DC Linkert Idle Tube

[billpedalino]

Further my inquiry, I have three idle tubes for three different carburetors; two DC-12's and a DC-7 (one is not usable, hence my idle tube search). I've noticed some differences between these tubes, mainly the lengths and the bleed hole diameters. However, I don't see any difference in the idle tube part number for the XL's DC-12 of the FL's DC-7 (P/N 27324-57). Does anyone know if these tubes differ?

Also, one carburetor has a bit of wear in the cast iron housing where the throttle shaft passes through and I'm concerned about a lean mix at the mod and higher air flow rates. It's odd that there aren't pressed-in bushing here, as in the Linkert M-series carburetors. I'm thinking of boring out these holes and using the M-series bushings. Has anyone done this?

[T. Cotten]

I've never bushed a DC, Bill..

But I've bushed plenty of Scheb and Linkert bodies for chokeshaft wear.

Fortunately, I have a special reamer that not only keeps the bores in line, but cuts to the precise interference for standard bushings.

It was military surplus from the late seventies.

....Cotten

[Omarttentmaker]

I've never bushed a DC, Bill..

But I've bushed plenty of Scheb and Linkert bodies for chokeshaft wear.

Fortunately, I have a special reamer that not only keeps the bores in line, but cuts to the precise interference for standard bushings.

It was military surplus from the late seventies.

....Cotten

Nice tool, Cotten. But how fussy would the alignment actually be? I did the work to a buddy's VL carb. Ran a piece of threaded rod thru the carb body and made a washer to hold the body against an angle plate. Stuck a shaft in a drill press chuck that aligned the old hole, and reamed the 2 holes thru for a press fit for throttle shaft bushings. I did have to start a hole in the threaded rod to allow the reamer to travel thru it Trimmed 2 bushings to the proper length, so that they were flush on the outside of the body on either side, and just shy of the radius on the inside for the bore. His choke plate now stays in place while riding, and works to pull gas thru the carb body for choking. I'm thinking the choke plate alignment in the carb bore doesn't need to be nearly as fussy as the throttle plate!

[billpedalino]

I've never bushed a DC, Bill..

But I've bushed plenty of Scheb and Linkert bodies for chokeshaft wear.

Fortunately, I have a special reamer that not only keeps the bores in line, but cuts to the precise interference for standard bushings.

It was military surplus from the late seventies.

....Cotten

Cotten,
Would you know if these piloted reamers remanufactured or are otherwise available anywhere? If not, would you consider reaming my cast Iron DC body for the bushings? I could probably have a reamer made, but the cost would definitely be excessive for one use.

[T. Cotten]

The choke isn't as fussy of course, Omar,..

(But there's still nothing wrong with getting it right!)

The throttle geometry needs to approach an ideal, not only to avoid sucking too much air at the shaft, but to last.
When installing bushings into HX Schebler models, they must be left extended slightly into the bore, roughed out with files, and then the whole bore finish-honed to provide the proper arc for a fresh disc to close upon 'ideally'.

Bill's DC would require the same treatment (but a lot easier than a Scheb!).

....Cotten
PS: There probably isn't a convenient source for a reamer like mine, Bill,..
But MSC etc. have .3155" reamers, leaving it up to your skill and patience to keep them in line.
And sorry, but I can't let anything more cross my benches until they are empty (except manifolds and float requests, of course!)
PPS: Doh! Its a Red-Line Reamer Co. of Millersburg PA, production, and stamped as only 5/16", when a .3155" is best for most bushings. Either I followed with another reamer,.. or the choke holes are often egged that bad anyway (attached).
Last note: With a cast iron DC, the final fit might be best performed with a very long Sunnen mandrel, especially if the replacement bushings are 'unique'. And I might suggest stress-plating it as well, even though cast iron is usually pretty stable.

[ihrescue]

Please see the attached sketch - I hope it's inserted (not the most user-friendly system).
The measurements shown are as close as I could get using a mechanical Caliper.

That's a darn good diagram Bill and effective attachment as a file too.

Mike Love

[ihrescue]

I've never bushed a DC, Bill..

But I've bushed plenty of Scheb and Linkert bodies for chokeshaft wear.

Fortunately, I have a special reamer that not only keeps the bores in line, but cuts to the precise interference for standard bushings.

It was military surplus from the late seventies.

....Cotten

Tom - regarding the "military surplus" reamer, was the military use for the reamer for repairing a worn carb bushing as well? Or another purpose? Looks handy.

Mike Love

[T. Cotten]

Tom - regarding the "military surplus" reamer, was the military use for the reamer for repairing a worn carb bushing as well? Or another purpose? Looks handy.

Mike Love

Doubtful, Mike!

As I tried to correct myself,.. It turns out to be a nominal size, so it could be generic.
(Although the leading end starts with long tapered cutting flutes, as if it was made to rough out our carb chokes perfectly: Just lucky?)

My father bought large lots at auction, and this was included with everything from piles o' empty leather binocular cases to inscrutable Sikorsky tools, now long gone. Except what I have stashed for four decades out of sentimentality.

Like these, a Chatillon, and a Nanasi (West New York, N.J.) spring scale, with 1964 Army calibration tags taped upon the back. Great for measuring HX airvalve springs.

....Cotten

[ihrescue]

Doubtful, Mike!

As I tried to correct myself,.. It turns out to be a nominal size, so it could be generic.
(Although the leading end starts with long tapered cutting flutes, as if it was made to rough out our carb chokes perfectly: Just lucky?)

My father bought large lots at auction, and this was included with everything from piles o' empty leather binocular cases to inscrutable Sikorsky tools, now long gone. Except what I have stashed for four decades out of sentimentality.

Like these, a Chatillon, and a Nanasi (West New York, N.J.) spring scale, with 1964 Army calibration tags taped upon the back. Great for measuring HX airvalve springs.

....Cotten

Ah yes - scales can be pretty handy and that one is neat looking. I use a fishing scale to measure a nominal torque of the swing arm on my Sporster. A tip provided in the HD Factory Service Manual. Thanks for those comments. Imagine getting salvage rights on some of the US occupied islands in the Pacific after WWII, instead much of it was pushed into the sea so it could not be used again.

Mike Love

[T. Cotten]

Back to Bill's dilemma, Folks,

It has two horns: Not just locating brass stock to fab one, but finding its critical specs.

My specimens were all on loan, and all went home, so..

Who has dead soldiers to dissect and inspect for Bill (and Posterity}?
(It is not unusual for different productions to have the same OEM number in the book, trust me.)

....Cotten

[Omarttentmaker]

The choke isn't as fussy of course, Omar,..

(But there's still nothing wrong with getting it right!)

The throttle geometry needs to approach an ideal, not only to avoid sucking too much air at the shaft, but to last.
When installing bushings into HX Schebler models, they must be left extended slightly into the bore, roughed out with files, and then the whole bore finish-honed to provide the proper arc for a fresh disc to close upon 'ideally'.

Bill's DC would require the same treatment (but a lot easier than a Scheb!).

....Cotten
PS: There probably isn't a convenient source for a reamer like mine, Bill,..
But MSC etc. have .3155" reamers, leaving it up to your skill and patience to keep them in line.
And sorry, but I can't let anything more cross my benches until they are empty (except manifolds and float requests, of course!)
PPS: Doh! Its a Red-Line Reamer Co. of Millersburg PA, production, and stamped as only 5/16", when a .3155" is best for most bushings. Either I followed with another reamer,.. or the choke holes are often egged that bad anyway (attached).
Last note: With a cast iron DC, the final fit might be best performed with a very long Sunnen mandrel, especially if the replacement bushings are 'unique'. And I might suggest stress-plating it as well, even though cast iron is usually pretty stable.

Never considered hand forming the radii on the inside edges of the throttle bushings.....Good tip!

[silver65]

It was my thought that the DC carb throttle body being cast iron and the brass butterfly shaft was the sacrificial metal by design that would get worn out and replaced not the holes in the throttle body. I would replace 27276-57 throttle shaft, 6227 washer and 27291-32 spring first on the throttle body rebuild. But over time and a lot of use, I guess the brass could wear down the cast iron.

[T. Cotten]

Unfortunately, Silver65,...

Soft metals can embed abrasive particles, and then act like a tool-holder to cut the harder metal.

A classic example were aluminum tappet blocks, which suffered less than their steel tappets.

....Cotten

[billpedalino]

I've never bushed a DC, Bill..

But I've bushed plenty of Scheb and Linkert bodies for chokeshaft wear.

Fortunately, I have a special reamer that not only keeps the bores in line, but cuts to the precise interference for standard bushings.

It was military surplus from the late seventies.

....Cotten

I've reached out to a tool maker to see what the cost would be to have a somewhat similar reamer fabricated. If anyone else is interested in one, please let me know. I'm sure the price would drop for an order for multiple pieces.

[billpedalino]

It was my thought that the DC carb throttle body being cast iron and the brass butterfly shaft was the sacrificial metal by design that would get worn out and replaced not the holes in the throttle body. I would replace 27276-57 throttle shaft, 6227 washer and 27291-32 spring first on the throttle body rebuild. But over time and a lot of use, I guess the brass could wear down the cast iron.

You're exactly correct. On this particular body, the throttle block side of the shaft (toward rear of bike) is worn about 0.015" and the throttle body hole is oblong by about 0.005". The opposite side throttle body hole (toward front of bike) is worn about 0.015" as is the shaft. So both were sacrificial.