Author Topic: Broken piston skirt while running?  (Read 288 times)

Sandyswift

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Broken piston skirt while running?
« on: June 07, 2022, 10:04:15 AM »
First I would like to say thank you, you have all compiled so much good information. I'm also sorry if this has been covered before. I tried scrolling threw and couldn't find exactly what I was looking for.

In march I pulled the trigger on an old fl350, always wanted a pilot, but the price was right. Seemed like it ran strong, replaced the shocks with some cheap Chinese fox knock offs, and was having a hoot. Then while going to check the mail(have a 1/2 mile drive way) I felt it go. About 4000-5000 rpm the piston skirt broke off. Ran for a out 5 seconds until I killed the engine.

Unfortunately I'm still waiting for the flywheel puller before I can split the case so I dont know the full extent of the damage.  A large part of the piston has been pressed into the bearing opening on the butt end of the rod. The rest has been finely ground and dispersed throughout the engine.

I would like to rebuild and keep the stock engine, but I am not familiar with how tough this engine is. Cylinder wall appears to be serviceable, but I am lacking tools to properly measure anything accurately.

My concerns are;
Is my crankshaft most likely bent?
Should I be worried about scoring inside the crack case?
The top end had 3 head gaskets, is this normal?
What else should I be worried about?

Looks to be all stock.
Thank you


« Last Edit: June 07, 2022, 10:09:36 AM by Sandyswift »

LiveWire

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Re: Broken piston skirt while running?
« Reply #1 on: June 07, 2022, 10:25:32 AM »
The skirt breaks when the cylinder is worn badly enough to let the piston rock back into the intake port. Cutting an arc on the bottom of the piston reduces the likelihood of that happening. You will probably have to go up two bore size, 1mm, from the current bore. The crank needs to be rebuilt. That is split apart, a new rod kit installed and the crank trued. I find it unlikely that the cases are not cracked. You could clean it up on the outside to look. It might be cracked at the front into the counter balancer though and not be able to see. You might look for a used bottom end if yours is cracked.

The first gaskets from Honda had a top and bottom layer. A spacer was added in between to lower compression when they were having scoring issue with the pistons.

https://www.aftershockmotorsports.com/index.php?main_page=page&id=1

Sandyswift

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Re: Broken piston skirt while running?
« Reply #2 on: June 07, 2022, 09:46:51 PM »
The flywheel puller came early and I was able to split the case. I found two large cracks in the flywheel half of the case. One could easily be seen from the exterior of the engine, the other is running through the oil balancer housing.

Dont know how I missed it the exterior crack, but didn't really look.

Looks like I will be looking for a for a new engine. I have found one for 1000$ a couple hundred miles away.

The gentleman I bought this from had replaced all the seals and said it was a very solid engine. Do you guys normally rip down a newly purchased unit and give it a once over?

Any ideas?
Thank you
« Last Edit: June 07, 2022, 09:50:01 PM by Sandyswift »

LiveWire

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Re: Broken piston skirt while running?
« Reply #3 on: June 08, 2022, 09:06:40 AM »
The last FL350 I bought, I had the seller drive onto my trailer then I paid him. It was never started again until I rebuilt the engine.