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29th Jan 2015, 06:30 PM #1Most Valued Member
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Cast aluminium engine casting hole, brazing rod or spool gun?
hey guys thought this would be the best forum to ask this
i recently purchased a dirt motor bike and the chain came off on the old owner punching a small 5x3mm hole in the crankcase, the crankcase is cast aluminium
i have three options
JB weld it (looks dodgy to new buyers if i sell it)
weld it with aluminum brazing rod
or
weld it with my spool gun
pulling the engine apart to repair such a small hole will result in me rebuilding the engine and spending $700-$1000 so its just not economical
what would u do in this case?
crankcase hole 001.jpgcrankcase hole 002.jpg
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29th Jan 2015, 07:43 PM #2Philomath in training
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Looking at the pics, I wonder whether you will be able to get the casting clean enough for any of those methods. The heat from brazing or a spool gun needs to be considered too as that close to the sprocket shaft there are likely to be bearings and seals that may be affected.
Although it's not the answer you want to hear I would be strongly considering doing at least a partial strip down so that I had access to both sides of the cover, could clean it properly and remove any seals that might get hot. Failing that I guess you are back with the dodgy looking JB weld.
Michael
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29th Jan 2015, 08:43 PM #3Most Valued Member
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Michael the engine has a load of grease and grime chocka block all over it so the pictures are of it uncleaned
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29th Jan 2015, 08:53 PM #4Philomath in training
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A good Al weld requires the metal to be really clean. I'm thinking that some of that grime and oil has gone into the pores of the material and as soon as you apply heat it will contaminate your weld. Similarly the JB weld requires a clean surface to adhere to. You might be lucky and cleaning the surface with something like acetone will do it but you might have oil in the hole too that will interfere.
Michael
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29th Jan 2015, 09:02 PM #5Senior Member
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Irrespective of how you carry out the repair, the first thing I would do is replace that very worn-out sprocket, otherwise history will likely repeat itself with another hole or worse.
Chas.
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29th Jan 2015, 09:15 PM #6Senior Member
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Out of left field, what about drilling and tapping a bolt into it.
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29th Jan 2015, 09:54 PM #7Senior Member
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Looks like your only option is the JB Gaz.
I wouldn't touch it with a mig or brazing rods, that casting will just go snap crackle and pop and make a bigger mess. Not to mention the counter shaft bearing and seal just near by.
I also wouldn't be drilling anywhere without knowing what's in behind.
The only way I have been successful in repairing motorcycle casings is total strip, clean, bead blast, acid wash then tig welded.
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29th Jan 2015, 11:52 PM #8Most Valued Member
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Not the answer you want to hear, but there is only one truly viable option. TIG weld it. I would have every confidence that a competent welder will be able to effect the repair with the engine assembled and doubt that even the rubber seal will be damaged. I used to do quite a few similar repairs and can't remember killing a bearing or seal.Mig will not be remotely successful as the degree of contamination will be far too great.
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30th Jan 2015, 11:11 AM #9
I would suggest TIG welding it for the best quality repair, or as a cheap and easy option fill it with "steel knead it" epoxy putty after a very thorough clean. That stuff sticks like ship to a blanket and can be made to look very neat.
Cheers.
Vernon.
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Bite off more than you can chew and then chew like crazy.
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31st Jan 2015, 09:29 AM #10Most Valued Member
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That "knead it" epoxy certainly does work well. The only downside to it is that if you ever decide to repair the casing properly with weld, your poor welder will call you all sorts of creative names and invent a few new ones into the bargain. It is horrible muck to try and fully remove before welding.
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31st Jan 2015, 10:20 AM #11
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31st Jan 2015, 11:20 AM #12Senior Member
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History
Hi Bloke
Never thought I would see a post like this. Back in 1973 I had a K2 Honda 750/4, couple of mates wanted to go for a ride up at Tambourine Mt, in Qld, had a chain on the bike that had gone past its limit in stretch, yeah yeah, i know what ya all thinking, I took three links out, went for the ride, hooking into a left hander up the mountain and giving it a handful, BANG.
Chain snapped, punched a matchbox size hole through the crankcase, right on the split between the two halves. Bike was taken back to Brisbane in a ute. Rang my m/cycle mechanic, he knew a bloke that had a new kind of welder, that might just be able to repair the hole. With the help of the ute drive, we pulled the motor out the frame, delivered it to the mechanic, he stripped it down, cleaned it, and passed it onto his welder mate.
When I got it back, you could barely see where the damage had been done, the welding was that good. The mechanic said joining the two halves back was no problem either over the patched area.
That "new kind of welder" has improved over the years. My advice to you mate, is do it right, pull the motor out, strip it down, clean it thoroughly, get it welded by a person who knows their stuff. On the other hand, I have seen a hole repaired by Devcon Alloy on a XT500 engine successfully, no leaks, and remained sealed to this day.
DD
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31st Jan 2015, 12:36 PM #13Most Valued Member
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I used to get quite a few come into work where they had patched it with knead it or similar to get out of the bush and back home again, then wanted the weld repair done. The same as people who Sikaflex or silicone holes in boats "just to get us through the summer."
I agree with you that if you decide to use knead it, you may as well leave it there until it fails if it ever does fail for that matter.
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