Modern Vespa

I installed a DR 130 on my V90 with a 19-19 last week due to no compression or power.

I've been dialing in the jetting to get it running very good. I was into about 45 minutes of my ride and it started bogging down, then the rear tire skidded I trailered it home to inspect the damage.

I noticed my air filter vibrated of of the carb, so I thought maybe it was too lean. So I did a plug chop and it looks good to me. On further tear down I saw that the piston had a huge gouge on the left side, and the cylinder was scored. When I was attempting to take the piston off I found a broken circlip which is the culprit. I reused the old style circlips because they're easier for me to install so it's my mistake as always.

Fffffff!

Man that's a drag.
(NPI at all.)

Good luck on getting it sorted.

Oh man, that sucks! What a bummer....

Ouch!

Ask me how I know what happens when the clip was omitted during assembly. The resulting gouge is even more impressive when it snags a transfer port.

Mmmhhh... All that misery for a circlip, that is an expensive mistake
I don't think the circlip is bad, it is most likely the way it has been installed.
This is a good reminder to closely inspect after circlips are in.

You could be right, but both spun freely in their grooves. I believe the mistake was using the original clips.

That is proper unluck ! I've been running CR cross bikes for ages (80,125, 500), replacing pistons every X hours of use and always reused old clips because news ones are too stiff and love to jump in places you need 30 mins to find out, and never had issues. They are C clips, super simple, no holes for the tool. Maybe your had some fatigue and broke...

You're right on there. Most kit manuals will caution against reusing the piston clips.

Okay, I believe you. I've owned a few bikes also.

Time to chill with my other hobby.

Wrong clip type for DR piston at all. It is "square" and DR have "round" one. So even if you will install pair of new "square" clips in DR piston it will be fail too.
It is better to use C-clips or at least G-clips.

Thank you very much roland87 for this, now I understand what I did wrong.

Now back to music.

Many years ago I bought a KTM as non runner.

Guess what kind of clips the previous owner had used

original Piaggio?

I killed the top end on my VBB this way a few years ago.

it suuuuuuper-sucks.

This is the exact thing that happened to me. I even raced mine on the track with no problems. Daily drove it for a whole summer no problems. Then raced the corsa (600mile street race) and no problems….until the very last mile before the finish line and the circlip popped out and scored the cylinder and the bike wouldn't run. I pushed it across the finish line for the win still….🤭 lesson learned. Old style clips are enticing to use since they're much easier to install, but it's square peg round hole type of situation.

Spot on JohnDon

The piston MUST be designed for "square" clips. Original and some Grand Sport pistons have "square" clips. Double G-clips also very easy to install, but G-clips holds their place better. And C-clips is the best.

I think one cause for these failures is metal fatigue. If you look at a seger-type lock ring, there is thick middle section that thins out and then thickens again towards the ends. When revved harder than stock engine, the ring flexes on the thinner, weakest section. The ends with holes are rather heavy when compared to regular wire type G-clip.

Do this flexing enough times and you have a snapped lock ring that has the snowball's chance in hell finding it's way out without giving the top end and the rider a bad day.

I loved those double G clips that GranSport sold. And I really have so much trouble with the C clips.... why are they so much better Roland?

FINYoshi I think main factor is that the grooves for clips in piston have corresponding shape.
"Square" clip - "square" grooves. Same for the "round" ones.

Ginch there is a video on YouTube FMP channel.
In two words - C-clips is best due too it have both sharp ends what prevents clip to move/spin in the groove. G-clip have only one sharp end and Double G-clip haven't at all.

For the readers, C clips are the best as they have less weight.
Sounds like crap but it isn't.
At low rpm there is no issue but at high rpm the G Clip, double G or eye clip ends can start to pull out of the groove, which might cause them to jump out or fatigue.
The C clip has no end mass therefore stays put at high rpm.

Oof!!!!

I almost reused the original wristpin circlips when installing my malossi kit. Luckily I just happened to mention it at the scooter shop when I was buying some parts, and they warned me right away. Sorry this happened to you!

kef ls50s? NICE

Yes, thank you. I could buy a few vintage vespa's for the price of that turntable.