Holley Carb Restoration-Part 10-Throttle Body

[Gerard F.]

Didn't get much done today, so let's call this one Throttle Body, part A.

Spent most of the morning trying to get the little vacuum tubes out of the throttle body for plating and dichromate coloring. Finally realized that there was no way to get them out without destroying them.

So I decided to plate them in place. Here's the masking job:



And here they are plating away:



When you see that little sizzle from the tubes, you know they are plating. It helps to move the part around so the plating comes out bright. After about 10-15 minutes, here they are coming out of the plating tank:



Then after a 20 second dip in the dichromate, the tubes looked like this:



Then took a break for lunch to let them dry off and decide what to do next. Crazy what we do for the fun of it.

(Continued next post)

[Gerard F.]

Re: Holley Carb Restoration-Part 10-Throttle Body

Well after lunch I figured I'd do a little cleanup up of the throttle body with a nylon brush and dremel with a wire wheel. I found this dremel head was most useful in cleaning out the bores:



Then it was on to blowing out and cleaning all the little passages out. I found one idle feed on the secondary side, plugged up or not fully drilled. So I drilled it the size of the other side (.020-#76 drill bit):



Then it was on to bushing the throttle shaft with my AED throttle bushing kit:



This kit uses a reverse reamer which holds the shaft position by passing the shaft through the opposite side and attaching it to a drill. Very easy to use, do one side, then reverse and do the other:



Ran out of picture space. Continued next post.

[Gerard F.]

Re: Holley Carb Restoration-Part 10-Throttle Body

I carefully measured the depth of cut so that the bushing would fit flush:



Then after reaming both sides, I'm ready to press in the brass bushings with a piece of allthread, nuts and washers:



I used 1/4" allthread, but would recommend 5/16".

Here's the finished bushing in place:



Well, ran out of time as usual. Will continue with Part B of the throttle plate and maybe final assembly over the holidays.

Happy Thanksgiving

Having fun,

[Timothy B.]

Re: Holley Carb Restoration-Part 10-Throttle Body

Looks good Jerry,

How does the primary shaft fit these bushings?

Don't do the secondary bore before installing the teflon bearings to check, if it's like mine you will not have to bush.

[Gerard F.]

Re: Holley Carb Restoration-Part 10-Throttle Body

Looks good Jerry,

How does the primary shaft fit these bushings?

Don't do the secondary bore before installing the teflon bearings to check, if it's like mine you will not have to bush.

Tim,

The replacement primary throttle shaft fits very tight into the brass bushings. I'm hoping that with a little wear on the olive green coating on it and with some wear on the bushings that it will loosen up.

The original secondary shaft fits very loosely in the unbushed openings. I'll try it with the teflon bushings before deciding whether to brass bush the secondary side or not.

One thing though, on the primary side. After installing the brass bushings, I noticed a small hairline crack in the boss around the passenger side bushing, just a hairline about 3/8" long. I think it is just cosmetic as it isn't as long as the bushing, but I hope it doesn't start traveling.

Do you know of any aluminum epoxy or product that I can use to fill the crack and prevent future traveling?

[Timothy B.]

Re: Holley Carb Restoration-Part 10-Throttle Body

Jerry,

You can get a reamer for these bushings to loosen them up a bit. I would try to get that primary shaft to where it's not restrictive when moving. If the throttle return spring ever breaks the spring on the throttle shaft should help return the blades to idle.

What is the diameter of these bushings and the OD of the primary shaft. My memory tells me the shaft is about .367-8 so a 3/8 drill bit (.375) may do the trick.

Can't help on the epoxy, I use JB Weld (it works good for aluminum) but I am not repairing the vent tube boss on this 3810 because of breakage. I will drill deeper and install a longer vent tube with loctite and that's it..

Can you send me a pic of the damage in the base you are refering too. Do you think it happened when you installed the bushing?

[Michael M.]

Re: Holley Carb Restoration-Part 10-Throttle Body

Jerry,

Great job so far on the photos and carb rebuild. For the hair line crack do some research on a product called Marine Tex. It's a heavy-duty structural epoxy which bonds to aluminum and is impervious to gasoline. It comes in three colors, but get the gray color. It should be a close color match to your base plate.

[Gerard F.]

Here's the crack

Jerry,

Great job so far on the photos and carb rebuild. For the hair line crack do some research on a product called Marine Tex. It's a heavy-duty structural epoxy which bonds to aluminum and is impervious to gasoline. It comes in three colors, but get the gray color. It should be a close color match to your base plate.

Tim, Michael,

Here's the crack I'm concerned about:



Should I be concerned about it traveling. It happened when I pressed in the brass bushings.

Thinking about just filling it with an aluminum based epoxy. Any other products out there to bond this crack.

Also, anyone know of an aluminum protectant to preserve the shine on the aluminum. I keep brushing this base plate to a bright finish but it goes to pot real soon.

[Timothy B.]

Re: Holley Carb Restoration-Part 10-Throttle Body

Jerry,

I feel your pain, that crack is approx the same length as the bushing. I would have a few words with the maker of that reamer because it's definately to small of a bore to press that bushing with the knurled end into place. After all, this tool is made specifically for bushings on carburetors.

That being said I don't think it will spread, some red loctite may fill and seal the crack and just leave it, at this point you can't do much more.

Take that valve guide bushing and grip the throttle shaft and let me know if the shaft moves freely with the bushing compressed. That and the thin OD is what attracted me to this fix.

Don't drill the secondary until you fit with teflon bearings first, mine is fine without any bushing. If there is any interference here the vacuum will not pull the blades open..

[Clem Z.]

Re: Holley Carb Restoration-Part 10-Throttle Body

i would not set up the shaft to bore clearance any tighter than the holley spec to make sure you don't have a binding problem with the carb on the engine after it heat up.

[Gerard F.]

Re: Holley Carb Restoration-Part 10-Throttle Body

i would not set up the shaft to bore clearance any tighter than the holley spec to make sure you don't have a binding problem with the carb on the engine after it heat up.

Clem, Tim,

There seems to be a problem causing the binding with the center bearing of the primary throttle plane. Either the throttle shaft is slightly bent or the center bearing (which is not bushed) is too tight.

The ends of the shaft fit real easy into the bushings from both sides, but the center bearing on the shaft fits tight through the bushings, and as soon as it is homed to the center bearing on the throttle plate, it starts binding at full open throttle.

I really suspect it is a slight bend in the shaft. It there an easy way to make sure the shaft is perfectly straight, or is it just trial and error with a straight edge?

Incidentally a 3/8" (.375") drill bit won't fit through the bushings but a 23/64" (.359") will, and pretty loosely.

[Clem Z.]

Re: Holley Carb Restoration-Part 10-Throttle Body

Clem, Tim,

There seems to be a problem causing the binding with the center bearing of the primary throttle plane. Either the throttle shaft is slightly bent or the center bearing (which is not bushed) is too tight.

The ends of the shaft fit real easy into the bushings from both sides, but the center bearing on the shaft fits tight through the bushings, and as soon as it is homed to the center bearing on the throttle plate, it starts binding at full open throttle.

I really suspect it is a slight bend in the shaft. It there an easy way to make sure the shaft is perfectly straight, or is it just trial and error with a straight edge?

Incidentally a 3/8" (.375") drill bit won't fit through the bushings but a 23/64" (.359") will, and pretty loosely.

roll it on a flat glass plate. the bushing reamer should be 3/8" -.375" diameter

[Gerard F.]

Re: Holley Carb Restoration-Part 10-Throttle Body

roll it on a flat glass plate. the bushing reamer should be 3/8" -.375" diameter

Couldn't tell with the flat plate glass which way to bend. So I used a straight edge and trial and error. Must have had that shaft in and out 30 times with a little bend here and a little bend there. Honed out the center bearing slightly with a piece of sand paper on a 23/64" drill bit.

Now it snaps closed instantly with the little spring on the shaft.

Thanks for the help.

[John H.]

Re: Holley Carb Restoration-Part 10-Throttle Body

If you want to stop the fracture, I would drill a small hole at the end of the fracture line and then fill in with what ever you are going to use. You need need to do that otherwise the crack will continue to migrate.

[Gerard F.]

Re: Holley Carb Restoration-Part 10-Throttle Body

Jerry,

I feel your pain, that crack is approx the same length as the bushing. I would have a few words with the maker of that reamer because it's definately to small of a bore to press that bushing with the knurled end into place. After all, this tool is made specifically for bushings on carburetors.

That being said I don't think it will spread, some red loctite may fill and seal the crack and just leave it, at this point you can't do much more.

Take that valve guide bushing and grip the throttle shaft and let me know if the shaft moves freely with the bushing compressed. That and the thin OD is what attracted me to this fix.

Don't drill the secondary until you fit with teflon bearings first, mine is fine without any bushing. If there is any interference here the vacuum will not pull the blades open..

Tim,

I think I'm ready to go for assembly:



Note that the 3810 is actually double stamped in the corner of this original throttle plate.

I am very surprised what a little Mother's Mag and Alum Polish will do with a microfiber cloth, plenty of cuetips, and lots of elbow grease. Filled the crack with metal epoxy, then wire brushed the excess off, applied the polish and it hardly shows.

I test fit the shafts and finally got the primary to snap back on the shaft spring, it fits nice and tight in the bushings and moves freely. No room for any teflon bushings.

On the secondary shaft, you were right about the fit with the teflon bushings. With 4 teflon bushings, the secondary fits tight and moves very freely.

So I think I'm good to go, after I touch up the top and bottom surfaces with some 220 grit on a piece of plate glass. Thanks for the help.

Having fun,