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Discussion Starter · #1 ·
I've always thought dual carb panheads were pretty much the coolest thing. And it always seems like the ones I see are half finished, and or really crudely done (with the few exceptions of the ones that pop up now and again that are purportedly old George Smith heads, of S&S).

I had some old heads that were pretty beat up from swap meets, so I decided a few years ago to see how hard it actually was.

I can say that I will never attempt to this again, but they are finally done and on a motor, waiting for the bike to be finished.

Before starting I had to decide on carbs so I could plan for flanges, etc. Linkerts are cool, but also expensive. Technical limitations to me were
  1. worry about flexibility in tuning
  2. Bolting them to a flange on the head would be problematic, especially with the smaller three bolt carbs
  3. The length especially with air cleaners, was also a concern.
But I still wanted a carb that wasn't anachronistic, but that would give me a decent shot at tuning and reliability. The Amal 930 carbs checked all of the boxes. So I went with Amal 932s, and I got the new premier version of the carb that supposedly has improved metallurgy on the slide and bore.
 

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Discussion Starter · #2 ·
I was sorta flying blind. Other than seeing pics I could find on the web (basically just external shots) I wasn't really sure where to locate the hole, how big to go, etc. So I started small (maybe 1"), and gradually got bigger so I could see how things were going to play out.
New item by Scott McKelvey

Then I could start getting an idea of inside diameter, outer diameter, and come up with a plan to fill the old intake port to create a smooth transition inside. I didn't take (or lost the pics, as this was a couple of years ago).
  1. But I got aluminum tubing that matched the diameters as closely as possible.
  2. Flat stock to cut the flanges
  3. Started LOTSA welding on the heads to fill in the old intake port and build up any areas to make smooth transition.
  4. Then did another face cut in the mill to make an even surface to set the spigot in.
  5. Before welding in the spigot, I built it first. Machined the ID on the lathe, made the flanges, then cut both to fit, and welded together (inside) so I didn't have a bunch of welding to clean up.
  6. The a final inside diameter clean up on the spigot on the lathe
RCfA
 

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Discussion Starter · #3 ·
I forgot to mention that before all of that, there was a bunch of basic repair: busted fins, stripped threads, including busted top motor mounts.

The exhaust ports weren't great, and one head needed valve seats (my most hated repair in a panhead). I chose to leave both to someone with tooling to do them early and precisely, as the very last step, once I was sure this was going to work (neither I could do without insane amount of one-off effort). More on that later.
 

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Discussion Starter · #4 · (Edited)
I started by welding and pressure testing one head first. I learned a couple of things and ran into some issues.
  1. Aluminum welding (especially this thick) is absolutely not my specialty. I learned alot experimenting with tungstens and rods. FYI- brown zirconated tungsten was way happier than any green I tried. My poor 225 Lincoln Precision Tig was definitely maxed out.
  2. Pressure testing time- I had random little invisible holes all over, but most notable was
    1. the top motor mount stud (because the intake machining had exposed the blind threaded hole to intake passage). The only viable solution for this I/was sealant/epoxy.
    2. My plan of only welding the carb flange on the inside had leaks because it overlapped with the outside welding against the top motor mount. Hard to explain, but I ended up having to weld the outside flange on both spigots.
New item by Scott McKelvey
 

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Discussion Starter · #6 ·
Last steps were to clean up all threads (head bolts+rockerboxes), and finish a few fins. As you'd expect, the rockerbox holes were toast. One head was already 1/4-20, so I made both heads the same. Yes it requires alot of drilling, but it's the max size that works, and its way stronger than stock,. Since these were non stock heads, I didn't have any heart burn
htthttps://photos.app.goo.gl/QXvJ7B1RXnTsSd5D9


It was time to send off for valve seats in one head and exhaust ports on both.

i sent them Nuumetal (Instagram) that was supposed to do everything. But it turns out he's a hell of a welder but not equipped to do anything else other than hand dress welding.

So I shipped to @duanes-powertain for legit valve seats. ZERO complaints-thorough, responsive, etc. Because of the work to do the seats, it made sense to have him do guides, valves, etc (which I'd normally do), so that was a little foreign to me, but well worth it. He uses all kibblewhite, like I would.
 

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Discussion Starter · #7 ·
Now with the heads back in my possession, it was time to get to business. I had no decent stock rockers and blocks, I used an aftermarket kit. I had to test fit and knock down a couple of burrs, but no complaints.

First was to sand the head gasket surface on a granite flat. That took 1-2 hrs. I know some recommend counter boring the headbolt inserts, but I firmly believe that will lead to early demise of the head.

Derek sent me kibblewhite valve seals which I've always thrown away because the don't fit pre '81 heads. BUT he clued me in to turning down the lower spring collar to a .025" lip. That will hold the spring and allow the valve seal. So I'm excited about that.
New item by Scott McKelvey
 

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Discussion Starter · #8 ·
So that brings us to today: waiting on parts to actually go finish the bike. Amal carbs, cables and throttles became a whole new world I had to learn about. I'm running with the 2:1 cable setup, and no choke bits. Major departure from normal Harley stuff.
 

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Scott, what a skilled gent you are.

A friend who builds a lot of bikes had a few knucks converted to dual carb for customers, not quite the same but I've been there and seen the work that goes into the spigot albeit being iron it's a different ball park but the process is similar.

It's no small task, and to go at it blind and get it done, amazing.

Duanne is the chap based out of the Prism HQ isn't he? I've heard good things about his work - some jobs are worth paying for!
 

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Discussion Starter · #12 ·
Scott, what a skilled gent you are.

A friend who builds a lot of bikes had a few knucks converted to dual carb for customers, not quite the same but I've been there and seen the work that goes into the spigot albeit being iron it's a different ball park but the process is similar.

It's no small task, and to go at it blind and get it done, amazing.

Duanne is the chap based out of the Prism HQ isn't he? I've heard good things about his work - some jobs are worth paying for!
Yes that's the same Duane. I'm not nit-picky, but I'm fair. These are basically 80-100yr old parts we're all working with, so I alway factor that in. And I have to say I was more than happy with every step of the process with him: communication (which is my bigges issue these days), cost, quality, choice in parts, thoroughness. He even caught a couple things that either I didn't see, or that I knew but didn't care about, so I can say he's thorough for sure. And he's clearly investing in serious tooling to stuff proper and repeatable.
 

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Discussion Starter · #13 ·
3 points that I didn't make clear, that I wanted to highlightnow, since the reason for this post is the annals for the next guy that wants to attempt it.
  1. Before you start welding anything, plan ahead for the carbs, tanks, etc. For example left leg clearance, how will the carb actually mount, and will they fit under your gas tank. I can say that I didn't have a plan for tanks, but the Amals would be a real problem with stock tanks.
  2. Intake leak testing is probably more important than ever.
    1. Porosity is going to be an issue. Just like you do intake leak tests for the smallest bubble, now you have miles of aluminum welds where they will likely be. So be prepared for repeated testing and welding.
    2. Think about how you're going to seal any holes that you open up. For example the top motor mount stud hole is likely going to be exposed to the intake tract, so have a plan.
 
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