Hitachi VC42-4A Carburetor Rebuild

[Esteban]

Excellent writeup Paul. Your pictures are textbook! Congratulations!

I noticed one difference with my VC42 carburetor and it is the drain plug at the bottom. Nice feature. Mine doesn't have it. In my case, it's not the original that came with it, but rather an original replacement bought around 1972 that my dad changed.

[r1lark]

Esteban, thank you for the kind words! As far as the bowl drain, I'm sure that is especially helpful in areas where there might be contamination in the gasoline delivery systems. Since my Patrol is quite early, perhaps the drain was deleted for cost purposes?

Continuing the VC42 reassembly................

As mentioned in the previous post, the original idle mixture screw had to be reused, since the replacement did not have the correct thread. However, the original was in fine condition, and I would rather use good condition original parts as opposed to replacement parts. The following picture shows the location of the Idle mixture screw #58. and spring #57:

PXL_20250930_151235186.NIGHT with arrow.jpg

Next reassembly step is to install the main jet into the carrier, and install these into the main carb body. But first, as a reminder. during disassembly I opted not to remove the main nozzle tube #25 and its packings #27 & 28. Besides these packings not being available any more (for any Studebaker people reading this, they are NLA -- No Longer Available ), these packings position the nozzle tube to a specific position in relation to the venturi. The picture below shows this dimension as 7.8 millimeters. Mine measured 7.7 millimeters, pretty close to spec, and I wasn't about to try to remove it.

PXL_20250930_193141080.NIGHT.jpg

A new main jet came in the rebuild kit, and was a size number 135 as is the original, but I opted to reuse the original jet:

PXL_20250930_152812510.NIGHT.jpg

Install the main jet #31 into the jet carrier #29, the following pic shows the two parts plus the original fiber washer:

PXL_20250930_152532474.NIGHT.jpg

This is a good spot for a reminder that the slot sizes on a lot of carb parts are somewhat odd (width of slot, and length of slot), and the brass parts can be easily damaged by not using the correct sized screwdrivers. Take some of your cheap and/or worn out screwdrivers and grind them to make them fit the screw slots. Here is a pic of installing the main jet into the carrier using a 'customized' screwdriver:

PXL_20250930_153246850.NIGHT.jpg

The washer #30 in the kit was an aluminum washer, not my favorite but I didn't have a fiber washer that size. The aluminum washer had some roughness on one side that concerned me. Note that the following picture makes the washer look much worse than it really was because of the magnification:

PXL_20250930_170347279.NIGHT.jpg

A piece of plate glass and some crocus cloth with WD-40 smoothed it up:

PXL_20250930_170557319.jpg

Following pic shows the main jet and jet carrier installed. As Esteban has noted, this design makes it easy to change the main jet if desired, but the problem is finding other size jets (I believe he obtained different size jets in Columbia):

PXL_20250930_171134764.NIGHT.jpg with arrow.jpg

We will end this post here, since I'm getting an error when trying to add additional pictures. More in the next post.

[Esteban]

Fantastic! Your pictures, along with the corresponding descriptions are excellent!

Regarding the main jet sizes, I’m pretty sure that Solex carburetors are the same. Once back home I’m going to try to take pictures as defined as yours and probably we can spot some Solex markings, like the Hitachi logo on yours!

[r1lark]

Thank you again Esteban for even more kind words. And we will look forward to finding out more about the potential interchangeability of the Solex jets!

Continuing the VC42 reassembly................

Next items to install are the main air bleed #33; the slow jet #35; and the slow air bleed #34........these are shown noted in red in the following picture. These are all located in the same general area of the main carb body; I tied a wire around the slow air bleed when it was removed to make sure the two bleeds didn't get mixed up:

PXL_20250929_202558821.NIGHT.jpg cropped.jpg

Install the main air bleed #33 in the location shown in the following picture:

PXL_20250930_171855326.NIGHT.jpg

Note that when installed, the main air bleed will protrude somewhat above the surface of the main carb body:

PXL_20250930_172141799.NIGHT.jpg

Next, install the slow jet #35 in the hole indicated by the red arrow:

PXL_20250930_171855326.NIGHT.jpg with arrow.jpg

The following two pictures show the slow jet #35 being installed; note that this jet is a #55 size, that it also sits above the main carb body gasket surface, and that it is not covered by the carb top making it accessible for cleaning without removing the carb top:

PXL_20250930_172530168.NIGHT.jpg

PXL_20250930_172549382.NIGHT.jpg

Finally, install the slow air bleed #34 as shown in the next two pictures; it also protrudes above the gasket surface of the main carb body:

PXL_20250930_173011663.NIGHT.jpg

PXL_20250930_173153212.NIGHT.jpg

Next to install is the accelerator pump nozzle and associated parts; the individual illustration numbers and the actual parts are shown in the following picture:

PXL_20250930_174135274.NIGHT.jpg

I like to take the 'original' check ball #41 that was removed from the carb on disassembly, put it into the main carb body, and hit it several times to help reform its seat. The following picture shows this:

PXL_20250930_175343569.NIGHT - Copy.jpg

After doing this, remove the old check ball and install the new check ball into the main carb body.......just be careful not to turn the body upside down until the rest of the nozzle parts are installed, or the check ball will roll away into the farthest corner of the area you are working in!


Had hoped to use the fiber washers that had been ordered, instead of the aluminum washers that came in the kit, but the red fiber washers' OD was not large enough in this location. The second picture shows the new fiber washer on the left, the 'original' fiber washer removed during reassembly, and the aluminum washers included in the kit, and another of the new fiber washers on top of the nozzle #47 showing the mismatch:

PXL_20250930_175839503 - Copy.jpg

PXL_20250930_180401076.NIGHT.jpg

Install the nozzle, washers, screen #48, and pump jet #49 and tighten. I apologize that I didn't take a picture of the nozzle assembly installed, but here is a picture from the disassembly showing the nozzle and associated parts in place:

DSC00016.JPG

More reassembly to follow on the next post. As always........comments, corrections, and additional info is much appreciated!

[r1lark]

Continuing the VC42 reassembly................

Next on reassembly is to install the power valve "seat 2".......I made up the term "seat 2" because Nissan did not show this item on the exploded parts diagram, but this "seat 2" is what item #37 power valve seat fits into. (In my mind, they should have called #37 the power valve needle, but they didn't consult me. ) Below is a cropped picture showing the various power valve parts, and the red circle is around the power valve "seat 2" and gasket that I drew onto the exploded parts diagram during disassembly:

Power Valve Parts 1.jpg

Underneath the threaded area where the power valve "seat 2" threads into is the power valve jet p/n 16204-58000, which isn't shown on the exploded parts diagram either. During disassembly, I decided not to attempt to remove this jet since it is so small, and I'm sure new old stock or even used jets are super hard to come by if I ruined this one. Did make sure the jet and passage were clear. Here is a picture of the power valve jet in the main carb body, taken during disassembly; my apologies for the lousy picture:

DSC00053.JPG arrow to jet.JPG

Since the rebuild kit didn't have the correct thin copper washer, I had ordered some of those based on dimensions. However, since in my experience the current supply of copper washers are too hard (especially the ones sold as brake hose washers), I annealed the washer to soften it before installing. You may not be as OCD as I am, but if you want to do this, use a butane or mapp gas torch to heat the washer until it gets cherry red, then dunk it very quickly into water. The water dunking does not harden the copper as many think it does. Heat the washer just until it gets cherry red, then pull the flame away quick and dunk it quick. I hold it with a piece of stainless tie wire. The following picture shows the torch, wire, and copper washer:

PXL_20250930_185857185.NIGHT.jpg

The washer may turn a pretty purple color, which is ok, but any black should be cleaned off, I used some WD-40 and crocus cloth.


Install the copper washer and power valve "seat 2" and tighten in tbe location shown in the following picture. A drop or two of thin oil on the washer will help hold it to the bottom of "seat 2" while installing:

PXL_20250930_191423363.NIGHT.jpg

Next install the power valve vacuum piston #39, the piston spring #36, the power valve seat #37, and the "stopper" (or screw) #38. You may want to use a couple of drops of light oil to lubricate items #37 & 39. Install the parts in the orientation shown in the the first picture. The second picture shows the vacuum piston and power valve seat assembly installed, but before the screw #37 was installed and tightened:

PXL_20250930_192257961.NIGHT.jpg

PXL_20250930_192420731.NIGHT.jpg

There is no adjustment of the power valve that I can see. The carb section of the Nissan shop manual has a long paragraph regarding "adjustment" of the power valve on page 86, but it makes absolutely no sense to me.........it talks about raising or lowering an "adjusting nut" that does not exist on the exploded parts diagram or on my carb, and there is no threaded stud for a nut to attach to. If anyone can enlighten me about these instructions, it would be much appreciated!


Next install the accelerator pump check valve #45. You may remember that on disassembly I removed the check ball out of the check valve after pulling the accelerator pump, not realizing that the whole check valve was supposed to be removed along with the check ball. I was glad to see that a new check valve was included with the rebuild kit:

PXL_20250930_201304903.NIGHT.jpg

But when comparing the old versus new check valve assembly, there was a difference in size as shown in the following picture:

PXL_20250930_203834633.NIGHT.jpg

The issue I had is that the threads on the new check valve don't fully engage the threads in the main carb body because of a different positioning of the threads. If I had one of those cute little mini-lathes, we could have machined the extra length of the hex off the bottom of the hex, and corrected the dimensions; however, I don't have a mini-lathe, and I'm not a good enough machinist to do this on my 1940s-built Logan lathe. Therefore, the original check valve was reused with some slight modification (butchery) to keep the check ball contained:

PXL_20250930_204247928.NIGHT.jpg

The check valve is installed in the following location (see red arrow on this picture of the assembled carb), using a fiber washer instead of the aluminum washer from the rebuild kit:

Check Vlv 1.jpg

In preparation for installing the accelerator pump components, I always soak the leather (at least, it looks like leather to me ) diaphragm in Neats Foot oil to soften it. The diaphragm is part of the accelerator pump piston/spring assembly #42 & 44 which comes in the carb rebuild kit. The following pic shows the diaphragm soaking.............and this seems like a good stopping point.

PXL_20250930_204943393.NIGHT.jpg

More reassembly in the next post.

[RiverPatrol]

Excellent details, it make me want to rebuild a carb. I think you've done this before.

[r1lark]

Excellent details, it make me want to rebuild a carb. I think you've done this before.

Grab one out of your stash and let's get started River! And yes, I've done this before, but not with carbs that are so hard to find parts for. Have done plenty of Studebaker 2 barrel Strombergs and 4 barrel Carter AFBs.


Continuing the VC42 reassembly................

We are ready to install the accelerator pump parts. First let's do a little polishing on the guide rod #32, shown in the first picture (pic taken during disassembly before ultrasonic cleaning) with the red arrow pointing to it. Since this slides thru a brass-looking bushing in the main carb body, it needs a quick polishing with crocus cloth and WD-40 (second picture) after its bath in the ultrasonic cleaner. It only takes a minute or so to strap clean it and rinse it off with brake cleaner:

DSC00101.jpg guide rod.jpg

PXL_20251001_174139508.jpg

Put the spring #40 on the guide rod #32 (first picture), add a couple of drops of light oil to the guide rod, and install into the carb body as shown in the second picture:

PXL_20251001_174355933.NIGHT.jpg

PXL_20251001_174445761.NIGHT.jpg

Ensure the guide rod moves smoothly up and down.

Remove the accelerator pump piston/spring assembly #42 & 44 from the Neatsfoot oil and wipe away the excess oil:

PXL_20251001_174553979.NIGHT.jpg

Carefully insert the piston/spring assembly #42 & 44 into the accelerator pump well in the main carb body. CAUTION: using a small screwdriver or similar, gently help the diaphragm get just past the top lip pf the accelerator pump well, THEN use a larger screwdriver blade to keep the diaphragm edge from getting caught and damaged on the the cutout shown in the following picture by the red arrow:

PXL_20251001_175103746.NIGHT.jpg with arrow.jpg

Once the diaphragm is fully inside the accelerator pump well, gently push it down.


The rebuild kit should include the small linkage clips and cotter pins to use during reassembly; the following picture shows the ones included in this kit:

PXL_20251001_175423097.NIGHT.jpg

Position and push the guide rod #32 down onto the top of the accelerator pump piston/spring assembly #42 & 44, and install the cotter pin #43 as shown in the following picture (pic taken during disassembly, forgot to take one during reassembly ):

DSC00015.JPG with circle.jpg accel pump.jpg

Next, insert the accelerator linkage crank rod #55 into both the bottom of the accelerator pump guide rod #32 and the throttle valve shaft #50 as shown in the following picture:

PXL_20251001_182238964.NIGHT.jpg

Install the linkage clip #56 onto the end of the crank rod #55 as shown in the following enlarged/cropped picture:

PXL_20251001_182238964.NIGHT.jpg enlarged.jpg

Ensure the guide rod and accelerator pump piston/spring assembly move freely when you move the throttle valve shaft.


Next we will install the fuel level gauge #16, packings #18 & 19, and the gauge set screw #17; these parts are shown in the following picture; the black washer is one of the original pieces of 'packing' #18/19:

PXL_20251001_183419604.NIGHT.jpg

As discussed earlier in this thread, the packings are not included in the rebuild kit. After a lot of internet sleuthing, I purchased some chemical resistant Fluorosilicone sealing washers that should work. The info on these washers including part number is near the end of the fist page of this thread. You may also remember due to stupidity I broke the actual sight glass. The whole saga about finding a solution to that is covered on the first and second page of this thread.

Insert a sealing washer, then the level gauge, and then another sealing washer. I added a few drops of oil to the upper sealing washer and the bottom of the gauge set screw #17 after noticing what looked like the washer bunching up a little when the set screw was tightened. CAUTION: ensure that the glass level gauge is properly inserted down into its bottom "hole" before tightening the set screw, or you will brake the level gauge like I did!!

PXL_20251001_183843739.NIGHT.jpg

Tighten the set screw as much as you feel comfortable; it seems to go to a certain point and stops, and that may be how the set screw and body is machined -- but once I had it together, I did not want to take it apart again to see if that was the case. The set screw #17 needs to be staked in place; I waited until the seal of the Fluorosilicone sealing washers had been tested by putting fuel in the bowl. Following is a pic of the set screw installed, and then a second picture of the set screw finally staked in place (stakes are pretty ugly but should be functional):

PXL_20251001_183852652.NIGHT.jpg

PXL_20251008_143237886.jpg

The high points of the stakes were stoned down to ensure they didn't impact the sealing of the cover gasket.


Next, install the bowl drain and fiber washer; these two items are not shown on the exploded parts diagram, but can be installed at any time in the sequence. I used one of the red fiber washers that were purchased since the rebuild kit didn't seem to have a replacement:

PXL_20251001_184220126.NIGHT.jpg

More reassembly in the next post. As always -- advice, corrections, and comments are welcomed!

[Esteban]

Long overdue! Once I saw your last post I remembered that I had to take a picture of my VC-42 carb. Had to dig in my parts box. This carb was replaced long time ago, but it was always taken care. Until one day the main fuel jet carrier (#29 in your diagrams) came out will all the aluminum threads of the body. I tried all sort of gimmicks until one day I closed it shut with epoxy . I can assure you that it was never overtighten!

Previously I had installed in my other Patrol that I had way back then the Carter YF-1V that came out of a 300cid Ford Bronco from 1980. This is the carb that I still run.

Here's the picture of the fuel level sight glass. I place a paper behind for clarity. The level lines are centered in the space as you can see, and are separated 2.5mm or 0.1". The picture of the caliper didn't come as clear as expected.

Hitachi VC42 Fuel Level.JPG

[r1lark]

Thank you Esteban, excellent picture!! I'll blow it up and print it out, and use some math to figure out the measurements on the actual sight glass. It does look from the picture that the space between the two lines is centered (or just very very slightly below?) in the sight glass as you mention.

This helps me immensely!

[Esteban]

Paul,

I measured carefully today. The top mark is exactly 7.7mm from top and the bottom mark 7.7mm from bottom, The marks are separated 2.5mm.

Hope that helps.