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seized engine ?

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Apr 26, 2007
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#1
My beloved CR 125 was working well then kind of stalled on me mid way through a corner of a MX circuit. I can not move the kick start . I can change gears and roll it in neutral. Have I seized the engine and if so does that me a complete replacement is the best action??
 
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Oct 19, 2006
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#5
Excessive heat causes engines to seize. This could be caused by a lack of oil, cooling system not functioning properly, excessive blow-by of the piston rings, etc... Basically, whatever causes the piston to expand in the cylinder until it actually binds up.

There is another type of seizure, which would be a bottom end bearing including either main bearing or the connecting rod big end bearing. These can be caused by excessive wear or lack of lubrication.
 
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#6
Great info 76GMC1500.... I did notice heat from the bike while going up a trail climb about 30 minutes earlier. I have drained the oil and found 3/4 of a liter I imagine that is enough to keep things lubed up. The Radiator was full. As you can tell I am not a mechanic but keen as to understand my bike, would you suggest I remove the top end myself for inspection or just leave it for a pro?
 
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Apr 16, 2007
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#7
Before i say anything im just going to say this is exactly why i got rid of the 2 stroke kx80 and got the dr250 4 stroke,
right,the oil you have drained is gearbox oil, they are on about lak of 2 stroke it is totally seperate to the gearox oil, like the guys have sed it can be lots of things, it could of been you were just due and new piston and rings or one of the other things, you need to take the head off and see if the barrel is scored(this is where the piston rings have scraped the barrell and makes the engine incompressed, if the barrel is scored you need it either bored out,relined or a new head(will cost a bomb for a new head, unless you get a reconditioned one like i did) then you want a new piston and rings but before all this you need to flush all those little metal bits in the bottom end, this is vital if you dont get all the bits out one of them will cum up and score the barrel again and all you time and work is down the drain, the best way to do it i say is put your engine on clamp (with the topend off) so it cant move anywhere and get some premix (better too use a richer mix than ur usual at first) pour some into the bottom end and keep pulling the kickstart up and down after you've spinned the engine about ten or twelve times, if anything cums to the top be sure you get all of it out then tip the fuel back out and do it again until nothing cums out and if there are any scraping or noises that dont sound to good dont bother puttting the topend back on because there is an 8/10 chance if its making a dodgie noie when the crank is turning the are bits of metal stuck in the bearing and the only way of getting it out is either starting it which it will run for about ten minuites then do the exact same thing again or spliting the engine and checking the crank and it is probs worth renewing the crank too
 
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#8
ok thanks Adam_co sounds like you have seen this before. Looks like I will be spending time getting the head off and checking that barrel. My reason for checking the amount of gearbox oil was I thought the box may have dried out and caused the problem there. I am running 40:1 mixture and had only put about 4ltr through it on the last outing.
 
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Apr 26, 2007
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#9
Well I have removed the cylinder and found the piston missing 1/4 of the front lower edge. After removing 2 broken pieces that had got stuck between the fly wheel and the crank rod there is easy movement of the crank. I have several small pieces on the floor of the crank. Can I flush them out through the oil drain hole using more fresh oil? I have also noticed some magnetic oil plugs for sale are they any good considering what has happened I thought it might be an idea to pick up any more bits that might still be there.
 
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#11
Renegade your crankcase and transmission are lubricated separately,the oil you put in your gas lubricates the piston and crank,transmission oil does not lube the crank except in a few applications not yours!By losing the bottom skirt I would guess its from excessive skirt clearance.I hope you decide to split the cases,about 300 bucks more and you have a fresh motor!
 
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#13
Hey thanks for the info on the crank lube situation I was wondering how that happened, so if I was to only flush the crank with oil to was away any fine broken parts where would the oil be retrieved from? in regard to a previous post to me that my mixture of 40:1 may be to lean I have noticed the crank has a nice thin layer of oil on it so I am guessing the 40:1 may not be to lean ? How do I check my new piston will not have the same excessive skirt clearance problem?
 

IndyMX

Crash Test Dummy
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Jul 18, 2006
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#14
Renegade rider said:
Hey thanks for the info on the crank lube situation I was wondering how that happened, so if I was to only flush the crank with oil to was away any fine broken parts where would the oil be retrieved from? in regard to a previous post to me that my mixture of 40:1 may be to lean I have noticed the crank has a nice thin layer of oil on it so I am guessing the 40:1 may not be to lean ? How do I check my new piston will not have the same excessive skirt clearance problem?

I don't believe you are going to be able to just flush the crank with oil to get any stray broken parts out. If you don't split the cases now, you will most likely be doing it after a short time anyway. And if the bottom end isn't trashed now, it most likely will be when you have to split the cases later.
 
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Jan 22, 2006
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#15
Renegade, your piston skirt clearance problem was most likely due to piston wear. You will have to spend some coin to get that motor back to tip-top shape again. Once you do, you will want to replace piston and ring(s) periodically. Piston and rings for your bike is under $100. Not only will you enjoy having a fresh motor, but it will help prevent having a piston break apart and cause this kind of damage again in the future.

Exactly how often depends on your riding style, oil, maintenance, etc. A compression tester may be a good investment for you, too.