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Offline TotalNZ

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Piston Diagnosis
« on: July 02, 2013, 07:34:47 AM »
Here are a couple pics of pistons that have been damaged.
Both from my bikes, one's pretty obvious lets see if anyone gets the other.
These first three are from my TM300MX



These next three are CR250



Sorry those pics didn't come out very well.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline Jeram

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« Reply #1 on: July 02, 2013, 07:44:39 AM »
whats the CR head like? same marks?


Burn pattern is ****

Skirts look good

weird scratch marks (or maybe cracks, cant tell from photo) on dome

edges of the piston erroded (or broken away)


Most clues point towards detonation, and I would supect the piston dome marks are from a previous situation.

=too much ignition advance for the given fuel/air/engine setup

so either back off the advance, increase the fuel quality or back off the engine tune.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline TMKIWI

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« Reply #2 on: July 02, 2013, 09:05:53 AM »
Looks like you left the ring in too long on the TM.
Craig at MXparts has wossener in stock for them. I got him to bring some in a couple of years ago.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
If you don't fall off you are not going hard enough

Offline TotalNZ

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« Reply #3 on: July 02, 2013, 09:30:48 AM »
Looks like you left the ring in too long on the TM.
Craig at MXparts has wossener in stock for them. I got him to bring some in a couple of years ago.
Yeah that piston's at the end of it's life at 60 hours but it's had 3 rings during that time so na wasn't any sort of lack of maintenance.
Yeah i get my pistons and most of my other parts from motocrossparts.co.nz they seem to have the best prices and quick delivery.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline evo550

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« Reply #4 on: July 02, 2013, 12:51:51 PM »
The tm pistons look like running lean, and exhaust port getting hot, potential air leak.. does it have a center bridge on exhaust port ?
That CR piston looks like something has rattled around in there, bearing cage, steel reed ??
Buggered if I know.
I look forward to taking home the Chocolate frog prize for this one....
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline TotalNZ

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« Reply #5 on: July 03, 2013, 08:08:39 AM »
Yeah the CR piston is pretty obvious, thats what happens when she's pinging her head off and you ignore it. Combination of lean jetting and old fuel, oops. Had the jets on order too, thought i'd get one more ride in.
The TM's a different story, Was starting to feel a bit soft so i pulled the barrel to find the piston looking like that. What a mess, Pretty disappointed actually this has been the first real problem with the TM. To be honest i'd noticed some porosity in the casting  previously and was never happy with the quality of the nickel plating in the barrel but didn't think this would happen.

Oh well off to the platers. This still doesn't change my opinion of the brand though, The majority of the other components are of a very high quality and beautifully made. Wish they'd payed bit more attention to the plating though.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline TMKIWI

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« Reply #6 on: July 03, 2013, 08:20:58 AM »
Oouch. :(
Haven't seen that in awhile.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
If you don't fall off you are not going hard enough

Offline evo550

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« Reply #7 on: July 03, 2013, 10:46:20 AM »
That exhaust port looks like it's been a bit hot, I noticed the first two TM pistons didn't have lube holes drilled, could that have played a part in the cylinder lining demise?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline TMKIWI

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« Reply #8 on: July 04, 2013, 07:59:40 AM »
That exhaust port looks like it's been a bit hot, I noticed the first two TM pistons didn't have lube holes drilled, could that have played a part in the cylinder lining demise?

The first 2 are the intake side evo. :D
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
If you don't fall off you are not going hard enough

Offline gc8steve

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Piston Diagnosis
« Reply #9 on: July 04, 2013, 10:09:21 AM »
have you checked the tm's airbox is sealed properly , my first piston looked very similar to yours and it was caused by a s#@t seal job at the factory  ><img src=" title="Angry" class="smiley"> ><img src=" title="Angry" class="smiley"> ><img src=" title="Angry" class="smiley">
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline TotalNZ

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« Reply #10 on: July 04, 2013, 10:25:28 AM »
have you checked the tm's airbox is sealed properly , my first piston looked very similar to yours and it was caused by a s#@t seal job at the factory  ><img src=" title="Angry" class="smiley"> ><img src=" title="Angry" class="smiley"> ><img src=" title="Angry" class="smiley">
Hey Steve welcome. Do you have a TM too?
Na airbox is sealed up well, There was pitting in the barrel from porosity in the casting from new. The plating was far from perfect right from the start, I noticed it first time i had the barrel of at 20hrs. The plating has just flaked away in big chunks starting from the small pits.
I had hoped it would last a little longer, But now when i replate it with a high quality job from NZcylinders it'll be better than new.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline gc8steve

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« Reply #11 on: July 04, 2013, 01:25:33 PM »

yes I've got a 2012 tm300en, fantastic bike but unfortunately I've had some issues from the start , first off I had a minor seize , I suspect the ring end gap may have been a bit tight from new as it was  under spec when it was removed after 50hrs but the bike ran fine didn't even notice it had locked up until  I took it apart and saw the damage , 2nd thing was I dusted it pretty good out riding in a big group ( I usually ride by myself so no dust) and it didn't feel right while riding after a couple hours and lost compression, found out later that the airbox seal is a little sus on some from the factory and during pre delivery the shop usually seals them with silicone from the inside but didn't do mine  ><img src=" title="Angry" class="smiley"> luckily I got away with just a hone and new piston and ring , it's been ok so far but i'll have to replace the barrel at some point as mine had a bit of plating missing at the top of the exhaust port when I did the first top end but I still haven't ridden another bike that's as good as the TM !
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline scotty dog

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« Reply #12 on: July 05, 2013, 10:40:33 PM »
Pffff its ya muffler bearings dummy,  on both bike's........ bit if emery paper on that cylinder and it's all good to go
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
F**K THE WHALES......................SAVE THE 2 STROKE!!!!

The hardest part about riding a 4 stroke is telling your parents your Gay!!

05 CR 250