Hi, my daughter is having problems with her Stijl KM131R Kombimotor . Two of the starter housing screws come loose/fall out probably due stripped screw threads. chatGBT says I need to use a Helicoil kit to put a new thread in.
Before I buy a good quality one, does anyone know if we have a good quality kit in Makerspace please? Also does anyone have past è period doing this that might help?
The engine is expensive so I’m keen go not take risks with a cheap Chinese set. I think the screw is M6 bug I need to bring in to measure, and the kit needed is likely Helicoil M6 × 1.5D insert (9mm deep)
I have some 8mm deep M8-M6 thread reducers in a drawer you can have, you’d need to drill out and retap the thread to M8, then screw in the reducer potentially with a bit of thread locker to keep it secure - we’ve got everything you’d need for this already in the metal shop
Hi Sean, thanks so much for your reply and suggestion!
I’ve been doing some digging into the issue - it seems like the bottom starter mounting thread is stripped, while the left-hand thread is only partially damaged, and the right side one if still really good. I’ve been learning about both Helicoil inserts and the M8-to-M6 reducer approach you mentioned.
Your approach sounds like a very robust repair but my concern is whether there is enough wall thickness. My understanding is the helical option removes less material so might potentially be a safer first step, but I have no experience in metal work. Have you done anything like this before on a small aluminium engine casings before, and do you think there would be enough material around the hole to go safely to M8? As you might sense, I’m quite a cautious person.
No pressure at all, but if you have some time to take a look at it with me, I’d really appreciate your opinion. My daughter’s whole business depends on the machine, so I’m keen to get it repaired successfully , and quickly of course.
Just seen this how to film and it’s made be both more relaxed and slightly horrified… he makes it look less scientific that I imagined … drilling out and tapping with a hand drill and a long extension arm
Okay I’ve misremembered sorry! They’re actually M10 to M6 reducers so you definitely wouldn’t have enough metal surrounding it to drill and tap an M10 hole
Potential solution with much less possibility of destroying the motor: how about making a few oversized bolts on the lathe, and leaving the hole as it is. At least that way you can take a few runs at the problem and have safety that you’re not going to make it any worse
Further research indicates that Helicoils are repair reccomended by Stihl, who even sell an OEM helicoil that is 15.4mm long to fit the 25mm screws they use.
I’ve ordered a Recoil 35068 Metric M6-1 Thread Repair Kit and some (M6 x 1mm x 2.5D) Helicoil Wire Thread Repair Inserts (15mm long) that should arrive tomorrow. If either of you are around after 7pm tomorrow evening and fancy lending a hand I’d be very grateful.
The other thing I learnt is that Stihl does not use standard metric M6 or M5 machine screws. Instead, they use specialized self-tapping, direct-assembly screws specifically manufactured by the German fastening brand EJOT.
They feature a highly specialized 30-to-35-degree thread angle profile. Rather than cutting out material like a traditional wood screw, they smoothly slice into the raw, unthreaded plastic or soft magnesium holes during factory assembly. They “cold-form” the plastic and magnesium alloy around them to maximize thread grip and prevent stripping. The new M6 Helicoil inserts, will change the previous soft metal screw holes into a heavy-duty, standard M6-1.0 metal machine thread, so the old screws will no longer work but a more standard M6 bolt will.
Hi, if you need a hand I will pass by friday evening as well.
if you are concerned of not having enough material one of the solution would be finding an imperial screw slightly bigger so you don’t remove too much material in your hole and then find the right tap for it in our tools. the other solution if the casting is big enough helicoil are magic i have repaired a thread which was supposed to be water thighs, it became even stronger than before.
