Whos got the louded moby cylinder?

Joe . /

Feb 27, 2023 08:17PM

I had a motobecane 7 a long time ago and it was far from quiet but I don't think I ever really cared enough to find out why. fast forward to now, I bought a 50v and rebuild the bottom end and the timing is set to 2degrees btdc.

the cylinder has a noticeably loud high pitched pinging/eeeeeeeee noise when running. It seems to be the cylinder fins achieving some sort of resonance frequency as I can grab the cylinder and head fins with both hands and it dampens it dramatically. I don't think its pinging from timing related issues but it is still a little concerning.

What does your cylinder sound like?

Re: Whos got the louded moby cylinder?

The Dude /

adventurewagen

Feb 27, 2023 10:31PM

If you look at old air cooled 2 stroke dirt bikes they had rubber inserts between the fins to dampen the pinging. It's normal.

Re: Whos got the louded moby cylinder?

Stephen Keller /

keller_stephen

Feb 28, 2023 01:31AM

Are the engine mount bushings worn? If so maybe they are allowing some extra vibrations?

Re: Whos got the louded moby cylinder?

🦺🥇b to the MOPO 🚨🚨🚨 eff /

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brianf

Feb 28, 2023 09:05AM

> The Dude wrote:

> -------------------------------------------------------

> If you look at old air cooled 2 stroke dirt bikes they had rubber

> inserts between the fins to dampen the pinging. It's normal.

Some Jawa mopeds have those! :)

Re: Whos got the louded moby cylinder?

Totally normal JBOT /

capturedbyrobots

Feb 28, 2023 12:58PM

Usually slices of pneumatic air hose or vacuum lines make great fin dampers.

Re: Whos got the louded moby cylinder?

Kelikaku קוטין /

kelikaku

Mar 03, 2023 08:53AM

I don't know if this might not apply in this case. I just took off my stock air filter and replaced it with this. The original setup was not completely quiet, but it wasn't loud at all. Now the new air filter gave me a little more throttle response, but the engine noise is about double than what it was before. Maybe a baffled air cleaner could cut down on some of your noise:

2023-03-0308.02.24www.myronsmopeds.com0a113370323f.png

Re: Whos got the louded moby cylinder?

Alan Jackson /

aljaxon

Mar 09, 2023 12:36AM

do you mean 2mm btdc and not degrees?

Re: Whos got the louded moby cylinder?

Born to be WillD /

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willd

Mar 09, 2023 09:52AM

> Alan Jackson wrote:

> -------------------------------------------------------

> do you mean 2mm btdc and not degrees?

I saw that too. I mean, it'd definitely be pretty loud oif the majority of your combustion was occurring in the exhaust...

MOPED ARMY

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