Modern Vespa

Hi all,

Just wondering:

How is the best way to install the 6204 flywheel roller bearing so that the crank fits into it?

Since it's a flywheel bearing I'd assume you tap that into the engine case first, but then how do you pull the crank through? With a crank puller? How do I manage to close the cases? Is there an order of operations?

I know I can use the two piece bearings—-but I have the 6204 so I might as well attempt to install and use it.

Thanks again everyone!

install it into the case, crank goes into the clutch side, ideally cold and then you lightly heat the fly side and hope that it slips on with some gentle persuasion.

I usually pop the seal in after it's all together.

Key word——hope.

Other notes: "gentle persuasion" aka use a hammer?

Hahaha.

Thanks greasy!

Save yourself the trouble and just install a NU204…

yes... dead blow or mallet with a block of wood. gentle like a cow scratching up against a post kinda deal.

if you go by the service manual (not saying you should):
1. fly side bearing goes on the crank
2. clutch side bearing goes into the case
3. crank gets pulled into the clutch side
4. fly side case is heated and the whole thing is assembled (PITA)

Alternate process:
1. fly side bearing goes into the case
2. clutch side bearing goes into the case
3. crank gets pulled into the clutch side
4. fly side bearing (with the case) is pulled onto the crank (no hammering, take it slow)
5. heat the fly side case around the main bearing and lightly tap the crank from both sides (this allows the fly side bering to shift slightly so it's not binding)

in all cases install the fly side oil seal after it's all together.

Thank you.

What do you mean by point #5?
Tap the crank on both sides?
Thanks again!

OR...........

Install a NU204 and case half goes in like butter, without heating, tapping, etc.

And it's a better overall bearing...

Ball bearings constrain movement along the axis of the crank, so with one on both sides of the crank can bind with side loads (where the roller bearing can float). As a result you can end up with residual side loads when closing the case while pulling the bearing onto the crank, depending on gasket thickness, tolerance stack up, stick slip behavior of the bearing on the crank as it's pulled in...

To remove those stresses step 5 heats the fly side case to allow the outer race of the fly side bearing to move side to side as needed. A very light tap on the crank with a soft mallet can help the outer race to move to a neutral position.

What is the difference between the 2 bearings?

Split type. Inner race on crank and case half just slides in...

Aww thanks.

it kinda comes down to difference between the one piece and two piece bearings is like assembling a pre-P motor and a P-motor, same operations basically.

I prefer the 2 piece for the ease of installation and the ability to crack the cases if need be and not worry about having to get another bearing and install it-- ie. changing gearing on the fly.