Honda CBR 250 Forum banner

hole in piston

2K views 5 replies 3 participants last post by  shisoshin 
#1 ·
Bought a 2011 CBR250 in the spring of 2014, that the person I bought it from said he drove it a lot for the first year he owned it, but had sat for about a year and with only 3000kms on it i figured he was being truthful.
Within a couple weeks of driving the bike I started noticing oil being forced out of the crankcase into the air filter housing and then filling the tube that exits down beside the kick stand, mostly when revving the bike over 8000rpm.
I figured the rings may have stuck from sitting so long , letting cylinder pressure into the crankcase, . So tried pouring some seafoam directly into the cylinder thru the spark plugs hole and letting it sit to see if it would loosen up the rings. The bike worked like a top for about three months before one day the bike started acting a bit strange for a few days before finally stalling and would not starting again.
Tore the engine apart this winter and found a hole in the top of the piston right where the intake valve relief meets the edge of the piston. The hole exited out the side of the piston right at the top ring grove. The top ring had broken into at least 10-12 sections, and where the hole exited, it scored the cylinder wall.
I'm guessing the engine had been run lean at sometime causing the sharp hump where the hole burned thru to over heat and melt thru the piston, but again thats just a guess.
Don't want to rebuild the engine just to have it happen again so was hoping to pick some brains on here to see if anyone might have a more informed opinion and what to check before rebuilding.
 
See less See more
#2 ·
Within a couple weeks of driving the bike I started noticing oil being forced out of the crankcase into the air filter housing and then filling the tube that exits down beside the kick stand, mostly when revving the bike over 8000rpm.
That's actually normal at those revs from what I hear and no reason for concern. But maybe some of the more experienced guys can confirm that.
 
#3 ·
I might have understated the problem of the oil being expelled by the motor Schroeder...lol..after driving the bike just a couple miles at high revs, the tube would fill up, and the oil would start to back up into the air filter housing and then start dripping out the little opening in the bottom of the housing I assume is meant for letting out any water that may accumulate in the housing. It would make quite a mess as it dripped down thru the bike and on the ground.
I believe the hole may have been in the piston for some time but because it exited the side of the piston at the top ring groove then the second ring kept most of the cylinder pressure from bypassing into the crankcase at 5000 rpms or less. But at the higher revs the second ring just couldn`t contain the pressure. Looks like the bike continued to operate until finally the gouge in the cylinder wall, caused by the broken ring and sharp edges of where the hole exited the side of the piston, became so deep that the cylinder compression became so low that the bike would no longer start or run.
 
#4 ·
what is 'acting a bit strange' for a few days ?

i'm not an engineer,, but one symptom is that oil
being 'forced out of the crankcase into air filter housing' etc,
which aside from overfilling with oil, could be effected thru
blow-by due to rings not being seated in over careful run-in
period [not, revving engine to high revs and back during
the first phase of run-in can cause rings to fail to seat]..

one factor to check is overheating, due to inadequate cooling
[loss of coolant fluid, ineffective pumps/seals etc]
gunk in fuel injectors might cause lean burning [heat]..

wrong plug tho unlikely could be one factor..
5hit fuel [including ethanol] could also play a role
if way to low octane thus fast burn combustion chamber
causing localised heating effects..

'it worked like a top for three months' takes a direct
causation further away from that storage period..
sounds on the face of it like a combination of factors,
possibly starting with the rings..

another good reason incidentally for buying new
when you know its been run in properly etc..

if you do rebuild it, best shot check everything
possibly related to overheating..
at least you will start with a fresh engine
with its fate in your own hands..
 
#5 ·
Thanks for the reply Shisoshin

The acting strange for a few days was just stalling a couple times, when coming to a stop, and hard to restart. Also while driving along it would feel like the engine would quit but restart right away, sorta like a bad misfire. Which I now assume was the compression getting so low the engine was barely operational. This lasted for 3 or 4 days before the engine finally gave up the ghost.
I am in the middle of rebuilding the engine, with all the parts already ordered,(piston, rings, cylinder and gaskets) just waiting for them to arrive. Since it looks like about a week for the parts to get here I figured I`d ask for some opinions about what might have caused the piston hole.
Since I bought the bike used I have no idea how it was treated or maintained before i got it and i`m leaning towards the hole had already started in the piston when i got the bike, and proceeded to get worse over the time i owned it.
I checked the injector, the ohms range is in spec and it is being cleaned at a local shop. The two seasons i drove the bike, it never showed any signs of over heating with the indicator never going above three bars. Spark plug was the factory one which should rule out something to do with the plug.
Like you say Shisoshan , I'm starting with a new engine and Ill know it will be broken in proper...When I bought the bike it was about $1000 below what most people were asking for cbr250`s in my area, which leads me to believe the seller knew there was something wrong with the engine and just wanted to dump the bike, which of course is just speculation on my part.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top