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ZS throttle shaft - how to determine excess wear
- Thread starter tdskip
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TR4
Jedi Knight
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I believe there should be very little movement on properly fitted shafts. One test is while the carbs are still on the car, squirting carb cleaner at the point where the shaft enters the carb body and see if that affects the RPM's. That tells you air is being sucked in past the shafts. I removed my shafts and on my carbs and had excessive wear to them so simply replaced the shafts with good success. if the carb body is worn, the body needs to be bored out and sleeves added to correct that issue.
guzzul
Jedi Warrior
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Re: ZS throttle shaft - how to determine excess we
Pretty much *no* perceptible wobble is a good start. These carbs will accommodate a little bit of play, particularly if the rubber shaft seals on them are in good nick, which will help with keeping air from getting sucked through the throttle shaft. But not much.
Hopefully any wear you do detect will be mostly in the throttle shaft itself. When you pull the shaft you will see the wear marks where they rub against the carb body bushing, and you can use a micrometer to verify wear. Shafts are not expensive, nor are seals. Often replacing the shaft and seals will do the trick. If you notice quite a lot of wobble, you may need to consider reaming out the carb bushings and installing an oversize shaft, or replacing the bushings.
Check the butterfly discs closely as well. They tend to wear on one side more than the other as the throttle shaft return spring 'torques' the shaft a bit when you open the throttle. When you remove the disc this wear should be apparent, because the piece where it mounts in the shaft will be longer than the rest of the disc.
Pretty much *no* perceptible wobble is a good start. These carbs will accommodate a little bit of play, particularly if the rubber shaft seals on them are in good nick, which will help with keeping air from getting sucked through the throttle shaft. But not much.
Hopefully any wear you do detect will be mostly in the throttle shaft itself. When you pull the shaft you will see the wear marks where they rub against the carb body bushing, and you can use a micrometer to verify wear. Shafts are not expensive, nor are seals. Often replacing the shaft and seals will do the trick. If you notice quite a lot of wobble, you may need to consider reaming out the carb bushings and installing an oversize shaft, or replacing the bushings.
Check the butterfly discs closely as well. They tend to wear on one side more than the other as the throttle shaft return spring 'torques' the shaft a bit when you open the throttle. When you remove the disc this wear should be apparent, because the piece where it mounts in the shaft will be longer than the rest of the disc.
Re: ZS throttle shaft - how to determine excess we
There really shouldn't be any play. For a very slight movement, I would try a new shaft first, and you WILL need a new butterfly disc. Note that some ZS carbs did not originally come with o-rings on the throttle shafts. There are "cups" which fit on the outside which will also seal the throttle shafts.
Finally, if you do need to ream the bodies, see this article:
https://www.chicagolandmgclub.com/driveline00/1001/jasw.html
I redid the ZS on my Herald last year, what a difference!
There really shouldn't be any play. For a very slight movement, I would try a new shaft first, and you WILL need a new butterfly disc. Note that some ZS carbs did not originally come with o-rings on the throttle shafts. There are "cups" which fit on the outside which will also seal the throttle shafts.
Finally, if you do need to ream the bodies, see this article:
https://www.chicagolandmgclub.com/driveline00/1001/jasw.html
I redid the ZS on my Herald last year, what a difference!
TR4
Jedi Knight
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Re: ZS throttle shaft - how to determine excess we
The ZS throttle shafts on my TR4 carbs did not have o-rings or cups fitted to seal the shaft so a good shaft fit was required. Mine did have very slight movement with the new shafts installed but they work real well so I did not choose to bore the carb body for oversized shafts or to insert bushings. I have a spare set of carbs I rebuilt that are only slightly better than the ones installed but I have not tested those yet.
The ZS throttle shafts on my TR4 carbs did not have o-rings or cups fitted to seal the shaft so a good shaft fit was required. Mine did have very slight movement with the new shafts installed but they work real well so I did not choose to bore the carb body for oversized shafts or to insert bushings. I have a spare set of carbs I rebuilt that are only slightly better than the ones installed but I have not tested those yet.
TR3driver
Great Pumpkin - R.I.P
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Re: ZS throttle shaft - how to determine excess we
Why? Do they wear that badly on ZS carbs? My H6 SUs had a lot of play in the throttle shafts, to the point that the butterfly was dragging on the bore and holding itself open. But the butterflies looked OK so I reused them, no problem.70herald said:
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Re: ZS throttle shaft - how to determine excess we
Yeah, they will, Randall. I've redone some that looked like they were easily 1/64"+ worn. Spring and/or linkage apparently puts a side load on 'em. I spent a good deal of time puzzlin' over whether or not there was some mis-alignment the first time I saw it. In the end I just replaced 'em along with shafts as part of the rebuilds.
Yeah, they will, Randall. I've redone some that looked like they were easily 1/64"+ worn. Spring and/or linkage apparently puts a side load on 'em. I spent a good deal of time puzzlin' over whether or not there was some mis-alignment the first time I saw it. In the end I just replaced 'em along with shafts as part of the rebuilds.
poolboy
Yoda
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Re: ZS throttle shaft - how to determine excess we
TD, when you remove the thin brass cups that fit over the "rubber" bushings, it might be a good idea to be gentle with them. The new ones that came in the last kit I got were a little too big in the O.D.
I was left with the choice of reusing the old ones or polishing down the new ones to fit inside the carb.
After polishing one, trial fitting, polishing more...I ended up reusing 3 old ones. I think their function is more or less as a keeper for the actual bushing.
You know that the screws holding the disc are flared at the end of the threads and will offer resistance to your efforts to remove them ? *** Make sure you have or shape a screwdriver blade to fit the screw slots ***
And don't forget to polish the screw holes on the shaft for burrs that might snag the new bushing on the way back in. And lube the shaft or I.D. of the bushings.
That's about the only complications that I've run into on that step.
TD, when you remove the thin brass cups that fit over the "rubber" bushings, it might be a good idea to be gentle with them. The new ones that came in the last kit I got were a little too big in the O.D.
I was left with the choice of reusing the old ones or polishing down the new ones to fit inside the carb.
After polishing one, trial fitting, polishing more...I ended up reusing 3 old ones. I think their function is more or less as a keeper for the actual bushing.
You know that the screws holding the disc are flared at the end of the threads and will offer resistance to your efforts to remove them ? *** Make sure you have or shape a screwdriver blade to fit the screw slots ***
And don't forget to polish the screw holes on the shaft for burrs that might snag the new bushing on the way back in. And lube the shaft or I.D. of the bushings.
That's about the only complications that I've run into on that step.
guzzul
Jedi Warrior
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Re: ZS throttle shaft - how to determine excess we
You can get away with a little movement as long as you have a good air seal on the shaft. A new disc will also help if the disc is worn. As the disc wears, the throttle shaft tends to have a little more side-ways play. A new disc helps kind of 'true' everything up IMO.
Sounds like you might get away with a new throttle shaft and seals. When you pull the shaft you will be able to see the wear clearly (and measure it if needs be). I'm assuming you already have the shaft return spring and linkage disconnected when you are checking for movement. If not, I expect you will notice more play when its just the shaft and disc with nothing else to hold it.tdskip said:
You can get away with a little movement as long as you have a good air seal on the shaft. A new disc will also help if the disc is worn. As the disc wears, the throttle shaft tends to have a little more side-ways play. A new disc helps kind of 'true' everything up IMO.
TR3driver
Great Pumpkin - R.I.P
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Re: ZS throttle shaft - how to determine excess we
Wow, that is a lot of wear. I see your point. Fortunately the Stag carbs don't seem to have that problem, but of course their linkage is completely different (and I did install the updated linkage from a later Stag).
Wow, that is a lot of wear. I see your point. Fortunately the Stag carbs don't seem to have that problem, but of course their linkage is completely different (and I did install the updated linkage from a later Stag).
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Re: ZS throttle shaft - how to determine excess we
YIKES Yis!! Check the throats of the carbs where the butterfly closes and be SURE those aren't scraped! I've seen 'em as bad as that but usually the body of the carb is FUBAR if that's the case. :shocked:
YIKES Yis!! Check the throats of the carbs where the butterfly closes and be SURE those aren't scraped! I've seen 'em as bad as that but usually the body of the carb is FUBAR if that's the case. :shocked:
guzzul
Jedi Warrior
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Re: ZS throttle shaft - how to determine excess we
Randall - here's a sample (sorry for the kind of fuzzy focus, but hopefully you can see the wear pattern).
As Yisrael notes, this one has almost 1/16" wear on the left side too. The back edge of the disc actually wears a little more than the front. And, of course, it is essentially wearing out-of-round, so trying to get any kind of stable idle (let alone a closed throttle) with this is pretty difficult. BTW - the worn edge cuts like a razor.
Randall - here's a sample (sorry for the kind of fuzzy focus, but hopefully you can see the wear pattern).
As Yisrael notes, this one has almost 1/16" wear on the left side too. The back edge of the disc actually wears a little more than the front. And, of course, it is essentially wearing out-of-round, so trying to get any kind of stable idle (let alone a closed throttle) with this is pretty difficult. BTW - the worn edge cuts like a razor.
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Re: ZS throttle shaft - how to determine excess we
I replaced the shafts and butterflies for the ones on my TR4; no bushings to worry about. Runs much better now.
I replaced the shafts and butterflies for the ones on my TR4; no bushings to worry about. Runs much better now.
Re: ZS throttle shaft - how to determine excess we
Yep that is close to what mine looked like however, I think mine might have been a bit worse! Fortunately the rest of the carb was in good condition. The butterfly fit in perfectly and the throttle shafts also fit in perfectly. Well worth the tiny bit of effort, since it works like new.
Yep that is close to what mine looked like however, I think mine might have been a bit worse! Fortunately the rest of the carb was in good condition. The butterfly fit in perfectly and the throttle shafts also fit in perfectly. Well worth the tiny bit of effort, since it works like new.