Polini head options

I am building a px200 with a polini 208cc kit. The scoot has a 60mm crank. It seems I have two options for the head. 1). I use a head with standard squish and add a 1.5mm basegasket on the cylinder, or 2). I buy a head machined for use without such packing, as advertised in the SIP catalogue (I think worb5 make it)
Can anyone give me an idea as to the different performance characteristics of either set-up? I have seen plenty of engines using the 1.5mm gasket, but never one with these other heads. Want to make sure ther’re OK before buying one.

Also, I have just the standard polini kit, and believe I need to get it honed to reduce my chances of seizing. Does anyone have figures for the amount of clearannce I need to aim for?

cheers.

hello Nicegold,

both the heads that you have seen in the picture have to be used with a 1,5mm gasket. As far as regard the performance I slightly prefer the power curve that I get with the one on the left (SCK) but this with a Malossi 210 kit and normal 57 stroke.
For the Polini 207 and longstroke I can’t tell yet, as I told you I still have to finish the engine. With Polini and normal stroke a prefer the head on the right of the picture (PM, Stoffi). This doesn’t mean will be the one I will prefer using longstroke, since the power band with longstroke will change… so if you can wait a little I could later report my experience. I will compare also the one of the two that I prefer with the W5 head already OK for longstroke and then I could say something about.

And thank you Mikke for your appreciation.

Have a nice week - end all of you.

Thanks again Curare. I’ll look forward to your report on how the different heads perform. Until then I guess I better decide on an exhaust and do some more carb research!

hello Nicegold,

my engine is ready, but right now too cold out there to play with heads.
For ignition I would start at 17.
MAybe you will have to mill some alu of the slots of the ignition plate to be able to go to this number.

As far as the carb setting I don’t have any experience with 26 and Polini and longstroke but I would start at 135 - 132.

Maybe you will have some hard time in setting your carb out.
With rotative induction and longstroke in the past I found a little hard to set the carb if you don’t modify the porting.
It tends also to short circuiting.
this can be solved with a little work to the exhaust port and in the worst cases to the ports angle.
If you are not happy or will have any problem just write again.

hello,

yes it is a good idea but I would not worry about seizing since with the price of the polini kit it is possible always to have a spare one just in case !

The problem I most often saw with polini 207 is piston breaking.

And I would chanfer the ports . This really you should do.

…is the immigration law of New Zealand very strict with italians?

hello nicegold 90,

just did the driving test in this still cold weather.
I used Polini 207, Polini 207 with longstroke, and Malossi 210 normal stroke and three heads: Worb5 2,5 clearence for longstroke, SCK for normal stroke (Scoter center), and Stoffi’s head for normal stroke.

For Malossi 210 the best is the Stoffi’s head.
I felt the SCK loosing in acceleration even though better overev so it could be an option in case you use short gear (21/65 ). Or if you are a fearfull person and want to avoid any risk but avoid at the same time a little performance.

For Polini normal stroke no Stoffi. Better SCK.

For Polini longstroke Stoffi with 2,5mm head gasket a little flat at high rev and more heat. Not my favourite. Too much compression.

Worb5 head for longstroke is the best all round with Polini 207 standard barrell and longstroke, it gives you the feeling the engine breaths and cleans itself well. Good compression, good power curve.

For the Polini 207 ported barrel and longstroke between Stoffi’s head with 2,5mm head gasket and Worb5 head for longstroke I would say it depends. Up to midrange Stoffi’s head is more responsive and you can use less adv. timing. More acceleration , but more heat, could be problematic with hot weather.
Worb5 head looses a little in acceleration response and low mid but better in high rpm.
Then you could modify this two heads…it is what I am doing now…

…and when I will learn how to do I will post in my net address the dyno graphic.

Good morning Curare, you think your are an electronic dinosaur bu tdamned you are a Vespa scientist and I guess that’s more then a good balance, maybe we will be able to help you little there!

Have a nice weekend!

Mikkke;D

Thanks for all your advice Curare, I look forward to your assessment of the heads. And your photos of your engine porting are a big help.

Cheers Nicegold.

PS, I’m about to buy a righthand RZ to go with this engine… any thoughts?

Thanks Curare for sharing your expeince. I had wanted the RZ righthand because this engine will be raced occasionally on a track in anticlockwise direction, so lefthand clearance is vital.

It will also be used around town 2up, so the power in low-mid range is very welcome.

Very interesting to here the problem will be at higher revs. I had planned to add a t5 4th gear to help the scoot rev out… maybe I will revise that plan…

I had considered the SIP performance, but was concerned about ground clearance. Have you used this exhaust, does it hit the ground all the time? If clearance is OK I would go for that… maybe I could get it cut and lifted a little? I don’t care about the spare wheel.

Another Idea I had was to buy the rz righthand, and use it just for the track (which is built for go-carts so very tight and low-mid range power very useful) and use just a sito plus around town?

Thanks agin for your help.

Nicegold90

HI Curare, thanks for staying in touch. My engine too is very close to completion. Have decided to use a worb5 head (standard piaggio milled for 208cc) to begin with. Will be very interested to hear the results of your testing.

I’ve fitted 26mm carb, T5 4th gear 60mm crank and SIP performance exhaust. Any idea where I should start with timing and jetting on this engine?

Any advice much appreciated.

Cheers, Nicegold90

Hi Master,

I thnk that we are al interessed in some good pictures.

Go on Curare, show us the way

hello,

the Worb 5 head is at the beginning made to fit the malossi kit that has a bore 0.5mm larger then polini.
Since I remember the use you intend to do with this engine,
I will start without using the 0,5mm head gasket and trying to get the ignition advance as less as possible without loosing performance.

Italians are welcome here - as long as they bring vespas with them!

…and I forgot,

with your set up (polini 207 standard and longstroke) and exhaust I prefered the HP flywheel, both for response and for power curve, it gives you better low-mid to mid-high it looses a little on max speed. Though should check it with warm weather if with it cooling is an issue, since sometimes can be.
But with the polini barrel ported, the HP flywheel kills the clutch fast.
Maybe would be reasonable to stay with a PK flywheel, but just to let you know.

…and I forgot the other option I tried was SCK head with 2,5mm head gasket with standard Polini 207 and longstroke.
Very similar to Worb5 head but worb5 has the same low, mid but slightly better high rpm.

Thanks again Curare, I will take your advice on the exhaust. There does not seem much difference between the SIP Perfoamnace and the EVO?

As for the carb, yes, I will try a larger carb in time, but for now will use maybe a 26mm si.

One last question, I plan to hone the Polini kit to increase clearance to about 4000, does this sound right? I hear they come from factory with about 2000 (although I have not yet measured myself)

I am also getting the exhaust port and head ceramic coated to help with heat issues. The piston crown will get the same treatment, while the piston skirt will get a teflon/malignum?coating to attract oil and smooth out seizes.

… all I would do with the barrel, for your need, and I repeat for your need, would be honing and chamfer the ports.

hello nicegold 90,

the engine almost ready to test the heads. I will start the test next week. So either keep contact here or ask me at my personal e-mail.

One other question Curare, hope you can help…

The head I bought from worb5 comes with a note saying that the squish is 1.2mm if fitted as-is, and 1.7mm if fitted with a .5mm head gasket. Which should I go for? I had planned to use a gasket and go for 1.7mm for safety, at least while running in…?

I’d be happy to hear your opinion.

Cheers Nicegold90