Modern Vespa

If the piston is not contacting the head or crank web, there's not much to worry about. The fast idle can make it sound worse. Does the noise change when the clutch lever is pulled and/or in gear?

330F is a high temperature for a 177. If the timing is ok, then the jetting is lean. This can make it noisy.
Many sound similar while they warm up.

Over the winter I dropped the engine out of my 09 Stella to split the cases and upgrade the crankshaft to a Mazzu economy 57mm, and replace all bearings+seals+gaskets as preventative maintenance. I also swapped out the primary for a Malossi 23/64 straight cut set, rebuilt the clutch, new cruciform + T5 4th gear, and disabled/removed the autolube system. Finally, I installed a GGR hot reed and cut out the reed block bar.

After getting everything back together and starting it for the first time last week, the engine now makes a loud metallic tapping sound that sounds a lot like piston slap. I have ridden it around 50 miles since then and the noise has not gotten any better or worse, and of course I am hesitant to ride it any further until I can fix it.

It sounds EXACTLY like the video in this thread, including the sound mostly going away in higher RPMs. https://vespa.proboards.com/thread/5709/noise-crank

I came to the piston slap theory after ruling out these possibilities:
>Autolube shaft bouncing from vibrations
>Flywheel contacting part of the case or cylinder
>Crankshaft contacting the reed stop plate
>The GGR carbon reed I got is just THIS obnoxiously loud for some reason (I guess this is still possible but I highly doubt it.)
>Incorrect wrist pin needle bearing (Used both the original LML and the one supplied with the Mazzu crank (which is currently installed))
>Piston rings installed incorrectly

But how could I get piston slap if it made no such noise right before I tore it down back in September? Does the piston to bore clearance magically get worse if the top end is sitting on a shelf for a few months? The up/down wobble is no worse than when I first installed the kit.

The kit has ~1800 miles on it and it has never been seized. I have never reached a cylinder head temp higher than 370F (measured with a Trailtech TTO under the sparkplug), and 99% of rides it stays under 320-330F.

What carb and jetting?

I should clarify, it only gets that high if I ride it pretty hard, most of the time just riding around town it is under 300F.

Clutch/gear does not make a difference, only RPM affects it.

On a 177, if well set up, the around town at speed limits, should be nominally 200F.
Change the air corrector urgently. Start with an AC120. This will make the temperature plummet.

On a 177, if well set up, the around town at speed limits, should be nominally 200F.
Change the air corrector urgently. Start with an AC120. This will make the temperature plummet.

I came to the piston slap theory after ruling out these possibilities:

>Incorrect wrist pin needle bearing (Used both the original LML and the one supplied with the Mazzu crank (which is currently installed))

Spontaneous piston slap is interesting, I'd be worried also. Did you check crankshaft before install to make sure it's true? Maybe it's twisted a bit causing issues? Or it was doing it previously and you didn't notice and you're now sensitive to it because of refresh.

Where did you buy the Piaggio bearings from? I see them on SIP but their shipping to the US is a little pricey.

I was told by another user that my current setup should actually be on the rich side, and that going down to a 125 main should be about right. Now it's all too lean? I have tried jetting with the 140 AC before and changing idle jets, screw, mains and swapping between my BE3 and E3 atomizer and I could never get rid of that hesitation. It isn't confined to 1/4 throttle, it makes it much harder to rev up onto the pipe period.

I was on the even leaner jetting (BE3, 122) for most of that 1800 miles and both the piston and head have no visible damage from overheating. There is some carbon buildup which I believe to be from the excessively oil-rich leaky autolube system, hence why I removed it.

As a sanity check, pull the flywheel and make sure the magnets didn't pick up a washer or something.

As a sanity check, pull the flywheel and make sure the magnets didn't pick up a washer or something.

Just a thought.

Hec

Yep, just checked and theres nothing on the stator or the flywheel. Was kinda hoping there was since that would finally put this case to rest without me spending more money haha

I think I will pop the clutch cover off to see if the clutch is contacting something. After talking with a friend I do not think it is piston slap anymore, since there is no way a top end can spontaneously get it like that.

Checked the magnets and stator plate, everything is tight and I didn't see anything out of the ordinary.

I think I will pop the clutch cover off to see if the clutch is contacting something. After talking with a friend I do not think it is piston slap anymore, since there is no way a top end can spontaneously get it like that.

If there is nothing contacting the clutch inside the cover or whatever, I am pretty confident that the crankshaft I received has a conrod opening just slightly larger than the stock LML one, causing both of the wristpin bearings I have to be too loose. In that case I will buy the Piaggio ones and hopefully one will fit just right.

If that doesn't fix it then I think all my hair will fall out

I listened to that video. What ever is making the tapping is rhythmic. The tapping sound speeds up with increasing RPM and vice versa. You mentioned you installed a Mallossi 34/64 up gear kit. Is it possible there is a rivet or two, on the cush gear cover plates, that didn't get peened down enough to clear the crank bearing?

And I assume you've confirmed it's not something obvious like the flywheel hitting the cover?

Can you turn it or kick it over without it running, e.g. pull the plug lead, and hear it?

Just ordered all 4 bearing options from scooterwest. Really hoping that we've finally figured out the problem!

The bearings I listed from Scooter West were 15mm I.D. That's the size my engine required. Please make sure to measure your old bearing size size. There are also 16mm I.D. bearings.

Update: Used the #4 bearing, the sound is still there. Made no difference.

I am going to look under the clutch cover next, but now that I have conclusively ruled out anything to do with the actual "engine" part of everything, I am a little more comfortable about riding it.

Maybe the the new plates I put in are striping the clutch cover?

I will be updating my previous post with some pictures of the piston and cylinder.

Is the crank touching the crank case?

You've done everything but swap the top end and open up the cases now. Any way I can convince you to swap top end first?

Bearings came in! I ordered the ones linked in Hec's reply from scooterwest. #1 and #2 are too loose, #3 has a very minimal amount of play between the wristpin and conrod, and #4 is a little snug to get in but there is no play at all. The mazz bearing is as loose as #1. Interestingly, the LML one is slightly tighter than #3.

Just as an experiment, I tried putting the same wrist pin back into the old LML crank with the LML bearing. It's so tight I can't even press it in by hand!! I remember having to use a C clamp and a 10mm socket to get it on and off. Guess it just clicked in my head that that's not normal. Both the LML crank and bearing have "III" marks.

I was spinning the crank by hand to see if I could feel anything contacting (like Hec's other hypothesis of one of the primary gear rivets), and I could not feel anything at all. Completely smooth rotation all around.


Here are some pics of the piston and head. They looked the same when I originally tore the engine down for the crank swap. I cannot feel any of the cylinder grooves with my fingernail and they look less severe in person.