threads, they will help register the tap on the more compromised threads.
A good quality "T" style tap wrench will help hold the tap parallel to the bore, and give some leverage and control.
 
My issue was the hole was distorted at the end due to the case being dropped. Judicious use of an improvised tool to take the distortion out and VERY CAREFULLY inserting the tap to engage existing threads was the only way out short of opening the hole up on the mill and making an insert of some sort. It worked.
 
MikeG said:
what is the size of the sump plug used on my 71 Commando engine? Its the larger plug with the screen, replaced with one of Comstocks sump breathers, but I can't seem to find a tap or thread chaser the proper size. It measures 1 3/16 OD on the plug thread and is 20 TPI. I've seen it listed as 7/8 (whitworth?) but nothing I find is that TPI count.
Click to expand...
It's a Whit Form thread, ie a Whitworth thread angle with a TPI that falls outside the standard TPI table. Norton used lots of these Whit Form threads.
 
Just in case you have not found a solution….there is a 1 3/16” British CEI tap for sale on British Tools and Fasteners website. $165.
 
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