Linkert M74B

[duffeycycles]

They can leak in many places,one is the rivet that holds the inserts in the heads.Another is the inserts to heads around the threads.If you actually have o-rings it is not stock.Either stock or modified, any point in the system can have a leak.Carb to manifold etc.

[T. Cotten]

Like Duffey posted, Laurie,...

Not only are there many common places to leak, some leak at "impossible" places (little 'blisters' of foam form at porosities after a half-minute or so, and yes, they do affect performance!):

MANBLSTR.jpg MANBLSR2.jpg

Those were 'plumber's' castings, but here's modern S&S O-ring leakers:
S&SPORE.jpg
S&Spore2.jpg

Without bubbles such curses could never be cured.
(Note the first two had been perforated with a port, shown here repaired,
in a frustrated attempt at some better idea, because they were not diagnosed.)

Note also that the manifold-to-carb connection cannot be bubble-tested, so please arbitrarily grind the manifold flanges to *flat*,,... because they never are!

FLNGDST4.jpg

....Cotten

[Laurie]

They can leak in many places,one is the rivet that holds the inserts in the heads.Another is the inserts to heads around the threads.If you actually have o-rings it is not stock.Either stock or modified, any point in the system can have a leak.Carb to manifold etc.

yes mate the heads were modified before I got them to O Ring type manifold

[Laurie]

Like Duffey posted, Laurie,...

Not only are there many common places to leak, some leak at "impossible" places (little 'blisters' of foam form at porosities after a half-minute or so, and yes, they do affect performance!):

MANBLSTR.jpg MANBLSR2.jpg

Those were 'plumber's' castings, but here's modern S&S O-ring leakers:
S&SPORE.jpg
S&Spore2.jpg

Without bubbles such curses could never be cured.
(Note the first two had been perforated with a port, shown here repaired,
in a frustrated attempt at some better idea, because they were not diagnosed.)

Note also that the manifold-to-carb connection cannot be bubble-tested, so please arbitrarily grind the manifold flanges to *flat*,,... because they never are!

FLNGDST4.jpg

....Cotten

Cotten
hope to get at it tomorrow, but I will also flat sand the flanges Thanks for the advice!

Cheers & Beers

[dukekleman]

Laurie,
If your carburetor body is warped more than 0.015" , I would suggest you straighten it out prior to sanding.

This will minimize the material lost when sanding which aids in retaining thread depth.

Hope this helps!
Duke

[T. Cotten]

Like this, Duke?

FLNGDST3.jpg

flngprs3.JPG FLNGPRSS.jpg

I found that 13 ft-lbs is enough to distort the flanges:
FLNGTST.jpg

One bright customer zipped two of his carbs on with an impact, and even broke the castings at the bushings!
JWCRACK.jpg

....Cotten
PS: A late note on the importance of assembly torque:
When I honed bores clean, it was always torqued to a plate. If a disc is cut to that exact bore, it will not install to zero daylight unless the plate is re-applied, as if installed to a manifold!

OEM discs seem to have been produced intentionally sloppy and undersized.

[dukekleman]

Yeah, along those lines.
Certainly over-torquing and heat are the culprit causing major failures.

Duke

[T. Cotten]

Yeah, along those lines.
Certainly over-torquing and heat are the culprit causing major failures.

Duke

Where's the heat come from on a carb flange, Duke?

...Cotten

[dukekleman]

Cotton,
Heat Transfer/soak from it's encapsulated environment.
most damaging rises seen after shutdown.

[T. Cotten]

Cotton,
Heat Transfer/soak from it's encapsulated environment.
most damaging rises seen after shutdown.

If your carb and manifold get hot enough to distort, Duke,...

They are on fire!

....Cotten
PS: Fastener stress alone is enough.

[dukekleman]

It's the heat and torque combination that I mentioned earlier that does all the damage.
The torque applied correct or incorrect combined with the heat realign the metallurgy and cause issues, just like all other components in the engine and transmission. The term "green" , "seasoned" often get thrown into the conversation.
Once the initial run in has occurred , you'll always notice it doesn't occur like it did to the extent.

Hope this helps,
Duke

[T. Cotten]

It's the heat and torque combination that I mentioned earlier that does all the damage.
The torque applied correct or incorrect combined with the heat realign the metallurgy and cause issues, just like all other components in the engine and transmission. The term "green" , "seasoned" often get thrown into the conversation.
Once the initial run in has occurred , you'll always notice it doesn't occur like it did to the extent.

Hope this helps,
Duke

We are talking cast steel and cast iron manifolds, Duke,...

Plus insulating gaskets to the bronze carb flanges.

Do you really think a couple of hundred degrees makes the flanges warp?
I will give vibration some credit!
But its the gaskets that give the flanges room to move with fastener stress.

(Bronze actually becomes more malleable when chilled, and 'brittle' when heated.)

....Cotten
PS: Aluminum manifolds warp the same way.

PPS: Shouldn't the carb/manifold junction be cooled by the incoming air, plus vaporizing fuel?
(I've heard legends that they could ice up!)

[dukekleman]

All metals and plastics change with heat, torque and vibration.
Cryogenics is another process used.
Once those parts have all been seasoned, they tend to hold their dimensions much longer. Unless you sand to much off and thin it down...

[T. Cotten]

All metals and plastics change with heat, torque and vibration.
Cryogenics is another process used.
Once those parts have all been seasoned, they tend to hold their dimensions much longer. Unless you sand to much off and thin it down...

You mean, Duke,...

Our half-century and older hardware ain't seasoned?

Even if it was kept outside?

....Cotten
PS: We all agree, seasoned or not, metal moves!

[dukekleman]

No the opposite, I mean it is seasoned. Now once they are straighten out, it'll stay in formation longer than it did way back when it was new.

Hope this helps,
Duke