Modern Vespa

yea... after i talked to u guys i went and gave a second look and saw that they were gapped on an angle and I had them on wrong... after that they slid in easy breezy

And you're still having heat issues? What's the compression on the top end now with the fresh rings?

major ones.... in fact, after everything cooled down, I couldnt even move the piston with the kickstart... I pulled the cylinder back off to avoid damage...

I am at a loss... I feel defeated... I want to walk around with my head down like charlie brown while sad piano plays in the background

I do not know... how would i check that out

Get a compression tester.

the difficulty there is, as mentioned up top... the piston is not moving very freely right now... I took the cylinder back off because i couldnt push the kick starter down...

True. Check your piston-to-bore tolerance.

how would I go about that?

So ...as easy as slapping together a new top-end is, you left out some pretty important steps!

A critical thing is measuring of the gap on the piston rings. You push them down inside the cylinder using the piston so that they are even pushed down there, and you use feeler gauges to measure the distance of the gap.

If the gap isn't big enough, than the rings aren't going to drop into the groove on the piston far enough and will stick out too far ... and then you'll be generating a LOT of friction / heat as they rub against the cylinder walls.

( you'll probably have HELLA compression, right up until the time your piston welds itself to your cylinder wall! )

gooot it. Yea, I bought it all together so I didnt think to check for error... good call. I can grab the necessary tool for that from my girl's parents house this weekend...

When I called up my dad he also mentioned a possible issue with the oil line... so I will have to check on that too

turns out the measurment tool was in my car, not hers...


SO

.2mm was a tight fit when measuring the piston to bore tolerance...

.18 fit easily... Should it be a squeeze or does that mean the rings are off?

I honestly don't know. It's written in the haynes manual what the ring gap should be.

scooterhelp had them down as .2mm. i did as recommended and filed it just a little so that the 2mm fit easily.

is there a best way to check out your oil line?

To check the oil line, pull the tube from the carb, blow a tiny bubble (less than 1cm) and reattach it. When the engine is running, you should see the bubble move into the carb.

big development of the day!!

sooo its not getting stuck in the cylinder (rules out oil line)


its getting jammed up on the way back into the case...

confusing? very...

Bad bearing?

I dont know... right now it seems to be moving in and out of the cylinder just fine... I am completely stumped.


Added:

to top this off, I started assembling things again and though I dont have a compression checker.... I can tell you that after just a few pushes on the kick with the plug in the cylinder, the compression went up to the point where i could hardly move the kickstart. I would call that "hella" compression

After getting my hands on a compression checker, my psi is 165...



Where to next, sensei's

(you guys are awesome btw)

Is this level of pressure ok? Or will I be welding it into the cylinder in no time...

I know its higher than it should be, stock

-G

i know im reviving an old post.. but seriously.. remove the engine and bring or send it to a reputable vespa mechanic like Bar italia in van nuys or Fullerton Vintage in, well, Fullerton.

You are going to need a full blown rebuild in order to cover your bases. replace the carb, replace the seals and bearings. Jet it right and then and only then will this nightmare end.

This will not be cheap, but its worth piece of mind and your safety to do it. Let them have carte-blanche over the process.

Dude... 165 on a stock engine is insanity. You should be at like 120. What on earth is causing all that compression!? I'd consider putting a riser pad inbetween the head and cylinder just to lower your compression!

whats wrong with doing it himself?

any update on this greg?

bore tolerance should be .005 on a stock cyl. 165 psi is crazy.