1985 250R Piston Damage

[Helidaddy]

So I bought this a few years ago and it seemed to run fine. I never REALLY rode it, just about two minutes slowly putting around the parking lot before tearing it apart for various maintenances, and it hasn't been run since. Finally got back to it after a while, took off the exhaust and found a damaged piston.







When I took the piston out, there were NO pieces of the ring left! So now I'm thinking... do I have to split the case to find missing pieces or do you think they just blew out the exhaust? This may sound dumb, but would it do any harm to rinse out the case with gas or some solvent a few times by turning it upside down to dump it? (Engine is out)

Can anyone tell what may have happened to this one? I mean, I know it got hot but is there any tell tale sings of the cause? I have no way of knowing the premix ratio the guy was running. The reeds don't have the stoppers and I don't know if they're stock or what. The bike is pretty much stock otherwise.

BTW, anybody know what piston this is? Honda? I'm pretty sure it's 0.25 over, due to a marking on the remaining ring that says 25


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[atc300r]

To much oil in the pre-mix. The oil gets between the rings and when it gets hot it expands and blows out the rings. Iv seen this type of stuff with weedwackers and chainsaw a lot . Some people think 20-1 mix is good then 10-1 should be better.Arts pistons are oem Honda.

[RIDE-RED 250r]

Any chance whoever bored the cylinder didn't chamfer the ports and the ring caught a port window?? Or too tight of ring gap on that ring perhaps??

I only ask because rarely do people who don't understand things go with more oil in the premix. Most go with less in an attempt to address what is really a jetting issue and so forth.

But that piston does look to have some hours on it. Hard to say how long it was run like that.

What you say is interesting atc300r, I have not heard of that phenomenon. Although I run 32:1 in my R's and 50:1 in my saws per Husqvarna's recommendation. The richest premix I run is about 24:1 in my 1960 Johnson 18hp outboard.

[Helidaddy]

Interesting you mention the port chamfering. I'll get better pics of them ASAP but whoever did the cylinder did a horrible job IMHO. I think he even forgot one window.

The ring gap is a good point but we'll never know because it doesn't exist anymore, lol. I'm not sure but do the Honda OEM pistons need the gap adjusted like the Wiseco?

And as for the mix I'm thinking I remember what he said when I bought it, me not knowing anything, I thought it was a little too much oil. I want to say he recommended 20:1 but not sure.




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[nd4speed]

Looks like a ring snag and maybe it kept running on one ring?

Bummer....I have had ring gap be ok out the box and other times I had to file them. But , yeah port chamfers are kinda important.

Rings are real hard metal and having them floating around in your crankcase and in your main/crank bearings would probably be not good.

[yaegerb]

IMO you have several things going on there. I agree that one of the rings caught on a un-chamfered window....likely causing it to jostle and crack in several places. I would like to see the piston wash, can you show pics of the crown? To me it looks like too low octane, insufficient cooling, lean jetting or a combination of those. I would also like to see the cylinder. And yes, I would split the cases to find the missing bits.

[oscarmayer]

looks like ya ran lean, got too much water in it or something along those lines.
You were defiantly starting to burn a hole in the top. the bottom charring and discoloration ring outside the black area is evidence of that. I would not be suppressed to find the rod to be damaged. can we see the top of the piston and the dome and plug?

the piston swelled up form over heating due to lack of cooling and/or lean conditions. (lean can be caused by air leak into the area from bad reed cage gasket, bad intake gasket, cracked intake boot, ETC. but it got too much air for sure at some point.

[Helidaddy]

Ok here's the piston crown...


And here's the one pic I have of the jug before cleaning. I was trying to capture the chamfering...



I will get better pics of the jug soon. I work all night so it'll be tomorrow.

And the rod... What damage should I look for there?


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[yaegerb]

That crown has close to zero wash which indicates a really lean mixture. The other item I notice is the black spot on the on the underneath side of the piston. IMO, lean jetting and/or insufficient cooling. Better make sure your water pump is also functioning properly. Also I would look into getting that cylinder bored and chamfered correctly.

The rod should have zero up/down play and 1/16th side to side is within tolerance. More than that and get a new rod.

[Helidaddy]

The cylinder is definitely getting bored and chamfered correctly. Now I just have to find a place around Sacramento reputable enough to do it. I'll get pics of the plug tomorrow also, but it seemed black and wet IIRC


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[Helidaddy]

One more thing… I cleaned off the carbon on the crown and you can see dings and dents from the debris hitting the piston. Not too many though, so it looks like it was run like this for a while


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[yaegerb]

One more thing… I cleaned off the carbon on the crown and you can see dings and dents from the debris hitting the piston. Not too many though, so it looks like it was run like this for a while


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What does the dome look like?

[Helidaddy]

Dome looks good but I'll get pics of that too.

Looks like the one thing he got right is the bridge relief. Don't see any damage on the piston from that

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[Helidaddy]

Okay, here's the pics. The plug is a BR8ES


Cleaned up the piston a little to reveal the dings

The dome isn't in bad shape. Just a few dings


And the jug, I'll just put links to the pics; I feel like I'm putting too many pictures in this thread!
http://i882.photobucket.com/albums/a...CA96AB2050.jpg http://i882.photobucket.com/albums/a...21A659BF8F.jpg http://i882.photobucket.com/albums/a...9A76642FE4.jpg http://i882.photobucket.com/albums/a...CC83738D61.jpg



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[yaegerb]

I am surprised that dome doesn't have more damage...I do see a few nicks in there and that piston is fried. Make sure that when they have your cylinder they also mill the top/bottom of the cylinder and the bottom of the cylinder head. With that much heat I guarantee its warped.