Marvel Schebler Thread Size?

[stevieb49829]

I'm working on a TSX155 off a MH 101 Jr. The threads in the hole that hold the needle valve seat need a cleaning before I screw in the new seat. Anyone know what pitch and size these threads are? They seem to be an odd size. steve

 

[used red MN]

I'm working on a TSX155 off a MH 101 Jr. The threads in the hole that hold the needle valve seat need a cleaning before I screw in the new seat. Anyone know what pitch and size these threads are? They seem to be an odd size. steve

TimmyD who says he is a plow guy claims it is 8-32 in this post. Seems fairly small for a jet that would also have an internal hole, but I have very little knowledge of MS carbs.
Old YT post

 

[Tim PloughNman Daley RIP]

I'm working on a TSX155 off a MH 101 Jr. The threads in the hole that hold the needle valve seat need a cleaning before I screw in the new seat. Anyone know what pitch and size these threads are? They seem to be an odd size. steve

M'S used standard INCH sizes on all parts - nothing special. 8-32, 10-24, are typical sizes on the carbs. Advise caution so you don't break a tap off. Never use reamers or drills. Remove CARB and place parts in a coffee can and add CAR CLEANER or MINERAL SPIRITS and soak for a week or more. Try using pipe cleaners and old guitar strings to chase out ports in mineral spirit bath. Compressed Air blow out. Wash in a Pine Sol solution bath after, final blow dry. Start rebuild.

 

[Eric in IL]

I'm working on a TSX155 off a MH 101 Jr. The threads in the hole that hold the needle valve seat need a cleaning before I screw in the new seat. Anyone know what pitch and size these threads are? They seem to be an odd size. steve

I'm going to take a guess that it might be a 3/8-27 thread.

 

[used red MN]

TimmyD who says he is a plow guy claims it is 8-32 in this post. Seems fairly small for a jet that would also have an internal hole, but I have very little knowledge of MS carbs.
Old YT post

Seem the idiotic time limit of one hour to edit my reply expired. So…
Oops, a needle valve could be a couple of different things in a carb. The float needle valve seat is probably not an 8-32. I would tend to be more in agreement with Eric.

 

[stevieb49829]

Thanks guys. I think the 3/8-27 is probably right. I used a different top that had good threads, because I didn't have the right tap on hand. I'll have to jot down the specs and look for a tap, IF I ever want to use the other top. I did booger up the slot on the idle jet, even with an impact tool, but some heat and an easy-out worked well. I had enough leftover parts from a couple of kits and it's almost all back together now. Thanks again. steve

 

[T.R.K.]

I am thinking there may have been more than one thread used in those Marvel Schebler carburetors. Some of the seats are 3/8 extra fine threads. I am thinking I have cleaned others with a regular 3/8 fine thread tap.
If you have anything of the old seat left and don't have a SAE thread pitch gauge yourself, See if any of your friends have one.

 

[stevieb49829]

I am thinking there may have been more than one thread used in those Marvel Schebler carburetors. Some of the seats are 3/8 extra fine threads. I am thinking I have cleaned others with a regular 3/8 fine thread tap.
If you have anything of the old seat left and don't have a SAE thread pitch gauge yourself, See if any of your friends have one.

Just for grins, I'll get my machinist rule out and count them. 7 threads in 1/4", so the 3/8-27 is correct. steve

 

[stevieb49829]

M'S used standard INCH sizes on all parts - nothing special. 8-32, 10-24, are typical sizes on the carbs. Advise caution so you don't break a tap off. Never use reamers or drills. Remove CARB and place parts in a coffee can and add CAR CLEANER or MINERAL SPIRITS and soak for a week or more. Try using pipe cleaners and old guitar strings to chase out ports in mineral spirit bath. Compressed Air blow out. Wash in a Pine Sol solution bath after, final blow dry. Start rebuild.

Tim, do you use a special paint on your carbs, in case they get doused with gas? steve

 

[Tim PloughNman Daley RIP]

TimmyD who says he is a plow guy claims it is 8-32 in this post. Seems fairly small for a jet that would also have an internal hole, but I have very little knowledge of MS carbs.
Old YT post

Sorry, 8-32 not Needle Valve, didn't read post thru. Thread likely an NPT or the industry standard fuel and brake special 7/16-24. Will get into it more and get back to ya all.

Tim Daley (MI)

 

[timcasbolt]

I've never heard of 3/8-27, but they're readily available on ebay and amazon. about ten bucks.

 

[4wdtom]

I would say it is a straight thread, not a taper as you want it to seat on the gasket, not the taper getting tight.

 

[Masseyharrisnut]

I'm working on a TSX155 off a MH 101 Jr. The threads in the hole that hold the needle valve seat need a cleaning before I screw in the new seat. Anyone know what pitch and size these threads are? They seem to be an odd size. steve

Hi Steve. Not sure on thread size but all I do is put a small wire brush in my drill and run it through. I have a few different sizes and they are about an inch and a quarter long. Bought at our local Napa store. Have a good weekend.

 

[wore out]

I've never heard of 3/8-27, but they're readily available on ebay and amazon. about ten bucks.

3/8" - 27 is the thread used by the tubes in table lamps, a kit with several such tubes is pictured above.

It is the straight thread version of 1/8" pipe thread, a nut from such a lamp will thread onto a 1/8" pipe thread nipple until it reaches the larger part of the tapered thread. I don't think the threads on a MS main jet are THAT large?

 

[Tim PloughNman Daley RIP]

I'm working on a TSX155 off a MH 101 Jr. The threads in the hole that hold the needle valve seat need a cleaning before I screw in the new seat. Anyone know what pitch and size these threads are? They seem to be an odd size. steve

OK, to be sure you need an original seat to measure with a mic across the Major OD. ALL Carb parts are basically the same but I don't know if the Massey unit takes the same seat as the TSX-241. Why do think you need to chase the carb seat threads? Cleaning at rebuild with a simple nylon or fine brass bottle brush will clean off any gunked up threads. The seat has a fibre gasket under it. Be sure to get old one out and area free of debris before new one is set in. I would not be trying to run a tap down there; it's not necessary. The seat on the TSX-33/TSX-241 Carb uses a 3/8-27 UNS nominal size. NOT tapered. A big mistake fellas make when rebuilding their carb is to assume all passages must be drilled, reamed, or retapped. Wrong. Unit was deigned to a certain diameter spec on passages and wallowing it out with a drill will alter the design flow. A tap can easily be bottomed out and thus risk breaking or stripping out the threads. I suggest you always place carb halves and parts in a coffee can and submerge in CARB CLEANER or MINERAL SPIRITS and let set for at least a week. Then chase ports with pipe cleaners or old guitar strings and blow out. Put your taps, drills, and reamers in the toolbox.

Tim Daley (MI)

 

[stevieb49829]

OK, to be sure you need an original seat to measure with a mic across the Major OD. ALL Carb parts are basically the same but I don't know if the Massey unit takes the same seat as the TSX-241. Why do think you need to chase the carb seat threads? Cleaning at rebuild with a simple nylon or fine brass bottle brush will clean off any gunked up threads. The seat has a fibre gasket under it. Be sure to get old one out and area free of debris before new one is set in. I would not be trying to run a tap down there; it's not necessary. The seat on the TSX-33/TSX-241 Carb uses a 3/8-27 UNS nominal size. NOT tapered. A big mistake fellas make when rebuilding their carb is to assume all passages must be drilled, reamed, or retapped. Wrong. Unit was deigned to a certain diameter spec on passages and wallowing it out with a drill will alter the design flow. A tap can easily be bottomed out and thus risk breaking or stripping out the threads. I suggest you always place carb halves and parts in a coffee can and submerge in CARB CLEANER or MINERAL SPIRITS and let set for at least a week. Then chase ports with pipe cleaners or old guitar strings and blow out. Put your taps, drills, and reamers in the toolbox.

Tim Daley (MI)

It looked like a bit of hard carbon or scale rust in the first thread or two. I saw the brass threads on the old seat partially stripped on their way out of these dirty threads, and the new seat did not want to hand-thread back in. I don't chase threads unless they need it. The major outside diameter on the new seat is a couple thousandths over 3/8. The old seat was about .010-15 under that, because they were partially stripped on their way out of the hole. I know I didn't have the proper tap to chase these threads, so I switched to a top that had clean threads and will work on this top once I get an appropriate tap.

On a side note, I did NOT try to get the main jet out of its hole. Just made sure there wasn't any debris in it or behind it. I'm not sure there is any treatment that would loosen up that tiny brass jet on an old rusty carb, so it could easily be replaced. I was very carefull of that jet when I drilled the piece of nozzle out and chased those threads. The new nozzle went right back in and tightened down on the fiber gasket. I've done that one before, the same way. Just very time consuming to get it out and thoroughly clean. Thanks for your help on this. steve

 

[Mike(NEOhio)]

I've been following this. I currently have two TSX 264s and a TSV 13 in pieces so I pulled them out to see for myself. The float needle seats are all 3/8-27 as was stated. I really thought it would be 3/8-24 but my tap would not go in. My thread pitch gauge only has 24 and 28, neither one fit so I pulled out my 1/8-27 NPS tap and that was it. pitchwise, however, 3/8 pipe is .402 OD.

 

[Mike(NEOhio)]

It looked like a bit of hard carbon or scale rust in the first thread or two. I saw the brass threads on the old seat partially stripped on their way out of these dirty threads, and the new seat did not want to hand-thread back in. I don't chase threads unless they need it. The major outside diameter on the new seat is a couple thousandths over 3/8. The old seat was about .010-15 under that, because they were partially stripped on their way out of the hole. I know I didn't have the proper tap to chase these threads, so I switched to a top that had clean threads and will work on this top once I get an appropriate tap.

On a side note, I did NOT try to get the main jet out of its hole. Just made sure there wasn't any debris in it or behind it. I'm not sure there is any treatment that would loosen up that tiny brass jet on an old rusty carb, so it could easily be replaced. I was very carefull of that jet when I drilled the piece of nozzle out and chased those threads. The new nozzle went right back in and tightened down on the fiber gasket. I've done that one before, the same way. Just very time consuming to get it out and thoroughly clean. Thanks for your help on this. steve

I've had good luck getting brass jets and nozzles out just by heating with a propane torch, just enough till they will smoke a bit. Clamp the carb to the bench so I can use both hands on the screwdriver or wrench. And use a good screwdriver, usually both hands and my chin.

 

[stevieb49829]

Hi Steve. Not sure on thread size but all I do is put a small wire brush in my drill and run it through. I have a few different sizes and they are about an inch and a quarter long. Bought at our local Napa store. Have a good weekend.

Hi. Are you talking about running a tiny brush through the jet orifice itself? I'm not sure I'd be able to find a small enough brush, other than the one I got from the dentist. I think they call them inter-dental stimulators (LOL). steve

 

[Masseyharrisnut]

Hi. Are you talking about running a tiny brush through the jet orifice itself? I'm not sure I'd be able to find a small enough brush, other than the one I got from the dentist. I think they call them inter-dental stimulators (LOL). steve

I Just use them on the ports after the jets are removed. I’m going to get an ultrasonic cleaner and give that a try on some of my old carbs.