Hole in the Piston

V

vinnie

New Member
Hey Guys,

I was riding my bike and heard an awful metal ringing like banging metal from my engine. I stopped and checked out basically nothing (I'm an idiot for not walking it home, which was 500 ft away, and taking off the head).

Here is what I found after riding without hearing the noise again, since I didn't check the piston cylinder until last night. I had dents all over the head and top of the piston. I figured out that a metal rod forced itself into the top of the piston and that's why the noise stopped. I pulled the rod out and realized that I can fit a paperclip all the way through the hole, which means it would not be a pressurized combustion chamber. I filed the little metal rod, which I think came from the spark plug, and jammed it back into the hole so that I have a flush fit with the top of the piston.

I realize this is probably not that safe to continue riding on. The cylinder walls do not really have any scoring, by the way - so I want to know from you guys this:

If I buy a new piston and head, will that work or have I done too much damage? Check out the attached picture, which was taken before I filed down that protruding rod (filed away from the engine - not in the cylinder). I'm not a broke college student, but close to it. Let me know what you think...I appreciate any advice you can give me!

This is the piston I would buy to replace my damaged one:
http://www.ebay.com/itm/221289988397
 

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vinnie said:
Hey Guys,

I was riding my bike and heard an awful metal ringing like banging metal from my engine. I stopped and checked out basically nothing (I'm an idiot for not walking it home, which was 500 ft away, and taking off the head).

Here is what I found after riding without hearing the noise again, since I didn't check the piston cylinder until last night. I had dents all over the head and top of the piston. I figured out that a metal rod forced itself into the top of the piston and that's why the noise stopped. I pulled the rod out and realized that I can fit a paperclip all the way through the hole, which means it would not be a pressurized combustion chamber. I filed the little metal rod, which I think came from the spark plug, and jammed it back into the hole so that I have a flush fit with the top of the piston.

I realize this is probably not that safe to continue riding on. The cylinder walls do not really have any scoring, by the way - so I want to know from you guys this:

If I buy a new piston and head, will that work or have I done too much damage? Check out the attached picture, which was taken before I filed down that protruding rod (filed away from the engine - not in the cylinder). I'm not a broke college student, but close to it. Let me know what you think...I appreciate any advice you can give me!

This is the piston I would buy to replace my damaged one:
http://www.ebay.com/itm/221289988397
Click to expand...
The little metal rod was from your upper needle bearing so you have bigger problems than the piston.

The rods will be in your bottom end and of course you need to pull your cylinder and remove the wrist pin from the piston to see the needle bearing.
 
That bearing looks a lot different than what I found jammed in my piston. Can you provide a link to what part you mean? It was a solid approx 1mm diameter by 3 or 4mm in length. Also, would I be doing more damage by continuing to use the engine? It seemed to run better when I made that metal rod smaller. You can see it in the picture I uploaded sticking out...it is very small

Thanks a lot for the quick response!
 
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MBR is referring to a single bearing roller that has come out of the bearing assembly.
See the link for a pic of the bearing assembly. Look at the rollers that are in it. That is most likely what has damaged your piston and head. These stock factory bearings are notorious for failing. So far you are lucky if it has not damaged a port in the cylinder. Do not run the engine until after installing a new bearing or catastrophic damage will occur.
http://www.bikeberry.com/engine-kit-parts/view-all-parts/crank-connector-bearing.html

I am in no way suggesting that you get a new bearing from bike berry. There are much better quality bearings available. Do a search in this site for "bearing" for more info in the subject.
Here is one to get you started:
http://motorbicycling.com/showthread.php?t=36334
 
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vinnie said:
That bearing looks a lot different than what I found jammed in my piston. Can you provide a link to what part you mean? It was a solid approx 1mm diameter by 3 or 4mm in length. Also, would I be doing more damage by continuing to use the engine? It seemed to run better when I made that metal rod smaller. You can see it in the picture I uploaded sticking out...it is very small

Thanks a lot for the quick response!
Click to expand...
The needle bearing rolls on those small metal rods and when the bearing fails all the rods bounce around inside your engine causing all kinds of damage.

Remove your piston from the connecting rod to see for yourself.

Be warned that the piston rings have small pins at their ends in the ring grooves facing the intake side.
 
Okay so you guys are right. I took the cylinder off, removed the pins, and popped out the piston pin. My bearing is missing three rods (great...). I have two halves that were still attached. Meaning that 2 of the rods look like they broke in half. So what now?

I can order the bearing and install it, but do I need to take apart the bottom of the engine for the missing rods? I also should get a new piston, bottom cylinder gasket (it ripped), and head, I am assuming. Let me know what you guys think...I really appreciate the advice!
 
Your assumptions are correct. Also, get a new head gasket or at least anneal your old one before re-installing it.
You may get lucky and be able to remove the hidden roller bits from the bottom end without total engine tear down. I have done this in the past on 2 stroke motorcycles by turning the engine up side down and flushing out the crankcase cavity with kerosene over a catch basin. Of course this required me to get creative with a flushing mechanism, a thoroughly detail cleaned spent fire extinguisher refilled and pressurized with kerosene. (an anti-fire extinguisher?) Easy, no but easier than tearing the whole engine apart. Some folks here have been lucky with a can of carb cleaner but then you are left with how to pre-lube the bottom end bearings before restarting the engine. Drooling pre-mix oil down the inside walls of the crankcase, guiding it so it flows onto the crankshaft bearings and dribbling a little onto the big end connection rod bearing will work.

A total engine tear down would however be a good experience in exactly how these engines work and you can familiarize yourself with all the bits and pieces inside. Compared to most other scooter type engines, this is easy to do. Get a complete engine gasket kit and while all it's guts are exposed I suggest replacing all the cheap factory bearings with quality ones if you feel up to the task.
There are threads here on this site that walk you through the process.
 
Thank you for the advice! I reached out to my automechanics teacher from high school and he is going to let me do the tear down with him in the shop, which is really helpful for me. I want to be prepared with the right parts. Here is what I am going to order...Do I have the right bearing for the 2 crankshaft bearings and are the upper and lower needle bearings the same?

2 Crankshaft bearings http://www.bikeberry.com/engine-kit-parts/crankcase/202-main-bearing.html

1 Upper Needle Bearing http://www.bikeberry.com/engine-kit-parts/crankcase/crank-connector-bearing.html

1 Lower Needle Bearing - Don't know if that is the same as the upper needle bearing

1 Piston measured out correctly to the right dimensions - hope it comes in and fits

1 Gasket Set
 
Lower needle bearing (big end bearing). I don't know. Most folks never have an issue with them. It is always the upper needle bearing (small end bearing) that have a horrible reputation of failing early on.

Do not, I repeat... DO NOT buy any bearings of any sort from Bike Berry. All they sell are the same crappy factory bearings that the engine was born with. Why replace crap with crap?

Read the bearing thread I shared with you in post #4.
Do a search on bearings in this here forum.
 
Alright, I got my replacement piston (same dimensions) and quality upper needle bearing installed. I also checked the crank seals, but they were fine. My question is this: how free is the piston to move when I turn the magneto? It moves, but has a lot of resistance. I just wanted to make sure everything was installed properly...I also had a lot of oil on the inside of the cylinder from when I installed the new piston. Thanks for your help everyone
 
Whenever I try to turn the engine over by the mag rotor alone (rarely) I usually use a socket and short breaker bar on the rotor retaining nut, only turning it clockwise. It can be done with just your fingertips grasping the rotor, but why torture yourself?
You should feel fairly moderate resistance. If it is easy there is something weird going on.
 
Okay, so I am now back in DC and installed the engine back onto my bike. I could not get it to start, though. I could hear the piston going up and down because I was engaged rolling down hill. I could also use the throttle and hear a difference in sound, but it would konk out even quicker. Bottom line is: the engine will just turn until I stop, but has no power at all-completely bogged down.

I checked the spark plug- it was wet with oil. I cleaned it with starter fluid, but it didn't get much better.
I also noticed the CDI wire rubber shield broke, but the metal wire seems to be intact.
Now that it is sitting for a few hours, the exhaust is just dripping unused oil.

What should I do? It's an old spark plug so I am upgrading to a NGK. I am also assuming I should order a new CDI. If I should, where should I order one from? Thanks a lot everyone!
 
I had a similar problem but with mine my nt carb was flooding and my cdi was messed up so I took my carb apart and cleaned which stopped the flooding problem and on the cdi I got me a new one and installed it I tried it all out works good I hope me telling what I had to do on my similar problem helps.
 
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