Repetitive bearing problems with 22/68 primary

[KTy]

Alloha,

Let me explain what's going on, I need your opinion on this one...

I have a VNB5T in 8" fitted with a PX125E Arcobaleno engine (EFL for germany ?). The original primary ratio is 20/68.

From Piaggio, the 21/68 exists, the 22/67 also, but not the 22/68, even if it referenced here: http://scooterhelp.com/tuning/vespa.gear.calc.html

I properly rebuilt the engine (bearings and so forth), I drove a 22/68 primary with the standard 125cc cylinder, for 3000km. After ~2000km, I had a strange noise, I could "remove" it when I disengage the clutch... So far, the crank bearings were on my target.

I put a Polini 177 plug'n play on it, I drove 300km and the crankshaft bearing really start to make me pity...

I opened the engine, I changed everything (gasket, the whole clutch, bearings, gear spacer, cruciform,...etc), matched the transfers, anticipated the crank and put a Polini manifold along with a PHB28, Leo pipe is "okay" with the 177. So far so good.

Engine is powerful, really good fun... Except that crankshaft bearings start again to cry (

So, basically, I ruined 2 sets of crankshaft bearings in ~4000km, I started investigate... :plemplem:

Bearings were given by a friend of mine who works in this buisness, he says they are *really* good quality ("better than SKF").

So far I have two options in my mind (assuming that I carrefully put the bearings in the cases): :uargh:

* My flywheel is unbalanced (it is an original PX without the teeth for the elestart)

* The 22/68 primary can be fitted, BUT it is the responsable for my troubles.... :grr:

Any help, feedbacks or ideas would help, thank you !!!

It's not me , but this guy is saying "Whouuuu, nice engine !!"

KTy -

Bearbeitet 10. Juli 2006 von KTy

[Klingelkasper]

If the primary drive should really responsible for eating up your crank bearings something with the clearance between gears must be very wrong. Radial clearance between the gears is o.k.? Another posibility could be a damaged engine casing, for example bearing seat on clutch side is worn out or maybe left and right bearing seats of casing are not accurate in line. Are you shure that your crankshaft ist not twisted or bended?

[Green Bastard]

Could is be, that your crankshaft is skewed!

You could checkis with a dial gauge! If it is skewed, the bearings every time going to wear out!

edit says: I'm too late!!

Bearbeitet 10. Juli 2006 von Green Bastard

[KTy]

I'm not sure if the crank is perfectly aligned, that's a good point. Visually, even at mid-high RPM I cannot see the crankshaft misaligned (from the flywheel point of view).

However, just after a quick ride from my work place to where I live (5km, 15minutes city driving with some short acceleration), I realized that the flywheel is *really* hot... I cannot put my hand on it !

Could be a clearance trouble....

Anyone riding a 22/68 with no problem at all ? Help !!!!

Bearbeitet 10. Juli 2006 von KTy

[sidewalksurfer]

Maybe the *really* good quality bearings aren´t that good? This is not to say that they are crap in general, but maybe they just haven´t the correct specification for use in a Vespa engine. There are a lot of differences between bearing specifications, depending on the purpose they are designed for.

Personally, I´m not too good at explaining the differences, but I´m sure there will be someone doing this soon. Must have something to do with axial and radial stresses the bearing can be exposed to.

Bearbeitet 10. Juli 2006 von sidewalksurfer

[BugHardcore]

Anyone riding a 22/68 with no problem at all ? Help !!!!

As far as I know this primary was used originally by Piaggio in all PX150 models except the very early (22/67) and the very late (21/68). At least my pre Arcobaleno engine came with it.

[KTy]

Maybe the *really* good quality bearings aren´t that good? This is not to say that they are crap in general, but maybe they just haven´t the correct specification for use in a Vespa engine. There are a lot of differences between bearing specifications, depending on the purpose they are designed for.

With my friend we have just double-checked that the bearing were *way* overrated for a vespa engine... The first set of bearing that I screwed was from a "vespa" dealer...

As far as I know this primary was used originally by Piaggio in all PX150 models except the very early (22/67) and the very late (21/68). At least my pre Arcobaleno engine came with it.

Are you sure ??? I cannot find any information on a scooter with original 22/68...

I start thinking it could be the crankshaft...

Bearbeitet 10. Juli 2006 von KTy

[discotizer303]

Ahoi,

there are two different width for the 22 wheel.

Maybe you have the wrong one that never fits with your engine.

At the moment i haven´t got the right messurement. sorry

[undis racing team]

Can you tell us the excat descriptions of the bearings, there are some out the with 1 bearing more, and i have simalar experience like you with them

[KTy]

there are two different width for the 22 wheel.

:plemplem: (

Can you tell us the excat descriptions of the bearings, there are some out the with 1 bearing more, and i have simalar experience like you with them

I will try to find the exact references... :uargh:

[KTy]

So, the bearing on the clutch side is a 613912, same as SKF, but with one more ball !

But I won't blame to rapidly the bearing as I had the same problem with a "regular" bearing from SKF.

I will investigate on my flywheel balance, on the possibility of a twisted crankshaft and on the 22/68 primary combo that I find more and more suspicious !!!

Again, if someone can gives me the exact references of an original Piaggio 22/68 primary ratio, I would appreciate.

Also, could anyone explain to me (mechanically speaking) how a clutch with 22 tooth from a 22/67 engine (early P125X and early P150X) can be fitted in place of a 20 or 21 tooth on a PX125E, PX125 EFL, early PX150 EFL ...

Bearbeitet 11. Juli 2006 von KTy

[KTy]

Okay,

I was given other stuff to investigate:

My clutch bearing could be moving in the case AND my primary bearing and/or primary axis could be in bad shape. Actually, last week-end I saw that my primary transmission could move for about 0.5-1mm, I did not realize how bad it could be...

Damn'it :grr:

Bearbeitet 11. Juli 2006 von KTy