Aerox (minarelli lc) seized, omg what a story!!

Ben Dover Swe

Well-Known Member
Omg what a story this is!

Was out driving, suddenly I hear this high frequency "PEEEEEEP" from the dashboard. Wtf - I have no such warning speaker? And no warning lights were lit. I thought it must be the speedometer or something. A while, 5-7 minutes, later I start losing power, I get a bad feeling and instantly turn off engine.
Smoke and crackle sounds, the engine is clearly very, very hot. I check the water coolant reservoir - it is empty, and have condensation drips inside.

I wait till engine cools, and walk to a closeby house and get some water to fill in. Check engine temp, it is <100 c (water from cylinder does not evaporate). So I try electric starter - no go. I feel the kick starter, it is very heavy/stuck, but it will move with a bit force - I reckon the piston/rings is jammed.

I wait a while, thinking. Suddenly water comes out from underneath scooter. When checking where water comes from - it comes out from the carb air intake (!) - the intake where the air filter usually is strapped onto (I run without unfortunately). Also zips out from everywhere - the spark plug, the 4 cylinder bolts (long ones), from the gasket between engine block and cylinder.

This tells me 2 things - water is flooded everywhere, even goes up through the reedvalve and out the carb.

Question 1)
Is it repairable, or just sell it as a junk object for $350 instead of working condition for $1000?

Question 2)
Now what, what steps do I need to follow? I am worried about getting out all the water, prefferably without splitting the engine.

Question 3)
What might have caused this? I get a feeling it might be the thermostat, since the "PEEEEP" sounded like an old tea pot on a stove, the water might have stood still in the cylinder head, eventually evaporating and forced out the top. The vapor inside water reservoir also hints the same. If it was a common water leak, then I would not get boiled water, just overheat? (NOTE: Apparently the previous owner did not fancy the heat sensor - it was unplugged). I will check the thermostat tomorrow by boiling it.

Question 4)
What should my shoppinglist contain? New cylinder kit, gaskets, needle bearing, heat sensor, and thermostat if it is broken, I presume - anything else?


Regards!
 
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Quite an adventure you've had there. There are a few things to consider first:
1. Did you use a special coolant, or just regular water? If it's regular water you are lucky and probably don't need to split the crankcase, tho due to the overheating, the bearings might be affected and if that's the case you will need to split it! If it was a special coolant you should have a look at what it consists of and maybe post it here. If it's based on some weird stuff it might be affecting the bearings... :-/ tho usually I think that's not the case.
2. Before you order anything take the head and cylinder off. Most likely the piston jammed as you said. Once it is off you should be able to freely move the crankshaft. It should spin very easily, if it doesn't there is more broken (which most likely means bearings...). You probably need to take the variator out as well and maybe the stator to get a better feel of the movement of the bearings.
3. About repairing: It depends on above. New cylinder is cheap, but if it's more it can get pricey, especially if you can't do the work by yourself!
4. About what caused this: How long were you riding that scooter? You say you run without an airfilter. Have you changed the main jet to accommodate for the extra air in the mixture?
5. Actually most engines run fine without the thermostat and it is actually better to remove it. The reason the thermostat is fitted, is so the engine doesn't run too cool. Stock engines take a long time to warm up when the coolant is cooling them down so much. Once you run a tuning cylinder kit you should remove the thermostat. The peep sound was most likely caused du to boiling water and the pressure it created. It probably caused a leak somewhere, so question remains why did it overheat?
Once we can answer these points we can create a shopping list, tho your list looks quite good already :)
 
Quite an adventure you've had there. There are a few things to consider first:
1. Did you use a special coolant, or just regular water? If it's regular water you are lucky and probably don't need to split the crankcase, tho due to the overheating, the bearings might be affected and if that's the case you will need to split it! If it was a special coolant you should have a look at what it consists of and maybe post it here. If it's based on some weird stuff it might be affecting the bearings... :-/ tho usually I think that's not the case.
2. Before you order anything take the head and cylinder off. Most likely the piston jammed as you said. Once it is off you should be able to freely move the crankshaft. It should spin very easily, if it doesn't there is more broken (which most likely means bearings...). You probably need to take the variator out as well and maybe the stator to get a better feel of the movement of the bearings.
3. About repairing: It depends on above. New cylinder is cheap, but if it's more it can get pricey, especially if you can't do the work by yourself!
4. About what caused this: How long were you riding that scooter? You say you run without an airfilter. Have you changed the main jet to accommodate for the extra air in the mixture?
5. Actually most engines run fine without the thermostat and it is actually better to remove it. The reason the thermostat is fitted, is so the engine doesn't run too cool. Stock engines take a long time to warm up when the coolant is cooling them down so much. Once you run a tuning cylinder kit you should remove the thermostat. The peep sound was most likely caused du to boiling water and the pressure it created. It probably caused a leak somewhere, so question remains why did it overheat?
Once we can answer these points we can create a shopping list, tho your list looks quite good already :)

Yes adventure with murphy and his law :p

1) Bought it this summer and not sure what was in it. Probably just water, he didnt care about it at all.
I will probably split and replace all easily replacable parts though. It has 11 000km (!) on the trip meter thing, 2003 model. 11 something with no leading zeros at least. Will get a stage6 cylinderkit (streetrace or sportpro) and figure that even though the scooter is in very manhandled condition the engine want to be kind of reliable.
The current cylinder is naraku so not stock - prev.owner might have had problems too. Piston had marks of sieze on it before this happened. I saw them before but did not know what it was before image googling in relation to this latest adventure. The mark was 1 big area about as a thumb with some visible wear. We got new rings and tried, worked well so didnt think much of it.
My last trip: i noticed it would die on idle and hard to start when warm, like before but a lot harder to start. Would go around easy but just not start. Eventually did. Needed gasoline so stopped and filled. Would hardly start after this stop. Only with electric starter and throttle at just the right position for several seconds. Very hard to start. (Spark plug was cleaned previous to this trip/start of this story.) Soon after or right before this gas station stop, I noticed the boiling overpressure sound from water reservoir. Some minutes later it slowly died.
Not sure its related but lately i noticed the kick would jam in topmost position. Only when gently tapping it several times, it would release 1 cm and jam again, repeat and then it was loose. So two notches so to speak. I noticed no visible wear on the kickstart gearing, so a long shot is that piston got stuck somewhere. Oh, and the 4 cylinder nuts came loose very easily when disassembling, almost hand power on most of them.

2) cant check that right now im sorry, its in the garage/workshop far away.

4) Trip meter is 11- something with no leading zeros. 11 000 km? Without air filter is at least 100km, probably a lot more. When bought it had 12mm carb with 80 jet, no air filter, Gianelli Go exhaust. The scooter wouldnt start soon after buy, so swapped carb to a 17.5 laying around, among rebuild gaskets etc. Genuine dellorto, choke missing so plugged hole with small hose. Kept 80 jet. It started now, but would die at 1/2 throttle or more. Carb air mix screw made it die closer to WOT, also jetting up made it die later. Biggest jet was 90 and air mix screw all way in, this made it go to 90-99% wot before dying. Its large jet as hell but i figured 17.5 might suck in more air than 12. Hehe might have been stupid when thinking.. :p Beneath cylinder area there were a lot of oily goo residue.

5) Is it possible that this is a result of water leak? Water pump rotates when rotating variator.
 
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