Modern Vespa

hey... friend of mine gave me a pk 50 ss and i am considering in making a little tuned engine. i ve already have some parts and slowly i buy some more. the list of the parts i ve already bought:
malossi 136 mkiiii
reed valve malossi
mazzucchelli full circle 20mm
pk xl flywheel and stator 20mm
cosetta front fork
one bitubo rear suspension and
one carbone hi tech rear suspension
dellorto 25mm carb

till the moment i am missing:
clutch
primary gear
exhaust
gear cluster

any ideas about the set up or any ideas for the missing parts? was considering about vmc parts. cluster 10-14-17-20, vmc evo racer 52 stampata or vmc siluro sport. primary maybe something about 27-69? clutch that will hold the extra power?


this is it













PK 20mm cone flywheel stator

cosetta fork for better brakes!

Looks like a very fun project you have there.

I'm loving my 10-14-18-22 with 24/72 primary (50 3rd and 46 4th) on my 102cc, a bit short for your 136cc but with a 27/69 it looks perfect in paper.

I have the Fabbri racing Fb24 clutch with 5 springs, more than enough for my engine with half the springs; pulled out the 5 small sized springs, it was too stiff with my original clutch cover, but in your case with the pk (pinion and gear, right?) no problem at all - Although I have it for a short time I'm very pleased since it solved all my clutch complaints

My 2 cents

exhaust will be a consideration with your gearing. if you've got the longer legs at 27/69 you're going to be working it hard in the city to get into the power.

granted you have the short 3rd and 4th on that tree, but it still pushes to power out toward a touring set up.

if it's more of a city bike and has a expansion on it I'd consider a shorter primary like V90/100 sport

for the clutch i am considering this one
https://www.10pollici.com/en/homepage/classic-vespa/engine/clutches/smallframe/clutch-newfren-24-springs-vespa-50-90-125-et3-primavera-pk.2.1.34.gp.4011.uw
i ve found it in almost half price but i cannot find any info about that. i think it will hold easy the power of the malossi. dont know.
the thing i am really confused is about primary and gearing. i keep the pk50 gears and change only the cluster (10-14-17-20?) primary for that? or i have to buy a pk 125 complete 4 speed gear set and put an other primary like 27-69? i think in both cases i will have to put a cluster with at least short 4rth to avoid the gear gap from 3rd to 4th

Interesting project !

I recently purchased the 18-67 pirmary for my 3 speed usa special 50. it is not ready yet to be tested so i have no opinion about that

also you think i could go for this one too? its big bretha... i think that goin in this one i will need defenitly a big carb (30 maybe more). not quite sure if will match with the malossi kit

Have you got to machine the crank case mouth to fit the cylinder spigot, whats the width of the opening out of curiosity?

you mean if i got the engine case port matched with the cylinder?

Where the bottom of barrel goes into engine case , what's the width of the engine case mouth where the spigot bottom of cylinder fits in?

dont know. didnt strip down the engine yet. when i do ill let you know.
also i purchased this clutch in about half price (posting included) almost new.
now left gearing, primary and exhaust. for the exhaust i think i am turning to VMC siluro. their new exhaust but its new and havent seen any dyno results versus other exhaust to compare


newfren 25 springs (race?)

just got the 24 springs newfren clutch today. also i found the cluster and gears including shift and cross. 10-14-18-22 and 58-54-50-46 gears. thinking purchase em and also with a 27/69 primary would be just what i need for a touring engine. only thing that left is an exhaust....




spare plates and springs

just bought these. pk xl cluster and gears. i think that gears fit at pk50ss shaft. so right now at the moment i am missing a reinforced cross, exhaust and a primary drive. any ideas for the rest of the parts? any propose maybe?


gears and cluster. 10-14-18-22 and 46-50-54-58

27/69 is right choice. Even if it turns too long you can change only small cog for 26, 25 or 24. Polini, Benelli and DRT produces it.

On my 50 Special I use VMC short 4th tree(10-14-18-21) and 27/69 primary. And very happy how it works.

About exhaust you can try something from VMC or EGIG. Or classics VSP Road or PM40.
Also new new Polini Original is very good pipe. I installed one for customer PK and it fits like a glove. But IDK how it suits Malossi 136.
I'm personally using VMC Tork pipe and can say that it work very well with VMC GS-55 cylinder and not very expensive, but have terrible paintwork.

Your 25 carb will be enough IMHO. Few days ago I changed carb from 28 to 24 on my Special and was shocked how better it now runs.

I don't understand why you bought XL gears an tree? Isn't the gearbox identical with the 50 SS? My PK 50 S have same gears as XL. But on other side - I worked on engine from PK 50 XLS and it have totally different gears, gear tree, kickstart cog(15-10 teeth instead of 12-10) and kickstart shaft. Yes very cool pipe. I'm also very interested about it. No. Only PK XL2 have that type of clutch release.

Last edited by roland87 on Tue, 19 Sep 2023 13:20:45 +0000; edited 2 times

My PK 50 XLS came from factory with a long gearbox: 10-15-20-25 and 58-54-49-44
That's why I mounted 21/76 instead of the usual 24/72.


Cheers,
Luis

Seems that SS have similar gear box.

so.. what do you propose? to keep the original ss gearbox and just change primary or go for the 10-14-18-22 tree and 46-50-54-58? for the malossi 136

also i was tryin to find what kind of gearbox have the pk50ss but couldnt find any info in the net...

If I was right and SS have same gearbox as XLS then 27/69 primary can be too long. But you always have optionals cogs what I mentioned above.
Just split your engine and you will see what to do next. I see that you already have PK XL gearbox. So if you choose it check how it fits with kick start gear and quadrant. I bet it is non-compatible(if you have same as XLS gearbox)

Please take what I'm going to say with a good pinch of salt, since I have no experience.

On my Pinasco 102, with the gearbox I wrote earlier, I mounted a 21/76. And it's perfect.
I believe with a Malossi 136, with the same (long) gearbox, a 24/72 would be good.

Few weeks ago I finished PK 50 XLS for my friend. It have long gear box.
Polini 130 cast
Mazzucchelli racing crankshaft
Polini Banana exhaust
Vape Road ignition
SHBC 19.19 carb

And 27/69 primary gear.

It pulls good on 1, 2, 3 gears. But there is very big gap to 4.
Obviously 27/69 primary is too long for XLS(and maybe SS) gearbox.

So we decide to try 26T driven gear. Now waiting till it arrives.

Great job!

Out of curiosity, does it manage to pull 4th at all?

It pull but very slow. Need to rev really high 3rd. And even then there is acceleration very noticeable loss.

That's what I thought...
It that gearbox is long like mine is (PK50 XLS), I think you'll need something around 24/72 for it with a 130.
Maybe a bigger carb can help, but I'm not sure if that will be enough (nor the 26 teeth gear).

25/69 would have been better. I run it on the orange Special and my friend's avorio 50s…

But that's with a short gearbox, right?

24/72 is for 102-112cc. It will be too short even with long(XLS) gear box.

Roland,

My I ask you what speeds are you getting when revving it high in 3rd?

PK125 gearbox, one of the two has a shorter 4th (DRT tree)…

Sorry, but I not tried it due to run in period. Tried few times hold up to 60-70 km/h(GPS) on 3rd and then shift to 4th.

But I know what I'm talking about. Tried before lot enough different primaries on one of my old engine.

Oh, ok. Thanks

I know you do. Way better than me.

Thank you for letting us know your bikes and your work.
Keep up.

its time for a small update. the pk50ss i had it was in a really bad condition with lots of staff missing and not working. i found an other 1983 pk50ss with no papers but in better condition (frame seems not rotten and everything is on) but the engine is stuck. today i start dissasembly lots of parts to see if i can find why is nothing moving! also i took of the rear shock. i already have a bitubo rear shock. can anyone tell me if it will fit and what is it missing? i tried to search if this is the correct length for pk but no luck. maybe with a upper silent block and some kind of adapter will do the job..

Some pics of your Bitubo can help to identify it. What length is it?
Bitubo YLV shock is 380 mm length according to SIP.
Other shocks is 320 and 330 mm.

PK shock upper mount have two thick silent blocks - one inside frame and one outside, so it have noticeable longer rod than PX shock.


PK

PX

here are the pics. as already reilised that shock is for px and wont fit in pk.... so i will try to swipe the one i have with one for pk

Are you sure that this white is SS? Looks like S to me.
What prefix on vin number is? And engine number?
V5S1T(V5S1M) for SS
V5X2T(V5X1M) for S

Last edited by roland87 on Wed, 20 Sep 2023 08:22:31 +0000; edited 3 times

DR cylinder... Uploaded some engine and frame numbers

So S frame with SS engine.

Which is the actual difference the s with the ss frame?

I think nothing.