DC Linkert Idle Tube

[silver65]

Let's clear a few things up.

there was no sacrificial metal, nor that intention. The material chosen has a reasonable service life for a then new bike. Seems odd to us, but the bikes weren't built thinking about the tenth owner some sixty years later.

Second, ever wonder why the throttle body is separate from the carb body on a D.C.? After some fifty years of carb manufacture, linkert might have noticed trends and came up with a "new" design that allowed for super fast repair to worn bodies. Drilling and bushing is archaic compared to bolting on a new body in five minutes. Seems someone was thinking about service as well as changes to the carb. This becomes a key point in a moment.

As to all this reaming business, try a sunnen hone. More precise. No need for fixtures or extreme expenditure. Just a correct mandrel.

Finally, the shaft position is way, way more important than you may imagine. The D.C. Throttle disc is orienteted to uncover a series of bleed holes in the carb roof. When the shaft wears that positioning is lost. Dudes blame air bleed around the shaft, but in reality, it's throttle disc orientation. Shoving in new bushes may or may not reestablish the orientation and may or may not address wear to the throttle disc. Thankfully, the D.C. Is forgiving and you can tune around the screwed up position with float height, but now your bike is a bit rich at idle and speeds up to 30 or so.

Again, many bushes have been done at home in a drill press, and you often hear about hard starting and a fluffy low end response. There's a correlation.

With the tube, I sold a mess of D.C. Spares recently or I'd just send you one. If no one can come up with one, I'll pull one from a running bike in the coming weeks and measure one.

Let's muddy the water

If the brass parts were not intended to wear out and be replaced as part of a service then why did they make the replaceable parts and yes the brass was sacrificial such the brass bushings in the cam cover that would wear out and preserve the more expensive parts such as the cams throttle body and all the other places they used brass bushings like the shifter shaft and kick start shaft bushings. This was the same for the linkert DC carb. So yes that was there intention not like today in our throw away society.

Silver65

[chuckthebeatertruck]

If the brass parts were not intended to wear out and be replaced as part of a service then why did they make the replaceable parts and yes the brass was sacrificial such the brass bushings in the cam cover that would wear out and preserve the more expensive parts.So yes that was there intention not like today in our throw away society.

Silver65

To sum up; you have 4 overlapping theories:
1) brass was intended to wear faster than more expensive parts
2) replacements exist to protect more expensive parts
3) linkert copied harley's manufacturing philosophy
4) both linkert and HD were concerned with the machine 10-20 years after they sold their wares.

Let's address each.

To start with; there's no "brass" bushings/bearings in the units were discussing. They are phosphor bronze and are true bearings. The Society of Automotive Engineers (SAE) started grading bronze bearing alloys in the very early days of the industry and the most common bronze alloy you run into is 660. In this regard, 660 is a super long lived bearing material. It does wear, but wear is different from a sacrifice material.


To point two; if you think bronze bushes are meant to protect "more expensive" parts through the use of bushes, you're dead wrong.


Let's use your timing chest example to illustrate. First and foremost; HD was pretty clear bronze bushes would go 50K miles or more between service/replacement. And that's in the days of no oil filter or air filter and really bad oiling. To put it in perspective; that's roughly 2-5 top ends depending on the model and often around 50K the bottom is getting pretty rattly too. In other words, the whole MOTOR is pretty worn out about the time the bushes need replacement due to wear. When you do have a high mileage timing cover; it's not unusual to find the cam shafts worn undersize as well. IN fact, the whole thing can get so sloppy you find bushes loose in the cover.

Thankfully, early HD models had replaceable shafts on the cams. So, you replaced both the worn bush AND the shaft if needs be.

Hopefully that helps you understand the bronze is a bearing, not a sacrifice intended to wear faster than the "more expensive" part. It was simply meant to bear the forces in a way the alloy cover and alloy cases could not. By the time we got to sportsters; one piece cams were now common -- but they still wore out the shafts on high mileage bikes. HD would sell you one or two or all four cams. It was cheaper and easier than making separate shafts like in the early days of the 4 cam design. In other words, the engineers knew the shaft and the bush would wear -- and often at very predictable rates.


I'm not trying to bust your balls but rather help you understand there's a huge difference in our personal belief as bikers about these bikes going forever and the actual philosophy behind the engineering design. The bike had to last long enough for the owner to want to buy another one, but that is it. HD makes no real profit off selling parts for old bikes. They sell new bikes. WE want the bikes to last forever, they have never wanted that outcome.


Now to manufacturing: we often misunderstand the difference between making one bike and making 20,000 bikes. many people mistakenly believe the bikes were built using the sort of proceedures outlined in the fsm such as "line reaming" the timing cover bearings. But, that is not how the bikes were made. S imilarly, we have some weird belief that dealer mechanics were constantly rebuilding motors and old bikes for customers. They were not. Then as now; a lot of dealer tech work was new bike set up; 5 or 10K mile services; and accessory installation. So, separate out your belief from the necessity of making 20,000 bikes per year. You can't hand ream each case to each cover and turn a profit.

Then, you have to consider the use of the material and what it needs to withstand. The cases and timing covers were sand cast, high flow alloy into the early 70s. This is great for casting parts but terrible for holding up to spinning motor shafts. So, in goes the "replaceable" bronze bushings. They are among the most reliable bearings you could get in an under oiled design. As a manufacturer you can buy them as cast units in bulk with the OD already finished. Given a tolerance on the leading lip and you suddenly have three of four critical dimensions covered in your contract order. Then, all you need to do as a maker is finish the ID. That's a HUGE cost savings.

The second benefit is that when HD started using them, there was no positive lubrication to these bits in the timing chest. Only the pinion saw positive oil. Bronze bushes were (and still are) one of the best things for handling these conditions especially with dirty lubricant. They were cheap, easy to machine, and long lasting. They expand at a rate similar to the alloy they rest in. Almost any mechanic knew how to deal with them because they could be found on machines going back to Jamie Watt. These are all things that allowed for rapid and inexpensive manufacture with a good life expectancy in service.


But, at no time was an engineer thinking: "I should make these bushes wear out faster than the cam shaft so future owners don't have to buy cam shafts before they buy new bushes." That sort of thinking is the exact opposite of a vehicle maker's profitability.


Similarly, the reason for replacement bits is simple -- HD warrantied their bikes when new. If a motor died due to oil starvation -- there was a decent chance a bush would be damaged. Cheaper/easier to replace one bush vs. the whole timing cover in that case. It's the exact opposite for something like the carb throttle body. It's faster and cheaper to replace that vs rebush the worn plate and replace all the worn parts.

Back to the bronze bushes in the timing chest. Before you get too stuck on the wear issue; ask yourself why HD swapped the inboards for needle bearings made of hardened steel -- steel harder than the camshaft itself? The bronze worked fine on the K model and early XL; so why the change to a steel needle bearing? The answer is that the bronze bushes were getting deformed and wore out prematurely from the loads they were seeing. A needle bearing could take this load. But, if a needle bearing fails it does much more damage to the motor than the bronze bush. So, it is certainly not being sacrificed and it will destroy a cam shaft if it fails. Like the bronze bush, it is intended as a bearing. let that sink in; HD used steel to stop wear to bronze and create a super reliable system. Sort of pokes a hole in the "preserve more expensive parts" theory.

A really big test is the bronze bushes used in the lower end of many british twins. Look up BSA main bearing failure and ask yourself if those engineers intended the main bearings to be eaten up they way they were.

Now, let's address the third and fourth parts. Linkert is NOT harley davidson. They were a vendor. Their business was selling brand new carburetors in extreme volume to major manufacturers. They were not in the business to make carbs for life and they were not directly servicing the end user. Yes you could buy stuff from them directly, but it was not the primary company business. So, to assume Linkert designed a part so Harley owners could enjoy longer service life is an odd misnomer. Linkert couldn't care less. All they cared is whether HD bought their carbs. The wear to the shafts we are discussing doesn't happen on new bikes. It doesn't happen on late model bikes. It happens on high mileage or very old bikes . . .both of which are situations that are out of warranty and often many years after the new vehicle was sold.

And this brings us to the big elephant in the room: whilst HD touted reliability in its ads; neither it nor Linkert really cared about the guy buying a bike 10-20 years down the line. Their business was new sales -- not used and not parts. This later fact still shocks HD owners today who are angry dealers don't stock parts for their 50 year old machines and don't offer service on them. Walk into a buick dealer and ask them to service your 1959 Roadmaster and see what happens. Yet, for Harley, we feel it "should" be different.

I hope you understand I'm not trying to bust your balls. What you write is a very common sentiment/belief amongst vintage motorcyclists. Most are still mad that they can't call HD and get the date their bike was built and who bought it and what options/colors it had. If you think about it; the archiving of all those records so a NON-CUSTOMER can have info in 75 years is pretty funny. And you better believe you're a NON-CUSTOMER. Harley sells new bikes -- and unless you're buying a new bike; you're just a guy with an old bike that happens to be the same brand.

That last statement is the sad part and has led to the throw away sentiment -- but the original intent of the engineers is quite different.

[T. Cotten]

Don't look now, Folks,...

But Linkert didn't even develop the design.

George Schebler did,.. in the early 'Teens.

The design was practical, serviceable, and survived for generation after generation after generation.

Let us not forget his genius because of feckless modern business models.

....Cotten

[silver65]

IMG_1810.jpg Mr. I'm not trying

You made my point in your first paragraph and I will just call it the softer metal for you instead a certain "type" and this practice is still being used in modern manufacturing today, linkert did not copy HD, the philosophy was around long before the internal combustion engine. We all also know how things work and why a car battery only last around 5 years when they can make the to last 10-20 years but that would take the fun out of it. "It does wear and does not matter if do not like the word sacrificial"

Silver65

[T. Cotten]

Mr. I'm not trying

You made my point in your first paragraph and I will just call it the softer metal for you instead a certain "type" and this practice is still being used in modern manufacturing today, linkert did not copy HD, the philosophy was around long before the internal combustion engine. We all also know how things work and why a car battery only last around 5 years when they can make the to last 10-20 years but that would take the fun out of it. "It does wear and does not matter if do not like the word sacrificial"

Silver65

I thought 'sacrificial' only applied to water heater anodes, Silver65!

Two metals of the same 'hardness' never wear well against each other: Identical ferrous metal parts will gall.

Brass-on-bronze isn't a whole lot better.

Are we ready to talk carburetor lubricants, Folks?

....Cotten

[silver65]

Bill I think cotton was right with the 3/32 tube, your measurement in your diagram was .0940 OD the 3/32 tube is .0937 this my be the correct fit in the top of the carb body, and the base of the tube if you could find a good old horologist that was not cranky he could make a press fit plug to your specs.
, for the end of the tube on his watch makers lathe unless you go with plugging the end with solider. They most likely would have utilized a common size tube for there production.

[T. Cotten]

It wouldn't require a watchmakers's lathe, Silver65!

Just one with a decent chuck, and stronger reading glasses.

....Cotten
PS: I'm not a horologist, but I am cranky.

[billpedalino]

Bill I think cotton was right with the 3/32 tube, your measurement in your diagram was .0940 OD the 3/32 tube is .0937 this my be the correct fit in the top of the carb body, and the base of the tube if you could find a good old horologist that was not cranky he could make a press fit plug to your specs.
, for the end of the tube on his watch makers lathe unless you go with plugging the end with solider. They most likely would have utilized a common size tube for there production.

Yes - My intention exactly. I'll never be able to make that button in my South Bend 9A and my time is too limited and precious to waste. I'm 71 years old now and still working. Maybe in 10 years or so when I retire I'd have more time to mess with it. For now - a jeweler or watchmaker would be money well spent. He could make the button and I would complete the assembly.

[silver65]

I only mentioned a watch makers lathe because of the collet sizes used in there trade "very small". Also you might be able to find a old clock gear pivot made of brass the right size to make the bottom end of the idle tube without much manipulation.

[T. Cotten]

I only mentioned a watch makers lathe because of the collet sizes used in there trade "very small". Also you might be able to find a old clock gear pivot made of brass the right size to make the bottom end of the idle tube without much manipulation.

Why punish yourself, Silver65?

Just chuck up some brass rod, and carve it to exactly what you need...

Then sweat it on the tubing with minimal soft-solder, cut it to length, and drill the bleed hole last.

It ain't that micro, just hard for old eyes to see.

....Cotten
PS: I found a bunch of horologist tools when the town's ancient watch shop owner passed. Don't know how to use most of them... But the demagnetizer does wonders on polarized floatvalve needles. Or so a compass tells me. Can't have them attracting abrasives!

(Tried to upload a catalog scan of the demagnetizer,... but one attachment is all that's allowed?)

[silver65]

Watch shops and there owners is becoming a lost art along with good mechanics to work on the older cars and bikes without all the electronics. The watch demagnetizer is very old and a compass could tell you if your mechanical watch is magnetized or they have a new APP for smart phones that will also tell you, and that is also great for magnetizing screwdrivers and tools for small screws and nuts that you don't want to loose. Watches can either run fast or slow when magnetized and this happens exposed to a magnetic field and I am sure you know how that works.

[T. Cotten]

Watch shops and there owners is becoming a lost art along with good mechanics to work on the older cars and bikes without all the electronics. The watch demagnetizer is very old and a compass could tell you if your mechanical watch is magnetized or they have a new APP for smart phones that will also tell you, and that is also great for magnetizing screwdrivers and tools for small screws and nuts that you don't want to loose. Watches can either run fast or slow when magnetized and this happens exposed to a magnetic field and I am sure you know how that works.

I use a permanent (speaker) magnet to polarize screwdrivers, Silver65!

But I've never used any of my several de-magnetizers (de-Gaussers) to 'magnetize' anything.

Just like floatvalve needles, you don't want your motor's connecting rods to attract metal at their poles,

....Cotten
PS: A compass is a helluva lot cheaper than any kind of phone! So are metal filings on paper.

[silver65]

That demagnetizer you can put a screwdriver in the middle of the CT plug it in or turn the switch hold the driver in the middle without touching sides for about 10 seconds and pull it straight out slowly away from the CT and it will demagnetize your screwdriver or in reverse go into the CT slowly hold for 10 seconds then de-energize CT and magnetize the screwdriver, same for the old tractors or the fairbanks Morris XLCH magnetos when the magnets get weak you re-magnetize the magnets in the rotor for a better spark. Thats also how they demagnetized watches.

[T. Cotten]

That demagnetizer you can put a screwdriver in the middle of the CT plug it in or turn the switch hold the driver in the middle without touching sides for about 10 seconds and pull it straight out slowly away from the CT and it will demagnetize your screwdriver or in reverse go into the CT slowly hold for 10 seconds then de-energize CT and magnetize the screwdriver, same for the old tractors or the fairbanks Morris XLCH magnetos when the magnets get weak you re-magnetize the magnets in the rotor for a better spark. Thats also how they demagnetized watches.

I think I understand, Silver65!

What's a CT?

Thanks in advance,..

....Cotten

[silver65]

CT is a current transformer and is like that circular demagnetizer you have when you put voltage through it creates a magnetic field and push or pull a metal plunger through the center like in the old pinball machine flippers, or a 24v door bells. CT,s are also used in in large electrical services for metering electricity they run service wires through the CT's and measure electrons that flow on the outside of the wire for billing. I know you have heard about CT scans doctor slides your hole body in that big doughnut at the hospital for a full body imaging.