Polini Speed engine, strange sound

[Dea_944tTopic starterBerichten: 87]

I recently built a Polini Speed engine with Polini 72cc cylinder.
At first everything seemd fine byt after ~400km I got a strange engine sound. At first I thought it was an exhasut leak but it’s more of a mechanical sound, listen to the video below.

Could it be a bearing? the only part that was re-used from an older engine was the crankshaft.

/Dea

[De BrandweerBijdragerBerichten: 571]

I think its a problem with your flywheel.

[Dea_944tTopic starterBerichten: 87]

Removed the flywheel but there were no obvious issues.

I did however find some suspiciuos things:

The flywheel contact area with the cranskaft is not optimal. As can be seen on the picture below the flywheel seems to “vibrate” or “move” causing markings.

The clutchdisc also seems to move and has caused a mark in the crankshaft:

The clutchdisc has marks on the rear side from the bearing, I compared with some other clutchdiscs I have and none had these types of marks.

/Dea

[zevenenergieDonateurBerichten: 4167]

I have never seen this type of coils.

The The clutchdisc has strange marks indeed. Its make,s me wonder if you had enuf torque on the nut:|
The disk has to fit tide aroud te cankscaft.
If not, it wil get more and more play.

Overal, it looks like the nut was lose:con
And now i think of it, did you had this ring fitted?
https://www.jmpbonderdelen.nl/vespa-ciao-si/motordelen/koppeling/koppelingsring-citta-ciao.html

[FonSBijdragerBerichten: 5228]

zevenenergie :
I have never seen this type of coils.

These are oldtimer / early type coils. 60’s & 70’s. They work with a heavy flywheel, not ideal on this kind of fast engine…

[Dea_944tTopic starterBerichten: 87]

I changed the clutch disc (to another used one, should probably get a new one) which solved 95% of the problem.
Still have more transmission sounds than I want but it hasn’t changed since the change, ~500 km

On the coils they fit with the thin walled flywheel, 21 mm wall width.
How many flywheel variants are there?

[niek1992BijdragerBerichten: 1882]

i’ve had this happen to me too when i used an imitation segment-holder. used an old rusty (original!) one and the problem was gone.

the “half-moon” is not optimal, causing the segment-holder to knock when idle. when revving it’s tight against the spot you see on the crankshaft.

im not sure if better tightning of the crank-nut fixes this. If i remember corectly, the crank-nut on my engine was as tight as could be.

[Gebruiker]

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