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Case mount threads destroyed

3K views 13 replies 7 participants last post by  northstarrick 
#1 ·
Hey I have a 2013 Polaris Assault 800 with around 3000 miles that I got for a really good deal knowing it had some stuff to fix. He also said it was rebuilt but apparently not very good lol. Long story short needed to replace half the bulkhead and after I got the motor pulled out I found out the bolts that attach the motor mount plate/bar to the motor came out (or were never put in right) and destroyed the threads for the bolts in the case. One is shaped like an oval and the other has half the bolt snapped off inside it. This is going to become the beater sled so I don't really want to buy a new case. Anything cheep that works is the right solution in this case for me. Also before you start worrying about the next owner, I part out sleds and when it blows it will join them.

What is going to be the best way to deal with this? Solutions I have thought of so far-
  • Attempt to drill the holes out and rethread them
  • Weld the plate on to the case
  • JB weld the plate on (or a different adhesive)
  • Say fu*k it and work some duck tape and zip tie magic
That last one is mostly a joke but any advice or thoughts it greatly appreciated!
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#4 ·
I would split the cases , weld a boltyo the broken one and extract it , weld up the bad hole and redrill and tap it. Or. Have a decent machine shop do it for you. Then I would reassemble the engine myself . It would give you a chance to examine what ya got and replace seals /gaskets and potentially do a better job than the previous owner
 
#7 ·
Yep I have another one already that I was planning on putting on. I have welded a decent amount but never welded aluminum. If I decide to weld it and redrill it I would probably need to have a place do it. Anyone know an estimate on how much it would cost for them to just fill in the holes or an estimate? What would be the best place to do this? I live just outside of rochester MN so if anyone knows a good place near there that could do that and wouldn't be insanely expensive that would be great!

Another thought I had would be like they said possibly drill them a size bigger and tap them. Would I need to fill the one side where the hole is more of an oval? I don't know if I want to go that big with the hole to ensure I still have enough strength in the actual case bole holes.
 
#8 ·
You should really only need to weld the hole that is ovaled out and extract the other bolt.Aluminum needs to be VERY clean to weld.On the hole that is all ovaled out I would drill it bigger or use a die grinder or dremel to get to bare aluminum.If they use a spool gun it wont put as much heat into it as tig welding.I just mention that in case you are trying to do this without disassembling the engine.
 
#9 ·
i dont know if repairing the bolt holes will be the only issues you have to deal with, after looking at that case half, it looks pretty beat up ,even with a new strap , it will never sit flat, it will continue to loosen the bolts no matter what , because its not flat,for a good fix imo, i would replace that case half and please dont sell it to someone like that
 
#13 ·
You can NOT replace just a case half.
They are line bored as a unit.If you fix those holes correctly there is absolutely no reason it wont be fine.
I have cracked cases and holes in cases welded up all the time because these cases arent easy to find.
If you ever see a case for sale that doesnt have matching numbers on the halves just walk away .It might look fine to the eye but the crank bearings will not seat perfectly.
 
#14 ·
yup crank case's are bolted together and line bored/honed to .001- .0015 of crush bearing fit. no two cases are the same and should never be replaced by just half the case. it can be done but needs to be machined and reline bored/honed. i repair crank cases all the time. it needs to be tig welded. built up where the plate mounts and machined flat. then drilled and tapped. but a good used case might be cheaper? they are out there. a new crankcase is $1000 +
 
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