Modern Vespa

So.. I am putting together a small frame for myself from a bunch of bits, starting with a Primavera frame, and a V90 engine.

I am currently rebuilding the motor and replacing the flyside crank bearing.
My question is about the the spacing of the inner bearing onto the crank. Ive seen tons of instances of installing bearings onto large frame cranks and have seen gauges for getting them installed correctly (1mm?) but, how is the small frame different in this regard, if at all?

Thanks in advance!
-m

I've always just knocked them on without much thought, tbh.

the two piece bearing is easier to install, but the one piece is a little more stout... but if you're running a small taper crank it's probably fine.

I guess you could knock the inner onto the crank, throw the outer into the case and then slip the crank in and see if the race lines up properly?

Didn't really think about it too much either. Now that I am, I figure the smallframe engine design is older and therefore used a simpler bearing/looser tolerances? Smallframes came out 66 I believe and a P design in 77. 11 years of R&D or management change to say switch it??

I am also interested on this. I'll be installing the two piece bearing (NU204) on the "Special" I'm building for my brother in law. Does it also need to be spaced as the ones on the P engines??

I thought the whole gap thing was all caused by the oil pathway in the flyside half of the case? Since that's machined in at a certain spot/angle, it set the bearing at a certain spot which in turn made you add the 1mm gap for the race on the P crank?

another consideration is that it is an entirely different style of bearing. the fly side on P is needle roller and these are not, even the two piece.

but really, I don't think the tolerance is that big of a deal at all. knock it on and move ahead to the next item on the checklist

Awesome, Thanks! was just worries about tapping a pretty pricey bearing on to far and having the try and pull it (and possibly damage it)

Stuck some Delrin on the Lathe and made a nice bearing installation tool. While I was at it I took a chuck and made a seal install tool. Worked a treat!
drove it down til it stopped (supporting from inside the crank, as not to put any load on the crank pin) installed the outer into the case, test fitted the cases together and all seems good!

Thanks again!! Next up converting to 4 speed!

-Mike

What's the story behind the NPN transistor on your wrist?

ehh im just an EE.
Spacecraft electronics by day, analog(ue) synthesizers by night!

Very interesting post

I'm also rebuilding a V90 engine, and been wondering the very same thing about how far onto the crank to press the inner fly-side bearing half, as I'm also using a 2-piece N204

Did you simply press it on until bottomed out and stopped?

Did everything go back together okay?

PS ... great job on that DIY delrin bearing/seal driver

Just drove the bearing until it felt seated. Did a dry fit of the crank with the cases and everything seemed smooth. This also agrees with the all the comments so far as well, so I'm happy and moving along with the build!
-m

Thanks!
I'll be installing mine in the near future, so it's great hearing from someone who's actually had some hands-on experience with the very thing that's had me wracking my brain.

PS - Good to hear everything's coming along well on your build.

So I am working on converting this V90 motor to 4 speed. I was having fun trying to install the new cruciform / detent balls and spring. I looked down at my bench and saw the two old kick start buffers I pulled out of the cases.. the tabs on the buffers that normally would slide into the case fit nicely into the grove of the drive shaft. Slid the cruciform slightly onto the shaft and used the two old buffers to push on the detent balls compressing the spring. Then I just pushed the cruciform the rest of the way on.

Put the new gears on. There is quite a bit of play in the gears. with a 0.85mm spacer in the back and a 0.9mm on the front of the stack, there still is ~0.6mm play. Is it okay to stack another shim, or should I just get a single thicker shim?



Thanks!
-Mike

The NPN tat is hard core!

I mean it is SOLID state.

personally I'd go with a thicker shim, you're close to outer limit of play so I'd shove a fatty in there and suck up the difference.

trick on the cruciform: use and old one and shove it on from the other direction to retain the balls and spring, just follow it along and click click click worn one comes off. installing the new one is the reverse!

if you're starting from scratch, well... god speed. I like to use an old push push rod that has a cup end (the hollow body of a ball point pen works in a pinch too) and clamp up the axle in a vise.

Went ahead and ordered a couple thicker shims to do a single, rather than stacking.
How much play should I aim for? Luckily when I was installing, the balls only flew across the shop like 3 times. the buffers worked ok, but wish I would have thought to use the 3 speed cruciform. great tip!

Replaced the crank bearings, installed the new 4 speed transmission and fit the the case halves together.

Everything feels nice but there is a slight clicking when I turn the clutch basket. I'm sure it is the christmas tree, very slightly ratcheting on the kickstart gear.
Is that normal?
If I hold down the kick start lever it's the same sound only much louder. (As to be expected)

Kick start spring not full seated?

-Mike

Pulled the cases back apart. Found the Christmas tree was not 100% seated into the bearing. Heated the cases with my heat gun, tapped it down a little bit more with a soft mallet. Put the cases back together, everything all smooth no clicking.

-Mike

Still following your progress on this build ... All good Stuff!

With the cases back together the next step, top end.

Have this DR130 sitting here.. 90 cc piston compared to the 130.

Installed the cylinder to the case. Installed the stator (6v points)
Adjusted timing 17-ish BTDC

Stuck on some shrouds, intake 19/19 with 80 main jet, temporary upside down Sito exhaust (have a Faco ET3 I'll put on the bike) a coil, and jumper wire.

Hooked up some fuel, gave a couple "kicks" and immediately came to a nice idle!

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