Cracked alloy crankcase - can it be patched?

Submitted: Monday, Jun 23, 2003 at 19:01
ThreadID: 5611 Views:6018 Replies:10 FollowUps:7
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Hi everyone, I have a motorbike with a crack in the crankcase following a stack. Years ago I recall seeing a product used where I used to work that was basically "liquid steel", you applied it and it went hard and you could file it, grind it, whatever. Does anyone know of a similar product for alloy, and has anyone ever tried a repair like this and been successful (or otherwise)?

Thanks, Tim Z.
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Reply By: desert - Monday, Jun 23, 2003 at 19:37

Monday, Jun 23, 2003 at 19:37
No, but you can get special non-ferris soft filler rods and have it welded, but obviously it has to be stripped and cleaned.
AnswerID: 23311

Reply By: matt - Monday, Jun 23, 2003 at 20:44

Monday, Jun 23, 2003 at 20:44
I have used a 2 part pruduct called devcon which worked brilliantly for a couple of years until i sold bike. Just make sure the surfaces are clean and free of oil and i grooved out the crack first . Im sure i bought it from a bearing wholesaler such as CBC or Skefco. Hope this solves your problem.
AnswerID: 23321

Reply By: Martyn (WA) - Monday, Jun 23, 2003 at 21:09

Monday, Jun 23, 2003 at 21:09
Tim Z,
As mentioned by Desert and Matt, the important bit is to have the crack clean and free from any grease or hydrocarbon. Depending if you are looking to do a temporary repair or a long term repair will determine your method of repair, Devcon will work a treat, but is good as a patch it won't be load bearing so if the component is under stress or strain and relying on Devcon to hold it together it won't. These days you could get it welded up successfully, you just have to be aware of the deformation that can happen when you get heat involved, this requires checks and machining but is load bearing. Quick fix, can't beat silicon providing it's the right grade, this is a lot better with vibration than the Devcon and will seal for a long time providing the right preparation is done up front, again not load bearing but will act as a patch. I had silicon on the crankcase of my 2.2 Jackaroo for about three years when I had a crack behind the starter motor, never lost a drop of oil and was still good when I sold it. Hope this helps. Keep the shiny side up
AnswerID: 23325

Follow Up By: zigglemeister - Monday, Jun 23, 2003 at 21:54

Monday, Jun 23, 2003 at 21:54
Thanks Martyn,
Looks like it'll be Devcon or silicon, as I don't want to strip the crankcase right down. Two questions - any tips where I might get Devcon over the net (I'm overseas, in Vanuatu - a bunch of islands out in the Pacific) - I have tried CBC and Skefco as per Matt above but didn't get real far. Secondly, any tips as to what grade of silicon - are you talking about the black stuff, or one of the clear ones?

Thanks for your help, Tim.
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FollowupID: 15505

Follow Up By: Martyn (WA) - Tuesday, Jun 24, 2003 at 20:03

Tuesday, Jun 24, 2003 at 20:03
Zig,
RTV silicone is what is used in hydrocarbon applications, I think that's it anyway, Loctite Ultra Blue 587 is the brand and product name, someone like Blackwoods will ship overseas as will other major corps, you might have to wait a while but I'm sure it will get there, until it arrives buy some more oil and some kitty litter.......Keep the shiny side up
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FollowupID: 15573

Follow Up By: zigglemeister - Wednesday, Jun 25, 2003 at 10:46

Wednesday, Jun 25, 2003 at 10:46
Hehehe, thanks for that, this bike's gone beyond the kitty litter stage when it comes to oil leaks - you should see my nice shiny black boots!
Thanks for your help, Tim.
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FollowupID: 15635

Follow Up By: zigglemeister - Wednesday, Jun 25, 2003 at 10:46

Wednesday, Jun 25, 2003 at 10:46
Hehehe, thanks for that, this bike's gone beyond the kitty litter stage when it comes to oil leaks - you should see my nice shiny black boots!
Thanks for your help, Tim.
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FollowupID: 15636

Follow Up By: zigglemeister - Wednesday, Jun 25, 2003 at 10:46

Wednesday, Jun 25, 2003 at 10:46
Hehehe, thanks for that, this bike's gone beyond the kitty litter stage when it comes to oil leaks - you should see my nice shiny black boots!
Thanks for your help, Tim.
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FollowupID: 15637

Reply By: Kev - (Cairns,QLD) - Monday, Jun 23, 2003 at 22:26

Monday, Jun 23, 2003 at 22:26
My mate snapped his chain on a moto-x bike and it took out part of the crank case that surrounds the cluch engaging shaft.

As a temporary fix he used "kneed-it" to seal the crank case and it even allows the cluch shaft to turn.
That was a year ago and still going ! Anything is beter than striping down the c/case.

I too would recomend Devcon (plastic steel), i used to use it on my tinny when it sprung a leak and seemed to bond to the aluminium very well.

Kev.
AnswerID: 23327

Follow Up By: zigglemeister - Tuesday, Jun 24, 2003 at 07:22

Tuesday, Jun 24, 2003 at 07:22
Thanks for that, I like to hear success stories! As you say - anything is better than stripping down the crankcase!
Tim
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FollowupID: 15514

Reply By: Joe - Tuesday, Jun 24, 2003 at 08:20

Tuesday, Jun 24, 2003 at 08:20
Ziggle,

Motorcycle crankcases are load bearing, and if the crack is in part of the main crankcase structure then using some sort of metal bog will not work and will cost you more in the long run as the crank starts to run out when the bearings shift etc.

However, if the area is not part of the main load bearing structure then you can bog it all back together.

I couldn’t offer any definitive advice until I saw the problem.
AnswerID: 23338

Reply By: Member - Bob W - Tuesday, Jun 24, 2003 at 08:27

Tuesday, Jun 24, 2003 at 08:27
Hi,
DEVCON plastic steel type 'A' or an equivelant product (which I can not recall at the moment) is about $40 for 500 grams which will mix up to the size of an apple.
Available at industrial suppliers such as 'Blackwoods'
If it is a hole rather than a crack then cover with shaped piece of sheet metal preferably fixed with screws or pop rivits first.
I have used probably at least my own weight in this stuff on repairs on ships machinery over many years and swear by it -- as a temporary repair (lasting years !!)
Regards
Bob W
AnswerID: 23339

Reply By: Truckster (Vic) - Tuesday, Jun 24, 2003 at 10:50

Tuesday, Jun 24, 2003 at 10:50
yea used something similar to the Devcon or Kneed it stuff on my TT, actually runnin a too big front sproket at Amaroo, and wore a small hole in the case..

Nutha bloke had this stuff, and it was black/silvery color, you rolled it up and it went ROCK HARD in round an hour. I mean HARD!

Again as others have said, the clean surfaces bit is critical.
AnswerID: 23357

Reply By: Member - Mal - Tuesday, Jun 24, 2003 at 14:47

Tuesday, Jun 24, 2003 at 14:47
Zig,
When you think you have it clean enough, give it a final spray with Electrical Contact Cleaner available at Dick Smiths or electrical/electronic suppliers.
Mal T.
AnswerID: 23366

Follow Up By: Kev - (Cairns,QLD) - Tuesday, Jun 24, 2003 at 18:14

Tuesday, Jun 24, 2003 at 18:14
Acitone is good for cleaning and it does't leave a residue.
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FollowupID: 15561

Reply By: zigglemeister - Wednesday, Jun 25, 2003 at 10:51

Wednesday, Jun 25, 2003 at 10:51
Thanks for your help everyone,
As it turns out I have to split the crankcase anyway to change the kick starter return spring which has broken :-(
But I don't know of anyone on this island who does non-ferrous welding, so the Devcon will probably be the go.
Tim
AnswerID: 23458

Reply By: Suzuki Viagra - Thursday, Jun 26, 2003 at 00:32

Thursday, Jun 26, 2003 at 00:32
get it properly mig or tig welded by a pro whiel it's apart and don't stuff around with anything else.

Years of experience as an ex motorcycle mechanic here - nothing else will last properly and it won'tcost much while it's apart to weld.
AnswerID: 23535

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