Crank taper options for Primavera engine

[vespaman1]

Hi - First a quick introduction as this is my first post. My name is Daniel and I live near San Francisco, CA. I started and ran scooterhelp.com for about 17 years but with kids, life and work felt like I didn't have the time to update it well enough. I got an offer I couldn't refuse and sold it (for better or worse) about 3 years ago as the new owner had more free time to update it. Recently with the kids getting older, I found that working on scooters has come back into my life and I picked up a barn find 1975 Vespa Primavera and I can't remember my own scooter knowledge.

This bike has points and I hate points. The motor runs but has obvious crank seal issues (runs great with the choke on) and so I'll be replacing those. It reminded me that the cranks on smallframes differed through the years with the flywheel cone getting larger with the PK series. Since I am rebuilding the motor I have the opportunity to replace the crank and have more compatibility with electronic ignition flywheels because it shares the crank taper with the P series bikes. If the crank is fine is this worth it or are there plenty of electronic kits for the older crank bikes?

As the flywheel side bearing area got bigger through the models, did the cases change at all? Can a PK crank be fitted into a 1975 Primmy casing by simply having an oil seal with a wider inside diameter? And then if I went for the PK125 which has an even bigger flywheel side diameter, does the outside diameter of the bearing still fit in the flywheel side casing?

Thanks,

[boreham]

Hi Daniel, welcome to the forum, the cases are essentially the same, you can use the larger taper crank with a conversion bearing and the larger seal. The later cranks are 24mm and are used on the PK XL and ETS models, the standard PK used the same smaller taper 19mm
The conversion bearings are readily available from any good supplier, the code is 6005, there is a 2 piece alternative as the PX NU1005, but they are quite pricey

Good luck with the build

[henri]

welcome daniel ,and thank you for scooterhelp.com ,its been a godsend over the years .
cranks come in 3 sizes ,the smalltaper 19mm seal 20x47x14 bearing ,large taper 20x32x7 seal an same 20x47x14 bearing ,an the ets/pl170/pk xl crank which has a large taper 24x32x7 seal and the 2 part 25x38x15 needle bearing .whilst small taper an large taper cranks fit into the same cases straight swaps to fit a ets crank into non-ets cases ,or a normal crank into ets cases needs conversion bearings an seals .
a ets crank into non-ets cases its a 24x32x7 seal an either a 2mm spacer and a 25x38x12 bearing ,or the expensive 25x47x14 2 part roller bearing .
none ets crank into ets cases is a 20x25x15 inner bearing track onto crank an then the 25x38x15 needle bearing an a 20x32x7 seal for a large taper crank .
all the fancy retarding ignition systems are offered in small an large taper types ,but if wishing to stick to stock pk ignition small taper flywheels are getting tricky to find .large taper flys are common , an can be used with a crimaz conversion taper kit .H

[jbcollier]

Welcome! Thanks for all those wiring diagrams!!

The first question is, "What is the goal for the scoot?

Fix up and keep stock or mildly tuned?
- stock crank will be fine. Points are fine and last a long time. They are also easy and inexpensive to diagnose and repair. You want to go electronic? Go for it. You won't gain anything on stock or mildly tuned engines though.

Tune the engine for 10 hp+?
- it would be a good idea to go for a larger taper crank and a lighter flywheel. 20mm taper is plenty strong unless you are building a monster (say 30 hp+).

The most important thing is to plan out what you want. I eventually built a 20-ish HP engine. I did it in five stages: three different top ends, three different cranks, two electronic systems, three gear boxes, three exhausts... you get the picture. I spent 3x what I needed to spend. Figure out what you want first. It's much cheaper that way.

Rock solid, basic build: stock crank, points or simple electronic, basic Polini alloy 130 kit, up-jetted 19mm carb, Polini/Malossi "banana" exhaust, 90/100 primaries with a stock 4spd gearbox. This will out run a P200, climb most hills without having to shift down (no, not on "those" San Fran hills), and top out 60-ish mph. I've built lots of these for my friends and they love them.

Components I recommend if building a more powerful engine:
- Polini cranks, beautifully made and balanced! Engine is much smoother.
- Quatrini kits. Beautifully made, well supported and deliver their stated power reliably.
- front disc brake. I use a PK fork paired with a PX caliper and a radial master: powerful with beautiful feel.

Good luck!

[noreaster]

First off, legend! You helped me so many times with my Rally 200 when I was a kid!

I was in the same boat when building my current project and it was confusing at first. There's the 19/20 tapers that fit small frame flywheel, 20/20 tapers that fit large taper flywheels (but most electronic ignition manufacturers produce 20mm flywheels for smallframe), and the ETS 24/25 crank that use 20mm cones.

Scooterwest in your state sells conversion bearings and seals to fit an ets crank in a Primavera. It's a one piece, but you can get the dims and source a two piece bearing from SIP or locally.

Vape ignitions are pretty available in the states. They are offered in 19 and 20 mm cones, static or variable, and A/C or D/C for those that wish to run a battery.

[Jimmy D]

Can't help with the technical query but just to add my profound thanks Daniel, Scooterhelp was my bible when I got into scoots just over a decade ago and is still hugely valuable for things like model/serial numbers etc.

[jedihunter]

Wanted to say thanks for scooterhelp, essential for buying scoots stateside!
Plan the build, but if it were mine I'd go large taper crank from the get go. As for the ignition, The vape has worked for me on multiple bikes, both ac and dc. It's easy to set up, and seems a quality bit of kit. Keep us updated with the barnfind!

[tzsteve]

go big

there is no substitute for size
i think it works out at about 60% stronger
at the point where the taper typically snaps.

[vinrouge]

Along with the rest of us, would just like to say thank you for all the how toos, wiring diagrams and all round advice on the site.

[vespaman1]

Great to hear scooter help.com is still working well for everyone and thanks for the help now on to my next question...

[tzsteve]

?

[gugne]

Thanks for Scooterhelp. It was the place I found first when I got into restoring 6 years ago. Helped me no end.