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Thread: SU Mod: Sealing worn throttle bushings

  1. #1
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default SU Mod: Sealing worn throttle bushings

    A plastic cap (screw cover) from ACE hardware's parts bin and sealant/goo/glue seal the outside bushing nicely.





    Installed



    A thin washer and an o-ring seal the inside bushing with negligible effect on the throttle return.


    Click image for larger version. 

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    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



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    Registered User Zforce's Avatar
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    You just demonstrated the difference between a parts changer and a mechanic
    JoeyVee likes this.
    1971 240Z hls30-17121 L28/E-31 SU's "B" 4-speed 3:70 gears.

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    Nova Scotia,Canada,Earth Blue's Avatar
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    Nah, I defined thrifty canuck eh?

    Lets hope the engine heat does not loosen the glue or it will be RTV time.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

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    You rock Blue! Nice work.
    Jeff
    Northville, Michigan
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    Boat Anchor Repairman Captain Obvious's Avatar
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    Neat ideas Blue.

    Are you sure that you didn't preload the position of the butterfly plate towards the O-ring?

    By that, I mean... When the butterfly is completely closed, the side-to-side movement of the throttle shaft is restricted because the butterfly is a tight fit in the carb bore. But when the butterfly is opened, the throttle shaft can move back and forth a bunch before either the butterfly or the linkage bits hit the carb body.

    If your O-ring is compressed when the throttle is closed, then it will pull the butterfly towards that side of the bore, but when the throttle is opened it may wear the butterfly plate or bore prematurely in that location from the constant scraping every time you open or close the throttle.

    Not saying it's a big problem. Just a thought.
    Last edited by Captain Obvious; 08-08-2011 at 06:54 PM.

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    Nova Scotia,Canada,Earth Blue's Avatar
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    Excellent point!

    Presently the side force on the shaft is minimal as the O-ring is very low in height. As well, I am guessing that a leak would suck the washer in closer, especially at idle.

    I could put a thinner washer there to completely unload the butterfly valve but I did not have one here in NJ.

    Maybe I should just drill out another plastic screw cap, sand it to the correct height then glue it on... yes I think that would be even better! At $0.20 each it is not a risky venture.

    Thanks for your insight! Another set of eyes and brain is great!
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


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    Nice idea. Many years ago I did something similar with teflon o-rings. Difference is I turned a slot in the shaft andsipped the o-rings onto the shaft where they sealed against the bore of the carb. Worked fine, but my machining skills were not the best and it could have been better...
    Julio
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    Boat Anchor Repairman Captain Obvious's Avatar
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    Don't get me wrong... I wouldn't get all worried that you're cutting huge chips off the inside of your carbs at any great rate. It's just that I've seen some carbs from other applications that were wallowed out to the point where the butterfly's wouldn't seal anymore and getting them to idle and come off idle without issues was impossible.

    How long would it take for you to get to that point? Probably years.

    Another thought is that I've seen some other carbs that had actual seals on the shafts from the factory, and they didn't use O-rings. They used non-round cross section seals with the lip direction such that the vacuum would suck in the direction that would increase the effectiveness of the seal. I'm no seal expert, but it makes me wonder if O-rings are the correct choice for vacuum application. Maybe it's a tradeoff between seal effectiveness and friction? But... Any seal will be more effective than "none".

    Lastly, I'll cut you some grooves in your shafts if you would like to try putting some O-rings on the shafts to seal inside the bushings in the carb bodies like what Oiluj suggested. I've even got a bag of "X" cross section (non) O-rings laying around here somewhere that might be close to size.

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    Blue, were you happy with this fix? Did it last?

    Matt

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    Worked fine. But CO's mod is the right way to go.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  11. #11
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    Butter smooth. No leaks.






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    That's awesome. Might have to try it. Wonder if my grandpa's old shopsmith can be used to turn that.

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    That's exactly what I did, except I didn't have a lathe.__Chucked the shaft in a drill press and made a holder for a section of hack-saw blade to make the groove, followed by a fine file.__Wasn't nearly as pretty as CO's, but it worked fine...
    Julio
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    I would caution everyone to use Teflon(PTFE) rings, and not plain rubber. Just imagine a ring deteriorating in gas fumes and heat to the point that it breaks and gets sucked into the intake. Where to get some PTFE rings of the appropriate size?

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    Quote Originally Posted by ConchZ View Post
    I would caution everyone to use Teflon(PTFE) rings, and not plain rubber. Just imagine a ring deteriorating in gas fumes and heat to the point that it breaks and gets sucked into the intake. Where to get some PTFE rings of the appropriate size?
    PTFE turns really well-if you can machine the rod, it shouldn't be a stretch to turn down an easily found but oversized rings-or a rod that could be bored and wafered.
    A Z is beautiful from any angle, I just happen to prefer to view from the drivers' seat!

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    Isn't this what Z Therapy is for?

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    I used Viton. I'm not worried about fuel or the heat.

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    Ok, I swapped over my other set of SUs. Car fired right up, idled too high...oops, forgot the return springs. Put them on, and it idles just fine. Sprayed a little carb cleaner around the throttle shafts, and got the same effect as with the other carbs. A slowing of the idle speed. Maybe this is normal? I can't imagine throttle shaft bushings being air tight. There must be some leakage.

    Why am I worried about this in the first place, you may ask? The car runs fine. It all started with diagnosing hot running at highway speeds. After checking everything I could think of, I thought maybe its running lean, so I started looking for air leaks. I may have solved the highway heat problem, it was bad connections in the inline fuse holder on the electric fans. I just need a hot day to test if it's cured. Should I just stop messing with these carbs?

    BTW, I also solved the vapor lock problem. First, I bent the fuel rail back as far away from the head as I could. This helped a lot, but didn't cure it. Next, my other set of carbs came with insulators that were over twice as thick as the ones with the other carbs. These cured the problem.

    Matt

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    Quote Originally Posted by ConchZ View Post
    Sprayed a little carb cleaner around the throttle shafts, and got the same effect as with the other carbs. A slowing of the idle speed. Maybe this is normal? I can't imagine throttle shaft bushings being air tight. There must be some leakage.

    Why am I worried about this in the first place, you may ask? The car runs fine. It all started with diagnosing hot running at highway speeds.
    I thought the expectation when you sprayed carb cleaner near a vacuum leak was that the idle would go up, not down??

    And I would guess that vacuum leaks around the throttle shafts wouldn't have much of an impact at highway throttle positions. I would expect that even if you were getting some air past the throttle shafts, it might have a big impact on IDLE, but once you cracked the throttle plate enough to maintain highway speeds, the impact of that leak would diminish.

    I mean, you never WANT that leak, but it's impact goes down as the throttle position goes up. A little late now (as you already figured out), but I don't think leaking throttle shafts are making you run hot on the highway.

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    Quote Originally Posted by Captain Obvious View Post
    I thought the expectation when you sprayed carb cleaner near a vacuum leak was that the idle would go up, not down??
    .
    Starter fluid or ether would make the idle go up, but carb cleaner isn't combustible. As for throttle shaft leakage at highway speeds, you are probably right. The unmetered air getting past the throttle shaft bushings would go down as a percentage of total air flowing through the carb, as compared to its percentage at idle. Since I don't have idle problems, is it safe to say that my slight leaks around the throttle shafts is pretty normal?

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    Quote Originally Posted by Captain Obvious View Post
    I thought the expectation when you sprayed carb cleaner near a vacuum leak was that the idle would go up, not down??
    .
    Starter fluid or ether would make the idle go up, but carb cleaner isn't combustible. As for throttle shaft leakage at highway speeds, you are probably right. The unmetered air getting past the throttle shaft bushings would go down as a percentage of total air flowing through the carb, as compared to its percentage at idle. Since I don't have idle problems, is it safe to say that my slight leaks around the throttle shafts is pretty normal?

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    Quote Originally Posted by ConchZ View Post
    Starter fluid or ether would make the idle go up, but carb cleaner isn't combustible.

    Since I don't have idle problems, is it safe to say that my slight leaks around the throttle shafts is pretty normal?
    I surely won't claim to have seen them all, but every carb cleaner I've ever run across is highly flammable. I'm not talking about the engine degreasers... I'm talking carb cleaner. Mostly acetone, methanol, tolulene, etc.

    And for the shaft leakage... As designed without a pliable seal there, some leakage will naturally occurr. But as long as it's not "excessive" you don't have to do anything about it. There's others on the forum with much more carb experience than myself, but my read on it would be if you can tune the carbs at idle without having to go some unusual amount of turns down on your nozzles, your plugs look good, and you're getting good power while driving, then I wouldn't worry much about the throttle shafts sealing.

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    Quote Originally Posted by Captain Obvious View Post
    I surely won't claim to have seen them all, but every carb cleaner I've ever run across is highly flammable. I'm not talking about the engine degreasers... I'm talking carb cleaner. Mostly acetone, methanol, tolulene, etc.
    You are correct, carb cleaner is flamable. My bad. However, spraying it into the carb of a running car in my experience usually results in a stumble. It isn't flamability, but rather liquidity that is the problem.

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