Just had to push my bike back over 3 miles after the engine bogged then the rear wheel locked up for a second then died the engine is not locked up though as you can still push the kickstart down and there's still a tiny bit of compression left so what your thoughts I'm thinking I may have done a piston ring. It's typical as I have just had a spare barrel rebored and was expecting it Monday with new piston, rings an small end bearing and was going to swap it over then but my concern now is would any damage to the crank of occurred when it locked up for a second before it died. I will strip it down tomorrow to see what's gone on with the piston/cylinder I'll post some pics up of the damage.
That's unlucky it died just before you swapped it over! As long as there's no play in crank I wouldn't bother doing bottom end if you really don't want to. It'll have to be given to someone who can tear the crank apart if you do want it done. My little KX 100 I got over a year ago was seized when I bought it, and with scores down the cylinder but no apparent damage to bottom end I just replaced the piston + gaskets and the thing is still running today. All be it not outputting anywhere near full power but it's a fun field bike nonetheless.
-- Edited by MIGHTYMAN on Thursday 30th of April 2015 09:19:50 PM
Don't assume anything you will have to strip it down and investigate.
Check big end float and main bearing play. There should be some side to side play with the rod but no up or down. If that checks out then you ought to be alright. However if a gearbox bearing has gone you won't know till you split the cases.
They are so easy to rebuild can be done very cheaply with the bare minimum of tools mate. Under 100 quid for every bearing and con rod, decent quality.
pics as promised it caught the exhaust port and snapped the top piston ring but luckily it stayed in the piston one thing I did notice was there was no peg in the piston where the top ring locates. The crank is fine a theres not a mark on it and zero play I also flushed the bottom end but found nothing in there at all do you think its possible that it any bits went out the exhaust.
-- Edited by gooner78 on Friday 1st of May 2015 04:16:37 PM
Yeah those rings shouldn't be exposed to the ports. I wonder what happened to the peg. What piston is that? Mitaka?
They do make good pistons but personally I just stick to the better ones like Wossner and wiesco. You know where you stand when you spend the extra pennies.
Or of course genuine.
The bore looks okay really. Bit of scoring but could have been worse.
Did you say it was suppose to br rebuilt this weekend anyway?
I was expecting my newly rebored spare barrel and piston kit early next week so was going to swap then one thing I will say though is that it put good ding in the exhaust port that the pictures don't really show. I'll probably flush out the bottom end again tomorrow just to make sure I have not missed anything so it's ready for the new top end. I'm not sure what make the piston was as when I got the invoice for the engine rebuild it just said 56.65 piston kit so it could of been anything.
You have to be careful what you use flushing the engine out with. I don't want to worry but you don't want to be using petrol as it will dry out the crank seals and they may start to weap.
I Had the same issue as well mate locating pin seamed to disappear lol see my piston attached lol :)
had cylinder rebored no issues since "touch wood"
anyway if you're using mitaka pistons FYI
COPIED FROM MITAKA SITE >>>>
Now finally, the most perplexing cause of failure. Ring pegs. On the face of it, if a ring peg moves either in or out, it would be natural to assume that is has not been a tight enough fit. Whilst we have seen batches of pistons where the peg could be pushed in with a finger nail, we have also seen peg failures where the peg has simply been worn away by the piston ring or worried until it has loosened. Under these circumstances, we need to look elsewhere for the cause of the ring peg failure. Obviously the peg is being loosened by the sideways forces exerted by the piston ring. These are brought about primarily by the ring moving in and out of the exhaust port (and to a lesser extent the transfer ports) causing it to change shape. If the ports have been enlarged, this will put extra load on the ring peg and may cause failure. If the peg is in the centre of the piston, the loads on the peg will be balanced and less likely to dislodge it. Another cause of ring peg loosening is damage to the exhaust port bridge. If the bridge has not been relieved after re-plating, serious wear and damage will occur and the plating will fail. This puts loads on the ring and peg, causing the peg to loosen and fall out. When the peg is seen to have failed, this is wrongly assumed to be the cause of the failure and not the result.
In conclusion, if a piston fails it is important to establish the cause of failure before simply blaming the piston and fitting another one.
That is mad its identical but luckily I had a call from the people doing the rebore and they still have not done yet I won't be getting until next week so I'll be getting a vertex piston instead of the mitaka one after reading that.
I Had the same issue as well mate locating pin seamed to disappear lol see my piston attached lol :)
had cylinder rebored no issues since "touch wood"
anyway if you're using mitaka pistons FYI
COPIED FROM MITAKA SITE >>>>
Now finally, the most perplexing cause of failure. Ring pegs. On the face of it, if a ring peg moves either in or out, it would be natural to assume that is has not been a tight enough fit. Whilst we have seen batches of pistons where the peg could be pushed in with a finger nail, we have also seen peg failures where the peg has simply been worn away by the piston ring or worried until it has loosened. Under these circumstances, we need to look elsewhere for the cause of the ring peg failure. Obviously the peg is being loosened by the sideways forces exerted by the piston ring. These are brought about primarily by the ring moving in and out of the exhaust port (and to a lesser extent the transfer ports) causing it to change shape. If the ports have been enlarged, this will put extra load on the ring peg and may cause failure. If the peg is in the centre of the piston, the loads on the peg will be balanced and less likely to dislodge it. Another cause of ring peg loosening is damage to the exhaust port bridge. If the bridge has not been relieved after re-plating, serious wear and damage will occur and the plating will fail. This puts loads on the ring and peg, causing the peg to loosen and fall out. When the peg is seen to have failed, this is wrongly assumed to be the cause of the failure and not the result.
In conclusion, if a piston fails it is important to establish the cause of failure before simply blaming the piston and fitting another one.
Did you find anything in the bottom end after those pistons failed because I got nothing out of mine at all after flushing it out I even had a good route about with with a magnetic cable under the crank to see if I could locate any bits of broken ring or the locating pin but nothing.
Nope nothing in the bottom end, if your rings and piston were intact then i wouldn't worry about it anything should have been shot out the exhaust port
Suspect that it wasnt even a mitaka piston. Hard to tell from those photos but theres plenty of cheaper 20 quid piston kits on ebay available. I've never had an issue with a mitaka piston personally. Have you checked your PV clearance? could be that it was hitting that which caused the ring to wear, then brake.
Suspect that it wasnt even a mitaka piston. Hard to tell from those photos but theres plenty of cheaper 20 quid piston kits on ebay available. I've never had an issue with a mitaka piston personally. Have you checked your PV clearance? could be that it was hitting that which caused the ring to wear, then brake.
The cylinder is pretty much scrap now as I sent it for a rebore and they said the damage to the exhaust port was to deep and it needs to a new liner and I'm not paying £200 for that so I'm on the look out for decent barrel if anyone wants to sell one.
Ive never had any problems EVER with a Makita piston kit since I can remember even in MX and Enduro bikes never mind a DT. That looks like heat damage that's expanded caught the port and ripped the locating peg out.
Suspect that it wasnt even a mitaka piston. Hard to tell from those photos but theres plenty of cheaper 20 quid piston kits on ebay available. I've never had an issue with a mitaka piston personally. Have you checked your PV clearance? could be that it was hitting that which caused the ring to wear, then brake.
I don't think it was a mitaka piston as the circlips were different.
Suspect that it wasnt even a mitaka piston. Hard to tell from those photos but theres plenty of cheaper 20 quid piston kits on ebay available. I've never had an issue with a mitaka piston personally. Have you checked your PV clearance? could be that it was hitting that which caused the ring to wear, then brake.
The cylinder is pretty much scrap now as I sent it for a rebore and they said the damage to the exhaust port was to deep and it needs to a new liner and I'm not paying £200 for that so I'm on the look out for decent barrel if anyone wants to sell one.
Who is inspecting the barrel? I'd get a second opinion if I were you. Tough to say just looking at the pictures, but the damage doesn't look too bad.
Try PJME is Wolverhampton - very good at what they do.
__________________
Just because I don't care, it doesn't mean I don't understand...!
Suspect that it wasnt even a mitaka piston. Hard to tell from those photos but theres plenty of cheaper 20 quid piston kits on ebay available. I've never had an issue with a mitaka piston personally. Have you checked your PV clearance? could be that it was hitting that which caused the ring to wear, then brake.
The cylinder is pretty much scrap now as I sent it for a rebore and they said the damage to the exhaust port was to deep and it needs to a new liner and I'm not paying £200 for that so I'm on the look out for decent barrel if anyone wants to sell one.
Who is inspecting the barrel? I'd get a second opinion if I were you. Tough to say just looking at the pictures, but the damage doesn't look too bad.
Try PJME is Wolverhampton - very good at what they do.
It was pjme that I used the pictures don't really show the extent of the damage to the exhaust port as it took a quite a nice chunk out of it and has a small crack as well.
-- Edited by gooner78 on Friday 26th of June 2015 04:59:22 PM
