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JNM

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  1. On this model, the jug bottom has 2 dowel pins on the corners, one on the exhaust side, one on the intake side. The exhaust side, which is close to my leak had no oring, just a slip fit of the pin. I will check the parts diagram again, but pretty sure this is correct. so seems to be relying on the gasket to seal, assuming oil is even traveling in that cavity. It may be head bolt only. The weeping seems less after running the engine a few times, but still there even if slowing down. Not sure I want to torque the head bolts tighter but starting to wonder if they needed a little more tightening from the beginning. some have suggested not to reuse the old bolts as they may be throwing off the torque reading off. What’s more baffling, After 10 mins of driving in only first and second gear it stalled out and would not start. Checked compression and it went from 200 to 90. I let it sit over night and rechecked compression and it went back up to 130 and I was able to start it. I have never seen anything like this. Going to remove valve covers and see if oil is making its way to the head. Something is clearly amiss, so going to tear back down and give it a second look. In addition to proper seal, I think I now also have to consider oil blockage and/or pump pressure issues, recheck valve seals.
  2. Thanks for the detailed replies…. I definitely followed what you outlined and placed the gasket on flat surface surrounding the small Oring and the large oring around the jug. I am worried I did not counter sink it enough into that groove before installing though. One follow up question …. is there a good way to test if oil is getting up to the head? I was looking for a bleeder screw, but not sure mine has one, I’ll double check.
  3. Hello, Acquired a used big bear 400 4x4 that would not start and debugged to compression issues. Tore down the head and determined the lower jug and piston were no good. Cleaned everything up well, got a lower new jug, piston, and all o ring / gaskets, and reassembled. Head bolts tightened to 30ft lbs which is slightly beyond spec of 29, but not grossly over. ATV started right up after fix, but after idling about 5 mins, I noticed a small amount of oil weeping from the front bottom of the jug; you can see occasional oil bubbling out to surface through gasket. Note: I did ensure to include the rubber o ring on the bottom of jug. I also get white smoke, which appears to be coming out the spark plug side of the head gasket. The head gasket was a 3 ply metal gasket. When I originally tore down the cylinder, there was black residue on all gasket mating surfaces. Should I have used a little gasket sealant on all gaskets? Everything I read seemed to indicate this should not be required. Looking for advice to help prevent these leaks assuming I tear back down and redo a second time. Thanks
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