Author Topic: CB160 Exploded Piston! (PIC) (Read 2179 times)

OakBehringer · « **on:** October 07, 2009, 04:59:47 PM »

Top three rings are seized, too. What would have caused this?

Bike is a barn rescue, so I didn't do it.

mystic_1 · « **Reply #1 on:** October 07, 2009, 05:57:10 PM »

Debris in the crank sump maybe? Looks like it come down on something.

mystic_1

Green550F · « **Reply #2 on:** October 07, 2009, 08:14:32 PM »

Don't know? I've broken rings and melted crowns, but never broke a skirt before!

OakBehringer · « **Reply #3 on:** October 07, 2009, 09:40:23 PM »

Quote from: Green550F on October 07, 2009, 08:14:32 PM

Don't know? I've broken rings and melted crowns, but never broke a skirt before!

yeah! I thought it was pretty weird. Especially since the break is identical on both sides. Like it did hit something. I hope to figure it out when I get into the bottom end, tomorrow.

Sam Green Racing · « **Reply #4 on:** October 07, 2009, 09:50:03 PM »

Somthing has got to have broken inside to do that, the rings could be stuck with standing.
I'll have a look in my workshop manual when I get home and get back to you tonight.

Sam.

Sam Green Racing · « **Reply #5 on:** October 07, 2009, 09:52:44 PM »

I think I may have a set of used pistons and might have a set of new rings, I'll let you know tonight.

Sam.

bryanj · « **Reply #6 on:** October 08, 2009, 12:37:39 AM »

Thats been done when turning the engine over with the cylinders off and the skirt catches in the crankcase mouth, nothing to do with the siezed rings

KB02 · « **Reply #7 on:** October 08, 2009, 04:00:54 AM »

Not stock pistons? Right diameter but skirt too long?

Either that or what bryanj said.

OakBehringer · « **Reply #8 on:** October 08, 2009, 06:49:53 AM »

I like bryanj's theory. I'll get into the engine cases tonight, start a project thread, and report my findings.

OakBehringer · « **Reply #9 on:** October 08, 2009, 09:42:48 AM »

I take it back, I disagree with bryanj's theory. Look what side of the piston the cracks are on- it would not come down on the sides of the crankcase, only the front or back.

Sam Green Racing · « **Reply #10 on:** October 08, 2009, 11:24:22 AM »

Adam, Bryans idea that it was damaged during a build is correct but your idea that it was not done on the mouth of the cases is also correct.
KB02s idea of the piston being to long could be the answer and the piston has come into contact with one of the flywheels but if this was the case, both pistons would be damaged the same unless one was an odd piston.
I once got a phone call from a young guy who was having problems getting his block over his pistons. I told him to hang on and that I would be round to help him in about 1 hour.
When I got there, he was hammering like hell on a block of wood on top of the block.
He had a couple of wrenches under the pistons and across the mouths of the cases to stop the pistons going down into the cases.
He had missed putting one of the piston pin circlips back in and the pin was not all the way in the piston and was catching on the bottom of the sleeve stopping the block going over the pistons. Sure enough both pistons were cracked in the area that yours are Adam.
That motor has probably been put together by a PO with no brain.

Sam.

OakBehringer · « **Reply #11 on:** October 08, 2009, 12:21:22 PM »

Quote from: SamCB750A on October 08, 2009, 11:24:22 AM

Adam, Bryans idea that it was damaged during a build is correct but your idea that it was not done on the mouth of the cases is also correct.
KB02s idea of the piston being to long could be the answer and the piston has come into contact with one of the flywheels but if this was the case, both pistons would be damaged the same unless one was an odd piston.
I once got a phone call from a young guy who was having problems getting his block over his pistons. I told him to hang on and that I would be round to help him in about 1 hour.
When I got there, he was hammering like hell on a block of wood on top of the block.
He had a couple of wrenches under the pistons and across the mouths of the cases to stop the pistons going down into the cases.
He had missed putting one of the piston pin circlips back in and the pin was not all the way in the piston and was catching on the bottom of the sleeve stopping the block going over the pistons. Sure enough both pistons were cracked in the area that yours are Adam.
That motor has probably been put together by a PO with no brain.

Sam.

Makes sense. Wonder if I'll find any full-chunks in the crankcase, or if they've all been ground down to nothing. Will find out tonight!

tbpmusic · « **Reply #12 on:** October 08, 2009, 01:26:25 PM »

Wonder where the broken off pieces are?

??

Sam Green Racing · « **Reply #13 on:** October 08, 2009, 06:10:14 PM »

He's probably in the middle of finding out.

Sam.

754 · « **Reply #14 on:** October 09, 2009, 07:59:16 AM »

Where is a pic of the exploded piston?
I agree looks like they had something under the skirt to ASSemble it..

Green550F · « **Reply #15 on:** October 09, 2009, 09:39:00 PM »

sounds like some well thought out possibilities, and I'm SO glad I can claim to not have done those things!

bryanj · « **Reply #16 on:** October 10, 2009, 02:38:31 PM »

If you turn the crank whilst the pistons are on the rods(no cylinders fitted) and dont take care the piston can tip and the skirt catch on the crankcase when the rod flops to front or rear---frequently this put dinks in two places on same side of piston but it does depend on case shape

crazypj · « **Reply #17 on:** October 11, 2009, 05:42:52 AM »

Bryanj is right, seen the exact same thing happen several times when people tried to use 'piston stops' to hold piston in position when replacing cylinders.
Either used wrong tool, (screwdrivers, etc) didn't set them properly (only under one side of piston) or tried turning motor over.
There are a LOT of people out there that don't care, as long as it runs it's 'fine'
As I've taught about 5,000+ motorcycle students over last 9+ years I have seen things that most people couldn't imagine

PJ

OakBehringer · « **Reply #18 on:** October 11, 2009, 04:50:32 PM »

Quote from: tbpmusic on October 08, 2009, 01:26:25 PM

Wonder where the broken off pieces are???

They were ground to a fine powder! Oil filter was filled with it.

I have locked this thread. Please view and/or reply at my build thread here:

http://forums.sohc4.net/index.php?topic=59891.0

Thanks!

News:

Author Topic: CB160 Exploded Piston! (PIC) (Read 2179 times)