Piston Skirt Failure
 

I picked up a 1650 parts tractor from a Facebook ad that looks like it spent some not so quality time in a mud bog. The engine was seized when I got it.

I took the engine out of the tractor and put it on the bench. I drained the small amount of what looked like crude oil from the crankcase. I removed the head and pan. In the bottom of the pan I found a chunk of aluminum about the size of a quarter that ended up being from the piston skirt. I saw no other obvious signs of damage.

I used a block of 2x4 and a big hammer to persuade the piston down the bore. It got it to BDC and used the block and hammer on a con rod bolt to get it to TDC. Whatever was seized released and the engine spins freely now. The bore looks smooth with faint cross-hatching and no scores or scratches.

What could have caused the piston skirt to fail? Am I safe to start the engine as-is? I want to see if it burns oil or smokes before I buy a standard diameter piston for it. I wanted the engine for another tractor that has developed a smoking habit. I can use this one while I rebuild the other.

Thanks,

Bob

You want a guess?

I'd guess the rings rusted to the bore and stuck the piston. Someone tried to force the engine to turn over, kicked the piston sideways and broke a piece of the skirt off.

That guess is only good if the stuck engine and the broken skirt are related.

Can you run it? Depends. I broke a skirt off the piston in my 400 cc Suzuki MotoCross bike. Fell down in the crankcase and when the rod came around, it hit the broken piece and punched the bottom out of the crankcase. I glued the pieces back together on the crankcase and never looked back. Didn't seem to hurt the running any.

You may get lucky too.

PS. Probably not a good idea to run it if the skirt is broken off the thrust side of the piston but the only wat to tell is pull the pan.

Ya you can run it and see if it blows up, if not
then run it till it soon does. your money not mine.
Me, I'd take it apart and see what it needs to repair it properly.
It is a 16 hp kohler, a good engine and worth what it costs to repair.
What it is not, is a cheap china predator clone/throwaway.

If the rings were rusted to the bores to lock the piston, it likely won't run real well or real long anyway without service.

The other guess is the motor was just plain worn past "time to overhaul" point and the piston was just too sloppy loose breaking the skirt. Then is was parked because it smoked too much.

My opinion is no-go on running it until it is properly rebuilt.

Spend the money, do it or have it done right and it will serve you well for years.
Should be about $400 if you re-assemble it yourself.
Good luck!

I had a 149 fail the piston exactly like that,,
The tractor had been used for field mowing of several acres when I first purchased my place, and I did not have a bigger tractor,,

The hard pull of mowing caused a high strain on the 14HP engine,,
that strain caused the piston to wear a "step" in the bottom of the cylinder travel,
finally, the step become large enough, that the step caught the skirt of the piston, and broke it off.

The rest of the bore was perfect, this machine had received a new long block just before I purchased it.

Well,, my fix was to use some 60 grit emery paper, and hand sand the step away.
I bought a new piston, installed it, and the tractor ran perfectly for another decade.

Look at the bore at the bottom of the piston travel.

Since I found the piece of the skirt when I took the pan off before I started tapping the piston it wasn't due to what I did. I also found the tab off the governor arm in the sludge. That may be why it was parked, who knows.

I am not looking to run this engine before putting a piston in it. I wanted to start it to see if I could get away with a standard piston for the time being. Sorry if I made it sound like I wanted to blow up a 16HP Kohler. I'll tear it down and take some bore measurements to determine a path forward. CADPlans, thanks for the explaination, I'll check the bottom of the bore for a step.

I've used Cub Cadets since 1986 and have rebuilt a few over the years. I posted because I've never seen this type of failure before. I'm trying to get this engine going for as little money I can to buy some time. I have another Quietline that developed a smoking habit. It's my main worker and this engine could be used in that frame to get me a few months.

Glad you are investigating the problem properly.
A re ring and new piston in a worn bore but not out of speck, will work.
If you were going to use it as a primary mower/tractor I'd recommend a proper overhaul.
But many enthusiasts put few hours per year on their engines and tire of them/trade, long before they get to a point of a mandatory overhaul.
inspect/mike the crank journal closely,a failure there can destroy an engine.

I completely tore the engine down after work this afternoon and I'm glad I did.

The engine was run low on oil and the big end of the rod has transferred aluminum. The piston has damage on the valve side where the hole from the cylinder to the breather is. The skirt is broken on the other side. The rings did not have rust on them which is not what i expected. I think the piston damage on the valve side is what was causing the engine to not turn over.
There were broken thin washers behind the breather. This engine needs a rebuild.

I did measure the bore and it is in spec but im going to have a machist look at it. Thanks for the advice and encouragement to look further.

Where is the best place to get parts for this engine?

I don't know anything about this seller but a lot of folks on here said they have had good luck with his parts.

https://www.ebay.com/usr/bakt4kids?_...p2047675.l2559

I've used this seller before. Have had good luck with him, make sure you message him when you order your parts, like piston 0.020 over, and con-rod 0.010 under or he will send you standard sized parts.

Update on the engine.

I have a friend that owns a used tool store. He had a Starrett bore mic set that I used to measure the cylinder. It measured standard per the dimensions in the service manual.

I had the block cleaned up by a friend at a machine shop in his parts washer. This revealed pitting in the bore. I bought a 0.030" rebuild kit per the machinist's suggestion and had the cylinder bored and honed.

I started putting the engine back together today and ran into a few hiccups including finding the root cause of the failure.

What happened to this engine is a metal object got trapped between the cylinder and piston causing it to lock up. There was a deep gouge in the piston at the drain hole from the valve box.

When I went to put the valve turners back in I discovered that the intake side had failed. See the pictures below. There are small balls and springs in the turners. These objects came out, went through the drain hole and lodged themselves between the piston and cylinder wall.

So the problems I have now are:

I need to get a replacement valve turner

The crankshaft seals in the kit are the wrong size. Does anyone know the
correct seal numbers? The original seals were National 3120-RB and
49252RBO. These numbers were stamped on the seals. I called NAPA and
they didn't have them and couldn't cross the numbers. If someone knows
these seal numbers and could post them I would appreciate it. I want to
get them locally.

https://photos.app.goo.gl/XrdoEtN3jkUgWbdk8

https://photos.app.goo.gl/VGDPcHSiNnqTL22F6

yeah...

that's not supposed to happen :bigeyes:

Looks like the piece that's meant to hold everything in broke completely loose from the center! Can't imagine what someone would do to an engine to cause THAT!

Crappy luck. But sometimes being forced to do the job right works out better in the long run.

A tip for others for measuring bore diameters without inside mic's: Take one of the compression rings and de-bur the ends by pulling folded fine sand paper through them. Use a piston with a clean top and seat the ring square in the bore where you want to measure. With a feeler gauge record the gaps at each measurement. Use the very top, just below the chamfer and above the wear ridge (if there is one) as a base measurement.

Lets say you have a .010" gap as a base on a 3.500" bore diameter.

Just below the ridge is .015"

Halfway down is .018"

And the bottom is .020"

Divide the difference between the base measurement and next measurement by 3.14 and add it to the bore diameter.

So on the bottom measurement the difference is .010"; divided by 3.14 is 3.18 . Rounding that number brings you to a bore that is .003" bigger at the bottom.

You should have a caliper to determine if the bore is oversize already or if the piston is marked.

I always make it a practice to
check ring end gap!!
I got bit in the Ass back in '54 with a supposedly std. set of rings I installed in a worn bore, in a stove bolt chevy 6.
One set of rings had a .010 oversize top ring and when started, it ran for a few minutes then seized, bending a con rod.
That cost me a replacement junk yard engine.
Once burned, twice shy.
I was young and inexperienced.

The rotators probably got wrecked from improper use of the valve spring compressor.

Instead of getting UNDER the rotator base with the fork end whoever did the work, STABBED it, stressing the assembly to the point of failure.

Maybe and if it did that error caused a major failure when the engine locked up.

I got the engine back together and running. I got the correct seals and a couple solid valve bases. I have a few issues.

The ACR on thecam stopped working. it started fine the first few times then the starter struggled on the compression stroke. If I rolled the enginevpast compression it would turn over with the starter. I feel like I should look for a cam with a working ACR if I pull the head and see that the exhaust valve isn't moving when it should to releave compression.

The PTO clutch wasn't disengaging at first but released after using it a few times.

I have an oil leak that I'll address while figuring out the ACR issues.

It's good to be closer to getting this done. The grass is getting long and needs to be mowed.

It might be easier to just look in the valve box to see if the Exhaust valve is lifted a bit on the compression stroke but closes completely at about TDC.
Also, you get to check your Ex lash just incase it changed affecting the ARC,
and you can save a head gasket replacement. :beerchug:
Well anyway, that is the way I would go about it.

isavetractors... good place good people. they have rebuild kits for fair price.

one thing lol george said it in my thred... CLEAN THE MOTOR HOT SOAPY WATER ... i thought i did good with break clean and will it sits apart for a recleaning..
lucky i was watchin oil.

but yep i savetractors.com norm is a cool dude.. spoke with him on phone and wow what good guy he is..
i never tell anyone about any biz but them i will..
good utube channel also.. watch some of his videos over just for the fun of it..