Tapping a Carburetor float bowl Thread size anyone?

[peanut]

there was a screw missing from one of the float bowls when I went to overhaul them. it didn't take long to find out why....the thread has been stripped some time in the past

Wouldn't you know it... it has to be the one that is virtually a blind hole .!

I take it my options are limited to using a blind tap to tap it larger, fixing a nut on the bolt (probably not enough room and bodging it by fixing a stud in the hole with JB weld

Does anyone know what the carb screw sizes are ? it looks to be a 0.7mm thread but the screw shank measures 3.8mm ? so I guess its a BA thread ?

When I know what the next size up is I'll order up a tap today

 

[Speedthriller]

The screws are M4.

 

[Maurice]

M4 0.7mm pitch

Would helicoil or time-sert fit there? Given the load those are under I'd even use JB weld and re-tap it to same size.

 

[weekendrider]

peanut, this thread may help you.
http://www.650rider.com/index.php?n...ostorder=asc&highlight=carb+helicoil&start=24

 

[peanut]

thanks everyone thats very helpful.

I must admit I was a bit surprised that the screw measured so small but i guess it was either worn or it is the wrong screw.

It might seem strange but I think it would probably be stronger to set a stud in JB Weld and use a nut rather than tap JB Weld and screw into it

 

[Maurice]

It's going to be a royal pain in the butt, assuming you manage to use a nut there, to screw it on/off given the space available around it.

Just sayin'

I would personally try something like a timesert, but measure first that there is enough material left on the carb body.

 

[peanut]

It's going to be a royal pain in the butt, assuming you manage to use a nut there, to screw it on/off given the space available around it.


.

it would be just my luck to have to strip the carbs every week lol

 

[ANLAF]

peanut, looks like stud and nut is the best option. I have just got some time-sert for 14mm spark plug holes, i would be impressed to see 4mm time-serts (actually larger to fir the hole), but if they do, then I would look at Maurice's suggestions too. It will work with stud and nut, of course, and it is out of sight.

Anlaf

 

[weekendrider]

peanut, did you look at the thread I linked to?
A helicoil works. Still in service after five years.

 

[peanut]

yes I did ,it was very interesting thread. I'm stuck in the middle of welding my van at the moment so all work on the bike is on hold.

I think I will either drill and tap it at 5mm or use a helicoil type product but I haven't decided yet.
Thanks for your help with this, I'll come back with the outcome when I tackle it.

 

[CalsXS2]

I went through the same thing.

Since I didn't have anything to loose, I tried screwing a SAE thread screw in there just to see what happens. Well it worked. And is holding well. I've had the bowl off many times for re-jetting.

I'll have to see if I posted anything before on the size. But I'm thinking it was a 10-24, or 10-32. I'll see what I can dig up and let you know.

 

[CalsXS2]

I found the info.

I used a 8-32. Screwed right in. I think I had to use a washer at first because the screw was a tad to long. I think I later ground some off the length off so it was just right. Just remember to keep track of that screw.

Here's the link.

http://www.xs650.com/forum/showthread.php?t=8488

 

[peanut]

thanks for that info Calsxs2

I might try going through my box of screws first I've nothing to lose.

 

[TwoManyXS1Bs]

Hey, peanut, had same issue many years ago. I simply retapped the stripped bowl screw hole to 8-36, not an easily found size, but used in gunsmithing. You could do it with 8-32 std. 4mm is about .157" dia, #8 machine screw is .164" dia, just enuff to get usable threads. 0.7mm pitch is almost 36 tpi.

http://www.shender4.com/thread_chart.htm

 

[peanut]

thanks twomany thats an extremely useful chart.

 

[hard_y_rd]

I just stripped a float bowl screw. ARRgh. What size helicoil fits in there or can you retap. What did you end up doing peanut?

 

[CalsXS2]

Read my reply above. It's worth a try.

I've had my bowl off dozens of times and everthing has held up just fine.

 

[hard_y_rd]

Thanks CalsXS2. I might try the helicoil route. Wondering what size the tap is for the 4mm X 0.7mm thread helicoil? I guess the drill size is 11/64. Don't want to buy a kit just yet. Expensive buggers. And why does it have to be the hardest screw to get at?

 

[peanut]

I just stripped a float bowl screw. ARRgh. What size helicoil fits in there or can you retap. What did you end up doing peanut?

I put some locktite on it and screwed it back in gently and prayed its held so far.
Twomany had a good solution I thought (post above mine)

 

[hard_y_rd]

I don't think a prayer is going to work in my case unfortunately. All the threads came out with the screw. I wonder if you have to make the hole in the bowl bigger to accept the 8-36 screw?