LCGB Forums

I've finally been getting around to a engine rebuild that kind of started about 10 years ago yeah I know, but house moves, dodgy ex's and life in general have got in the way but here we are...
Anyway just popped in a new rear hub seal and noticed this very small crack in the casing







I know they are not the best pictures in the world but you can just make out the line of crack in the piccies, its barely a 1mm deep and was wondering if alloy welding is the only solution ( and delay the build probably another decade ) or could I just seal it with a chemical metal etc to prevent it cracking further? cheers fella's . Paul

That's a load bearing point, I'd get it welded. You say it's only 1mm deep; that would make it a scratch rather than a crack. If it's a deep scratch I wouldn't worry too much but if it's a crack I'd personally have it welded.

Like you say, it's hard to convey the detail properly in a photo, so I'm half guessing, but like I say, more than half the load goes through the layshaft and then into the casing via the bearing and end-plate. Hard to say the distribution between layshaft bearing and end-plate, but due to the cantilever arrangement, most will go through the bearing.

dickie wrote:That's a load bearing point, I'd get it welded. You say it's only 1mm deep; that would make it a scratch rather than a crack. If it's a deep scratch I wouldn't worry too much but if it's a crack I'd personally have it welded.

Like you say, it's hard to convey the detail properly in a photo, so I'm half guessing, but like I say, more than half the load goes through the layshaft and then into the casing via the bearing and end-plate. Hard to say the distribution between layshaft bearing and end-plate, but due to the cantilever arrangement, most will go through the bearing.

Looking at it again, its more of a hair line crack than a deep scratch (sadly) yeah its looking like its going to have to be welded as it could spread and really cause a potentially dangerous incident. Typical - the rest of the casing is perfect its going to have to wait as I'm between gigs now and can't justify ally welding bill thanks for the reply Paul

I would investigate the process of 'crack detection' which is something used in engineering to identify cracks & to what extent they affect the part. One method involves penetrant dies that may involve UV light, but there are X-ray machines etc.

My thoughts are that if the crack is not 'through' from the bore to the outer, then it may only need to be 'dressed' to stop it spreading. In other workers, just as a radius in a corner prevents stress, compared to a sharp corner, the crack may only need slotting with a round burr & polishing.

I'm loathe to have welded repairs on alloy castings that are loaded with zinc (as Lambretta castings are) as they tend to be porous as the result. A welded repair can look brilliant but I've seen them break or crack again. Not so bad in an over-ported crankcase mouth, but a scary thing in the instance of a repaired headset performed by a coded welder.

Even if the crack was tested & proved to need surgery, I would consider options to welding. A custom bigger replacement seal retaining plate in a good strong steel with extra depth both ways, pocketed to fit around the casting (inboard) would be far stronger than the original casing IMO.

Warkton Tornado No.1 wrote:Even if the crack was tested & proved to need surgery, I would consider options to welding. A custom bigger replacement seal retaining plate in a good strong steel with extra depth both ways, pocketed to fit around the casting (inboard) would be far stronger than the original casing IMO.

Cheers WK1, I was hoping you might have some alternatives to welding, I know from people getting cases converted from 125/150 to 200 cc that the ally of lambretta cases is less than perfect, and It would be at the back of my mind when riding - how safe is the repair. I'm intrigued by your possible solution but have no idea how I would go about it. Cheers Paul

Scooterslag wrote:
I'm intrigued by your possible solution but have no idea how I would go about it. Cheers Paul

If you were to place the brake shoes, pivot pins & cam in place, the seal retaining plate then stick a big blob of Playdoh/plasticine/Blue Tack etc on one corner, then place on a brake hub loosely, you should ascertain the kind of space that can be utilised by anything to take the place of the existing retaining plate. Then you could sketch it out to get some idea of what can be made.

A 3D CAD system is the modern alternative. Funnily enough, that's my proper job but to create a 'model' would involve also modelling the associated parts, which I cannot afford the time for @ present (my home was in a fire & flood some time ago. Long story)

If a 3D model were made, you could even obtain a 3D printed model to check fit/clashes etc.

Hopefully some other CAD designers are on this Forum & can offer you the favour. Or wait a year or two & I will be designing stuff specific to Lambretta.....

Not exactly David Bailey are you
If it’s a crack it needs digging out and welding by someone who actually knows what it is. I’d recommend Chiselspeed.
If it’s not cracked and is just a casting rag then it’s tea and biscuits all round and god save the queen.

bsso78 wrote:Not exactly David Bailey are you
If it’s a crack it needs digging out and welding by someone who actually knows what it is. I’d recommend Chiselspeed.
If it’s not cracked and is just a casting rag then it’s tea and biscuits all round and god save the queen.

Hopefully its tea and biccies , may even push the boat out and have a kit-kat