Linkert m74b rebuild

[lrcormier]

Got a new throttle shaft and bushings today. I installed the new bushings but what do I need to hand line ream. Although the bushings seemed loose on the shaft prior to installing, they are now tight and need to be reamed in order to install the shaft. Need recommendation for a reamer?

[T. Cotten]

See post #3, Louis!

Did you beat them in?

...Cotten

[lrcormier]

The bushings were pressed in using a vice, for removal of old bushings I used a 7mm tap and then inserted a 7mm bold and tap it out using a drift pin. Also had applied some liquid wrench to bushings, they came out without very much effort. Apparently the bushings are designed to compress slightly upon insertion and went in without much difficulty, entire procedure (remove old insert new) took less then 15 minutes. I guess I'll try the method mentioned in the service manual and use a 1/4 in drill but will purchase a new one for this use.

I've read a lot of post about replacing the bushings but no one states how they then fit the shaft by either using a drill bit or ream. After all, these carbs were designed in the day to be rebuilt by your average home garage mechanic without the use of any fancy machines, that is unless the body is still in serviceable condition.

[T. Cotten]

Does the shaft start to insert at all in either bushing, Louis?

....Cotten

[tfburke3]

I have an adjustable Starrett reamer I use but before I got it my method would be to tightly roll a long strip of about 180-220 grit cloth backed emery paper so it would just push in the bushings,the roll should slightly expand to snug,then spin in same direction as rolled and push and pull the paper up and down to lap to size.Usually there is not much to remove and the proper fit is as tight as possible but turns free.
Tom

[lrcormier]

Thanks Tom, that sounds like something that should work and will give it a try. I also got a suggestion from someone outside the forum that a chainsaw file use lightly would also work. I was prepared to buy a ream but these inexpensive alternatives could do the trick. If I somehow end up with to loose a fit bushings are also cheap enough.

[lrcormier]

Went to home depot for some emery cloth, they don't have that. Purchased a 7/32 round chain saw file and thought maybe I could wrap a piece of wet sandpaper that I already had, the file would provide good gripping for the sandpaper. I cut a 1/2 in strip of 320 wet sandpaper and spiral wrapped it around the file, this made a tight fit but managed to twist it through both bushings. I spun and pushed and pulled by hand and after about an hour and a half sheet of paper I got a shaft that fits snug and spins freely. Bowl float from Cotten is on it's way so now I just need to find a reasonably well fitting throttle disc and I should have a working linkert m74b. As the old saying goes, more then one way to skin a cat, thanks to all who provided input.

[lrcormier]

Concerning a tight fitting throttle disc, something that just occurred to me and got me wondering why is this so critical because when adjusting the idle you will need to screw the idle adjuster in which will slightly open the throttle disc. Doesn't this mean that the bike will never really operate with a throttle disc fully closed?

[T. Cotten]

I s'pose, Louis,..

If there was enormous daylight around a disc when fully closed (first attachment), perhaps it might idle, but that's certainly not the design; Fully closing the disc should shut her down.
(Note the plumes of carbon formed upon the disc from poor mixing. How it would be burned within the carb is mysterious.)

The more daylight, the more closed it must be to direct air at the bleeds, and the less control over the idle speed and mixture.

Beware also that when enough RPM is reached to cause the venturi to draw at the main nozzle, the idle circuit reverses itself, no longer metering fuel emulsion to the bleeds, but meters air to the bottom of the nozzle to emulsify fuel there. So an idle needle setting set rich for idle will lean the high speed circuit, and vice versa. The happy median that will give the best performance, fuel mileage, etc. is a lot easier to find with a happy bore and disc.

No wonder Linkerts are called 'crude' and 'simple', huh.

....Cotten

[kitabel]

Doesn't this mean that the bike will never really operate with a throttle disc fully closed

This is why I delete my posts...

[T. Cotten]

Doesn't this mean that the bike will never really operate with a throttle disc fully closed

This is why I delete my posts...

It frustrates me too, Kitabel!

But if novices cannot get the basics here,.. The AMCA mandate dies a little more.

(With DLX/Linkerts, I guess its my 'cross to bear'.)

....Cotten
PS: Everyone should get their questions answered, even if the Divas won't answer mine.