Modern Vespa

Anyone here that had to deal with broken threads on the motor when trying to fasten the muffler to the motor? I'm fixing a LX125 (2006) and the existing threads are completely thrashed. What have you done to fix that? Helicoil? Any tips for me? Right now using wire and straps. Not so good.

If you haven't done it before don't start out on a head. Take the head off and take it to a machine shop so you aren't buying a replacement head.

Should just be able to be drilled out and re-tapped.
Start spraying it now with a good penetrating oil and it might come out when they drill the old studs out using a left hand drill bit.

These were already destroyed when I got the bike, just holes basically - no thread really. Tried to cheer them up but I guess they are just lost. So I guess helicoil or some magic bracket attaching the muffler somewhere else might be the medicine.

Yep then helicoil is your option.

WEB-Tech, +1

I'd just replace the head personally. Not that expensive a job.

Then have spare header bolts which you replace each time the exhaust is removed.....so it doesn't happen again.

Oh sorry, I might have been unclear. This is the M8 bolts on the side of the motor to fix the exhaust. The studs on the head is fine (for now)!

Is there 2 bolts? On the side mount?

1 goes through to a nut, the other into a threaded hole?

Mine was an LX50

Depending where you are you might be able to find a 9mm tap and some studs?

I messed mine up. I got a bloke to tap it a little deeper.

Keenserts or Acme Inserts are very good for that sort of environment. While Acme is primarily known for products used in the capture of small, fast birds, their threaded inserts are excellent if you are in a purely metric environment. I think a Helicoil would pull out over time in that particular location. You can usually buy a couple inserts on ebay in the size you will need. As always, if you've never done this before, get at least one more than you will need.

https://www.acmeindustrial.com/insert_comparison.html

I've used thiss type on the same service on a VW engine. I used them because that is what the stores had at the plant I worked Drill and tap insert the widget and hit the progs with a punch to lock them in place.

So the thread insert is more or less a piece pipe with the inside and outside threaded instead of a wound up piece of wire. I have never see these but they seem like a great idea.

Those look brilliant Motovista. I've never used them myself but they are definitely going to be stronger than Helicoils, the most used repair for most folks.

Think you are right about this regarding being the best repair for the OP. Easier to fit too.

I think I may change from Helicoil in future when more strength is needed.

Thanks for posting that.

Thanks motovista. I'll try to find these on eBay. Bit more tricky than helicoil. But it feels like a place where you want solid threads (and some copper paste.

The first time I saw a helicoil, it came out with the spark plug of a 1969 VW bus engine. I screwed it back in and never did change that one spark plug. At the time, I had no idea what I was looking at.

Sadly one cannot always know how repairs were done by previous owners. Helicoil are supposed to be or can be Loctited in so as not to rely 100% on spring tension to keep them in.

-------------------------

Before we all prostrate ourselves at the altar of Acme we should remember that to install an 8mm Acme insert we have to drill the hole something like 11.2mm. whereas for an 8mm Helicoil we only drill an 8.2mm hole.

So in a tight spot Helicoil is better.

Depending on the OP's tool collection and ability it might be better (if there is a little bit of thread left to assist with screwing in) to simply to epoxy the existing studs with JB Weld hi temp. epoxy. There is not a lot of torque required for those studs?

Although it's over a year since I did any exhaust removal and refitting on my old LX.

I'm certain one bolt was longer than the other, and the longer went right through the engine casting to a captured nut on the other side.

Then the shorter bolt went into a threaded hole as talked about above.

Just behind the fan/Stator.......but mine was a 50cc

Or maybe even use a zip tie.

Digging around on the internet for reasons the best way to make a repair might not be best doesn't seem like time well spent.

This is one of those things you need to fix right, or it won't stay fixed. NorthernerBill's bike sounds like one that was fixed the way a lot of them get ultimately fixed. You drill through the case and put a nut on the other side of the case. It's a place where bolts break off and threads strip out all the time.

My father epoxied a cylinder head stud into an old bus engine. Well actually he filled the hole with epoxy and then drilled and taped it. Engine was still running years later.

In industrial construction one puts a "test tube" of epoxy into a hole then break the glass and screw the stud or bolt.

Experience is sometimes the best teacher. That and not overlooking other ways of problem solving.

If it can be drilled through and a nut and bolt used then that is probably the best DIY solution as everyone can drill a hole.