M-74 repair?

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George Greer
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M-74 repair?

#1

Post by George Greer » Sun May 04, 2014 12:04 pm

What is the material of choice to repair cracks in the body of a M-74B that has apparently been on a bike involved in an accident, and is cracked near the manifold's mounting flange?

I did not notice the crack until I took the body to work and had it cleaned in a Ultrasound Cleaning tank, and got around to the inspection phase on the carb.

I stopped there, and thought that I would inquire about repair procedure before moving on. Not sure if it can be repaired or not.........if not, I will not worry, and find another body.

Thanks

George



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Re: M-74 repair?

#2

Post by Cotten » Sun May 04, 2014 12:53 pm

A photo would help, George!

L&L used soft solder on the bowlstems.
I have used both brass and silver-solder on more structural areas. Here is an aircleaner flange repair:
acflng1.jpg
acflng2.jpg
Note that straightening must be done before adding filler, as it will widen cracks.
acflng3.jpg
Here, the silver-solder has been dressed and retextured.
acflng4.jpg
After grinding the flange, re-texturing, and enamelling, of course, the repair will be less visible.

....Cotten
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George Greer
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Re: M-74 repair?

#3

Post by George Greer » Sun May 04, 2014 2:24 pm

Cotten,

I will get some photos of the carb and post them.

I do have some silver-solder.

George

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Re: M-74 repair?

#4

Post by old.wrench » Sun May 04, 2014 5:43 pm

George,
If you use a good hi-temp hard silver solder like Safety-Silv or it's equal, you should end up with durable repair. I've found that the low-temp "silver bearing" (2%-4% silver) solders are O.K. for some stuff, but if the part is subject to any real stress, I like using Safety-Silv; and it flows so nice! Good Luck on the repair.

Geo.

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Re: M-74 repair?

#5

Post by Larry » Sun May 04, 2014 7:54 pm

This repair was done with Heliarc and Everdur wire.
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Re: M-74 repair?

#6

Post by Cotten » Sun May 04, 2014 8:43 pm

Wow, no bubbles at all , Larry!

I am not familar with "Everdur", but I could sure use a few feet.
Every application for me is trial and error, attempting all of the different "fillers" until one is friendly.

Geo!
I am not familiar with "Safety-Silv" either, but I did find a 5lb tube of "Stay-Silv" right before the Great Recession.
(The dumpsters have never recovered.)

....Cotten

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Re: M-74 repair?

#7

Post by old.wrench » Sun May 04, 2014 11:20 pm

Cotton,
You lucky dog! The 56% silver rod retails for about 10 bucks for a stick! (1/16" x 18")
If I'm not mistaken, "Everdur" is a brand name for good old silicon bronze, probably very similar in alloy to what you've used.
(the dumpsters aren't the only things that haven't recovered from the Great Recession)
Geo.

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Re: M-74 repair?

#8

Post by Cotten » Mon May 05, 2014 1:05 am

Geo!

"Silicon bronze" is what my tigmeisters insisted upon for cast iron, and sweetcheezes it was hard to dress.

The bronze castings of Linkerts (and pre-June of '29 DLX Scheblers) are plenty sturdy even if soft solder is used.

Carving is the hard part.

....Cotten

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Re: M-74 repair?

#9

Post by George Greer » Mon May 05, 2014 3:06 am

Fellas,

Thanks for all the assistance, I did get photos made yesterday.

I will upload them this afternoon when I get home from work.

George

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Re: M-74 repair?

#10

Post by Larry » Mon May 05, 2014 3:30 pm

Yes, Everdur is a brand of silicon bronze, rumored to have been developed specifically for the repair of bronze castings. It works well on cast iron because the melting point of the base metal is theoretically not reached, so the likelihood of cracking is greatly reduced. In practice, however, some of the iron can get into the weld, causing extremely hard areas. This doesn't happen when welding on bronze linkert bodies. The buildup is fairly easy to file or sand. It also machines satisfactorily, although great differences in hardness could cause a drillbit to "walk". Not likely to happen on a Linkert.

The wire welds very easily; anyone with a little tig experience can handle it. It also can be welded by oxy-acetylene using flux, although I've never tried it.

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Re: M-74 repair?

#11

Post by Cotten » Mon May 05, 2014 4:22 pm

Hopefully, Folks,..

The only stress a manifold flange should encounter is from the fasteners.

I found that anything over 13 ft-lbs will bend a four-bolt immediately, and even three-bolts display long-term distortion:
FLANGTST.jpg
It is still nothing that should crack a repair.
(I did have one customer, however, who overtorqued so drastically that it cracked the casting at the bushing,..
JWCRACK.jpg
....and caused his throttle to stick dangerously!
The sad thing is I did two carbs for him, and he immediately put the second one on, and thrashed it too.
He must have an impact.)

Straightening badly warped flanges before a final grind requires that a puck be inserted into the bore, with a precision hole through it for a 1/4" ground rod to keep the bushings in line:
FLNGPRSS.jpg
Bronze should always be bent cold, if not chilled.

....Cotten
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Re: M-74 repair?

#12

Post by George Greer » Tue May 06, 2014 3:08 am

Here's the photos.

Cotten, thanks for your photos, I now have a better idea of what I need to do.

But take a look at the last photo.......getting that "v" shaped area repaired might be a booger to repair!

George
IMG_1441.JPG
IMG_1431.JPG
IMG_1436.JPG
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Re: M-74 repair?

#13

Post by Bigincher » Tue May 06, 2014 5:15 am

And speaking of "bandwidth".....

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Re: M-74 repair?

#14

Post by 58flh » Tue May 06, 2014 12:31 pm

LARRY---By any chance Have you ever used a COLD-WELDER??--I asked here once & nobody had an answer.My buddie has one & Its for CAST-IRON WELDING!--& That -Silicon -Bronze rod you mentioned sure sparked my memory!--I used that to fix a broken Driver-side motormount in a Iron Block chevy!--It puddled good & IT WORKED!---The Machine itself upon close inspection was built in the late 1959 to be exact!--I would have to call him to find-out the Make or manufacturer.--Or perhaps you have a name??----,This cold-welder did great work on cast-iron ex. holes, cracks.& a House radiater/done in home repair!--The welder was light -(80lbs+/-) & looked like a Marshall 4/12 Cabinet.-Respectfully---RICHIE

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Re: M-74 repair?

#15

Post by Cotten » Tue May 06, 2014 12:49 pm

Sorry George,

But there's too many pics on the page for me to view now.

(My dial-up service is folding next month, so I may be scarce around here soon.)

The great thing about silver solder is that it will wick into cracks, and notching to a V like conventional welding can sometimes be avoided.
Preparation is critical, of course.

....Cotten

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