I also post on http://groups.yahoo.com/group/vespasmallframes

Here is a copy, (

Hi guys :~(

I need your help to diagnose some pictures I have taken after opening the top-end of my engine? Bad surprise? I think?

All the pictures are there: http://ktylife.free.fr/vespa/KTy133/Debug/ , full size so that you guys can zoom to the maximum !

So, what you have to know about it:

It?s my first ?ambitious? tuning project

Polini 133 cylinder rebored to 57.8mm, with admission: 132° and exhaust: 190° (I have also TA somewhere?I can find them if needed)

New piston (Polini)

Cylinder has a 5mm alu spacer, it was turned by 3mm at the bottom. Cylinder head was turned by 1.5mm. Squish should be = original polini + 0.5mm ?

Used (in bad shape) and turned Polini cylinder head. I know it was not the best way to proceed, but I?ve been told too late?

It has less than 100km, and I spent a tank of gaz to run it in, at neutral or slowly moving on the parking slot.

I ran it in with 4% of full-synthesis oil (Ipone). I messed up during running in, I put around 21° of advance while I was thinking I was around 15°?

You also have to know that I ran for maybe 5km without air-filter (carburetor sitting outside)

Carb was a f**** dell?orto PHBH28, I think it may be defective in a way as it is used and the engine didn?t reply correctly to carb settings?

I *may* have felt the engine slowing down like when it seizes, but because I have troubles with my carb, I?m not sure it was seizing,? even if some pictures seem to prove me wrong?

Big intake 6 reeds reedvalve from TZR125.

I always ran with cylinder air scoop and measured cylinder head (near the spark) was around 120°C.

I think I have overheated a bit? L (DSCN1995.jpg shoes little scratch on the piston head? ?!)

I don?t understand what could have damage so fast the cylinder like in DSCN2021.jpg ? It?s like particles but you don?t feel them when you touch the cylinder-wall.

I don?t feel the scratch on the side of the piston, but I do on the cylinder wall, exhaust side? Looking at the picture it seems worse !

Pffffffffffffffffff,  :puke:

I realize that I should have taken care of stuff that are much more important than what I was thinking? For example, I couldn?t measure precisely the squish? :P And maybe the used (and damage) cylinder head was not a good part to use (I was told it could help mixture ?emulation??)

Please, have a look at the pictures and feel free to comment and/or ask me questions?

Thanks !

KTy - 

thanks you too for your comments !

get rid of that crappy head! Get a Malossi head an dial in the squish clearance.

2% of good full synthetic oil is all you need. Motul 600 or Motul 800

looks like your engine sucked some dirt from the exhaust pipe, die you grind the header pipe inlet?

I prefer to jet new engines quickly and a tad on the rich side and then run to run them in like they will be ridden afterwards, hard.

like Gerhard said throw the Polini head in the bin!

57,8mm ( RIP

Your last chance:

Think about the GS-piston and a normal Malossi-head!

2% of good full synthetic oil is all you need. Motul 600 or Motul 800

I was told the ipone I use is the same oil as Motul :plemplem:

looks like your engine sucked some dirt from the exhaust pipe, die you grind the header pipe inlet?

Yes I did enlarge it a bit... Dirt from the exhaust ? Damn'Italians...

I prefer to jet new engines quickly and a tad on the rich side and then run to run them in like they will be ridden afterwards, hard.

Really ? Well I guess you obtain pretty good result :)

So, I'm more and more convinced about the dirt coming from the exhaust or from the exhaust transfer as this is the part of the piston that is the more "damaged" (See top of the piston http://ktylife.free.fr/vespa/KTy133/Debug/DSCN1993.JPG and http://ktylife.free.fr/vespa/KTy133/Debug/DSCN2007.JPG).

I am also concerned about the scratch ( http://ktylife.free.fr/vespa/KTy133/Debug/DSCN2006.JPG ) that you can see (but you can't feel them !) around the piston... Could this also be due to dirt or does it reveal a tendency to seize or could it be normal :wasntme: ?

KTy - (

Bearbeitet 6. April 200521 Jr. von KTy

57,8mm (   RIP

I know, but for my first "tuning" project I prefer to work on a used cylinder... Do you think it is possible to rebored it one more time to 58mm so that I can fit the GS piston or... ?

Your last chance:

Think about the GS-piston   and a normal Malossi-head!

Yep I know, I was discussing this with Olli ETS not too long ago...

So, in the end, from what you can see :), there are not much evidences of overheating , running too lean, tendency to seize or even knocking ?

Thanks !

Bearbeitet 6. April 200521 Jr. von KTy

I know, but for my first "tuning" project I prefer to work on a used cylinder... Do you think it is possible to rebored it one more time to 58mm so that I can fit the GS piston or... ?

Exactly! Rebore it to 58mm and fit a GS piston. That is the last possibility to use your Polini! (

I think i can remeber the carb comes out of the frame, isn`t it!?! Without an air-filter :uargh:

Now let us argue about the dirt

You also have to know that I ran for maybe 5km without air-filter (carburetor sitting outside)

I knew i was right... :wasntme:

Either the dirt came from the exaust or from the intake. Since the damage does not look too bad and the scatches are not even deep you can keep going whith this piston and cylinder. Get a Malossi head as Gerhard said clean the outlet and exaust pipe as far as possible and mount an air filter!

I knew i was right... :wasntme:

You're always right BBG !

What actually surprise me is how I am stupid to "forget" about such elementary safety things....

I pissed myself off !!

I hope I have learn my lesson, but I fear that I have some more to learn about other subjects...

That barrel and piston are definitely not yet done. Who cares about a few scratches even if you can feel them. That does not hurt performance or longetivity yet.

Looking at your rings and piston top I can see the engine is not even run in yet. There's more to come once the rings seal completely against the cylinder wall.

What I would do in your case:

Malossi head

dial in squish clearance at 1-1,3mm

run 2% of oil with 98 octane fuel

CHAMFER (very important!) all ports thoroughly where rings have to pass

CLEAN everything over and over again next time before you get the engine together

your work on cylinder and piston looks like you were pretty much in a hurry when grinding. It's easy now to make everything look sexy (and flow more) just take your time, it takes as long as it takes.

your work on cylinder and piston looks like you were pretty much in a hurry when grinding. It's easy now to make everything look sexy (and flow more) just take your time, it takes as long as it takes.

I don't have any excuse for the piston... But if you have any tips to work correctly the ports, it will help, it's hard to get there and do it cleanly ! Do you use any special-secret tools to work perpendicular to the cylinder ??

As I must remind you, I am a newbie in mecanics, and I don't ahve probably all the needed tools... :wasntme:

Thanks again

KTy -