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Discussion Starter #1
Hey all, this is my first post on the forum so if im doing something wrong, let me know. I bought a 05 brute force 750 yesterday that didnt run and the owner thought the motor was seized. Today I was able to get into it a bit and discovered that the motor wasnt seized but the tip of the sparkplug that goes to the rear piston was broken off and the motor turns over fine but something is causing the rear piston from completely going all the way up, thus keeping the crank from rotating freely. What kind of problems am I looking at and what could have caused that? the bike has 198 hours and 2250 miles with brand new aftermarket rims and tires and I paid $1200 for it. I am quite mechanically proficient but ive never dealt with an issue like this before. Any advice would be greatly appreciated.
 

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The head has to come off. Take off the rear head and check the piston/head/cylinder for damage left from the tip. Also check valves to see if any are bent.

I would expect piston and head damage. The only times i've seen a tip missing are from running lean/detonation.
 

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Discussion Starter #3
The head has to come off. Take off the rear head and check the piston/head/cylinder for damage left from the tip. Also check valves to see if any are bent.

I would expect piston and head damage. The only times i've seen a tip missing are from running lean/detonation.
yeah im thinking maybe a timing chain broke or was out of spec and a valve broke and smashed into the sparkplug. the other spark plug is pretty carboned up so could have been running lean. how much is a head on one of these things?
 

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Ebay is saying $200+ for a head. Hopefully the head isn't bad.
 

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The head has to come off. Take off the rear head and check the piston/head/cylinder for damage left from the tip. Also check valves to see if any are bent.

I would expect piston and head damage. The only times i've seen a tip missing are from running lean/detonation.
yeah im thinking maybe a timing chain broke or was out of spec and a valve broke and smashed into the sparkplug. the other spark plug is pretty carboned up so could have been running lean. how much is a head on one of these things?
Carboned up means rich on fuel, or burning oil.
Tear it down and see what's in there.
 

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Best advice is to buy a manual.
 

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see if anyone is parting out one on the exchange here. i had to rebuild both my heads and through the exchange, one internet place in GA, and ebay, i was able to stay under $400 for everything that i needed. just takes some time to find everything, seals, gaskets, heads, etc.
 

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Take it apart; don't go around buying or looking for parts until you know what you need.
 

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Discussion Starter #11
alright so i have an update. It looks like it dropped a valve and knocked a hole in the piston. the bottom end looks really good and there is no play in the rod bearings and everything looks straight. the rear head for sure has to be replaced and it needs new valves and probably new guides. the timing chain was really tight and the guides looked really really good. as far as the cylinder goes its pretty good but definitely needs to be honed. does this mean it needs to be recoated in nikasil or whatever it is? do yall think i should tear into the bottom end and replace rod bearings and stuff?
 

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i've broken the valves off on the front and the back cylinders! had to replace the rear head first, then about 6 months ago the front let go. one of them broke off in each case, and bounced around breaking the other ones off and chewing the crap out of the head and piston like bubble gum!
so this past one i had found out that the 2006 valve heads were weak for some reason, so i replaced them with 2011 Teryx heads that i got off the classifieds here, and the other parts off around the net. runs perfect now and have the updated heads, valves and all the other associated parts involved.
it is just starting to need the valves adjusted after that last build so it will be at my mechanics prolly this weekend. he can now do this in his sleep.

funny, i have all the pieces of the broken valves because they blew out of the motor into the exhaust. when we pulled the pipe off, they just fell out. had to keep them as momento's!

each time they went i was out hunting and the first time is was 20 miles away from the truck and second 7 miles away, so i just went as slow as it would go, knowing that the rattling was just chewing everything up in there, but i had to get back as i had 3 guns/ammo/gear on it and wasn't walking that far with all that stuff on my back!
 

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Discussion Starter #14
i've broken the valves off on the front and the back cylinders! had to replace the rear head first, then about 6 months ago the front let go. one of them broke off in each case, and bounced around breaking the other ones off and chewing the crap out of the head and piston like bubble gum!
so this past one i had found out that the 2006 valve heads were weak for some reason, so i replaced them with 2011 Teryx heads that i got off the classifieds here, and the other parts off around the net. runs perfect now and have the updated heads, valves and all the other associated parts involved.
it is just starting to need the valves adjusted after that last build so it will be at my mechanics prolly this weekend. he can now do this in his sleep.

funny, i have all the pieces of the broken valves because they blew out of the motor into the exhaust. when we pulled the pipe off, they just fell out. had to keep them as momento's!

each time they went i was out hunting and the first time is was 20 miles away from the truck and second 7 miles away, so i just went as slow as it would go, knowing that the rattling was just chewing everything up in there, but i had to get back as i had 3 guns/ammo/gear on it and wasn't walking that far with all that stuff on my back!

Yeah it looks like I need a new piston, and rear head. Will any head off of a 750 work? I probably am gonna have to replace the cylinder too because it has a few marks in it and it'll probably just be cheaper to buy another one than have that one worked on. All in all I'm glad the bottom end is ok. I'm gonna try and flush the bottom end out with oil and get the new parts for it and she should be running in a month or so. I'll keep y'all updated as the process goes along. The more I read about the BF the more I like it! I've been a Polaris guy until now haha
 

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If you really want a monster talk to fst or vforce john about a stock bore kit.
 
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