Cracked alloy crankcase - can it be patched?

No, but you can get special non-ferris soft filler rods and have it welded, but obviously it has to be stripped and cleaned.

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.

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

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.

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.

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

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.

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.

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

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.