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Reason for piston replacement

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Hey guys..

I have got a 05 Crf250X, Between 50-70 Hours, on brand new bike (need an hour meter) One bad intake valve would like to just throw new valves in and cut the seats, just so I can ride the next few months while I save up for a new piston and maybe a big bore kit... I know it is only a few hundred bucks more... but i am super broke and have already bought my valves...

If I am not burning any oil, havn't noticed any obvious loss of power (though if it decreased slowly I am sure I would not notice)

Why do you need to change the piston if it seems to be working fine? I understand when you are in there it is just easier and makes sense..

Is there a realistic chance of the piston just blowing up and destroying the engine if the rings are not even allowing blow by?

Thanks for the input.

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You should not need to replace the piston and rings on any 05 gas motor with those hours IF THERE was NO OILING or OVER HEATING PROBLEM.

If the intake valve had BROKE that is different and probably destroyed the head.

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Nope the engine is fine and still runs fine, my R Inake valve just keeps tightening up, so I just want to put new valves in and ride it for a few more months...

Why do people change them so often then? are they all burning oil... and why would the engine over heat due to a bad piston??

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No need for a new piston - once you get it back together make sure you do a compression test to ensure that it is in the limits

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Nope the engine is fine and still runs fine, my R Inake valve just keeps tightening up, so I just want to put new valves in and ride it for a few more months...

Why do people change them so often then? are they all burning oil... and why would the engine over heat due to a bad piston??

Horse first, cart second.

The engine would have a bad piston due to being overheated.

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The reason for the replacement is called better safe than sorry. Most people don't have access to the tools to check that the piston skirts are within spec's.

He is one reason.

Due to the piston height and design it is very easy with little wear for the piston to begin to rock in the bore. With just slight wear on the piston skirt the piston will rock and wear quicker, if this continues un checked the piston will begin to smack the head at the top of it's stroke. When this happens and is not caught one of two things will happen...

As the piston smacks the head, this will be transmitted to the rod causing reduced life and possible failure or the piston will eventually fail and then more than likely take out the bore and the rod at the same time....

Bottom line, this is done for the better off safe than sorry reason more than anything.

Now for people telling you that 50-60 hrs will not require a replacement is a load of crap for several reasons. I know that people have good intentions and I am not bagging on anyone, but sometimes advice is dished out with out complete thought or knowing the details. Do we know what level you ride at? do we know where you ride? Do we know what kind of abuse has been delt to the bike? do we know the what maitenance you perform? do we know how often you change oil and filter?

Manuals and manufactures service limits are there for a reason, when in doubt follow them, more than likely the will not make assumptions or feed you poor information (not that anyone has).

Now back to you real question. 50-60 hr is nothing if you take good care of your bike and you ride at a average level.

I change my piston just about every season. I have owned a 400 for 2 years, a 426 for 4 a 450 for a year and half and a 250f. All recieved new pistons every season. This was due to one reason "better safe than sorry". I know not everyone is made of money, I know I am not, but the way I look at it, if I am going to hassle with pulling the motor down to check a piston, my time is worth that extra $100. (once you figure you will be replacing rings already, base and head gasket).

Just my 2 pennies. good luck and fly low..

My point is that you now have been told two totally different things in regard to your piston. What are you going to do?

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Thank you guys for your opinions.. I completely agree with the better safe then sorry.. it is just the situation I am in.. I am a single guy that moves quite often.. so right now I am in an apartment and my bike is being kept at a place where I can not work on it... My right intake valve has gone to zero twice and I do not want to risk dropping a valve...

The bike was bought brand new last summer, it is my first bike and am learning how to ride on it, so have hit the limiter a few times but not many.. All I ride is trails it has never seen a track.. Rarely sees 5th gear..I change oil every second ride air filter the same and oil filter every oil change..

So my plan is to just take off my stock head at a buddies house.. get the seats ground and get new SS Valves put in the head (this will be my future spare head)

Then in about 3 months when I can afford everything at once, I will tear it all down and grease and change everything... Just don't have the time space or money at the moment but would like to get a few more rides in..

So all that considered, when I take my head off if I do not see any obvious damage from the piston rocking (would I see anything?) I will cross my fingers on this one.. might learn my lesson the hard way but we will have to wait and see!)

Thanks again and am still open to further discussion!

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The first thing you should do is buy a service manual. It has all the specs for measureing piston dimensions, ring clearances, cylinder dimensions etc. If you can't do it yourself, any good mechanic (Auto or M/C) can measure this for you. A Piston will not deteriorate unless it's abused eg. overheating, impact with valve parts etc. If it is within spec it will be fine.

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In simple terms the piston/rings in a crf250 should be replaced every 70-80 hours, it depends how hard you ride the bike... When the skirt on the piston wears it rocks in the bore creating piston slap and then when the slap gets to violent you get piston faliure. You said that you had 50-70 hours on it, I think it would be fine untill after 100 hours. I am speaking from personal experience.

I put a piston in at 115 hours on my 2006crf250r and my valves are perfectally fine, I adjusted them at 100 hours and when I put in the piston the valves have not moved one bit, that is normal riding, hitting the limiter now and then.

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I bought the service manual, man what a handy book I recommend it to everyone!! All the info I have recieved here is exactly what I was looking for, thanks.....

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