New product: MBScooters Ltd – threaded repair inserts

Every now and then a product comes along that's so useful it's hard to believe that no one else has thought of it. Such is the case with Mark Broadhurst's threaded repair inserts.

A constant source of frustration for Lambretta builders is the tendency for fixing screws to bond with alloy castings, particularly horncastings and mag housings. It's fair to say that most restorations involve at least one screw that's sheared off in place and as Mark explained, repairing the aftermath can be a time consuming and expensive process.

“Usually repairs arrive at the workshop when someone's tried to drill out a broken screw in a horncasting and the drill goes offset, half in the alloy and half in the screw. I've then got to slowly grind the old bit of screw out to find its centre, but this leaves the hole elongated and if I try to fit a helical or timesert there's no meat to cut the threads correctly. Usually the only cure is to grind it out, clean it up, weld the holes and then start drilling and tapping new threads, which can get very expensive.”

Fed up with these niggles, and looking to reduce the cost of the repair MB Scooters Ltd has now made oversize inserts. “They will repair some mag housing holes, most horncastings and some headsets. So long as the tool kit contains a drill, drill bits, metric taps and thread lock or strong retainer most people should be able to do this at home.

“If a thread is pulled out with some oxidisation, then it's just a case of running a drill through it to find clean alloy, tap to the outside size, use a screw and nut to hold the insert, add Loctite and screw it in place; then lock it down with the nut, unscrew it and it's fitted. Also if the screw needs drilling out you've now got a bit more leeway if you drill off-centre.”

The inserts have a small ring on them to stop them in the casting. “In some places you can leave the ring slightly proud with no issues. You can also use a small counter-bore, so the ring sits flush in the casting. Additionally the inserts can be cut or ground down on the reverse side to be neater. If you're not sure, then just send them to MB Scooters Ltd to repair and it won't cost hundreds of pounds!”

The new threads are 7mm outside diameter and 5mm internal diameter; 6mm outside diameter and 4mm inside diameter are also available.

Price: £3.50 each direct from MB Scooters Ltd. www.lambrettaspares.com

If a thread is pulled out with some oxidisation, then it’s just a case of running a drill through it to find clean alloy, tap to the outside size, use a screw and nut to hold the insert, add Loctite and screw it in place; then lock it down with the nut, unscrew it and it’s fitted.