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Hello All,
I have a 2005 Vespa PX150 (USA model) that has a higher pitched rattling when it is revved. It has done it since I purchased it a few months ago and I haven't been able to find the source of it. It is similar in sound to the glovebox rattle, but located near the cylinder.
It is not:
The fan cover
The gear selector cover
Related to clutch
The glovebox (although that rattles plenty!)
Here's a link to the video of it: https://youtube.com/shorts/rrP3p2FkGcg?feature=share
I'm only referring to the rattling noise when it is revved, not the whirring noise.

Maybe it's a normal sound for these, but I just want to double check before putting too many more miles on it. Thanks in advance for the help, it's been a blast to ride otherwise!
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Hi, did you check the gearbox oil?

Ps: I'm not a PX guy but it doesn't sound bad anyway
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100% piston slap. Clearance is too large in the bore and the piston is rattling at low speeds. Goes away a little when you rev it. Spec is .004". You're probably .008+

You definitely need to address it. Time for a bore and new piston or buy a new top end. If not, eventually the piston skirt will crack and send aluminum everywhere. Then you're in for bearings, seals, a new crank and the top end.
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Perfect excuse for a 177.
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MJRally wrote:
100% piston slap. Clearance is too large in the bore and the piston is rattling at low speeds. Goes away a little when you rev it. Spec is .004". You're probably .008+

You definitely need to address it. Time for a bore and new piston or buy a new top end. If not, eventually the piston skirt will crack and send aluminum everywhere. Then you're in for bearings, seals, a new crank and the top end.
Can't a failed small-end bearing or circlip also create that sound?
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Ray8 wrote:
Can't a failed small-end bearing or circlip also create that sound?
I'm no expert but I guess in theory anything that introduces slop into the piston movement could cause a rattle. I have yet to see just a small end bearing fail though. Always piston to bore or the big end bearing. I'm trying to think of reasons a small bearing would fail but everything else would be fine?

Circlip id doubt. It's either in its groove or out and making so much noise you know you're fucked. That's only for a second or two before it breaks things/seizes motor and then has no compression and is dead.
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Thanks for all of the responses so far.

The gearbox oil was checked as soon as I bought it and is still at the correct level.
I had a feeling the sounds were more than just the ol' rattle of an Italian two stroke. The scoot only has 2000 miles on it, but I guess it's not a bad time for a 177 lol.
I'll start pulling the top end apart later in the week and report back with my findings.

Best.
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question: what does it sound like when you pull the clutch in? anything change?

I'm kinda with MJ, it sounds like piston slap to me. the whirring sound is fairly typical but that clank is gnarly.
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Pulling in the clutch makes no difference in sound. I read so many other forums talking about that though.
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JohnnyGreaser wrote:
Pulling in the clutch makes no difference in sound. I read so many other forums talking about that though.
suspected possibly a loose clutch basket. but that rules that out.

*shakes magic 8 ball*

top end replacement is inevitable

so you do it now, or wait till it kerplodes and do everything.

or you go whole hog and do everything in one go out of an abundance of caution.
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Is the engine warmed-up in that video?
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Ray8 wrote:
Is the engine warmed-up in that video?
No, it was cold still.
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intrigued.
I hear a strange whining sound - as if my kids are in the room but Im not really paying attention.
I hear a rattle down low - and it alleviates a bit with rev.
OP notes that the sound he's talking about is when it revs up?

Are y'all hearing something different?
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JohnnyGreaser wrote:
No, it was cold still.
How does it sound at operating temperature?
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charlieman22 wrote:
intrigued.
I hear a strange whining sound - as if my kids are in the room but Im not really paying attention.
I hear a rattle down low - and it alleviates a bit with rev.
OP notes that the sound he's talking about is when it revs up?

Are y'all hearing something different?
My guess:
Exposed flywheel wizz, via most phones' tinny recording nature. Rattle maybe a cold piston skirt?
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Piston slap as stated above. Toss that jug and get a BGM 177, Som flafor of sport box and upjet. You ll be happy.
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charlieman22 wrote:
intrigued.
I hear a strange whining sound - as if my kids are in the room but Im not really paying attention.
I hear a rattle down low - and it alleviates a bit with rev.
OP notes that the sound he's talking about is when it revs up?

Are y'all hearing something different?
The wining sound is only there when I have the flywheel fan cover and engine shroud off.
You're right though, it seems there are several problematic noises at once. The low clunking is what I believe they are saying indicates piston slap. The original post, as you said, was actually about the higher pitched rattle that accompanies a rev. Perhaps they're both related though. As stated before, top end rebuild is inevitable.
Ray8 wrote:
How does it sound at operating temperature?
The low rattle is a bit better when warm, but definitely still present.
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It could either run for many fearful years with that noise or snap the conrod and mutilate the engine casings while out riding tomorrow. These things are very unpredictable.
Something is wrong in there. If it's piston slap, then you have a wide choice of kits to choose from. If it's the small end get a new crank, which should be 60mm to give you the best outcome for minimum effort on whatever cylinder you choose to run.
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Still think the audio is distorted.

Get it to operating temperature and post another video with the covers on.
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I'm terrible at noise diagnostics. My scooter had a rattle and the big end crank bearing ended up failing. It's hard to hear it in the video. Air cooled engines in general make a lot of mechanical noise.

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orwell84 wrote:
I'm terrible at noise diagnostics. My scooter had a rattle and the big end crank bearing ended up failing. It's hard to hear it in the video. Air cooled engines in general make a lot of mechanical noise.

Mine sounds almost exactly like that. I am pulling the engine today and will report back with my findings. Thanks everyone for all the help so far! Also, I have a spare brand new P200 top end laying around, they aren't compatible PX150 bottom ends correct?
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They aren't. I'm not sure how to check the con rod bearing. Some side to side play is normal. Fore and aft play is not.
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orwell84 wrote:
They aren't. I'm not sure how to check the con rod bearing. Some side to side play is normal. Fore and aft play is not.
Correct. Stud pattern on 150s is smaller than 200s.

Side to side ok. Up and down no bueno!

Look for marks on the skirt of the piston.
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As the crank bearing fails, the piston no longer travels straight and will scuff. As much as it sucks to find stuff not working, it's way better than having it come apart and take the case with it.
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I'm just going to say that a stock 2005 PX150 has got to be the most reliable engine of any shifty Vespa that was ever import to the US. With only 2000 miles on this scooter, nothing that rotates inside those cases could be worn...unless at some point there was an episode where either there was no transmission oil or ran out of 2 stroke oil. Could it be possible that there aren't any noises out of the ordinary? Perhaps the video that was made distorts the engine noise enough so it sound like something is the matter with it? I'm just throwing another 2 cents out on the table, but perhaps the said PX is a hypochondriac? At one point I owned 4 of those 2005 PX150's at the same time. They are so gutless in the restricted form that the engines are virtually bulletproof.
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Alright, engine came off today and I have some good carnage for all to see.
There's a little play in the wrist pin, bottom end feels tight up and down. Cylinder has many scratches and larger scrapes around the transfer ports, large enough to easily catch with a fingernail. Piston skirt also has lots of fine scratches. If you hold the piston still and put your hand on the flywheel and pull up and down, the crank bearings seem to have lots of play. A distinct clunk can be heard in both directions.
Looks like I have my work cut out!
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Here's a picture of the scoot, she'll be back on the road soon enough I hope!
Thank you all for so many helpful replies. I usually NEVER post on forums unless I absolutely need to.
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That engine has smoked a lot of cigarettes and done some hard drugs in it's short life!

You can see it had a bad head leak.
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Good catch. At least you will have something to rebuild.
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Sheesh...the previous owner really went above and beyond to ruin as much as they could in the minimal amount of time that they owned the scooter.
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Way worse than expected. Damage sounds similar to what can happen to jet ski engines when they're left full of water.

New cylinder kit costs the same as a rebore. 60mm crank is similar cost to OEM 57mm. Rotary pad is likely to be not well and either repair to original or convert to reed block, similar cost.

This is more of an opportunity than a disaster.
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bro, that thing is smoked.

like jack said, I'd be taking a deeper dive rather than just throwing a new top end on.

even with low miles, those seals are damn near 20yrs old. so, I'd be starting there. and in doing thems you can have a look at the crank and pad.

if any of that is questionable, then it be time to open the wallet and get the party started.

but at a minimum, a new top end and check your jetting and autolube system.
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whodatschrome wrote:
I'm just going to say that a stock 2005 PX150 has got to be the most reliable engine of any shifty Vespa that was ever import to the US. With only 2000 miles on this scooter, nothing that rotates inside those cases could be worn...unless at some point there was an episode where either there was no transmission oil or ran out of 2 stroke oil. Could it be possible that there aren't any noises out of the ordinary? Perhaps the video that was made distorts the engine noise enough so it sound like something is the matter with it? I'm just throwing another 2 cents out on the table, but perhaps the said PX is a hypochondriac? At one point I owned 4 of those 2005 PX150's at the same time. They are so gutless in the restricted form that the engines are virtually bulletproof.
2k miles on a stock scoot!

New guess is that bike was parked new in New Orleans, 2005.

I was about to post a video of my(kitted) scoot's rattle, from cold start to operating temperature.

Both the BGM and Polini 177's are rattlers. The buzzy VMC much less so, but I soft-seized it at CHT less than the BGM can take.
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orwell84 wrote:
I'm terrible at noise diagnostics. My scooter had a rattle and the big end crank bearing ended up failing. It's hard to hear it in the video. Air cooled engines in general make a lot of mechanical noise.

⬆️    About 8 months elapsed    ⬇️
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Hello All,

It took me much longer than I had hoped to post an update but the PX is back on the streets! It now has a new cylinder (177cc), piston, crank (the tolerances on the old one were concerningly slack), SIP Road 2.0 exhaust, carb (SI 24), clutch gear cog (22 teeth), etc. I also went ahead and did all gaskets, seals, bearings, etc since I was already in there. Crank bearings were definitely in need of replacement.

It was quite the learning process, as this is my first Vespa (plenty of experience working on Japanese bikes), but I have a whole new love for working on these scoots. I have a '64 V90 all in boxes, so at least this gave me some experience for my next rebuild! Thank you all for your help!

Johnny
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congrats!

now that you've got your feet wet, the V90 build should be only minimally frustrating!
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MJRally wrote:
Circlip id doubt. It's either in its groove or out and making so much noise you know you're fucked. That's only for a second or two before it breaks things/seizes motor and then has no compression and is dead.
Yeah...I've had a circlip kill a motor. It was definitely all-then-nothing... Facepalm emoticon
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