Author Topic: Repair of broken carb-fork CB 750  (Read 1827 times)

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Offline mec

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Repair of broken carb-fork CB 750
« on: June 07, 2012, 03:17:06 am »
hello,

have seen that this part (please help me what is the correct term for this fork?) is no longer available.
have seen also many broken forks seemingly because the incredible power of the engine overwhelmed the drivers capability :)

lets start, more pics than words:
you need all the stuff necessary to disassemble the carb mechanism, tig welder, file, saw for aluminium, a piece of 4mm aluminium, sanding paper.

i have done this repair 30 years ago without having a mill. but my small mill makes life easier.

first preparing the breaking point for welding, its no great issue to tig weld the pieces, onto the bandsaw for rough contouring, milling, polishing or smoothing.

thats it.

same repair i have done to a broken clutch lifter plate.


mec
Honda Monkey
Takeuchi TB 070
Massey Ferguson

Offline lucky

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Re: Repair of broken carb-fork CB 750
« Reply #1 on: June 07, 2012, 02:29:37 pm »
hello,

have seen that this part (please help me what is the correct term for this fork?) is no longer available.
have seen also many broken forks seemingly because the incredible power of the engine overwhelmed the drivers capability :)

lets start, more pics than words:
you need all the stuff necessary to disassemble the carb mechanism, tig welder, file, saw for aluminium, a piece of 4mm aluminium, sanding paper.

i have done this repair 30 years ago without having a mill. but my small mill makes life easier.

first preparing the breaking point for welding, its no great issue to tig weld the pieces, onto the bandsaw for rough contouring, milling, polishing or smoothing.

thats it.

same repair i have done to a broken clutch lifter plate.


mec

How did it weld? Was it very porous??
When you Tig'd it did it glow blue red or green?  Green would be a high zinc content.

I just had to replace one of those lifting arms on a set of carbs that had a missing arm.
I got one from Ebay for $25.00 but it was from a F model . All I had to do was drill and tap for an idle screw. No problem.

Offline mec

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Re: Repair of broken carb-fork CB 750
« Reply #2 on: June 08, 2012, 01:31:07 am »
welding was pretty good. not the best alu casting i have seen however. but porousity was minimal. the strength of the welding will not be as good as the undamaged part, but more than good enough for normal use at least.

colours: ??? will pay more attention the next time welding.

mec
Honda Monkey
Takeuchi TB 070
Massey Ferguson

Offline lucky

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Re: Repair of broken carb-fork CB 750
« Reply #3 on: June 13, 2012, 05:32:40 pm »
welding was pretty good. not the best alu casting i have seen however. but porousity was minimal. the strength of the welding will not be as good as the undamaged part, but more than good enough for normal use at least.

colours: ??? will pay more attention the next time welding.

mec

I learned about the color thing when welding a broken weed eater case.
It glowed green and was difficult so I went to welding supplier (a real good one),
And the salesperson told me that they have special TIG filler rods for high zinc content aluminum engine cases. So from then on I would strike an arc as a test and watch the color of the glow of the arc.

Trey it out on some clean 6061 and you should just see a nice blue arc.

 

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