Cracks in Alpino crankcase

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daveh

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UK
I have just found two small cracks in my 350 Alpino crankcase. There is one at each end of the slot for the bearing half ring on the secondary gear shaft. Hope the picture is clear.
Has anyone got any ideas for the best way to fix it? I see other posts mentioning that the 1000s use A356-T6 aluminum, did Laverda use the same for the Alpino, so will welding work?

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While I'm no welding expert, I'd say it would be difficult to get a thoroughly strong enough weld into that crack while still maintaining the shape and close tolerances. I had a damaged aluminum alternator cover repaired by welding, followed by filing and sanding smooth, but it wasn't a precision part like that crankcase. Perhaps a channel could be ground into the crack on the facing side, followed by a welded bead, but the crack in that groove would still be present and cause a weak area prone to fracturing. Will be interesting to see what experienced welders have to say about this-
 
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These cases normally do not crack in this area, especially not in a 350 with its handful of ponies! I'd suspect incorrect gearbox spacing and abnormally high axial loads to have caused this. The gearbox shafts are not designed to take axial loads, therefore the bearing bosses do not need to be excessivly strong. A run of weld with a laser would probably have that OK in a jiffy, without distortion and huge amount of post-processing.

I'd put a lot more thought on why it happened than how to repair it.

piet
 
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Piet's right. On other motors where that type of clip does carry a load from eg helical primaries, I've machined the outer lip away and made up a plate which screws to the case. At this end of the world I've not yet seen anyone with laser welding gear.
 
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GregT said:
Piet's right. On other motors where that type of clip does carry a load from eg helical primaries, I've machined the outer lip away and made up a plate which screws to the case. At this end of the world I've not yet seen anyone with laser welding gear.
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Closer than you suspect, Greg. Might to be a franchise near you...


Also look around for toolmaking companies specialising in repairs for casting dies, machinery housings, etc. Some of the main applications for laser welding. While the equipment still isn't bargain-level, it is becoming cheaper.

Looking at the picture a bit closer, that seems to be the layshaft bearing housing. There should be absolutely no axial loading present on that shaft. I'd check positioning/location of the selector drum, condition of the selector forks and search for shims that shouldn't be there...

Generally, it's the clutch end of the mainshaft that shits itself, and only on liquid-cooled 750s, which share the same basic crankcase. Not even the 600/650s make enough power to break the cases in this area under normal circumstances.

piet
 
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I looked around Sydney for Lazer welding a few years back and found nothing, but apparently, they have arrived and are relatively cheap, a couple of grand, kits can the bought locally. I tried interesting my local Tool Maker slash Aluminium Fabricator Tig Bloke. Hopefully he bight.
 
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Thanks for your thoughts. I suspect the cracks are probably from separating the two halves of the crankcase. After 35 years off road things were pretty locked up inside and it was hard to strip down the engine with the pistons seized. If the other end of the gear shaft lifted with the top case even a little bit then it would have put a twist on the bearing half ring in the bottom case.
I’m thinking I’ll go with welding and check the shims to be sure there’s no lateral loading.
 
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Laser welding in Havant Hampshire UK.

Laser Welding |

We have expanded our business into Laser welding. With this process we are able to repair very small or delicate components that with conventional tig welding would not be possible. The laser is a source of heat, but has the most unique ability to focus the heat on a tiny spot. The tiny spot can ...
www.e-m-p.biz
 
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Here some pictures off welded 500 cases.
First one after cracking, the other to avoid cracking.
 

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Otto said:
Here some pictures off welded 500 cases.
First one after cracking, the other to avoid cracking.
Click to expand...
Sorry, although it may be strong, that looks more like a dogs breakfast when compared to laser work... ;)

Combustion chamber skulls are tricky with some alloy needing to be removed first in order to fully penetrate the skull. Refilled after the cast iron is welded. Steel infill up to 75 Rockwell for bearing surfaces (I've even reclaimed MV Agusta crank main bearing races). Smaller repairs cause zero distortion and quick and easy post-processing. The cleaning-up of the repair of the widespread cam chain tunnel cracks is a matter of minutes with a file and oil stone.

markQLD said:
Yep, my money is on somebody got a bit too excited bashing on a new sprocket that was fouling on the spline? :unsure:
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Good point, Mark! Although I don't know of 500 aftermarket sprockets that would be that difficult to fit, it fits the pattern perfectly.

piet


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Preventive welding by team Cavazzin on my 600 TT2.
My ex wife's 500 had two sets of cases, both cracked right hand side.
Tim Parker or someone else on here will relate the problems with with crankcases at Daytona on the Ogier bike.
When I contacted Maurice Ogier a few years back in view of purchasing his race bikes laying rotting at the back of a hangar, he told me that he'd had a set of beefed up cases made awaiting machining.
Paul
 
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sfcpiet said:
Tim destroyed a set of cases while racing in the US with the Harris 580 sometime in the 90's. Moto Witt supplied a replacement set.

piet
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The welding on my pictures where from Andy J in the eighty’s and Horst Schreder , I think late nineties.
Laser welding wasn’t available.

Speaking about the Parker Harris: FYI he is back in Europe, in the Netherlands. Eva is making it ready for trackdays.
Now I know four Harris 500/600 bikes.
1, Uwe’s, 2. Andy, 3 Eva/Parker, 4 Mine. Do you know where number 5 is? Does it still exists?
 
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