What in the world happened to my piston?!

[Geoffrey]

Ok so this is the old piston. I'm getting a new piston put in tomorrow but... was wondering what in the world went wrong that its chipped off really bad in those two places? The motor never seized it just had low compression and wouldn't run and when he tore it down that's what he found. Thanks

 

[speedyslyder]

Ok so this is the old piston. I'm getting a new piston put in tomorrow but... was wondering what in the world went wrong that its chipped off really bad in those two places? The motor never seized it just had low compression and wouldn't run and when he tore it down that's what he found. Thanks
View attachment 29724

soooo that is the piston that came out of cylinder
how does cylinder look
here are some examples..
http://www.kenoconnorracing.com/Piston Death.html

 

[Geoffrey]

yes this is the piston that came out of the cylinder. well i mean this guy does have a shop and works on 4 wheelers so I figured he knew what he was doing

 

[Geoffrey]

nice! thanks! kinda looks like the sixth which would be the idiot that rebuilt it before me installed it wrong! at least thats what I'm hoping and not some sort of air leak or something

 

[Awk08]

So you're having the cylinder bored/honed to the next size that will remove the cylinder damage ?

 

[blasterboy91]

While you're at it, I would split the cases and have the crank inspected. With as much damage as the piston took, there might be a good chance something wiggled its way down to the bottom.

Enjoy the rebuild, take your time, grab a clymers and a beer. Have fun. Learn something new!

 

[Geoffrey]

Thanks!

 

[blasterboy91]

Can we get an update on how things went?

 

[Geoffrey]

Well we rebuilt it. And it was running. And the power was kina in and out but I figured it was just breaking in. Well the next morning I went to crank it and I couldn't get it to crank. So checked the spark plug and they had forgot to tighten it. And it was fouled Really bad. By the way the guy mixed the gas really rich but he said he just doing that to break it in. Anyway I got a new spark plug and it still wouldn't crank. So I just took it back to the mechanic guy and he called back later and said he got it to crank by pulling it. He said he was gonna let it cool down and try cranking it again and then call me. Haven't heard from him since lol. But I'm kina busy anyway.

 

[Markblaster]

Did you do the brake in the right way? Like in this video. Not just start it and ride.

 

[blasterboy91]

He is correct on going super rich on break in process. I mix my first tank at 20:1.

The hard to start issue is something to look at. An engine needs 3 things to run. Fuel/air/compression. Also, did he do a leakdown test?

 

[Geoffrey]

I don't know exactly how he broke it in. I think he started it once and just ran it a little. And then he started it again and ran it a little. And then he took off riding it. He said he was breaking it in. Then it died and then we had to pull it to get it to start. Anyway no he didn't do a leak down test. Wondering if maybe I need a new carb or something.

 

[blasterboy91]

No. You need a leakdown test. Otherwise, you might have to rebuild the entire engine from crank up. Don't ride it until you've tested it. The supplies cost you less then $15 and about 20 mins of your day.

 

[Markblaster]

Buy leakdown tester.
http://www.blasterforum.com/threads/leakdown-testers.55015/

 

[dirtysquared]

Was the cylinder bored/ honed to a new oversized piston like awk mentioned?

Running 20:1 on a break in is actually going to make your bike run fuel lean!

There is alot of things you've said here that throw flags and raise concern.

 

[blasterboy91]

There is alot of things you've said here that throw flags and raise concern.

Correct. The OP might be digging a bigger hole the he wished for.

 

[Blaaster]

He is correct on going super rich on break in process. I mix my first tank at 20:1.

The hard to start issue is something to look at. An engine needs 3 things to run. Fuel/air/compression. Also, did he do a leakdown test?

It is totally wrong to use a heavier than normal oil ratio for break in.

Adding oil removes some of the fuel in the mix and will create a leaner than normal mixture.

This lean mixture will create extra heat, maybe even to the point of detonation..

 

[Geoffrey]

so i guess i need to do a leak down test and drain the gas and put some in there 32:1 if the leak down test is ok.

 

[blasterboy91]

It is totally wrong to use a heavier than normal oil ratio for break in.

Adding oil removes some of the fuel in the mix and will create a leaner than normal mixture.

This lean mixture will create extra heat, maybe even to the point of detonation..

Ehhhh let's agree to disagree. My post is going to be long winded.


Yes, in theory a richer "oil/fuel" mix will result in a leaner "fuel/air" mixture. BUT, it's not as big a deal as some people make it out to be. For example, let's take 50:1 as an example. 50:1 premix is 2% oil, 98% fuel. Switching to a 32:1 premix your 3.125% oil and 96.875% fuel. You have reduced the fueling by 1.25% with the new mix. Lets say your carb uses a 250 mikuni main jet. In theory you would want to increase the size 1.125% to "compensate". A 253.125 size jet would be needed. This isn't even a 1/2 jet size bigger and would be a waste of time. Even on engines that are jetted right on the edge of lean it takes at least a 3% change in fueling to really see any difference in performance or high temps from my experience. So in short 50:1 - 32:1 isn't a big deal. switch from 100:1 to 20:1 and you might want to watch the mixture. Oil in the fuel has more effect on the octane and weight of the fuel. At least that the way I understand it.

 

[blasterboy91]

Your oil choice does come into play depending on your ridding style. Castor bean premix should be used only by those who keep the throttle pinned and the engine in the upper ranges of RPM. Most riders have a common issue that castor oil products will leave a carbon buildup. That said, castor does a great job of lubrication, but as mentioned, the engine needs to be run hard and fast the majority of the time. Those who do study up on jetting, have a full understanding of how it works, and how to accomplish optimum combustion, will find that they have a much better running engine than their pals.
But you also have to realize that jetting correctly means jetting to the style of riding you do.

The 20:1 thing you heard is fine as well. Do I run at that rate? Only for break in. You have to remember that the point of breaking in the engine is all about "Expanding & Contracting". During break in, the engine needs more oil to lube the components. Shifter cart guys run 16/18:1 on a normal basis just for that reason.
More protection, and more power. The secret is to get the right amount of air/fuel into the combustion chamber when it fires.