Retapping carb bowl drain screws to a common size - anyone?

[Guest]

Has anyone tried and succeeded at tapping new larger threads into their carb bowls? This M6x0.5 thread is bizarre, rare, and $6+ per bolt mail order for the Suzuki part. I can pay it, but it's kind of over the top to get another steel fastener that could corrode, which is what the last ones did.

I would do brass or nylon or even acrylic, but bolts with this thread pitch are like unobtanium. I could get a set of 4 slightly oversized bolts, file them down, cut new threads, but I'd rather alter the bowls to be a more normal size than try to fuss with rethreading tiny little bolts.

Is there enough material to retap it to say M8 or even just going to the nearest Inch size?

Looking at some thread size charts, I think that either 1/4 or 5/16 is the closest larger size.

[cowboyup3371]

Where are you paying $6 a screw? Ace hardware has them for a lot less and should still be open even in this lockdown.

[steveb922]

I think the OP is referring to the price of OEM parts. The size he needs (m6 x 0.5 pitch) is not common, but I would expect a specialist fastener supplier to stock them at considerably less than $6 each.

[chuck hahn]

Ive retapped stripped ones larger and had to drill bowl hole to accept the new screw.

[WilliamGLX81]

Ive retapped stripped ones larger and had to drill bowl hole to accept the new screw.

Did you have any issues sealing them with that change?

And even other places I've looked have them, but never in stainless or brass. They are still about 5-6 each because the thread pitch is very uncommon.

[chuck hahn]

No leaks here...

[greg78gs750]

ugh the very thought of putting imperial fasteners on a metric bike makes me cringe. My originals are nearly 40 years old now with no appreciable wear or corrosion. Do you store it in the ocean or something?

[WilliamGLX81]

Haha, yes I cringe at it too, but they shouldn't really need replacing very often. It sat a lot near (5 miles from) the ocean, and had a pair of leaking needle valves. Somehow that led to water getting into all 4 carbs and left me some nice globs of varnish+rust on the bottoms of them.

[Steve]

Are you saying that you need a new bowl (or more) or a new screw (or more)?

Or are you just commenting on the price of replacements?

If you need parts, let me know, I have spares.

.

[bwringer]

M6 x 0.5 is pretty much unobtanium. M6X1.0 is the standard M6 pitch, and M6X0.75 is rare but available. You can find a die in this size, but it will cost more than just buying the screws.

I've also never found an aftermarket substitute.

I did once tap a stripped float bowl to M7x1.0. My local hardware store had M7 stuff for some reason, and it worked OK, but I replaced the bowl eventually.


If you have a small lathe or know a bored machinist, I suppose you could figure something out. But overall, you're going to waste a lot less time and money just paying the $30 or so for new ones. They're zinc coated, so should remain shiny for a long time unless you're in the habit of parking overnight in swamps or low tide zones. In which case you have far more serious problems than the existential horror of rusty float bowl screws.


And, as Steve noted, there is no shortage of good used carb parts. If you need a good float bowl or some shiny-ish used screws, he can hook you up.

[WilliamGLX81]

Hey, everybody. I got creative and bought some mostly-zinc solder "brazing" rod as well as some hollow aluminum tube to try to solder in if I wasn't able to fill the hole.

I was able to fill in the hole and re-tap it, but I had leaks most of the times I tried it. I think 1 of 3 times I tried it, I didn't have any leakage. There was porosity in the solder material that I think allows liquid through.

I did try to use some flux from McMaster Carr, but it leaked most of its liquid out of the container in shipping, and caused more problems than it solved. I should probably give up at this point and take one of you folks up on the offer of a spare bowl.

[Rijko]

you may want to try take Eric up on his 'shameless plug'

https://www.thegsresources.com/_forum/showthread.php?257694-Buying-quot-bolts-and-wiring-quot-and-other-stuff-in-the-UK&p=2583906#post2583906

[Big T]

You're doing a lot of work for a problem that barely exists

[bwringer]

Yep, there are plenty of good used carb bowls and drain screws in the wild, just waiting for you to purchase cheap.

It's sort of a common "leftover" part when carb bodies are not salvageable.

[Steve]

Go back and read post #9. Offer still stands.

.