Modern Vespa

Dear all, I wonder if I can break the cam chain and connect it again with the same pin? I've been doing it on Pinarello bike, curious if that would work on a Vespa?

Why would you want to?

I thought to replace old cam chain using "sneaky redneck" method. Old chain keeps ok, but the sync marks are off the alignment, I also need to clean the head and piston from carbon deposit - I think because of that I get a spark plug knock, so the same time I will change the chain. Are there other methods of replacing chains without engine disassembly?

Can it be done? Sure. Is it a good idea? No. The bike chains are strong, but they are not spinning along at 6,000 rpm.

Much obliged for your answer Tierney. What to do then? Timing marks are off alignment by half of the link, I made ignition retarded, but riding with that isn't ok, I just idle it a bit to have a nice time along a coffee. Tearing down the engine isn't an option of cause. I'll do that maybe once rebuilding it in the new casing, maybe. What if I do the following: I'll push both chain pins out of links not entirely, just to split the chain, then I will connect new chain to the old one by the pin-less end and then, I'll press old piin back to the place and will tow the new chain around sprocket down inside engine then, I'll disconnect old chain moving old pin out and assemble new chain now fully pushing new pin back in place. The chains are made this way - pushing pins in - no? Timing chain pins, differently from cycling chains pins, not experiencing lateral force, just longitudinal, they also not having torsional load too. They are much like steps of the ladder, well, maybe I could try punching the craters at the ends of the pin with the metal punch, so riveting it a bit, if somebody will hold an anvil vertically. Would that work do you think?

On a bicycle chain - once you break a pin (push it out), that pin is done. Be it SRAM / Shimano - doesn't matter. But they are designed to be broken - so the remaining parts of the chain are intact.

So then you have the option of using a specially designed pin, or a quick link to re-connect it again. Re-inserting the original pin that you removed won't work properly. Plus, even when using the specifically designed pin or quick link - that will always be the weak spot. Hence most of them being single use.

Ps If a bicycle chain breaks, you might hurt your bottom/groin, or your shins… but you won't destroy your heart valves. 😂

How are you moving the chain to determine timing? You MUST move the crankshaft in the same direction as when the motor is running - i.e. CCW.

Otherwise you will be fighting the tensioner and you'll be off in your timing - by up to half a link...

There is no way to install bicycle chain by not shortening it, except maybe long-wheelbase touring bikes may accept stock chains, I might imagine why cycling chain brakes but cam chains breakage is a mystery - wrong ignition settings? The camshaft should stop rotating and then the chain will break.

Can you confirm you were rotating the crankshaft in the correct direction?

Thank you jimc, I do rotate crank shaft CCW, there's rotation direction on the magnet too. I thought to measure the difference and move pick up, but that's too much effort for a temporary fix.

To be exact, I rotate variations side crank CCW, magneto's side is clockwise as the arrow indicates. The chain is worn down so you can hear it clanking by rotating the crank back and forth. At the beginning I thought it is a loose rod bearing sound, happily found it is a chain clanking and, visually it extends and contracts as I wiggle the crank.

how do the tensioner and tensioner guides look?

sounds like you have a wear issue or failure in there somewhere. it's hard to believe that a chain would stretch enough to max out the tensioner components and still be serviceable. that's living on borrowed time, imo.

at this point I'd just pull the motor, split the cases and knock a new chain in there. it's a fair bit of work, but not expensive by any means.

Thanks greasy125, I didn't remove the head yet, waiting for the gasket and chain to arrive, the automatic tensioner has almost reached its length limit, several clicks left. If I make chain tensioning manually by one click it almost fixes the situation. And that's maybe the idea, you might be right - the guides may be out of shape! I'm close to the idea of not breaking the chain.

Perhaps you just need new chain guides? I've never heard of Piaggio timing chains stretching, but I guess there's always a first time.

There was same problem of chain stretching with ET4 some years before (https://modernvespa.com/forum/topic166510)
I couldn't get the answer how did it solve. Indeed, the chain can't stretch that much so half of the link's length would go missing. I'll try pulling the engine out tomorrow and let you know what happens. Thank you all for walking me away of the edge of the abyss!

Releasing the head bolts seems to be fixing the problem. New gasket, before get squished is 0.5 mm thick and the squished old gasket is 0.3 mm thick. Head bolts are 30 Nm max. - they maybe were overtightened, because I saw there was a small oil leak between cylinder and the head, so previous owner maybe attempted to fix that by tightening head. 5 clicks left on the tensioner. Going to clean carbon deposits that arent awfull, will screw head back with the new gasket, to see what to do next.

Lower tensioner shoe looks new. Another manual, from ET4 leader which is exactly this motor, it says tightening torques for the cylinder head main bolts are 11.8 ft lbs or 16 Nm - twice as less as the Lx's 150 manual says. I assembled it with the old chain, and measured the tensioners resource leftover - 1 click was recovered, now 6 clicks till the end. Timing mark mismatch is almost invisible and within reasonable chain wear limits. Thank you all for helping me not to ruin my time!

To complete the story propperly, I'm writing an update: I replaced the timing chain with a new one in the correct way. I was lucky that my transmission cover was old style and I didn't need special tools to open it. It took 6 h, but I didn't need to pull the engine out of the chassis nor remove the cylinder head. Yet I would suggest doing so since it would be a much easier and quicker performance. I didn't pull the engine out just because I did it the day before and such a repetition would be mentally difficult. Thanks to everyone pursuing me not to break the chain, now I see it was an absolutely silly idea.