2002 CR125 Project

[honda_power]

Picked this up in the weekend for $500. Has a blown crank. Came with full Pro Circuit system, couldn't really go wrong.

It looks like the tip of a plug has snapped off and been between the piston and head for a bit. I think itl be sweet to run it (the head not the piston), what do you think? Cylinder is fine.

[bogan]

I'd be inclined to give that head a skim, never know what those dents etc will do to the engine dynamics, could cause local hot-spots, or effect the swirly wirlys of the intake/exhaust gasses. Note: I've never heard of this stuff happening, but haven't heard of it not happening either...

pretty lucky to get away with the cyclinder though, I had a crank bearing let go on an 89, one of the balls got jammed between the cylinder and piston for a while, fucking both, the ploughed a couple of mm into the head!

[Brian d marge]

looks like the pinkly monkeys to me , , still 5oo is cheap well done

Stephen

[honda_power]

I'd be inclined to give that head a skim, never know what those dents etc will do to the engine dynamics, could cause local hot-spots, or effect the swirly wirlys of the intake/exhaust gasses. Note: I've never heard of this stuff happening, but haven't heard of it not happening either...

pretty lucky to get away with the cyclinder though, I had a crank bearing let go on an 89, one of the balls got jammed between the cylinder and piston for a while, fucking both, the ploughed a couple of mm into the head!

thanks for your advise, you certainly know your stuff. what do you mean by giving it a skim? a light sanding or a thin layer taken off the whole lot? would have thought that would affect it too?

it was my old flatmates bike, it would have been like that before he bought it which is why im not THAT worried about it.

It certainly is lucky that the cylinder is fine, all those missing chunks of piston must have been blown straight out. Your 89 certainly sounded pretty nasty.

[bogan]

thanks for your advise, you certainly know your stuff. what do you mean by giving it a skim? a light sanding or a thin layer taken off the whole lot? would have thought that would affect it too?

it was my old flatmates bike, it would have been like that before he bought it which is why im not THAT worried about it.

It certainly is lucky that the cylinder is fine, all those missing chunks of piston must have been blown straight out. Your 89 certainly sounded pretty nasty.

my first thought was to machine (mill) off the dents on the head, as the bad ones aren't on the dome bit, as iirc there is no coating on the head so it should be fine to do that. But you could probably do just as good a job with a dremel or similar and sanding bit, just to smooth out the surface. Make sure you don't get the surface that mates to the cylinder, stick the old head gasket on it when you clean it up to be safe.

One of the factors involved in most cracks is a stress raiser, which is generally a sharp point in the metal which causes the force lines to concentrate, which is why in many case removing material to make a smooth surface will make it stronger.

Yeh as you say, if its been like that for a while it probably won't matter too much. But i'm of the opinion if you see something that should be fixed, fix it, always!

That nikasil is bloody hard stuff, I'd give the porting and powervalves etc a very good check as well though.

Yeh wasn't too happy when my 89 carked it, didn't have the mechanical aptitude to do anything with it at the time so sold it off for cheap.

[honda_power]

my first thought was to machine (mill) off the dents on the head, as the bad ones aren't on the dome bit, as iirc there is no coating on the head so it should be fine to do that. But you could probably do just as good a job with a dremel or similar and sanding bit, just to smooth out the surface. Make sure you don't get the surface that mates to the cylinder, stick the old head gasket on it when you clean it up to be safe.

One of the factors involved in most cracks is a stress raiser, which is generally a sharp point in the metal which causes the force lines to concentrate, which is why in many case removing material to make a smooth surface will make it stronger.

Yeh as you say, if its been like that for a while it probably won't matter too much. But i'm of the opinion if you see something that should be fixed, fix it, always!

That nikasil is bloody hard stuff, I'd give the porting and powervalves etc a very good check as well though.

Yeh wasn't too happy when my 89 carked it, didn't have the mechanical aptitude to do anything with it at the time so sold it off for cheap.

ok thanks for that, will borrow a dremel and give it a cleanup. i can see what you mean about the stress on a rough surface.

yeah ill def give everything a good clean, powervalves full of black gunk

[honda_power]

so the cranks out, gave everything a good blow out with an air gun.

Seems the big end gave up. Crank bearings still seem fine, no up/down movement and not graunchy. what do you guys reckon, keep them or replace them.

[barty5]

so the cranks out, gave everything a good blow out with an air gun.

Seems the big end gave up. Crank bearings still seem fine, no up/down movement and not graunchy. what do you guys reckon, keep them or replace them.

for $30 odd each id replace them not worth the hassle if they fail soon after they are going to come off any way when you put in a new rod kit

[honda_power]

the last ones i bought were an all balls kit with seals for $90. Being a student im trying to save every cent haha... iv given myself a grand to buy and finish the whole bike

Iv got another crank to install already, my old neighbor used to race cr125s and luckily hes still got a hell of a lot stuff lying around for them, this crank was reconditioned and never installed.

[CHOPPA]

Id be putting a CR5 in it!

[honda_power]

i wish... cant afford a cr500 especially to tear it down just for the engine. You really need a 250 frame for that anyway, youd have to modify the whole engine cradle and even then the pipe still hits the front wheel

[B0000M]

is the 250 frame actually any different?

[honda_power]

yes, the engine cradle is a different shape, theres a few other changes as well, i know one prob with a 500 in a 125 frame is that the pipe hits the wheel when the forks compress

[tommorth]

custom pipe... what bout an xr600 motor

[honda_power]

all done, goes really well for a 125, may keep it for a while but if anyones after a mint 125 flick me a pm with a decent offer. not gonna let it go under value though. pro circuit full system, boysen reeds, reconditioned crank, wossner forged piston, race tech springs, have new graphics not yet installed etc etc