So the rebuild begins

[Gixxer340]

OK, so the piston basically grenaded. Shrapnel everywhere. I would like to get some advise from the group on a few things.

1. How do I get all of the pieces out of the bottom and and what should I inspect for to determine if the cases need to be split?

2. Should I go through the trouble and just split the cases anyway? Just significantly increases the time it will take me to get this thing up and running again but, if I have to, I have to.

3. I assume I should have the cylinder at least replated but I have included pictures for opinions. Maybe there is some thing that makes it toast and I would like to know that before I send it out to be done.

4. The head has some dings in it. Is this usable or should I just replace it? I would normally just replace it anyway but, it was modded by RB and I don't think that service is available any longer.

Any advise would be greatly appreciated.

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[Gixxer340]

More of the cylinder

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[Gixxer340]

Also, the best place to buy a piston kit, with all the necessary gaskets would be appreciated as well.

Thanks again,

[tucker]

What caused that?

[SS109]

That to me looks like a cast piston run past it's service limit (fatigue) or a seriously defective one. How old is that piston?

Ok, to answer your questions...

1. Refer to #2.

2. That engine needs to be torn down and a complete rebuild done. There is absolutely no way you can guarantee you've gotten all the pieces of the piston out. The pieces already have, or will if you don't get every bit out, damage the main bearings and possibly your new piston and cylinder. Time to split the cases IMO. Get a new connecting and have the crank rebuilt as I'm sure it's long overdue for it. I would recommend Crank Works since Cooksey isn't doing cranks any more. (http://crankworks.com/)

3. That cylinder I'm sure is salvageable with a replate. Contact Millenium (https://www.millennium-tech.net/) to get it done right. They can even supply the piston so the bore and piston will match.

4. I've seen worse looking heads reused. You could send the head in to Millenium as well and they might be able to machine it again. If not, you could always sand it by hand to remove any sharp spots (don't sand the gasket surface!) that could lead to detonation and just bolt it on. Lastly, you could get another head and send it along with your cylinder and have Millenium machine it, setting the squish, while they have your cylinder and piston.

Please, go with a forged piston. They don't come apart like a cast piston and can take longer service intervals without self destructing. Yes, they'll lose compression and power like a cast piston but won't grenade if you get lazy and put 200 hours on it.

[Gixxer340]

Thanks so much for the input. Just what I needed. As for your question; I don't know how old the piston was. could have been original for all I know. I bought the bike a couple years ago and I know the previous owner was not the original owner either. I should have known to change the piston but I really had no idea what it had on it. And I don't use the bike much. I guess I live, I learn.

What do I need to split the cases?

Thanks again
Jeff

[kdxsully]

You’re going to need a flywheel remover, clutch holding tool, a case splitter, and a crank puller if you plan to do the job yourself. Maybe a gear jammer. Close to $150 in tools.

[SS109]

Any used bike that you have no clue how many hours are on it it is always smart to install a new piston straight away.

You can do the job without the crank puller (using the heat/freeze method) but all the other tools I consider pretty much necessities.

[javjacob]

What SS109 said. Time for a full rebuild. Send the crank to Crankworks and send the cylinder to Millennium. Get a Wiseco piston kit and as for gaskets either OEM or Cometic.

[Gixxer340]

Thanks for all the additional info. I have some of those tools already except for the case splitter. Any recommendations on where to get that, or who make a good one.

Jeff

[SS109]

I have the Tusk case splitter sold by RMATV. It works great.

[kdxsully]

Yes, the tusk one. I’d recommend the crank puller over the heat freeze method because there’s less pressure to get it together and possibly screw something up. But it does work. I like installing bearings like that though.

[SS109]

Yeah, the crank puller makes it easier. I like them for being able to get the crank centered right where I like it. I know it's not critical but I'm a little OCD about it.

[tucker]

Are cast pistons that bad? I have never had one go boom on me. Assume it is because they get run too long?

[SS109]

Are cast pistons that bad? I have never had one go boom on me. Assume it is because they get run too long?

I've run cast pistons plenty with no problems. I actually really like Vertex cast pistons. Like you rightly assumed, running a cast piston too long, which leads to metal fatigue, is the issue. If you're religious about it and change them out every 100 hours I'm sure it would never be an issue. Of course, I would never even think about cast in a 220, only the 200.

[kdxsully]

Are cast pistons that bad? I have never had one go boom on me. Assume it is because they get run too long?

I've run cast pistons plenty with no problems. I actually really like Vertex cast pistons. Like you rightly assumed, running a cast piston too long, which leads to metal fatigue, is the issue. If you're religious about it and change them out every 100 hours I'm sure it would never be an issue. Of course, I would never even think about cast in a 220, only the 200.

The one benefit of cast that I like is it’ll expand at the same rate of the cylinder. Less chance of seizure. If you’re warming up your bike properly you don’t have to worry about that, of course.

[SS109]

Yeah, anyone who doesn't warm their bike up before ripping on it deserves a piston seizure IMO! That said, metallurgy has come a long way in the past 40 years. The risk of piston seizure with modern day forged pistons isn't nearly as bad as it used to be. Just warm your bike until you feel heat in the radiators and you're good to go.

[tucker]

Okay that kind of confirms what I thought - cheers. I use vertex pistons in my 2018 YZ125 and the results are great. I change my piston every 35 hours though.

[SS109]

If you're changing pistons that often then the cast Vertex will be great for you.