Threaded nightmare – Time-sert repair | SCOOTER SPORT
Our tame novice racer, Kirk St Moritz often performs his best work, phone in hand, whilst perched in the smallest room in the house. This week his aromatic musings involve thread repairs to his TV 200 race engine.
The time is certainly right; I’ve got a good half an hour of peace and quiet ensconced in my little inner sanctum whilst dropping the smelly kids off at the pool. So I’ll try to use this time constructively. Not for masturbation purposes but to attempt to write a tech article (I may have to cut this short though if my legs go numb!).
Right the basic situation is this, I’ve knackered a thread in my engine casing, specifically the gearbox endplate stud thread. This calls for a repair, a time-sert insert. It’s happened to us all at some point in time I’m sure. After all we’re dealing with alloy engine casings averaging half a century old. Engine casings which have been used and abused during their time by mods, scooterboys and in some situations by housewives scooting down to the local bakery for a fresh loaf.
Stripping a casing thread can be responsible for a tirade of Tourettes type outbursts from the most mild-mannered men on the planet. Frustrating to say the least. But fear not there are a number of different solutions to remedy these problematic periodic SLUkups which may also match your budget.
- Stepped studs
- Thread inserts
- Brass dowels
- Alloy weld and re-drilling/thread tapping
I chose a steel thread insert. A time-sert repair.
The time-sert kit consists of a steel threaded insert – various diameters and thread pitches are available. It also has a drill bit (very sharp, ouch!) a counterbore tool, a thread tap and an insert driver.
Don’t panic Mr Moritz!
Here’s the situation: The 50-odd-year-old alloy of the TV200 casing has given way. The thread has pulled out under the forces used to torque the endplate nuts down, this is bad.
Firstly I isolate the area so as not to contaminate any surrounding bearings etc. with alloy particles while drilling (I use tape or rags to achieve this). The depth of the blind hole must be measured to ensure you don’t drill deeper than necessary. You can then transpose this measurement onto your drill bit, thread tap and driver and mark them in order to gauge when to stop drilling etc.
Secondly I drill the old threads out. This can be done carefully with a cordless hand drill but care must be taken to keep the drill bit square to the face of the hole. Drill to the marked depth on the drill bit and no further.
Thirdly the stepped counter bore tool is used to open the mouth of the hole to a specific depth. This allows the thread insert to sit slightly below the original finished surface of the hole… Thus allowing there to be no interference of the final fit of the insert. This counterbore tool will only permit a pre-determined depth to be drilled and so measuring this process isn’t an issue!
Fourthly tap the new thread in the hole to the specific depth, which you have previously marked on your tap! My legs are starting to get pins and needles now and the kids are drowning…
Fifth is to fit the driver tool to a ratchet type tap wrench. It’s important to lubricate the driver with a little oil, don’t overdo it though. Screw the insert onto the insert driver until you feel some slight resistance and stop. I usually add a little Loctite to the outer threads of the insert for good measure.
Once the thread insert is seated with the top edge of the insert sitting within the counter bored surface, the driver should start to tighten up (this happens as the slightly tapered driver starts to expand the last few threads of the insert) this effectively locks the insert into place. Now it’s time to withdraw the driver tool. Oooooooooo errrr Mrs!
If all has gone to plan then the jobs a good en! You should be able to fit a new endplate stud and clean up your mess, nasty. Thank SLUK the writing has finished… It’s taken 45 minutes to write that and I’m not sure I can actually walk unaided!