MS 360 Pro down (again)

[Brian VT]

About a year ago I replaced the carb. and melted piston for my BIL.
He said it had been running great all year but it just quit. He said it was easy to pull over. I was hoping for a messed up decomp. button.
NOPE.
Any thoughts on what caused this ? (gouges left, right, and exhaust)
Anyone have a jug&slug they want to sell or trade ?

 

[pioneerguy600]

Top ring snagged in the exhaust port?
Pioneerguy600

 

[lone wolf]

Chunks of metal from the rings or lower bearings is my guess.

 

[rms61moparman]

Pretty obviously caused by a foreign object in the cylinder.
were both circlips in place when you dismantled it?
How are the bearings?
Spark plug electrode still intact?
No missing fasteners that could get into the induction system?
Muffler bolts?
No chunks missing from the rings?
Sabotage?


Mike

 

[Brian VT]

Pretty obviously caused by a foreign object in the cylinder.
were both circlips in place when you dismantled it?
Mike

The circlip I pulled to take the piston off looked normal. I just pulled out the other one. It looks funny.
One end isn't round anymore. It looks like it somehow got worn flat and a bit of that flat end may have broken off.
What might have caused that ?

 

[oscar4883]

Maybe a piece of casting flash was missed when the last piston was installed? I only ask because I had a Meteor recently with a good size blob of flash hanging off the bottom. Not the normal flaky stuff, this was something considerable in size.

 

[rms61moparman]

My best GUESS would be that the clip was a little weak and was expanding and collapsing on that end as the piston moved up and down, causing it to wear against the side of its groove.
I would think that a pretty big chunk of the end would have to be broken off and bouncing around in there to cause the amount of damage that your photos show.
Unless that clip is significantly shorter than the other I would look around a LOT more before I put that one back together.

The clips opening and closing is why some of these guys, especially the builders of the really HOT saws are very particular where the opening is located in relation to the reciprocating movements of the piston.
You would likely be amazed how much force is exerted from inertia on the ends of those clips inside an engine turning 14000 rpm or more.

It's kinda hard for me to tell from the pics how big the chunk is that is gone out of the top land of that piston but it looks to be pretty big.


Mike

 

[Oldsawnut]

Is one of your carb nuts missing??? Or +1 on the bottom end bearings

 

[Brian VT]

Maybe a piece of casting flash was missed when the last piston was installed? I only ask because I had a Meteor recently with a good size blob of flash hanging off the bottom. Not the normal flaky stuff, this was something considerable in size.

It is a Meteor piston. I just looked to see if I could find any evidence of where some flashing might have come off but it looks ok to my (untrained) eye.
I know enough to move the circlip's open end away from the slot but I didn't know it mattered which direction it faces.
I'm hoping that was all that failed was the clip. Live and learn.
Can I tell if there are bottom end issues without splitting the cases ?
Here's the circlips. Notice the wear on the upper right.
The clip's groove in the piston is gouged near the slot where you'd pry it out. (see 2nd pic in orig. post)
I don't know if that was OEM or I did it today or I maybe I had to pull the clip due to a screw up during reassembly.

 

[woodyman]

Did you use the original circlips when the piston was put in?You have to have something in there(maybe crankcase) that did that kind of damage

 

[Brian VT]

Did you use the original circlips when the piston was put in?

Nope. I know that's a no-no.

 

[rms61moparman]

Well there is definitely a piece of that clip missing!


Mike

 

[mtngun]

Here's the circlips. Notice the wear on the upper right.

My guess is the wrist pin rode over the circlip. That was a common problem on Golf pistons for a while, due to the circlip groove being too deep.

Wrist pin gets to sliding back and forth, bumping into circlip each time. Eventually circlip breaks.

Surprised to see that on a Meteor, though.

[/QUOTE]

 

[Brian VT]

My guess is the wrist pin rode over the circlip. That was a common problem on Golf pistons for a while, due to the circlip groove being too deep.
Surprised to see that on a Meteor, though.

I've had no problems with Meteors in my dirtbikes.
I don't have a tool that I could measure the groove with. It's water over the dam anyway.
What to do now ? Flush out the lower end and throw a jug & slug on it ?

 

[wigglesworth]

What to do now ? Flush out the lower end and throw a jug & slug on it ?

Yep. All you can do. Of course, I can dispose of it for a small fee.

 

[mhimes]

bottom end bearings :jawdrop:

 

[Brian VT]

Yep. All you can do.

Do y'all think the culprit has been identified or do you think there's a chance it's still lurking and waiting to eat another top end ?
I've never split cases so I'm a bit scared to get into it. Especially since it's not my saw.

 

[Brian VT]

bottom end bearings :jawdrop:

What suggests that it might have been the bottom end bearings and what is involved to check them ?
Gotta split the cases ?

 

[brokenbudget]

What suggests that it might have been the bottom end bearings and what is involved to check them ?
Gotta split the cases ?

i'd slit it up and take a look at the bearings. little bits of the bearing cage sometimes like asking for attention. usually by tearing up the insides of a saw.

 

[wigglesworth]

Do y'all think the culprit has been identified or do you think there's a chance it's still lurking and waiting to eat another top end ?
I've never split cases so I'm a bit scared to get into it. Especially since it's not my saw.

There is a piece of clip missing, so that is "likely" the culprit. But, its easy enough to check the bearings out. Pull the seals and have a look. Check the big end rod bearing visualy and flush the case. No need to split it.