Linkert m74b rebuild

[lrcormier]

Currently cleaning/rebuilding my LINKERT, and have a couple questions. Palmer's says that main nozzle 27732-50 must be installed with a asbestos or neoprene gasket, I could not find any reference to this gasket in the service manual or parts book? I've ordered a new throttle shaft and bushing kit, not sure if the new shaft will be all I'll need but according to the service manual the bushings should be line reamed using a .250 drill, I'll use the procedure in Palmer's for removal and installation but is there a difference between a .250 drill or 1/4 in drill or is .250 how machinest like to reference them?

[ryan]

Both ansi and iso .250" / 1/4" metal cutting drill bits should be made to drill a .250" hole with a tolerance of +.005" -.001"

I am sure folks will chime in, but I personally would use a chucking reamer which can easily be purchased in half thousandth sizes( .0005" ) The reamer will not have a flute span to get both sides at one time. I also do not know what the shaft clearance should be nor the size of the replacement shaft, fully knowing it is around .250"
"I am not sure what size you are drilling up from so this process may or may not work." I chuck the reamer in the drill on the flutes and use the shaft as a pilot which will go both holes, ream the first hole, stop leaving reamer, unchuck reamer, chuck reamer on the shaft on the opposite side, start drill and pull the reamer on through. Do not run reamers in reverse as it will dull them.
If you want both holes to be perfectly in line with each other and held to a certain tolerance, you would have to have your holes honed at an engine builders machine shop.

[T. Cotten]

I have only found the nozzle gaskets surviving upon some military models, LRC!

But I routinely cut thin PEEK seals for all, as often there is wear at the spigot or venturi hole. Any leakage at this point defeats the "accelerator sump" function. (Neoprene will not survive modern fuels; Original seals appear either phenolic like Micarta, or an asbestos composite.)

Goodson offers a .250" reamer with extended flutes. The more critical aspect is to keep the bushings aligned with a pilot when pressed in, and to avoid pressing against the bottom of the body's bores. (The pucks I use are counterbored for the bushing slightly to prevent this.)

Most bushings can be installed with very little re-sizing needed; Beware of some modern "stainless" offerings that are already shot out two thou over!
Damaged bodys where the bushings no longer align perfectly will require custom-cut bushings with undersized bores to allow the reamer or hone to correct them.

....Cotten
PS: Does anyone have M53 series literature that should mention seals? Does it also spec a different float setting? Thanks in advance as always...

[T. Cotten]

...I've read a suggestion that the bushings and shaft will last longer if you modify the throttle arm by adding a small piece opposite the cable end and use two small springs opposite each other, but pulling in the same direction...

Sounds a little 'Rube Goldberg' to me, Kitabel!

The obvious remedy for short life seemed like baked-on moly disulphide, until everybody said I was too expensive already.

Nobody's got K/Sport literature? (Out of my zodiac too, Folks,.. but its relevant.)

....Cotten

[kitabel]

Sounds a little 'Rube Goldberg

That was so helpful!

[T. Cotten]

Sounds a little 'Rube Goldberg

That was so helpful!

Rube was my hero, Kitabel!

(Tell me he didn't inspire the Big Twin hand-clutch.)

If its true that the M53 series used both a fat nozzle seal, and a fat bowl gasket missing from all other side-bowl models, then the float setting should be like 3/16" or so, unlike any other Model M Linkerts. Can anyone confirm or deny this from HD literature?

....Cotten

[lrcormier]

Thanks for all responses, also got this from Mike at lintertcarbs.com concerning a seal on main nozzle: "Louis,
Palmer is wrong on that. The only carbs that used a seal on the nozzle were the M53 , M53A1 . They have a shoulder in the body they seal against, all other linkerts the nozzle can push right through if the venturi is out, but not those 2 carbs. Mike".

I'm pretty sure I will need a new throttle disc, mine has the wear in tits on top and bottom where the throttle shaft holes are and lots of daylight around perimeter of closed disc. With a new disk installed will I still be able to see some light around the edges or will the bike not idle properly unless there is a perfect seal all around? T.Cotten I also sent you a personal msg.

[kitabel]

The throttle never fully closes, but the only light should be at 90° to the throttle shaft: at 3 o'clock and 9 o'clock.
Have you found a 9x disc?

[T. Cotten]

M841L&R (and probably M17L&R) also used the nozzle seal, Louis!

If you have an 'eyebrow' of wear in the carb bore from the throttledisc, just throwing in a fresh disc will not close up the daylight around it, even if it happens to be "NOS" size. They are "forgiving" if the groove does not extend all the way to the idle bleeds, but will not be all it could be, unless honed and properly fitted with a disc.

(Beware of commercial 'oversize' discs that are grossly oversized!)

....Cotten
PS: Since the disc should never operate fully closed (as Kitabel noted), the cause of wear must blamed upon a combination of slop in the bushings, and vibration.
An aggravation of this wear is caused when over-torqued to the manifold. Distortion occurs at any fastener torque over 13 ft-lbs (7 ft-lbs for 1/4" fasteners).

PPS: Nobody got the mousetrap joke, huh. I might as well go back to Peoria.

[lrcormier]

I plan on ordering a new 9X disc from Into The Wilderness, they appear to specialize on linkert parts and rebuilding on then see how well it seals, I don't see any noticeable eye brow, maybe just very slight. I do have access to a couple fully equipped machinist in San Diego but would rather avoid the complete hone and rebuild with oversize parts if I can avoid it. I'm curious though, it would seem that one could make some small modifications to the disc by simply some slight sanding of the areas that make early contact to the body, wouldn't this work?

[T. Cotten]

Please think about it Louis!

How could removing material close a gap?
The disc should be precisely beveled on its edge to nine degrees, to close properly in the middle of the bleeds. It also has 'facets' on both sides to narrow its edge precisely at the bleeds.

A perfect disc for an un-worn bore would be ~1.5625", measured at the throttle axis. (Please remember that the beveled edge makes the 'disc' oval.)
NOS samples are invariably smaller, probably for two reasons: First, they were probably "seconds", and secondly, a perfect disc will not seal perfectly unless the body is honed while stressed, and then installed under stress!

...Cotten
PS: Please make certain your vendor will accept returns..

[ryan]

M841L&R (and probably M17L&R) also used the nozzle seal, Louis!

If you have an 'eyebrow' of wear in the carb bore from the throttledisc, just throwing in a fresh disc will not close up the daylight around it, even if it happens to be "NOS" size. They are "forgiving" if the groove does not extend all the way to the idle bleeds, but will not be all it could be, unless honed and properly fitted with a disc.

(Beware of commercial 'oversize' discs that are grossly oversized!)

....Cotten
PS: Since the disc should never operate fully closed (as Kitabel noted), the cause of wear must blamed upon a combination of slop in the bushings, and vibration.
An aggravation of this wear is caused when over-torqued to the manifold. Distortion occurs at any fastener torque over 13 ft-lbs (7 ft-lbs for 1/4" fasteners).

PPS: Nobody got the mousetrap joke, huh. I might as well go back to Peoria.

Actually I did get a big laugh out of it. Actually, a lot of manufacturing for a simple cable pull. Lol

[T. Cotten]

Actually I did get a big laugh out of it. Actually, a lot of manufacturing for a simple cable pull. Lol

I appreciate it, Ryan,..

Anybody catch the Laurel and Hardy shtick?

(I was bored and razed in Peoria.)

….Cotten
PS: Back to topic, most carbs clean up at four to six thou over. Some not of course, but twenty over goes nearly into the idle well, thirty to oblivion!

[lrcormier]

My eyebrows are very shallow and are barely felt with my finger nail. I guess to be perfect the carb bore would need to be honed, but I would also think that some wear is to be expected and the carb should still function reasonably well. My first order of business is to purchase a descent throttle disc, can anyone recommend a vendor that they sourced a good fitting disc from? After installing a new disc I'll have my machinist take a look and determine if honing should be done. I honing is done does that also mean the venturi will need to be replaced?

[T. Cotten]

As I posted earlier, Louis,..

If the groove does not extend to the idle bleeds, they are 'forgiving'. If it does, the air directed in and out of the bleeds by the disc at idle and low speed is diverted, and the transition to high speed becomes difficult to tune: An evil "flat spot", such as has given Linkerts and DLXs a maligned reputation in modern times.

And yes, if the bore is enlarged, the venturi must be as well. They can be swaged oversize, and then cut to a light press fit.
A great many potmetal venturies have shrank and distorted to where they are loose in the original bore anyway, allowing for their own 'daylight' to confound tuning.
Ironically, a potmetal venturi swaged and cut to a light press fit will return to a nice slip fit after several months, but at least it will stay 'round'!

Aluminum venturies are not subject to shrinkage, however are far more difficult to swage. COLONY offers .025'' oversize venturies that can be turned down for most repairs.
Huge oversized discs would have to be re-cut as well, but by that point you might as well just cut one from scratch.

....Cotten
PS: It should be noted at this point that the idle bleeds are a very delicate orifice, metering not only by the diameters of the holes and width of the slot, but by their depth through the casting. Most start with ~.030" wall, and an eight or ten thou enlargement of the bore would reduce that by four or five thou, and hasn't proven detrimental, so far.
Twenty-five over would cut the wall depth by almost half, and most likely would risk affecting metering function, for better or worse, we do not know.
(It would certainly rob the casting of future re-freshenings by generations to come.)