HOW TO: Re-Bushing Kadron Throttle Bodies

[57baja]

So here's my super-duper triple-patented patented way to re-bush those old worn-out throttle bodies that Kadron is so well known for. If anyone has any suggestions as to how to improve this method, or any other insights, thoughts, or ideas; I'd love to hear them. I'm always eager to learn....




First, we start off with high-quality German bronze bushings manufactured inside in steel casings. These are impregnated with PTFE Teflon for maximum lubrication. These bushings should last for our generation, and many more after that. These are super beefy.

Check one out against the stock bushing still inside the carb. Look how thin and skimpy that little dude is compared to these. Like I said... You won't wear these bad boys out! They're a little expensive, but well worth it.

Here's another photo showing one of mine next to a different shop's that uses a tiny bushing like the stock one, and a urethane or plastic feeling seal. My bushing is the one on the upper left, while the other shop's "seal" is on the upper right, and their bushing on the bottom. When I cracked this one open, these pieces just fell right out there was so much play in them.

Here's another one that I had taken apart. I found one o-ring, one rubber seal, and two pieces of what looks like fish tank tubing inside it, cut to two different lengths. There were bushings in one side, and it was bare aluminum in the other! The holes were all four different depths, too!

Back to the build...

We see that if you try to get the screws out of these butterfly valves, they usually do this. They get all chewed up. They peen the back of these when they put them in so you don't suck one down in your intake system. Not a bad idea. We'll return to that thought later.

So what do you do? You drill them out. Better have some extras on hand. They'll need to be replaced, too. Also... I made a jig to hold the throttle body at he exact angle to facilitate drilling a straight hole through the retainer screw.

When you drill the screws out, you'll need to probably remove the threaded middle with an ez-out.

You might also need to chase the threads, so make sure you have a 4mm x 0.7mm tap handy Then, remove the throttle plate (butterfly). Remove the linkage arm and rotating stopper assembly and pull out the rod that goes through the throttle body.

After removing the throttle body rod, I put it in a vise and polish the shaft with strips of very fine sandpaper. I also clean the butterfly. It just looks nicer that way.

Here are a couple "BEFORE" and "AFTER" shots:

I made another jig to make the next part easy and keep the holes straight. Drill a hole in each side of the throttle body to fit the bushing. In this case, I use a 10mm diameter OD bearing (or bushing, depending on who you ask). The hole is 9.7mm deep to accommodate the bushing size.

Be careful! It's super easy to drill all the way through. Holes are much harder to "undrill", I've found.

Tap your bushings in (or press, as necessary). I'm also using a little JB Weld on mine to keep them from spinning when they aluminum heats up. If I'm going to be modifying the carb for vacuum advance, I cut a small piece of .0403" aluminum wire, coat it in JB weld, and fill the little hole in the throttle body as shown. Don't fill the wrong hole or your throttle body will be instant junk! This creates the proper vacuum signal for the VW distributors when adding the port for the advance on the case of the carb. The carb was pre-designed like this, but never imported into the USA with this factory option.

After 24 hours, I return and sand the filler smooth.

Reassemble very carefully, especially when sliding the throttle plate back inside the holder. Make sure its orientation is correct, as it sits very tightly inside the body when the butterfly valve is closed. Install your new screws and tighten them only when it seats right, checking, and double-checking everything as it opens and closes.

When everything's right peen the back of the screw. I also use Loctite on mine. Assemble the linkage connecting arms as needed. Remember: Stock ones have a left and right. The "Outie" is for the driver's side, and the "Innie" is for the passenger's side. Scat linkage has the ball drilled out and both offsets point the same way. The offset points out. I Loctite mine on, as well as re-bending the little thin washer.

Voila, you're done!


.... And yes.... I can do this for you. PM me if interested.

Here's what my garage often looks like:

We call it the "Kaddie Shack".
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awesome write up!
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[Humanure]

Nice how-to! I just checked my Kads that I recently bought and discovered detectable play in both shafts. You may get a PM from me in the near future.
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[Glenn]

Added to the FAQS/Sticky

thanks.
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[nsracing]

How are you setting the alignment on the shaft before you drill?

How much press-fit on the bushings w/ the drill bit? How about a sized reamer instead? They do come in fractional sizes for whatever bushing size you got, you know.

If the alignment is straight on the set up, you can ream right through, tap the bushings in and ream again to final size. And you will NOT need JB-Weld either if done this way. Money saved right there.

I would not use a drillbit on this job. But not bad considering.

Cool.

[57baja]

[jonvo4591]

Jeff, I just read the version of this that you have on your socalbajas site, and I see you've added the part about the vac advance. Nice to see what went on with my carbs
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[nsracing]

The reamers have enough lead angle to ream/cut right through the bore. And as it passes through also size the hole to the proper size. You will not need the drillbit.

You need a more precise jig for drilling or reaming the body. Make that your new project.

I can post a pic of a jig if you don't mind since this is your thread.

Cool man.

[ralf]

see now i wonder,

drilling the hole for the throttle shaft, not all the way thru so the bushing sits well etc


i wonder, if ur gona bore the throttle body, to a bigger size..


do u drill the bushing hole shallower?


good stuff btw..


and nice inputs NSR!

[jbrandt01]

Awesome, I'm going to do this sometime this week.

[57baja]

It's not MY thread. It's for the edification of all. Like I said, I'm always up for improvement. This is the procedure I came up with, and I've done a bunch of them this way. To my knowledge, this is the only thread on the net where this topic is covered (except my threads on SoCal, STF, etc). There seems to be a blanket of silence as to how to re-bush these, even though Kaddies have a known issue of wearing out throttle bodies.

Like I said... I'm totally with you on the reamer idea. \Eventually I'll incorporate that into my approach at some point, I'm sure. For now, it seems to be working fine with the drill bit. Although it is not ideal, I'm getting pretty good results.

Post up the way you do it. I'm certainly interested in seeing what you've got to add.
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[VanderBus]

Can you post where you bought those bushings from?
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[SGKent]

When you set the throttle plates be sure to check alignment of the 1st transistion hole. It should be 100% covered until the throttle just barely starts to open from idle. If not you can play with the plates to get them just right. It will enhance the smoothness of the transisition off idle.
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[57baja]

[thesatelliteguy]

MAN, i like the way you work. Im gonna be buying a set of your carbs as soon as i save up the money. Which will probably be a while since im back in school. But im dreamin' until then.
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[bdkw1]

[nsracing]

Well if you want to get technical, how about just using a boring head and bore right through there?

There are also piloted reamers and/or can be made w/ pilots. A reamer will self-center better than a drill. And if the reamer is short enough and stiff enough, it can bore a very straight hole w/ just its leading edges.

An ovaled hole should really be bored w/ a single toolbit tip as in an adjustable boring head. But such set up requires a milling machine and proper angling/mounting on the table.

But an endmill will also be good, provided the alignment is done so both holes are in one single axis. Only problem is the finish on the bores. It will not be as smooth as a reamed one. The endmilled hole will have chatter marks.

I use an endmill to move over a guide bore and follow it w/ a proper sized reamer to finish the bore.

[57baja]

Technical - Schmechnical.


I'm sure someone could do it the "right" way, and I'd be the first to admit that I'm no machinist. You guys are obviously much more qualified than I. I'm just a schmuck with a home-brewed recipe for a good thing.

We do get excellent results doing it the way we're doing it, however: with our goofy hamster-driven drill press and all! We've done at least 200 of them this way, and it seems to be working really, really well. I think we've had only one failure of a bushing, and to date, that's unverified until we get it back. That's 99.5% success rate!!!

Our Kaddie Shack T-bodies are far superior to the factory bushings, and we're running into more and more urethane ones that another shop has done that are wallowed out, too. I'd have to go out on a limb and say we've got the best ones in the business now, although I've seen some pretty good ones that look like they've been done with bronze valve stem guides by professional machinists.

The trick is getting the drill centered as best as possible in the hole, and knowing when to stop the drill bit, as it is important that when we press in the new bearings, that they bottom out at a certain point, as the depth setting helps to center the butterfly in the hole and eliminate binding. As we do more and more, we've deviated a little bit from the original write up I did here, but the basic principles remain the same.
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[bdkw1]

[nsracing]

The tool room still support the CNCs you have, don't they? Someone still has to make your tools for the CNCs.