New 250 Project Adventure

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Madman
Posts: 49
Joined: Thu Nov 24, 2016 4:24 pm
Location: France, but English

Re: New 250 Project Adventure

Postby Madman » Sun Jan 01, 2017 9:20 am

The trouble with stop drilling that crack is that a stop drill is only effective if it is bigger than at least 4mm, which then gives you holes to cover. I believe that brazing is the answer.
By the way, thanks so much for this very informative thread.

Snakeoil
Posts: 109
Joined: Fri Jun 17, 2016 12:10 pm
Location: Upstate NY

Re: New 250 Project Adventure

Postby Snakeoil » Sun Jan 01, 2017 4:13 pm

I remember there being a rule of thumb regarding the size of a crack stop hole. But for the life of me cannot remember what it was. I'm glad you mentioned this. I will research the subject.

I do tend to think that even if I drilled two 1/16" holes at the end of each crack that it would be beneficial. The problem here is I don't know if this crack was from the stamping process or it it was the result of vibration and the petcock acting like a pendulum and fatigue cracked the metal at that compressed area. The stamping certainly created a stress riser.

I'd be content to run one petcock if the tunnel were not so deep.

Thanks for the kind words and comment regarding the stop holes.

Happy New Year!
Rob

Madman
Posts: 49
Joined: Thu Nov 24, 2016 4:24 pm
Location: France, but English

Re: New 250 Project Adventure

Postby Madman » Sun Jan 01, 2017 6:10 pm

I have just changed the petcocks on my Mk3 and the M10 ones that I bought from Italy were both 2 way ones, off/on/reserve, so i only use one of them, the other is always off. If you need to blank the hole on one side then I believe it is an M10x1 thread, and you can get single inlet inlet bits for dellorto carbs rather than twin inlets.
The stop drill size was part of my training, over 25 years in aircraft engineering specialising in structural repairs. Anything less than 5/32" (4mm) will not stop a stress crack. If the crack has been there since manufacture then it won't be under stress anymore and does not need a stop drill at all, because it won't propagate.

Jordan
Posts: 1380
Joined: Fri Dec 24, 2010 11:29 am

Re: New 250 Project Adventure

Postby Jordan » Sun Jan 01, 2017 8:32 pm

I hope your proposed braze repair works.
If it fails a pressure test, maybe remove the the complete dished area including the boss and blank off the hole with a suitably shaped piece of steel sheet, overlapping the hole so it's not just a butt joint, braze on. Move to a new location along the tank and install a newly turned up and threaded boss with a flange. Solder or braze it to a new hole, not with a dished shape just flat against the flat tank bottom surface.

Snakeoil
Posts: 109
Joined: Fri Jun 17, 2016 12:10 pm
Location: Upstate NY

Re: New 250 Project Adventure

Postby Snakeoil » Mon Jan 02, 2017 2:51 pm

Thanks for the responses, guy. I did a bunch of research on line after posting initially and found several good articles on the subject of stop holes. Most were related to bridges and crack in the structural steel. Not really applicable, but interesting nonetheless. What was most interesting is the number of companies that have developed crack stopping repairs. They are all based on driving a pin into the stop hole. One firm swages a thick ring into the stop hole. It imparts compressive stresses on the material which arrests the crack since cracks initiate and propagate due to tensile stresses.

There is a aircraft manual on line and I down loaded the chapter on sheet metal. Lots of good info in their for forming sheetmetal with techniques, set-ups, etc. No hard info on stop hole sizes, just the use of them.

Found a truck body repair guide that appeared to be an OEM manual. They gave stop hole sizes based on sheetmetal thickness. 0.033 and under is a #40 drill and over is a #30 drill.

I did find an engineering paper that would probably take be the better part of night to read, not because it is long but because I'd have to relearn half the terms used in the paper. What I did glean from it, however was they tested stop hole sizes down to 1mm with measured success. But bottom line is a stop hole is only a temporary solution and with time and enough cycles the crack will reinitiate.

I tend to lean toward's Madman's thought that it is probably not going to propagate further and can be brazed shut as-is.

Appreciate the input.

regards,
Rob

Snakeoil
Posts: 109
Joined: Fri Jun 17, 2016 12:10 pm
Location: Upstate NY

Re: New 250 Project Adventure

Postby Snakeoil » Sat Jan 07, 2017 11:37 pm

Okay, back to tank. I pondered on this over the holidays and decided that the crack was from the stamping process and any residual stresses were gone. Brazing would probably impart new stresses into the area so I decided to solder it.

First I pressure tested it again after flooding the area with acetone. To my surprise, no matter the pressure I pumped into the tank there were no bubbles. It would appear that when I removed all the big globs of solder around the petcocks, I managed to solder the crack shut. That would never happen if you intended it to work that way.

But not content to let it be, I went at the crack area with some dental pics and some micro drills held in a pin vise in order to remove any discoloration, debris, corrosion, oxides, etc., that might be in the crack area. Sanded it, wire brushed it, scraped it again with dental pics and then soldered it one more time spreading out the soldered area to either side of the crack for better integrity. Pressure test resulted in zero bubbles so I think I'm good to go.

When I was done I decided to give the interior a good scrubbing with sheet rock screws, my favorite tank cleaning media. The idea was to assure all scale was removed down to the smallest bit. I'm thinking of hitting it one more time with the Evaporust.

When I was done, I flushed it out with alcohol and filtered the alcohol thru paper coffee filters to remove the fines. I did this several times and it was interesting to see just how fine the particles were that I was flushin out of the tank. They passed thru the paper coffee filter.

Below are pics of the finished crack repair and one of the fines in the bottom of plastic container after filtering the alcohol one last time in case anyone was curious.

regards,
Rob
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Madman
Posts: 49
Joined: Thu Nov 24, 2016 4:24 pm
Location: France, but English

Re: New 250 Project Adventure

Postby Madman » Sun Jan 08, 2017 9:24 am

That looks like a fantastic job that you have done there.
Anything in that pot is so fine that it would just go through the system.

Snakeoil
Posts: 109
Joined: Fri Jun 17, 2016 12:10 pm
Location: Upstate NY

Re: New 250 Project Adventure

Postby Snakeoil » Thu Jan 19, 2017 11:44 pm

Have been involved in other stuff lately. I picked up a new blasting cabinet off CL. I blasted the 350 tank at my friend Jake's because it was just too big for my Horror Fright benchtop cabinet. Before I remembered Jake had a good sized cabinet, I found this ALC unit and the price was 1/4 the price new. Saturday, I decided to go get it and I'm glad I did. Needed new gloves, but I had a spare set I'd bought for the other cabinet that would not fit. The fit the new cabinet like a...well.. like a glove.

So today, I reblasted the 350 tank because I'd missed some spots and the media in Jake's cabinet was a little spent. I also blasted the Monza tank and both came out nice.

I ordered the correct hot glue for dent pulling but that dent in the upper corner of the 350 was too rigid to pull. I soldered a stud on it and got a lot of it out. I filled the rest in with lead and will finish it with Bondo.

Here are the two tanks after blasting today. Will see if Charlie wants to do the skim coat with Bondo and then prime them or have me do the skim and he just primes them. I'm only priming them because I'm not sure what I color I'm going to paint the bike.
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KarstenH
Posts: 71
Joined: Sun Nov 20, 2011 5:44 pm

Re: New 250 Project Adventure

Postby KarstenH » Sun Jan 22, 2017 9:28 am



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