Engine Seized

[Carbon-Me1]

Hi Guys,

Whilst riding the other day my engine completeley seized locking the back wheel, luckily i was travelling at about 15mph through some quiet town streets, but was still a very scary experience! Had to push the bike back home (about 2 miles).
Does anybody know how i can check which part of the engine has seized? It's a 50cc bike so only one piston to worry about! I'm pretty sure the crank has heat seized (I thought the 2 stroke oil was all i needed to lubricate the engine as well as the coolant, but later found a motor oil inlet which had ran dry)Basically just need to know how i check where the seizure has occured because there is a complete crankshaft on ebay currently on at £35, auction ends tommorow evening and need to know it is that i need to replace and not the top end.

Hope you can help
Thanks

Stuart

Edited by Carbon-Me1 on Friday 22 February 20:25

[r5gttgaz]

9/10 times the piston will be welded to the barrel.

[Fire99]

well looking at it logically,the top end is lubricated by the 2-stroke oil in the fuel mix..

It is possible the piston is siezed by insufficient lubrication to the underneath but i'm probably with you that the crankshaft has siezed due to lack of oil.

now whether it has buggered the bearings is anyones guess but its more than possible.. so having a replacement crank (if its in good nick) is probably quite a good move..

[m3psm]

If it had no engine/gearbox oil it be, as stated above, the piston, but the gearbox is weaker that the crank so I'd look there before the crank.

With the bike in neutral, very gently try to kick it over. If the engine turns over when you kick it gently, then the crank and piston aren't seized. You could still have broken the rings though and/or badly scored the barrel so you'll need to inspect.

If it turn over when in neutral put the bike in third and try to push it slowly with someone sitting on it (to keep some weight on the back tyre). If the engine turns over, try the same in the gear it seized in, then the others.

To ispect the piston you need to take off the barrel. This means carb off, exhaust off and 4 bolts at the top of the head and another 4 or 6 at the base of the barrel. Once off you'll be able to inspect the piston and rings.

If everything is fine with no score marks on the barrel, then you'll need to dig deeper. Splitting the crankcase (even on a 2-stroke) is quite a daunting task if you've never done it before and needs a lot of new seals to put back together, so consider this before you dive in.

Good luck with it and I hope it's just a rebore, piston and rings.

[GreenV8S]

It's potentially a waste of money buying replacement parts until you've taken it apart and decided whether it's salvageable and what parts you're going to need. If there's a crank for sale now, chances are there'll be another one next week when you know what parts you need.

[bimsb6]

GreenV8S said:

It's potentially a waste of money buying replacement parts until you've taken it apart and decided whether it's salvageable and what parts you're going to need. If there's a crank for sale now, chances are there'll be another one next week when you know what parts you need.

cranks all over the place for a moto hispania ? i doubt it .
most likely will be piston seized as this is where most heat is generated and is generally the most common type of seizure on a 2 stroke .

[Carbon-Me1]

Okay, thanks for your help. Tommorow i'll check over the piston and barrel Hopefully it is that because i've rebuilt the top end on an old dirt bike before, but if it's anything else i'm not really going to know what i am doing! The auction ends tommorow and if its not the piston i'll just buy the new crankshaft because parts are in fact quite hard to come buy! Someone mentioned having to replace loads of seals, if i bought a complete crankshaft would i still face this problem? Also M3psm i have tried starting the bike in all gears and it is rock solid.

Thanks

[m3psm]

Carbon-Me1 said:

...Also M3psm i have tried starting the bike in all gears and it is rock solid.

Ouch!

A heat seized piston will usually (but not always) free itself when it cools off unless a ring break and lodged itself in one of the ports so it does sound a tad more serious I'm afraid.

Pull the head off first and look down the barrel to look for obvious signs, then try the barrel and so on.

If you pull the crank case aprt you will need new seals whether you use old or new parts because the oil will findits way out very quickly as will crank case pressure I'm afraid

[bimsb6]

you will need seals for both ends of the crankshaft the gear selector shaft and the gearbox output shaft and a gasket set .thats if it needs a full rebuild otherwise a top end gasket kit .

[Fire99]

correct me if im wrong but after owning a good few two-strokes, the piston will only sieze if its starved of two-stroke oil as that is what lubricates the barrel and top-end.

If gearbox oil has been starved then you are talking gearbox / crankshaft and maybe small-end bearings issues.

I could be wrong but i doubt the barrel has any issues..

[Silent1]

Sounds fairly terminal if it's rock solid

[m3psm]

Fire99 said:

correct me if im wrong but after owning a good few two-strokes, the piston will only sieze if its starved of two-stroke oil as that is what lubricates the barrel and top-end.

If gearbox oil has been starved then you are talking gearbox / crankshaft and maybe small-end bearings issues.

I could be wrong but i doubt the barrel has any issues..

Yep. Afraid you're probably right

[bimsb6]

m3psm said:

Fire99 said:

correct me if im wrong but after owning a good few two-strokes, the piston will only sieze if its starved of two-stroke oil as that is what lubricates the barrel and top-end.

If gearbox oil has been starved then you are talking gearbox / crankshaft and maybe small-end bearings issues.

I could be wrong but i doubt the barrel has any issues..

Yep. Afraid you're probably right

what is a "motor oil inlet pipe" on a 2 stroke engine ? sounds more like an oil feed to the engine from the 2 stroke oil pump to me . of course i could be wrong .