Modern Vespa

Hey All. So I am stumped with my GTS. It has 52 000 kms on, and I heard a dreaded engine knocking sound... I took it to my local Vespa specialists and we discovered that the oil was full of water due to a water pump seal failure. The Valve cam was also really worn.. So we did the following work on the scoot :

Video Here : https://youtube.com/shorts/ig1QBTvQ-mw
(Sound is worse than it sounds in the Vid)

1. Top end rebuild.
2. Water and Oil pump Rebuild.
3. Replaced valve cam, with second had Valve cam in good condition.

Once I got the motor back, I fitted in the scoot, and the noise was gone.. After about 20kms, the noise returned... I took the bike to the mechanic and the motor sounded fine, so I carried on riding the scoot. About 10 kms after the inspection, the noise returned.

So I checked the valves and they where a bit loose, so I adjusted the clearances as per robots video, maybe even a bit more drag then he recommends, but nothing silly.

I started the scoot up, and i sounded great, until I put the motor under some load and the metallic knocking is back

Some other notes below :

1. No metallic pieces in the oil, after checking twice.
2. I increased the oil viscosity to 10w-40, as per my mechanics advice.
3. Scoot runs so well it irritating...
4. Noise is consistent, from cold all the way to fan on.

I am not sure what my next step would be, any advice ?

So turns out there is no noise when motor is cold but gets worse as motor heats up.

Wow. This sounds exactly like the noise I attempted to chase down. Nothing in the oil, pulled and checked the top end, put it all back together and

no noise

for the first ~15km.

Then it's back to knocking. I will say it seems to be slightly less loud, but it's still there after warming up (I did get a little older and thus lost a bit more of my hearing so a few more years and the Vespa should be fine).

Thank you so much for the response, really great to hear someone had the same issue. So did you ever get it fixed, or just kept on riding the scoot with no issues ?

Are you sure the sound is coming from the engine and not something from the CVT transmission?

If you are sure it's engine related, then injectors are known to knock sometimes.

Also, might be worth trying a different fuel station and a higher grade of fuel on the off chance that it's fuel related.

Thanks so much Jake, could very well be given the change in noise every 30 to 40 kms... I actually never knew "Engine Knock" Would actually make a physical engine knocking sound. Defs worth a shot I see some people mention additives, I'll take a look and see what's available here in South Africa.

Negative for the CVT I revved it up a few times with out the drive pulley with no luck.

Thanks again will keep you posted

Sometimes the premium petrols include additives and cleaners as standard, so a couple of tanks worth could clear through any issues.

Looking into this some more, injector problems are often described as a "metallic knocking sound" - so it might be worth seeing if you can borrow / try a different injector.

Do you have a stethoscope or long screwdriver? Put the screwdriver handle to you ear and move the tip around the engine/CVT. When you find it you'll hear it.

Hell screwdriver to the ear, that's old, but works, Im in my 60s and done it and I can remember my grandad doing it to a Norton Commando 750 in the 1960s

Hello
I have just fixed the engine on my vespa gts 300ss with 6000km on the odometer. It sounded like the sound in the video. The fault was the exhaust lifter which was completely worn out as well as the camshaft. I changed the camshaft and exhaust lifters and the scooter is like new

Check the voltage regulator. If it's allowing the bike to overcharge, that can make it knock, but that's usually the fuel pump.

There must be a story there...that's not a lot of miles.
Great feeling when it's running normally!

Aand, welcome to MV!

Thank you
I bought the scooter used so I don't know its history. I think it has had too little oil; the first thing to break with little oil is at the top end.

Thanks all for the help.

I'm going to pull the cam out and inspect the rockers, I have a feeling they have worn ridiculously fast again.

Maybe due to a blocked oil passage, Is that possible?

Thanks

No, never went away. Only slightly better after reassembling (including a look in the transmission). So I've decided to not worry and just ride.

Hey All. So took the cam and rockers out I think they look acceptable?

However I suspect my timing chain needs changing, Is the adjustor in the image all the way out ? I am not sure how it works so dont want to open it

I think the valve lifter looks questionable. I would have exchange the one in the picture. Measure how far the tensioner is out; I believes it should not be more than about 2 cm. Can't figure out that the register chain should make a knocking sound? Could it be the crankshaft?

Rockers look toast, cam is pretty dicey, IMO. I'd replace all of them.

I think tensioner position determines chain replacement? If it was all the way down, definitely. Unfortunately tends to slip when removed. Whatever you do, remember to retract it when reinstalling!

Thanks Guys so much.

My mechanic swears the second hand cam and rockers he replaced 30 kms ago where clean, and that the motor is eating cams and rockers...

He mentioned I should remove the head and check the oil gallery, which I have just done, Was really hoping it was blocked, but blew it out with air and it seems clean.

Looks like this is the only channel ?

Mine seemed to go the same way. Looked passable on inspection last fall, reinstalled and a couple hundred miles later started clattering. Runs fine atm but still a bit nervous.

yeah man, those rockers are toast.

I'd replace along with the cam.

it's unlikely the timing chain has stretched. the adjuster default position is fully extended due to the spring tensioner- so when you pull it off it goes full extension.

As a auto collision adjuster I use to hate having to push used mechanical, a/c components, suspension parts, etc on our insureds, leaves a big question mark and more money and time for all parties if further problems surface in the near and mid-term.
Even when it's my own dime and the savings are significant, replacing a part that wore out or had a mechanical failure and hoping the used one doesn't usually isn't worth it IMO

Agreed. Paying school fees here...

However a friend has these for free, might be worth a test ?

Check the alignment pic though looks weird ?

The part look very good. The alignment is a bit strange, but if the rockers feels thigt after adjustment; try it !

Doesn't look quite right to me, but you can always try an assembly to be sure.

I sympathize with the budget issues....those parts are small, but they ain't cheap!

Thanks Guys, Did some more research looks like it's a 250 cam and rockers, will be getting some fresh parts and be done with this thing 😂