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OutdoorSteve

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Hi guys! I have a question for the experts. I have a 440 that has had a few cylinder kits put on and the end result is the same, seizure. The two kits I've put on were both "Hyway Kit" the fist one was big bore and we replaced a seal when that rebuild was done. Ran 20 minutes and then seized heavy marks on top and bottom of exhaust port and intake side has wear but no grooves just vertical wear marks. Initial thought was we missing a leak. During pressure/vacuum test the only leak was around the spark plug. sealed it up and test out great. Checked the rod and crank bearing and every thing I could possibly find to measure and/or inspect. After going above and beyond to find something wrong, with no results, I installed a new "hyway kit", stock size, and used a ton of oil to assemble and took all precaution while installing. Carb is at stock settings and clean. Pressure and vacuum is still good. Fire it up run for a few minutes, smoked a lot from the absurd amount of lube I used during assembly' but ran well. shut down the saw pulled the plug to make sure thing looked good. Through the plug hole I could see a light groove on the right side of the exhaust port. I removed cylinder and the vertical marks on the cylinder in all four corners are telling me it was on its way to seizure again. Piston doesn't have and wear sign yet but I have no doubt that a few more minutes of running would have resulted in seizure.

So given that four corner seizer is general caused by a piston expanding or heating up faster than the cylinder I would assume a lean condition but with all I did to prevent this I don't see how. I have checked intake boot and pulse hose and everything else. As far as I know I looking at a perfectly good bottom end that has a hatred for top ends.

My questions I guess are, what am I missing? Have you seen this before? What should we be looking for?
 

OutdoorSteve

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No pics yet working on that. Rings have no visual signs of wear or chips or cracks. The marks are on the edges of exhaust and intake ports, both sides of each. I feel like the bevel could be the problem. That was my first thought on the big bore cylinder. I was talked out of that and told that it was a lean failure hence all the checking I did before the new cylinder this time. I have been leaning that way myself.

Any more input on the subject is greatly appreciated. Want to cover all bases before I install and wipe out another cylinder kit.
 

huskyboy

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You checked impulse and fuel line/filter right? Oem hoses/filter or am?
 

Cracker Boy

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As said id look into crank and connecting rod bearings or bent connecting rod
 

Al Smith

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Just a thought .If you flipped the cage the rod would rattle around like a BB in a box car .I'm not sure you could bend a rod without it coming out of the saw .Dang rods are pretty tough,the piston should fail prior I would think .FWIW I've seen grenaded pistons on both Stihl and McCulloch and the rod never suffered a bit .However on the Stihl it did pack the mains full of shrapnel so they had to be replaced.What a flippen mess that was --I saved it ,it's residing in my shed along with the rest of what have turned into shelf queens .Good ole Stihl 038 mag,from a bygone era .
 

traffic903

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As others have said, bad rod bearing for sure. I know you said you inspected it but it can be hard to see. I've had this EXACT scenario myself on a 380 and that's what it was. Tried everything else. Went through 3 pistons and 2 cylinders before I found it. Lesson learned hard way.
 

MattG

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During pressure/vacuum test the only leak was around the spark plug. sealed it up and test out great.
Out of interest, to eliminate this when I P+V test, I've got an old plug I removed the washer from (just with a hacksaw and small pliers), then I grabbed an O-ring and slipped this down the plug thread. Works great, without stressing about stripping out the plug thread.
 

MattG

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As others have said, bad rod bearing for sure. I know you said you inspected it but it can be hard to see. I've had this EXACT scenario myself on a 380 and that's what it was. Tried everything else. Went through 3 pistons and 2 cylinders before I found it. Lesson learned hard way.
Why does this happen exactly? Just really curious......all I can imagine is that with sufficient rock/tilt in the rod, that when the piston driven back up in the bore, it goes at a very slight angle, enough to scuff hard against the cyl. walls, massive metal/metal friction = heat = seizure...

Is that about the size of it?
 

huskihl

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Why does this happen exactly? Just really curious......all I can imagine is that with sufficient rock/tilt in the rod, that when the piston driven back up in the bore, it goes at a very slight angle, enough to scuff hard against the cyl. walls, massive metal/metal friction = heat = seizure...

Is that about the size of it?
That, and the chunk(s) of bearing or retainer that went through the motor
 

MattG

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That, and the chunk(s) of bearing or retainer that went through the motor
Sure I was just wondering to the consequences of just excessive up and down play on the big end.

Not full scale bearing disintegration.

Either way, that should be easy to detect by yanking the rod up and down.
 

traffic903

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Why does this happen exactly? Just really curious......all I can imagine is that with sufficient rock/tilt in the rod, that when the piston driven back up in the bore, it goes at a very slight angle, enough to scuff hard against the cyl. walls, massive metal/metal friction = heat = seizure...

Is that about the size of it?
Short answer......yes. Rod movement at the crankshaft end is magnified hugely at the piston end. The next stage after scuffing and partial seizure is (as was mentioned) total rod bearing failure and bits of cage etc going completely through the motor.
 
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