Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

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Brian R Adams
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#46 Post by Brian R Adams »

[Sheepish Grin] Would it surprise anyone here to learn that reversing #1 and #2 plug wires at the distributor renders that bank of cylinders inoperable? But, significantly, no permanent damage (to the engine, anyway, not my ego) is apparent. As is often the case, I suddenly realized what the problem must be while lying in bed at 3:00 am. If only the engine had tried to loudly tear itself apart in that configuration, I might have stumbled on the truth much sooner. (While working on my fuel pump, I had also swapped distributors, that's how the plug wires came into play in the middle of fuel system debugging.) They say "live and learn" but I find one can live long enough to start unlearning stuff as well.

The upside of this minor oversight is that I redoubled my effort to study and "fix" the "bad" carb (and it's stablemate, for symmetry) by fixing niggling leaks, adjusting pump outputs, double checking all passages and jets, etc.

So now the Zeniths are well sorted, with reconditioned pump wells, new pump assemblies, pump outputs calibrated (I'm running them at 0.2 cc rather than 0.3), and I changed the idle jets to 50 and mains to 122. The upshot? The engine has never run better! No stumble when accelerating, no backfiring. This is the first time I've had functioning accelerator pumps since installing these Zeniths in 2013. (The car originally had Webers installed.) It's like having a brand new car.

Here's the 3M bristle disks and mandrel I purchased: 3/4" diameter disks, 80 grit (yellow), stack of 5 on the mandrel:

https://www.ebay.com/itm/3M-RADIAL-BRIS ... 2749.l2649

The mandrel is plenty long enough to chuck in a Dremel and reach the bottom of the pump well from the top end.

Thanks to all for the advice and encouragement!
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#47 Post by Ron LaDow »

"[Sheepish Grin] Would it surprise anyone here to learn that reversing #1 and #2 plug wires at the distributor renders that bank of cylinders inoperable? But, significantly, no permanent damage (to the engine, anyway, not my ego) is apparent. As is often the case, I suddenly realized what the problem must be while lying in bed at 3:00 am."

You are not alone, in both the error and the epiphany. Or the timing of same; waking up with the solution is a wonderful way to start a day!
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#48 Post by Brian R Adams »

Update: Do NOT waste money on the Swiss Army Vehicles pump pressure valve. They simplified (cheapened) the design, and from simple inspection I don't believe it will work well if at all. But also, the two I received had damaged threads. One I rehabilitated easily enough, but called SAV to get a replacement (free) for the other one, but they sent me an obvious old, used item! So stick with the NLA / Stoddard replacement part (linked to previously).

Brian
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#49 Post by Tom Dux »

Brian R Adams wrote: Fri Jun 21, 2019 9:11 pm
Ron LaDow wrote: Fri Jun 21, 2019 8:00 pm Brian,
Don't take those valves apart (I think that was on page one of the rebuild article from years ago). You can get them clean assembled and that gasket is simply not available.
But it is fixable. Clean the parts with that stuff you use to get the shower tile clean; most of them will make the bras shine. Put the spring and plunger back in, wipe some epoxy around the periphery of the piece with the male threads, put it together and give it overnight.
If all else fails, check with NLA/Stoddard; I haven't looked in a while but they offered new ones.
Well, it was weeping, so I had to take it apart. I'll probably epoxy it closed as you suggest.

Here's NLA's new item:

http://www.nlaparts.com/store/zenith-pu ... 22513.html


Also, Swiss Army Vehicles offer one, but they posted the wrong photo (not unusual for them - the description is probably correct):

https://swissarmyvehicles.com/haflinger ... th-ndix-32
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Brian,

What ended up being the fix here? Mine are weeping as well. Thank you!!!
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#50 Post by Brian R Adams »

Tom,

I tried the Swiss Army Vehicles replacement, found it was garbage. A friend got the NLA valve, and I assisted in the carb rebuild; as I recall it is a satisfactory option.

The simplest (and cheapest) fix is as Ron described. Take it apart (carefully, don't lose any parts), clean it up (discard the tiny seal ring if it's damaged) and epoxy it permanently back together. A small amount of epoxy, applied as if it's blue Loctite, seals it. The sprung plunger inside just needs to be free to open and close. I used JB Weld from the small toothpaste-style tubes.

Brian
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#51 Post by Tom Dux »

Brian,

Thank you for the reply and honest reviews of both SAV and NLA valves. NLA valves are tempting, but at $32+ apiece, I’d love to try and repair what I have.

I’ve been having trouble getting a straight answer from anyone, even the carb experts, about taking one of these apart. Most just say don’t do it, what am I missing!? What’s the mystery behind these little valves? The little inner piece just threads in and snugs into the larger w/ a gasket or an o-ring it looks like, no? Is there an “adjustment” involved?

So discard seal ring if “damaged” and use epoxy where, on inner threads? Or on the mating surfaces where seal ring once was!? Thanks again Brian and anyone else who can contribute!!!

Tom
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#52 Post by Brian R Adams »

Tom Dux wrote: Sat Apr 11, 2020 10:04 am Most just say don’t do it, what am I missing!? What’s the mystery behind these little valves? The little inner piece just threads in and snugs into the larger w/ a gasket or an o-ring it looks like, no? Is there an “adjustment” involved?

So discard seal ring if “damaged” and use epoxy where, on inner threads? Or on the mating surfaces where seal ring once was!?
There's no adjustment inside. It's designed to open at a static pressure. The reasons not to take it apart are "First, do not harm" and "If it ain't broke, don't fix it." Assuming it's not already leaking, if you take it apart, chances are the tiny seal, being 50 years old, will tear, and now you've induced a leak. As long as the upper threads are coated with epoxy, it won't leak. The little mating surface where the seal sits is not critical, but some epoxy will get on it anyway. If you put a drop of epoxy on one side of the screw threads, near the screw head, then it will be distributed all around the threaded shaft while twirling it home, and the glue will also work its way up the shaft and out around the head as it seats home. Avoid getting glue on or too near the skinny tip of the screw, the "business end".
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#53 Post by Tom Dux »

Copy all Brian... thank you. Curiosity got the best of me while waiting on a reply. I opened mine up, honestly the little plastic washer/seal did not look terrible considering. I mean I’m assuming it’s the original, it’s intact and really in “ok” shape. I cleaned up both brass pieces really good and the seal as best I could. Carefully re-assembled all and it’s been sitting now for 45+ min w/ mineral spirits in the AP chamber. No seeping or weeping as of yet. I’m not convinced that it’s “fixed” or will stay leak free... but a minor victory at the moment. Nothing changed other than a cleaning and re-seating. But I suppose sometimes that’s all it takes.

Slowly knocking off these Zenith leaks one at a time. The one that’s really working me over is the jet cover bolt... I know I know, a whole other can of worms. But man I’m really at a loss there. Leaking at the bolt itself, not the cover seal. Anyways. Thanks again.

Tom
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#54 Post by Ron LaDow »

Tom Dux wrote: Sat Apr 11, 2020 8:22 pm [...]
The one that’s really working me over is the jet cover bolt... I know I know, a whole other can of worms. But man I’m really at a loss there. Leaking at the bolt itself, not the cover seal. Anyways. Thanks again.
Tom
This is from an article on Zenith leaks I wrote several years back, Vol.40, #6 (sorry, can't seem to copy the figures):

First leak… On pre ’61 carbs, the most common source of leakage is presumed to be the O-ring sealing the jet cover. That is possible, but unlikely. Most often, the leak originates under the head of the fastening bolt and migrates as mentioned above. The cover is secured by an M7-1.0 bolt screwed into a boss with mating female threads, see Figure 2 . This shows a later (’63) carb casting which has the added support under the boss. Earlier carbs don’t have that support and over-tightening the bolt easily pulls the boss out of square with the casting. Now if you look, you’ll find the M7 fixing bolt under-head surface is sealed to the jet cover with a metal washer. And it works just fine, so long as the bolt is square to the sealing surface of the jet cover, which also requires the threaded boss to be square. During the second carb rebuild sometime in the last century, the hobbyist noticed some leakage and leaned on the wrench a bit and it was no longer square. Once that geometry is out of kilter, the metal washer cannot keep the fuel sealed in the jet cavity. Don’t bother with goo; it just makes cleaning more difficult when you fix it. You can only fix it by carefully bending the boss back square. Perhaps there are other ways to accomplish this, but the simplest seems to be clamping the entire carb body, between the ‘choke’ surface (Figure 3) on one side and the end of the boss on the other, pushing the boss back to square. Note that the intent and requirement here is to align the centerline of the threaded boss square to the sealing surfaces; flattening the end of it with files or some grinding tool will not do that. You can use any clamping device between the ‘choke’ surface and the boss to correct the warpage, just make sure the jaws are roughly parallel and smooth. A vise is nice, so to speak, so long as you can arrange for smooth jaws. In Figure 4, the body is clamped in a drill-press vise; a fairly common bit of tooling. In this case, the replaceable jaw was removed to accept the width of the carb body; you’ll have to work with what you have. A bench vise would do as well so long as you provide smooth jaws. With some jiggery-pokery, a large C-clamp will do also. You are finished when the surface of the boss is flush with the surrounding O-ring seating surface; this happens automatically as the clamping surface on the boss-side lands on the O-ring sealing surface, and it would take King Kong to clamp it tighter. You’ll find the zinc alloy has near zero elasticity; when the clamp pushes it flush with that sealing surface, it will stay right there and not rebound. Once the boss is pushed back square, run the fastening bolt into the boss to re-form the end thread that got a bit squashed during the clamping; this may take a couple of tries. You want to be able to finger-tighten the bolt until it seats so you can avoid over-tightening and bending the boss once again. As mentioned, it is not impossible for the O-ring to leak, just very rare. It happens when someone puts a scratch or a dent across the O-ring sealing surface on the carb body (see Figure 2). Such a scratch needs to be smoothed-out and blended into the surrounding sealing surface so the O-ring can conform to the sealing surface without providing a leak path. Files, sandpaper and a bit of time will do the deed. Now you can refit the cover with a new O-ring and new metal washer, finger-tight and then another 1/4 turn or so, maybe a bit more; the sealing depends on square and good surfaces more than torque on that bolt. If there are no scratches on the washer or the mating surfaces, the seal should be 100%. Given the parts are now at least 50 years old, there are scratches, and we’ll address dealing with them in this and other locations later.
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#55 Post by Michael Branning »

Ron, I went back and read your article and it’s an excellent example of the quality work from valued contributors to our club magazine. Since some on the forums are not members, I’m posing it here in PDF format so everyone can benefit.

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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#56 Post by Ron LaDow »

Thanks.
I didn't have the PDF, just the type-script.
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#57 Post by Tom Dux »

Ron and Michael, thank you both kindly for taking the time to repost Ron’s article. I had actually seen that somewhere before and forgotten that it existed, an excellent read and a big help in my current situation. Finally making some headway on these leaky things.

Another question to the experts, what is the meaning of the following scribe marks? Bottom side of each jet housing, “NLA 4-16”. Are these factory annotations or someone’s rebuild markings? Thanks.
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#58 Post by Tom Dux »

Ron...

Also in regards to the jet side cover bolt... I was able to get some resolution by clamping carb body in vice as you described and getting the boss nearly flush w/ cover o-ring mating surface. However was still experiencing some leak past bolt head and washer. I added an o-ring under washer on the exterior of cover and it’s working quite well. See any issue w/ this? Aside from being sacrilegious. I see it as fix and it’s easy enuf to carry a few spare o-rings in the glove box if one ever decided to lose seal and start dripping again. Thoughts!? Thanks again!!!
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#59 Post by Ron LaDow »

Tom Dux wrote: Thu Apr 16, 2020 12:30 am Ron and Michael, thank you both kindly for taking the time to repost Ron’s article. I had actually seen that somewhere before and forgotten that it existed, an excellent read and a big help in my current situation. Finally making some headway on these leaky things.
Another question to the experts, what is the meaning of the following scribe marks? Bottom side of each jet housing, “NLA 4-16”. Are these factory annotations or someone’s rebuild markings? Thanks.
Tom, suffice to say an absolute answer is not possible; Hans, returning from lunch one afternoon, could have done that. I doubt it.
Since "NLA" is a sort of a identifier, I'd check with the folks there to see if it means anything to them. I'd be amazed if you didn't get an honest answer.
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Re: Zenith Accel. Pump Plunger Assy. Sold In Classifieds: Feedback?

#60 Post by Tom Dux »

Ron,

Yes I agree that it’s a bit to coincidental to not be connected w/ THE “NLA”. I’ll bark up that tree when I find the time. Thanks again.

Thoughts on the ad hoc o-ring I’ve added to the jet cover bolt?

Tom
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