Engine guys...

scottessex

Sling-Wing Pilot
Joined
Nov 12, 2003
Messages
11,240
Location
central, ga
Aircraft
Dominator 582
Total Flight Time
200+
Seeking advice from knowledgeable engine guys.


I have 1.1 hours on my arctic cat engine, it quit on me today.
EGT's were 900*F water temp was 150*F
Rpm about 7000, it just quit. so I landed of course.
I Took the carbs off and there are seizure marks on the mag piston!!!! The engine is brand new, I broke it in, I checked the case for air leaks etc before I mounted it, new carb flange boots etc, oil injection, running Arctic Cat oil. Using fresh 91 octane fuel.
What would cause it to do this, the first engine did this at 6 hours, only much worse.
I'm about ready to pull my remaining hair out.
Thanks for any advice.

If I am lucky I might have something flying by Bensen Days 2010!
 
Geeze Scott,
If you did not have bad luck you would not have any at all.
I cannot help you because I am not a two stroke guy, Sometimes I think you need some magic dust or something to make those two strokes reliable and trouble free.
Before anyone jumps me I know there are many very reliable problem free two strokes out there running today but I do believe you have to know them well or else they will get the best of you.... magic dust helps as well I think.
Sorry to hear about your on going bad luck Scott, really sorry.
 
Scott, too little piston to cylinder clearance? At high loads the piston will heat and expand and seize if it is fit too tight.
 
Scott, too little piston to cylinder clearance? At high loads the piston will heat and expand and seize if it is fit too tight.

Bingo.

Rotax used die cast pistons so that they don't expand as much as billet. They also use more clearance, and the special edge rings make up for proper compression.

Depending on your distance of the EGT sensor, it looks like you are running your EGT too low. Should be around 1000F at cruse, and 1100F at full power. Reason why is carb buildup will cause it to seize too.
 
Assuming your inspection posts are accurate, and the carbs are delivering as advertised, the first thing that comes to mind is incorrect tolerances held during overhaul. Piston to cylinder clearance too tight. Its a bummer, been there. I still dig two strokes. Owned many.
 
Assuming your inspection posts are accurate, and the carbs are delivering as advertised, the first thing that comes to mind is incorrect tolerances held during overhaul. Piston to cylinder clearance too tight. Its a bummer, been there. I still dig two strokes. Owned many.


The engine was new from the factory.

Dennis I don't think it had time to build up carbon in 1.1 hours, I purposefully have it slightly fat until I got it sorted out.
Sucks bad.
 
Hey Scott, (1) fight with the 'factory', (2),buy a new set of rings, one piston, then hone to increase the clearances. You know this sheet anyways man... Get it right , and it will run like a scared rabbit. Still like to see a set of individual tuned expandos on that mill...
 
Sorry to hear that, Scott. Why don't you use a ROTAX ????

I had the greatest 1 hr flight tonight ! I need more fuel !

I really love my new oil injected 503.
 
This sucks Scott!

@Chris
IIRC Scott had a Rotax quit too!
 
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I don't claim to be an engine expert but I believe the Rotax's hold up better because they use a high silica content piston which makes it much harder, tougher, and much less likely to deposit aluminum on the walls of the bore or deform the ring grooves and have them stick. We're way tougher on our engines than those wussy snomobilers.

You could ask Joe Swanton what he thinks, He's beyond an expert, He's an engine GURU.
 
Suzuki makes great engines, I suspect once you get the piston/clearance issue resolved, that motor will work well. I just learned that "cam grinding" was done to mac pistons to keep them from seizing. Cam grinding is where the piston is ground to a slightly oval shape. The piston is constructed with more metal along the crown and pin bore and it is primarily heated from the top down (not uniformly). So it expands non-uniformly as it heats up. By grinding the piston to the required non-uniform shape when it's cold, it will expand into the proper uniform shape after it reaches operating temperature. That's how proper clearances are obtained during normal operation, which helps to prevent seizure or uneven wear. Anyway, not sure if that strategy might be useful for the Suzuki, but it's something to mull over.
 
The EGT will read different temps with the probe installed at different distances from the combustion chamber. I suggest checking with the Arctic Cat people to confirm where the probe should be in relation to the combustion chamber.

To get a correct EGT for the MZ202, the probe must be 1 3/8" from the exhaust flange. Mount it closer and it reads a cooler temp, farther away and it reads hotter. It's the reverse of what you would think.

It sounds like a lubrication or too high temperature issue to me. Could be a little of both though.
 
Scott, I swear you have no luck with engines dude!

Did you properly break in the engine before flying it?

Are you sure the oil you used will work with ethanol fuel ( a few MZ 202's were tore up lately from using oil that won't work with ethanol )

I haven't heard from the guy in a while and can't remember the last time he posted, but you might try to contact " GyroDude " on the forum here, Gary Safrit.... He flew one of those engines for years and apparently had good luck with it.

Didn't you say you didn't have the right sized carbs on it and were thinking of using rotax bing carbs or some other odd ball sized carbs? If this is the case, I would suspect the carbs more than anything else.
 
Hey Scott,
Did you put a oil mixture 100:1 in your first tank of fuel to make sure the oil injector is purged and working correctly?


Scott
 
did you make shore the carbs were sinked ...if not then one cyl would take more load and the other cyl would run lean (hot)...and it would not take much of a mist setting to do it .....it sucks to have some thing that nice and have melt down on you...
 
Aaarrrggg!!!

Aaarrrggg!!!

In my experience with Yamahas, none with snowmobiles, the piston often holds the answer to the cause of a seizure.

The top will show the signs of pre-ignition or detonation with a spray of small grey aluminum balls.

The inside will show where the heat was as the failure occurred with burned oil showing brown changing to black as the temperature goes up.

Outside under the rings will show if the ring was not sealing.

I feel that Yamaha is sophisticated in their choice of alloy for pistons and understands cam grinding a piston on a high level. I have not been successful at out thinking them.

I would recommend against increasing the clearance. I have not had success with going beyond the factory specifications. In my opinion some of the cooling of the piston comes from it’s proximity to the cylinder wall and the shape of the piston changes with clearence.

Once you determine the cause you can chart you course of action. I have found that it is easy to create new problems by trying to fix things that are not broken.

Is this the correct exhaust for this engine?

I wish you luck and patience, Vance
 
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