Vespa PX200 - Malossi - Blown engine

[225worb]

Oooooops not again...That a reeeeeeet Bast !!!
With the lack of milage judging by the top of the piston jetting is going to be hard to judge ??
Heat transfer to the crank from jetting is not a factor , the way the crank has grazed the sealing pad looks like a seizures happened however light or hard and the crank has twisted slightly causing the one area of web damage....
The sealing pad does play a roll only with regards to tickover ....setting it up well with scores/damage wont be as easy ! however it can cause alot more spit back,
Stick a reed on it and tune the nuts out of it ....
Get those casing transfers matched to the cylinder .......

[225worb]

Ouch..
There's seems to be serious blueing around the big end too...

[Jack221]

That blueing and slightly slipped big-end pin are all heat related. I doubt all were from the weak jetting. Notice of the part of the crank that touched was the thin part over the hole. Is it running auto lube?

[arrow]

That blueing and slightly slipped big-end pin are all heat related. I doubt all were from the weak jetting. Notice of the part of the crank that touched was the thin part over the hole. Is it running auto lube?

It doesn't have auto lube, it's an 1988 model, so I add the oil manually. I'm very careful when adding oil, in fact, I add ever so slightly more than needed. I'm using the standard measuring cup, may be I should be using a different one for Malossi, what do you think?

[Jack221]

No need for any more than 2% oil in any set up if it is jetted correctly. That is not your issue here. Are you positive you didn't forget to put the oil in the tank?
It is was clearly too weak but to blue the big end it would need something else. The score marks, rotary pad the actual seize up can all be jetting but not the blue big end.

[arrow]

No need for any more than 2% oil in any set up if it is jetted correctly. That is not your issue here. Are you positive you didn't forget to put the oil in the tank?
It is was clearly too weak but to blue the big end it would need something else. The score marks, rotary pad the actual seize up can all be jetting but not the blue big end.

I'm positive that I didn't run it without any oil. Is it possible that I overrevved the engine in the lower gears and that created the blueing? I went up to 8600 rpm according to the SIP speedo. This is not continuous of course, but I shifted up at this rpm. Could this be the culprit?

[holty]

i wonder if you have twisted the crank by over- reving the engine, ive done that to my cost, the twist would explain the sealing pad wear, maybe the twist might also account for the blueing at the big end caused by more friction if its twisted,and running out of allignment, i think you will need a crank rebuild and i would put a reedvalve on as well

[arrow]

The engine is now rebuilt with a X360 Reed valve. Short ride home during (light) snow didn't reveal much, especially I'm paranoid about engine seizing again but I sensed the much improved response at low rpms. It idles perfectly when the old disc valve setup was prone to stopping unless I blipped the throttle every once in a while at a stop light. I can't wait for the spring to arrive .

Here's a very short movie of it idling on the bench:

https://www.youtube.com/watch?v=cPHvydpJGT0

[Jack221]

Good job getting it back together so soon.
Ther previous problem with the slow running was just the set up of the carb. The constant need to blip the throttle can be just a badly set airscrew.
Now you have a nice new build get the carb set up properly and it will ride fast and reliable for a very long time. There are so many variables with needle carbs, which take years of experience to get right.

[arrow]

Hi again,

I bought a pressure fuel pump from SIP (http://www.sip-scootershop.com/en/produ ... +_98810000) and now need a "a smaller float needle valve seat should be used to ensure proofing against raised pump pressure." as SIP states.

According to Malossi the standard size in the PHBH 30 carburettor in the Malossi 210 Sport kit is this part:
Float Needle Valve DELL`ORTO 200 for PHB carburettor incl. float needle Ø 4,5mm and gasket (http://www.sip-scootershop.com/en/produ ... +_40094200)

I am guessing the smaller needle valve seat that I need to use would be either of the following:

* Float Needle Valve DELL`ORTO 150 for PHB carburettor incl. float needle Ø 4,5mm and gasket (http://www.sip-scootershop.com/en/produ ... +_40094150)
* Float Needle Valve DELL`ORTO 170 for PHB carburettor incl. float needle Ø 4,5mm and gasket (http://www.sip-scootershop.com/en/produ ... +_40094170)

There is also a 5.2mm needle in the sizes 200-400, but these are probably not what I need. What is denoted by these sizes by the way (weight, length etc) ?

I asked the SIP tech support but couldn't get an answer so far. I'm hoping someone will point me in the right direction.