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Post Info TOPIC: Sudden Compression Loss


DTR Newbie

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Sudden Compression Loss
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Howdy,

I was on my way to the MOT station when my 2000(W) DT125r broke down. It just stopped and refused to restart. With no warning what so ever.

 

after cleaning the carb thoroughly, new plug and checking the spark the only thing left was compression.

A compression test came back with 80psi (tested only a month ago at 140psi) :( I am currently in the process of striping the engine to see whats up.

 

My question is:

Whats the most common cause of sudden compression loss? is it more likely to be the crank seals or rings?



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Guru

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head gasket

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i blew my dt up ... but i fixed it.... Then i crashed it.... but i didnt fix it right and 2 scouser's come in the middle of the night and left me with a working bike 



DTR Legend

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First port of call would be to check the state of the top end.....Nothing to do with the carb mate. Sounds like you've got a shagged barrel.

Whip the expansion chamber off, get yourself a torch and have a good look up the exhaust port to check the condition of the bore/piston.



-- Edited by Energized on Wednesday 8th of January 2014 04:42:11 PM

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MDK


DTR Legend

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Could be either and no one is realy gona know till you wip the top end off .

not sure where it is but always good on any forum to add a little imput in other topics and post a hello newbie here thread .
you will find some guys are realy funny about this and will not answer or help out in some topics. as we see a lot just pop in ask a question get a answer then leave with out ever saying if they got the correct answer or if it is fixed .
as you may know when googling for help you get many hits on all types of topics where after reading to the end you never get what you was looking for cus some one never posted if they fixed the problem .

any ways im not like that and will try and help anyone out no matter how many posts they have .

so welcome to our lil forum great to see a new member and hope we can help out in some way once you get the topend off .

ps...post some pics of your dt we all love bike porn


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DTR125CO-1.jpg


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good clean up of a old batterd  dtr  95

 



Guru

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It's a unsophisticated 2 stroke. Like most 2 strokes there are no warning lights for failure. Only way you'd be able to tell is from experience.

Be nice to have a little welcome in the General Section before we spend time helping you :\

There isn't really a common fault it boils down to maintenance and how much.

My first point of call would be as Enny said. Check the exhaust port for damage. If you've had a seizure then you would want to find out what's caused it.

Take it apart and have a look would be my reccomendation.

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The Leviathan Project



DTR Newbie

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Fair enough vis-a-vis the introduction, see it all the time on many car forums i frequent. i will get right on that.

as for the bike its nothing special, just a great introduction to motobikes. Purchased in July to learn on and passed my full Mod2 test in Nov. so i was actually getting ready to sell it till this happend!

 

and this would definitly be the cause of my problems. broke piston ring took the piston with it. 

There is a slight mark on the bore where this happen, (Can feel it) so i think i may need a rebore aswell.

 

I think i will drop the bore into my local garage and see what they think.



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MDK


DTR Legend

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yeah thats the problem lol could also be a underlying problem to cause that maybe.

you collected or found all and every little bit of metal

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DTR125CO-1.jpg


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good clean up of a old batterd  dtr  95

 



Guru

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Best way to know is to feel the bore. I would say from the damage to the piston that chances are it will need a rebore. PJME / Grampian motors are 2 main places to go to. That piston looks like one of the £20 cheap ones from ebay to me. It could be mitaka and thats the cheapest i would go with. I use mitaka piston kits in road bikes but then I dont rag the hell out of them.

Looks like it could have caiught the powervalve. check the size of the bore. should be 56mm or 56.4mm as standard. If its oversized it may have hit the powervalve.

Use an athena head gasket for the rebuild.

Top of the piston looks like its been very hot so i would check your carb settings too.

It looks like its been blowing for a while as its all the way around and quite alot, not just where the rings broken.

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Guru

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And as MDK said, those little bits of metal could easily have gone down into the crank and are making a nice metal paste to eat your bearings away. Not rebuilding the bottom is a gamble.

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