Modern Vespa

I need the collective help of the forum. I was riding my GTS at a steady speed of about 25 mph when without any warning whatsoever I lost power. It seemed to be running perfectly. There was no knocking or any other unusual noise. There were no warning lights and the oil level is fine. The starter button produced a click but nothing else. One small, fortunate thing was that I was pushing distance from home.

I removed the transmission cover and variator. Everything looked normal but ominously the crankshaft will not turn. At all. In either direction. The next step would be to remove the valve cover and/or starter to see if there is anything obvious. It's getting late and with the holiday weekend coming up it might be a few days.

I'm wondering if possibly something like the starter drive might have come apart and wedged against the ring gear. Do you have any ideas as to what else I should look for?

Thanks.

Last edited by vintage red matthew on Tue Oct 20, 2015 6:30 am; edited 9 times in total

sounds like the charging system lead the a low battery.

Even with the plug out?

I haven't pulled the plug yet but it's not compression that is keeping it from turning over. It is locked up much tighter than that. The motor will not turn at all even when I put a small pipe wrench on the part of the crankshaft that is not splined. I did not get too aggressive with the pipe wrench. I used about 20 ft/lbs and it would not budge.

Just thinking about what's in a Vespa motor that would really lock up a motor I get starter motor jamming, timing chain failure or something in the cylinder. The oil and water pump along with the flywheel come to mind but I think you could still turn the motor with those 3 affected. Anyone have any other ideas?

Ominous was the right word. Could be a thrown valve. Whatever, it's engine out time.

Probably so. It seems odd to me. Traditionally a dropped valve happens at high RPM. This happened at not much more than idle speed. What about the possibility that something went acropper with the starter gear and/or Bendix? Before I pull the motor I need to have a peek under the valve cover and pull the starter. I am currently in the process of the early stages of buying a house so that is likely to consume my attention for some time to come. Luckily, in the mean time I have a new Buddy 170i to ride. I am open to any other ideas and I will keep you posted.

There is no bendix gear on a GTS250 - it's a sprag clutch ('freewheel'). Yes, they can disintegrate, but I doubt they'd make the crankshaft go rock-solid.

A magnet might have shattered and jammed in the stator I suppose, but there would probably have been a little warning of something amiss if that was the case.

It's all much easier to work on with the engine out...

With the variator removed, there's no stack pressure on the left shaft of the crank to secure the oil pump sprocket, so a seized oil pump wouldn't cause this condition.

Help me understand your problem. You were able to 'push' the scooter home but the crank is frozen. How did you do that? So before disasseembling the tranny was the rear wheel turning freely?

That should be no problem. He did not say there was anything wrong with the the CVT. According to what was described, this would be no different than you pushing your scooter around with it turned off. You can move your scooter around without the engine running correct?

The rear wheel is not mechanically attached to the motor unless the motor is turning fast enough to engage the clutch.

I haven't investigated further yet. I took the sidecar off my P200E but as I speak I am broken down on the side of the road with it. I started a thread on the NSM side for that. Haven't had much luck with scooters this weekend

BTW help ison the way.

Just for clarification. I did not mean to be dense. Mea culpa.

I had a flywheel come apart and lock up the motor, so that's worth checking. But first, drain out all the oil and check it for particles. Run a magnet through it. See if you get more than the usual amount of debris in it. Check the screen for fragments. If there are any metal fragments, the type and size of them will give you a clue as to what went wrong. If there aren't, I would definitely take a look at the flywheel before dropping the motor.

I am thinking Motovista is on to something that might solve the problem. In the GTS the water pump runs together with the crank shaft. It could be related to it. Not sure if that's what it was meant by the flywheel.

Thanks Max. Hachi had the same problem with a flywheel, I think.
If the top end let go, you will usually be able to tell when you take out the spark plug, because it will be mangled, or have metal fragments in it. I would also do that before dropping the motor.

Good idea. I'll do that.

Thought I would let you know what's going on. Not much. I am buying a house, moving and getting my old house ready to sell so iI have literally not had a free evening to work on it until a couple days ago. I pulled the spark plug and it looked fine as did everything under the valve cover. Then I removed the stator and was disappointed to see that everything looked good there too. I was then able to get a wrench on the crankshaft and got the motor freed up a little. It now turns easily either direction about 3/4 turn until it hits an obstruction. The next step is to get the motor out and the head off. I sure hope the problem is in the top end and not the crank or rod.

Wish me luck.

There were no odd noises from the engine when any of this happened ?

When it first happened I thought it was an electrical problem because it was running perfectly at low rpms and it coasted to a stop as if the switch had been turned off or a fuse had blown.

0n the left end of the camshaft there is a cap held on by a small bolt. Under that is a plate that does not seem concentric with thecap piece. I hesitate to take off the cap because I don't want to drop anything down into the motor. I tried to take photos but my phone camera does not have a flash and I have been strugeling to get light in there.

Can anyone tell if this is normal or if it's safe to take the end piece off?

Thanks.

that all looks kosher.

quick question... is the motor out?

-g

Not yet but it's pretty close. Most things are unhooked. I could probably have it out in an hour or so.

pull it and post a pic of the valves/head straight on.

also, you got any pix of the stator/flywheel and the plug?

-g

I think I'm going to stop for tonight. Getting a little frustrated. I'm not sure what my schedule will be for tomorrow evening. I'll try to get the motor out then if I have time.

holy shit! what happened to your oil filter?!?

hmmm... that all looks okay...

how'd the oil look when you drained it?

-g

also, in the pic of your flywheel. on the gear there... is that metal debris or something elese-- oil bubble, grease, lint, etx?

before you go tearing shit apart, run the crank nut back on there and see if you can turn it over. it takes a bit of force, but seeing that the nut goes on at 60 lb/ft you should be fine.

hell, with the plug out you should be able to run it over by hand with the flywheel even.

if it holds up, then you gots a problem fo' sho'

-g

I drained the oil to look for debris and I didn't have a proper oil filter wrench so I used big pliers. Oil was free from metal particles, by the way.

it's all good, i use pliers just the same. i didn't know if you had removed it or not, hence my surprise.

hmmm... the plot thickens.

keep the updates coming, the cause is there... somewhere... hopefully it's something simple!

-g

Matthew, I see you saw Waspmans post that he had a seize on his 250 on our ride back from Italy in June. Turned out a head oil channel got briefly blocked, leading to a broken camshaft. Maybe something to rule out anyway - here's his threads again...

Seized GTS 250? Thoughts and advice please.

Italian Aftermath...GTS250 engine rebuild

Got the lump out but no definitive answers yet. The top ends of the valves look OK. The valves can be compressed with a wooden hammer handle. The exhaust valves are a little harder to push in because they are partially open. I think I know the answer but the next step is to take off the head, right?

I would pull the cam and inspect. What are the valve clearances currently? Good valve clearances and a clean visual of the cam would be enough for me to call it good.

That would leave the lower end a suspect. But on a bike with good oil & regular changes I have never seen a 4 stroke Vespa lower end fail. Sure it happens, but apparently not much.

Sprag bearing nackered?

Good luck with it.

R

I can't check the valve clearances because I can't get a full revolution of the crank. Starting to look like a lower end problem.

Dusting off my spare motor.

Check that. Not so sure. I stuck a screwdriver in the plug hole and the obstruction occurs near the top of the stroke. Could the timing chain have jumped a tooth causing the piston to hit the valve?

No, the chain cannot jump, unless bad bad things have already happened. Your photos look too good for that.

A sweet replacement motor is a fine option...

Still thinking a bad Sprag bearing is more to be suspected than a bad lower end.

Once again good luck with it.

R

You don't have to line up the timing mark to check valves. As long as the valves aren't being lifted, you should be able to get a reading. If the exhaust valves look a little open no matter where the cam is, that's bad.

Also, you say the crank stops just shy of TDC. Is that overlap or compression? How far in the other direction will it turn? When it stops, is the cam lobe beginning to open a set of valves?

I can turn the crank about 270° in either direction. Turning the crank in one direction opens the exhaust valves. Turning back closes them. The intake valves don't appear to move any, if at all. I will check for clearance when I get home.

I am tending to think it has something to do with the valves because the piston comes up exactly (as far as I can tell) the same amount whichever way I turn the crank. I think next I'll remove the rockers and cam and have a look see. I would rather not remove the head if I don't have to but the odds of that are, admittedly pretty low.

Keep in mind that the cam only turns half a fast as the crank. If you want to check top end v. bottom end, take the timing chain tensioner off, then take the timing sprocket off the cam. Be careful not to drop any pieces down the chain galley. Turn the cam so that all the valves are closed. In fact, turn it the whole way around and make sure it doesn't bind up anywhere. Support the chain so that it can still feed down as the crank turns and see if your crank still stops at the same places.

+1 one to what drew said on the timing chain trick.

but, i'll add, mark it with a paint pen so you can get your timing set lined back up!

anyway, that right there will tell you if it's top end or bottom end.

i can't really tell from the pix if you dropped a valve, but on visual inspection you'd notice one that was "shorter" that the rest...

my money is still on starter sprag clutch or bearing.

-g

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