Soft seized - Am I fucked?

I've been fixing up a Vespa Bravo that belonged to a friend of mine. It's got a Malossi 65cc kit on it with a Proma Circuit pipe. It's been one damn thing after another with this bike. I finally got it up and running, then the aluminum head gasket blew. I fixed that, and it seemed to be running great again, but after hitting 40 or so on a long flat, the engine halted completely and while the back wheel didn't lock up, the clutch immediately acted as a hard brake.

Taking off the cylinder, looks like I soft-seized. The culprit seems to have been a leak around the paper gasket on the cylinder base, though it wasn't ripped. It did run after I let it cool down, without any obvious problems. My question is this, though--judging from the scuffing on the piston and cylinder, is there anything I can do to clean that stuff up (and if so, generally what does it cost)? Secondarily, the bottom piston ring broke (I believe this is a result of me trying to get the cylinder back on, not the soft seize)--can I run with just the top one, or is that like, super dumb or whatever?

Thanks for any help and/or advice.


Re: Soft seized - Am I fucked?

Overpriced Parts /

More like too high Timing, not jetted right, Not protected by head temperature gauge and or you blasted too long without a good long break-in,

A good break at normal moped speeds/short full throttle runs in is needed because when new piston to cylinder clearance is very tight it doesn’t have a good size gas oil mix cushion between piston and cylinder and gets hot and expands very quick so it locks up

But if you give a good 300 mile break-period both parts wear together allowing more space for the gas oil mix cushion to form,

During the break in You’re able to figure out Bad you timed it wrong, jetted it wrong by different runs, Spark plugs readings, head temps whatever.

Some people may tell you to run that kit, there’s no way I would,

Why would somebody want to run a cylinder and piston that looks worse then one has 10,000 miles of normal wear on it on it

Re: Soft seized - Am I fucked?

Break-in? No, this kit has been around since 2005 or 2006 and had many miles on it. Not a break-in issue.

Tuning? Maybe. But again, it's run for a long time before being put on ice in 2007 until 2020.

Timing? Unlikely, for the same reasons, as well as the fact that I never messed with the timing, and it runs like a champ in general.

Since my engine was smoking copiously due to burning oil leaked out onto the cylinder, and since there was a clear oil trail between the cooling fins on the underside, I'm going to stick with my original diagnosis of air leak around the base gasket. Thanks though.

Re: Soft seized - Am I fucked?

I know roffman is not wrong. But, it is just mopeds man. I have had a few kits of mine soft seize. Usually going downhill and probably not advanced enough timing. However I have put hundreds of miles on soft seized kits with no additional issues. I will remove the head and inspect the cylinder. If it feels smooth still and not scratched or pitted in any way then you are good to run it still. The shape of your cyl matches the shape of your piston and rings.

You can obviously still end up with some blow thru but it wont be much. Obviously address your possible causes such as air leaks or timing, but running it can be just fine.

My concern now would be that you snapped a ring. The new ring will not match the new shape of the cyl as well as the ring that was in during the seize. You can lightly smooth out your cyl if it feels scratched up, but any amount of material you remove from the cyl walls will be gaps for gas to blow thru.

Again it's just mopeds. Be safe but have fun. Fix thing when they break

Re: Soft seized - Am I fucked?

If it were mine , I'd simply sand any high spots down on both the piston and cylinder .

Clean the ring landing .

Yes , you can run with just the top ring , no problem .

Definitely use good gaskets . I'd even use a spray sealer on the base gasket .

Sure it makes for harder clean up , but , it also helps seal any air leaks .

Re: Soft seized - Am I fucked?

Did you soak your gaskets or use them dry?

edit: wait I just reread your post... its aluminum so nvm (edited)

Re: Soft seized - Am I fucked?

clean it hone it run it, probly ok. shit happens. base gaskets leak if the studs get loose

Re: Soft seized - Am I fucked?

Hey Matt, remove the one good ring, sand all the seized spots on piston and cylinder with a high grit, put good ring on and run. It'll be fine.

Obviously make sure your gaskets are good a give it a spray down test to verify no leaks.

Re: Soft seized - Am I fucked?

Thank for the help y'all, got some new rings from Treats, sanded down the scuffed parts of the piston and cylinder with 800-grit then 1000, and used a brake hone tool to try and re-hone the cylinder. It didn't work that great since the pads caught on the ports. Whatever. I put it all back together and now it won't start, but that's another issue. Just hoping I didn't put the piston back in upside down. :P

Re: Soft seized - Am I fucked?

the material on the cases might be too narrow to make a good seal with the kit, build up the transfer area with some jb weld to ensure a good seal.

also it needs that fan shroud thingy on top of the cylinder toi. (edited)

Re: Soft seized - Am I fucked?

I’ve had really good luck with the brake hone, you just have to keep moving in and out, at least for me that helped me stay off port edges back when I had any.

Re: Soft seized - Am I fucked?

Richard Eberline /

Done, cooked and throw away.

Re: Soft seized - Am I fucked?

Dirty30 Dillon /

If you were too aggro with your honing, which may be because you were snagging ports, it's very possible you tossed your bore too wide.

Re: Soft seized - Am I fucked?

Hey Matt,

I'm glad you're working on Sean's bike. One of my fondest MF memories is you using the power of the variator to help push Sean up a hill that his bike was struggling on.

Also us installing that malossi kit on my old kinetic (and me breaking my first piston ring). Good times.

I hope you're well.

Brian. (edited)

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