KTM Engine failure....

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7/8/2018 12:22 AM

Piston and bore pics.....whats your diagnosis? Photo
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7/8/2018 5:06 AM

My diagnosis is the color orange

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7/8/2018 5:09 AM

Debris in the motor, how clean was the filter?

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"Hope is not a strategy"

7/8/2018 5:34 AM

If there was also damage to the cam journals, then I suspect faulty oil delivery. If journals were not damaged, then dirt as already expressed above.

Paw Paw

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7/8/2018 6:23 AM

Thats obviously not an OEM piston. All your clearances check out before putting the new one in?

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7/8/2018 1:45 PM

MX915 wrote:

Thats obviously not an OEM piston. All your clearances check out before putting the new one in?

Thats an aftermarket big bore kit. We triple checked clerances because it was a tight squeeze to get the piston in the bore, they were fine. It ran for 1.1hr then this.

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7/8/2018 2:13 PM

Go back stock

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Take it to the limit, one more time!

7/8/2018 2:50 PM

I see a lot of KTMs with dirt causing issues. Amazing how many people don't install the air filter properly. PawPaw is on the money.

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7/8/2018 6:15 PM

What brand aftermarket big bore kit?
Size?

Paw Paw

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7/9/2018 3:21 AM

Paw Paw 271 wrote:

If there was also damage to the cam journals, then I suspect faulty oil delivery. If journals were not damaged, then dirt as already expressed above.

Paw Paw

Definitely not dirt, I have checked the intake track and there is no sign. Also it was run in around slashed grass headlands, no dust or other vehivles around. The faulty oil delivery could be it and that would explain the scoring on the piston pin which is a concern, could one of the oil injectors be blocked, and if so how? I am putting it back together with the standard bore and piston this weekend so hopefully I have cleared out whatever it might have been.

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7/9/2018 3:24 AM

Paw Paw 271 wrote:

What brand aftermarket big bore kit?
Size?

Paw Paw

Pm me if you want to know, I dont want to name them here as it may not be their fault. But the piston was tight in the bore, ring gap was fine but I didn't measure the piston clearance. I will this weekend.

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7/9/2018 3:28 AM

piscokid wrote:

Debris in the motor, how clean was the filter?

Filter was fresh, still spotless. Total time on bbk and filter 1.1hrs.

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7/9/2018 4:26 AM
Edited Date/Time: 7/9/2018 4:28 AM

That tight piston fit could be the issue as it can create excess heat and cause the piston to fail. Was it a forged piston? If so, the expansion rate of the piston would be faster than the cylinder and the tight fit would cause the failure.
Was the engine put through several heat cycles prior to riding it?
I did not see the upper 2 rings in you photos. Were they stuck or just destroyed?

Paw Paw

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7/9/2018 4:55 AM
Edited Date/Time: 7/9/2018 4:57 AM

Paw Paw 271 wrote:

That tight piston fit could be the issue as it can create excess heat and cause the piston to fail. Was it a forged piston? If so, the expansion rate of the piston would be faster than the cylinder and the tight fit would cause the failure.
Was the engine put through several heat cycles prior to riding it?
I did not see the upper 2 rings in you photos. Were they stuck or just destroyed?

Paw Paw

It is a forged cp piston, it is a 1 ring piston (+oil ring), which is melted in the groove in the pic. The second groove is not a ring groove, cp call it an accumulator groove, it is not deep enough for a ring to fit. The bike idled for 5 mins after install, then ridden for 25mins slowly the next day, oil then changed, ridden for 30 min a couple of weeks later, then ridden for 5 kilometers the weekend just gone before she stopped.
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7/9/2018 7:07 AM

Not enough clearance for the conditions. Got hot and stuck the bore.

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Race Bike: 2018 KTM 350SXF

Other Bikes: 1985 CR80R, 1990 CR250R, 1998 PW80, Specialized Fuse Comp 29.

Sold: 2016 YZ250F, 2012 CRF250R

7/9/2018 11:54 AM

Not saying this is the failure mode but I would never idle a race bike for 5 minutes.

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7/9/2018 3:12 PM

What brand coolant are you running?

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7/10/2018 1:19 PM

Just took the it to a performance shop for assessment, their opinion is that the gudgeon pin was too tight not allowing the piston to pivot freely....

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7/10/2018 3:58 PM

fullysicmate wrote:

Just took the it to a performance shop for assessment, their opinion is that the gudgeon pin was too tight not allowing the piston to pivot freely....

I just find that hard to believe.

Paw Paw

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