Tuesday, January 26, 2010


On wednesday, i was bored, and still frustrated with not having fixed the leakage issue on the ciao, so Alex, Joel, Jimmy and I tore it apart again (I can get the whole engine out in about 7 minutes now, most of that is removing the pipe) And I was finally able to figure out what was going on. In addition to the Decomp valve still leaking quite a bit, It appeared that when I used the face mill on the cylinder, It cut unevenly where it caught on the edge of the broken off fin. I should have broken or ground that fin off to start with, but you live and learn, eh.

Back in the machine shop, I took the cylinder and lined it up in the lathe, clamping the cylinder skirt. I was in a bit of a hurry to finish it up, and forgot my rule about doing this sort of thing... you have to run a piston inside the skirt or it will break the skirt off. I just had to take a few .001's off, so i wasn't too concerned, but when i started up the mill, some boner had left the feed engaged and right away the tool ground into the face of the cylinder and did this:

What a buzzkill.

I also went ahead and took the head down a couple .001's, which was probably a bad idea because now the extra tall piston i made is hitting, so i'll have to machine that stupid thing down again.

Yeesh, look at that nasty decomp, no wonder it was leaking, carbon and gunk all over...

Oh well, thats mopeds, should have left well enough alone when I had the chance. It looks like the cylinder will be fine with the skirt broken off, but if it eats it, I'm on the lookout for a new stock vespa cylinder. Anybody got one they'd like to get rid of? I've got a parts grande lined up, but i'm pretty sure thats a 10mm pin bike, so i'd rather not back track and rebuild another whole engine.

The good news is, break-in appears to be going well. I was concerned about re-using the old rings, but i cleaned them up with a little sand paper, and re-honed, and it looks like they are sealing really well. Given the wierd compression issues, i was worried they hadn't sealed, but this pic says it all:

The transfers also seem to be pretty well matched, the burn pattern on the piston is a little bit dark, but i'm 99% sure thats because of the wicked air leak causing things to run a bit hot.

You can see on the piston the hot spot from the decomp valve leaking (also perhaps because of the wierd head shape around the decomp) and there is a big black mark where the head wasn't sealing that well. Hopefully cleaning the decomp again and fixing the sealing issue will take care of my shitty low-end and maybe even 'fix' the misfire situation.


  1. machine shop lessons the hard way.. are the pits.

    just occured to me: ever consider using valve cutting tools to clean up decomp seats?

  2. bonerjamz. i'm 99% sure i've got a stock ciao cylinder for you. let me know if you need it.

  3. I think the picture of the piston rings says it all, but what it says is learn to use macro and no flash on your camera.

  4. srsly phil. why you gotta hate. wtf is 'macro' and 'flash'

    gabe, i might be wantin' that cylinder. i'm gonna assemble everything up tonight and see where i'm at... maybe we can trade some work or something. if you want to trade for Zack's avanti zetakit, you can probably get a pretty nice ransom out of him.

    i was thinking about using some valve grinding paste, because the stock vespa decomp valve has a flat-head screwdriver slot that i could turn with an electric drill. no paste unfortunately. maybe some dirt and oil? I hear thats what makes all of nate's bikes so fast.

  5. graham, I hope you're kidding... but I'm going to bite anyways because I am a loser. FML. :-(

    Macro is a mode found on almost all modern point-and-shoot cameras that allows a close focus for detailed shots. Look at your camera, either on the case or in the "shot mode" options will probably be a flower icon. Pick that and bring your camera up close to the subject.

    Flash is the light that goes off in dark situations. seriously man you'd better be kidding here.
    Look for the lightning bolt icon (probably) and there should be an option to disable it.

    decomp ----->use toothpaste.

  6. toothpaste, genius!

    yeah, i know, usually i take pretty decent pictures on here, but i didn't want to set everything up in my makeshift photo booth.

  7. I like dirt and oil, but toothpaste probably works better. Nothing but <3 for cranks.