250-500cc Shattered piston on my '11 wr300

What do you think? Time for a new piston? I discovered this carnage tonight after pulling the reed block out to check for cracks because my top end has been flat for the last 6 rides/weeks (but the bottom and mid has been killer) despite changing mains richer and leaner and repacking the silencer. This is a Vertex B size cast piston. Not sure how this happened. I checked compression 4 rides/weeks ago and it was at 198 psi, then looked up the exhaust port and the piston looked pretty good despite having nearly 3,400 miles and almost 300 hrs (180 hrs/2,300 miles since last top end). I'm not particularly hard on the engine. I ride single track in the woods in Western Washington usually lugging in 3rd gear just under the pipe, and I keep the jetting a tad on the rich side. The last few rides have been very wet and I drowned the engine twice in deep puddles requiring trail side triage to purge H20 from the cylinder and crank.

So here are my questions:

1. How did this happen/what are the suspected causes?
2. Where did the fragments go? The upper half of the cylinder and head look ok, but the piston is heavily gouged below the rings, but only on the intake side. No signs of cylinder or head gouging.
3. Do I need to spilt the cases to inspect the crank and look for fragments?
4. Could this possibly be the source, or a contributor to, the lazy top end I've been experiencing?
5. Can this happen to a forged piston, or be less likely to happen?

Thanks!

Intake side = not so good


Exhaust side = looks good.


Top = not bad for 180 hrs (I use Motorex full synthetic at 50:1 w/92 octane non-ethanol)

Age caused that, 300 hours on a two smoker piston is awesome, check your cylinders fine and not out of round and none of the piston took the nikasil off.

Its a tough life being a piston even if your just putting around.
Next time do your piston at 200 hours.

Did it do 180 or 300? I'd say 100 hours tops for a cast piston regardless. Hope bottom ends ok with chunk of piston floating round in there?! Any play in rod n smooth to turn by hand? Maybe time for bottom end to be sure?! Drownins wouldn't have helped things. Go forged piston shouldn't crack them!!!

I would split the case and replace crank and main/rod bearings. Any remaining fragments down there will destroy your new piston in short order.

300 hrs on the cylinder and 180 hrs on this "B" piston (120 hrs on the original oem "A" piston). No vertical play in the rod and it turns smoothly by hand. Wondering if I washed some/most of the shards out through the sparkplug hole when I purged the water from the cylinder and crank (had the bike upside for this task). I couldn't see anything in the bottom of the cases last night, but vision is obviously obstructed with the crank in place. The cylinder does not appear damaged at all from this, but it looks like most of the cross hatching is worn off. I'll take a closer look later today, and send it off for replating if necessary. Maybe time for a port job just for the heck of it? I'll split the cases. Might as well replace bearing while in there too. Right?

Wow, the 'damage to symptom' ratio doesn't add up here. how the heck did that hold together. i'd say your water ingress incidents must have had something to do with it.

So piston grenaded @ 180 hours wow!
Had a cr 250 that went bang washed crank out with petrol rinse and repeat, ideally split cases but that being said its your machine.
Blow out with airline and keep going untill you know its clear, don't rotate the bearings if poss as you may grind the piston shards into the races..

Cast pistons don't appear to be as durable.

Perhaps the cylinder at 180 should of been re lined.
Your inlet imprint is visible on the piston and the crack seems to follow the lower curve in the left side.

My thoughts is piston slap is the main cause of that one.

Split the case as a preventive unfortunately, especially when you have broken pieces from the piston. You may have gotten the large pieces out but the unknown is whether anymore have been grounded down and now floating in the case oil....you can thrown in kero or diesel to repeatedly rinse out the bottom end.
It can happen to any piston forged or cast but generally a cast piston is more prone to shatter once they reach their service life, much like a modern day car where the timing belts need to be done at 100K (km) and then you drive 10km over and the thing snaps.A forged can take a few more hits and can exceed the service life before it gouges the cylinder wall usually in the form of a cold seizure or shatter...simple replacing rings can prolong the life of a forged piston.
Drowning the motor and not properly clearing it my have contributed to the piston slap but l suspect worn rings and then drowning cooled the intake side quickly causing it to shatter...hard to say really.

Curious Brian, how was the tranny oil after all those drownings?

Dirtdame...how many hours on the 300? At least replace the rings, heck if you're over 120+hrs, forged pistons are cheap!!

I would say water ingestion definitely contributed as well as the grit contained in it as well. Brian, I am not too far from you and I have both the case splitting tools as well as the husky crank installing tools.

ohmygewd, tranny oil looked fine after the first drowning as it was a quick plunge, but after the second drowning, which was quite thorough as the puddle I went down in was 3 feet deep and the bike went over sideways as I lost my footing) the oil was definitely off color, but not a lot of water in it.

rancher1, thanks for the offer. I may very well take you up on that. I think I'll split the cases and give things a look over and replace the bearings while in there.

I inspected the cylinder and there is no more cross hatching. The lower half of the cylinder (below the intake/exhaust ports) has some galling, but above that all is well except for the missing cross hatching. Thinking I'll send it out for replating. Other than Millennium Technologies, who else is a reliable replater? Anyone in Washington state or Oregon?

Thanks everyone! Great discussion. Glad to provide the fodder...sort of.

Powerseal sposed to be good. Dunno where they located. 300 hours not a bad innings for the bottom end anyway-think of it as preventative maintenance(make ya feel better?)

Pretty standard what looks like galling under the ports..take a scotchbrite and wd40 and scrub the cylinder in 45dgree angles and the galling should come off. If there is no visible scratches (feel of a fingernail) then you may have escaped a replate - if you have a bore gauge, or can get a hold of one, measure the bore 10mm from the top and work around from first from intake to exhaust and then 45 degrees using the bolt holes as your guide. Work your way down the whole bore and jot down all the measurements - if everything is in spec then no need to replate.

Water in the tranny means that the bike has probably ingested some water, outta interest, where does the crankcase breather hang? I reroute the breather up to the top of the tank with a one way check valve on all my bikes.

Dirtdame - man that is really great hours!!

PS. Good luck!!

On the WRs once the intake side wears enough to see visible grooves it allows the piston to rock enough to catch the edge where you broke it on the bottom of the intake port and break the skirt. The 300s are worse for this than the 250s but both can do it. Pull your reeds a couple times a year and when you see the smiley face wear in the intake skirt it's time for a piston. You obviously went a few too many hours. It's a big gamble to not split the cases, personally I would split them and do a rod & bearings.

What causes the death smile?

Here's a photo of my piston removed after 4-5 years of moderate use. Bike was running fine as far as I could tell but I changed it just to be safe over the last few months.

http://www.cafehusky.com/attachments/image-jpeg.64530/