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Post by ebolaparty on Mar 22, 2015 9:01:01 GMT -5
I have a znen 150t-9 which has the BN157QMJ engine. Have been reading a lot about these particular engines needing top-end rebuilds pretty early on. Mine has been maintained well, but finally seems to have given out on me after about 3,200 miles. Long story short, the engine is seized. I ran through all of the basics before cracking it open. It seems like the piston is stuck in place. It refuses to move, even when trying to gently use the kick starter. I want to pull it apart to take a better look, but can't get the piston out. So, first, how should I proceed here? Also, will the standard 157qmj top end rebuild kits fit this engine or do I need one specifically for the BN variant? Thanks in advance.
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Post by tvnacman on Mar 22, 2015 9:05:54 GMT -5
remove your valve cover to get started. I suspect the common rebuild kits will work just fine.
John
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Post by ebolaparty on Mar 22, 2015 9:16:36 GMT -5
The valve cover and head are off, cam is pulled off etc. Wasn't very clear about that, my bad. Basically I'm not sure how to get the piston unstuck to access the clips and remove it from the cylinder.
Edit: Just to be a little more clear, the top end is already pulled off. The problem is that the piston only sticks out of the crank case by about an inch, not enough to access the clips to remove it. The engine wont move so I can't push the piston out any further.
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Post by JerryScript on Mar 22, 2015 11:31:16 GMT -5
The jug comes out of the engine, so if the piston is stuck in the jug, it should push the jug out. If you can't pull on the jug and get it out, then it sounds like the crank itself is frozen somehow, which requires splitting the case.
For now, put a bunch of penetrating oil into the cylinder on top of the piston and let it soak, then try to force it out with a rubber mallet.
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Post by tvnacman on Mar 22, 2015 12:29:27 GMT -5
The jug comes out of the engine, so if the piston is stuck in the jug, it should push the jug out. If you can't pull on the jug and get it out, then it sounds like the crank itself is frozen somehow, which requires splitting the case. For now, put a bunch of penetrating oil into the cylinder on top of the piston and let it soak, then try to force it out with a rubber mallet. I thought the same thing too, but the piston will never stick out beyond the jugs sounds like the crank is jammed. John |
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Post by mopojo on Mar 22, 2015 12:35:51 GMT -5
The jug comes out of the engine, so if the piston is stuck in the jug, it should push the jug out. If you can't pull on the jug and get it out, then it sounds like the crank itself is frozen somehow, which requires splitting the case. For now, put a bunch of penetrating oil into the cylinder on top of the piston and let it soak, then try to force it out with a rubber mallet. I thought the same thing too, but the piston will never stick out beyond the jugs sounds like the crank is jammed. John Can also put a 2x2 board to top of piston and whack it with a mallet: Softly? |
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Post by ebolaparty on Mar 22, 2015 13:39:17 GMT -5
The cylinder/jug is completely removed and the piston is protruding from the crank case, just not enough to get to the clips to remove it. Will try penetrating oil and tapping it lightly with a rubber mallet to see if that frees it up. Thanks for the feedback.
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Post by onewheeldrive on Mar 22, 2015 15:18:08 GMT -5
Better check the rod bearing after you get the piston off. Sounds like more than a top end issue/rebuild, unfortunately.
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Post by tvnacman on Mar 22, 2015 15:53:58 GMT -5
could be jammed in the area of the starter clutch oil pump.
John
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Post by geh3333 on Mar 23, 2015 10:43:13 GMT -5
If the piston is seized up high in the cylinder , then trying to turn the crank will not help. Unless the piston is seized down low at the beginning of the cylinder there is no way to remove the piston from the crank unless you break it free from the cylinder.
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Post by mopojo on Mar 23, 2015 16:00:06 GMT -5
The cylinder/jug is completely removed and the piston is protruding from the crank case, just not enough to get to the clips to remove it. Will try penetrating oil and tapping it lightly with a rubber mallet to see if that frees it up. Thanks for the feedback. So you are at the point of removing the piston itself. We are talking about the clips what hold the wrist-pin in place? Then the crank itself will not turn to get the piston at TDC (top dead center - furthest from the crank)? Can a pic be posted? Thanks mopojo |
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Post by geh3333 on Mar 23, 2015 16:17:52 GMT -5
The cylinder/jug is completely removed and the piston is protruding from the crank case, just not enough to get to the clips to remove it. Will try penetrating oil and tapping it lightly with a rubber mallet to see if that frees it up. Thanks for the feedback. So you are at the point of removing the piston itself. We are talking about the clips what hold the wrist-pin in place? Then the crank itself will not turn to get the piston at TDC (top dead center - furthest from the crank)? Can a pic be posted? Thanks mopojo I think he means the jug is unbolted from the case and when he turned the crank it pushed the jug and piston ",which is still seized in the jug " up so you can see the rod, but the piston is too far inside the jug to be able to remove it from the rod , because he can't get to the pin. So he must break it free from the cylinder to be able to go any further. That's the problem with the piston seizeing anywhere but the bottom of the cylinder. |
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Post by mopojo on Mar 23, 2015 16:38:54 GMT -5
Ah. Maybe I should reread the thread. I get a bit turned 'round at times. Age and smoke, I reckon.  Thanks, geh. |
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Post by geh3333 on Mar 23, 2015 16:45:46 GMT -5
Ah. Maybe I should reread the thread. I get a bit turned 'round at times. Age and smoke, I reckon. Thanks, geh. Happens to all of us , except I usually say something that has already been said , or something that was meant for a different thread , lol , and I look like a idiot. |
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Post by onewheeldrive on Mar 23, 2015 16:48:16 GMT -5
He has the top end off completely. The piston is at the very bottom position barely out the case hole, making it hard to reach the circlips.
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