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Enduro Engine - 2 stroke Cylinder, Piston, Tranny, Bearings, Clutch, Pipes & Silencers, etc.


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  #31  
Old 10-15-2020, 02:24 AM
Mikeyx Mikeyx is offline
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You are not gonna believe this... but I'm not making this up.

On her maiden voyage with the new piston & cylinder, I got again a piston failure!

Now riding with a 180 main jet instead of 175; recommended W24 plug instead of W22. Riding at 95 km/h and revving the engine in 2 s intervals instead of a steady throttle. Some 1 km on a highway the engine stalled, the rear wheel locked and gave a good rear slide and almost got rear-ended by a street bike before I found the clutch lever. Scary shit! Engine again with no compression.

Findings:

- spark plug intact and having a healthy dark brown colour (as if mixture was ok)
- top of the piston intact w/o any damage whatsoever (timing is correct?)
- sides of the piston having identical damage as in the pic I posted above

- the oval timing thingy in place in the stator backing plate (timing correct)
- crank shaft can be rotated by the coolant pump impeller (cooling ok)

I mean, does it leave any other option apart from an incorrect oil/gas mixture?


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  #32  
Old 10-15-2020, 05:22 AM
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Anders Anders is offline
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Quote:
Originally Posted by Mikeyx View Post
You are not gonna believe this... but I'm not making this up.

On her maiden voyage with the new piston & cylinder, I got again a piston failure!

....

I mean, does it leave any other option apart from an incorrect oil/gas mixture?
What type of oil and what mix rate (in %) do you use?
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  #33  
Old 10-15-2020, 07:44 AM
Mikeyx Mikeyx is offline
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I've been using fully synthetic 2-stroke oil for bikes @ 2%. Of course, I may have measured the oil incorrectly or not mixed it thoroughly before using.

I just recalled my mechanic telling me that he had noticed a small leak in the flywheel side crank seal. If that were the culprit, then a lean mix would have caused my issues. But the brown color on the plug still shows somewhere else.

The mechanic will show the piston and cyl to a friend of his who is an expert on twostrokers. If he concurs with a lean mix, then I'll first put the engine together with a new piston and try spraying start pilot into the flywheel housing before replacing the crank seal.
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  #34  
Old 10-15-2020, 10:19 AM
Doc Brown Doc Brown is offline
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Did you measure cylinder bore of the new cylinder? If so what were the figures and which piston size did you choose?
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  #35  
Old 10-15-2020, 10:37 AM
Mikeyx Mikeyx is offline
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The vendor mentioned that the cylinder is "A" and hence purchased "A" piston (71.94 mm).

Cylinder bore was marked, but I do not recall it. It was some 0.5mm larger than the piston.

But let me remind that similar damage was done to a new A piston installed in the old OEM cylinder.
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  #36  
Old 10-16-2020, 10:58 AM
Moto7man Moto7man is offline
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Default Diesel

Quote:
Originally Posted by (F5) View Post
Diesel is the business, better than gas for absorbing water.
Yes, and Diesel has a much higher flashpoint than gasoline, so diesel is safer to work with in this situation.
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  #37  
Old 10-16-2020, 11:08 AM
Moto7man Moto7man is offline
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Default Leak Down Test

Just my 2 cents, if you have a flywheel side main seal air leak, you will have a lean condition and seizure. The air leak could vary in volume and you could have a brown plug reading at a certain throttle opening then an immediate lean condition based on leak volume and throttle opening. Your mechanic should have replaced that leaking flywheel side main seal, then performed a new leak down test on the engine.
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  #38  
Old 10-16-2020, 05:55 PM
Jacob 'Berg Jacob 'Berg is online now
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Seems like there should have been some detonation/pinging if it was lean enough to seize the piston in the cylinder. If the damage is on the exhaust side of the cylinder and piston only, you were likely running lean.

Any sign of detonation on the piston crown?

Any aluminum on the plug? Look closely with a magnifying glass.

Check the bottom of the piston for a heat pattern.

Was the bike warmed up properly? Sufficient lubrication? If you have a four corner seizure it may be due to cold seizure or insufficient lubrication.
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  #39  
Old 10-17-2020, 12:50 AM
Mikeyx Mikeyx is offline
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^Now all parts are at the workshop - so I cannot take photos or inspect them.

I was coming home from an MX track, so the engine was surely warm.

Major damage is around the exhaust port. Minor seizure also on the intake side. Piston crown still good as new; with W24 plug.
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