New user, new owner and big problem

3067 Views 25 Replies 7 Participants Last post by Dennhop, Jan 19, 2018

Dennhop

Discussion Starter · Nov 9, 2017

I've got a 2005 big bear 400. Had some issues with the starter spinning, but not engaging the engine. I did a bit of research, it all led to the starter clutch being bad. Replaced the starter clutch, same issue. I tore everything apart, and found the gear on the crankshaft assembly for the timing chain was cracked, allowing it to slip on the crankshaft when trying to turn over. My issue now is the only reference to that part is as part of the entire crankshaft assembly, which is around $420 or so. Is there any possibility of finding just that gear, pulling it off the crankshaft and replacing it by itself, or do I need to split the case and replace the whole assembly?

I'll see if I can upload a picture.

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1 - 20 of 26 Posts

okbear

· #2 · Nov 9, 2017

Welcome to GC. We have a lot of great members here. We’ll get you squared away.

jvictory1974

· #3 · Nov 9, 2017

Welcome to GC , a lot of times parts aren't available separate not sure on this. You might try to find a salvage crank and swap the gears if possible....good luck

mainehunter

· #4 · Nov 9, 2017

Welcome to GC. Wish I could help. Seems to me that piece must be replaceable on it's own. Like JVictory said, bet you could find a salvage one and do it that way. Good luck!

Dennhop

Discussion Starter · #5 · Nov 30, 2017

So I think I'm going to just go and order an entire bottom end-$400 for the whole thing, vs $450 for a new crank. That all being said, what am I looking at having to do to pull the motor out of the quad? I figure it can't be super hard, but what all do I need to disconnect and remove to do it? Any tips/tricks from anyone who's done it before?

okbear

· #6 · Nov 30, 2017

A service manual will save you some headaches. You can download one cheap at tradebit.com. Then you can print it or just refer to it on your computer.

Dennhop

Discussion Starter · #7 · Dec 14, 2017

got it. The "new" bottom end is sitting in the garage, planning on pulling the motor this weekend, and before I tear it down, I'm going to run a leakdown test to make sure the valves didn't tag the piston when the gear broke loose. As long as that's good, I'll drop my head on the new bottom end, put new rings on the piston, and throw it all back together. Hopefully it works.

mainehunter

· #8 · Dec 14, 2017

Dennhop said:
got it. The "new" bottom end is sitting in the garage, planning on pulling the motor this weekend, and before I tear it down, I'm going to run a leakdown test to make sure the valves didn't tag the piston when the gear broke loose. As long as that's good, I'll drop my head on the new bottom end, put new rings on the piston, and throw it all back together. Hopefully it works.

Let 'er rip! Good luck. We like pictures here if you have a chance!

Dennhop

Discussion Starter · #9 · Dec 15, 2017

Ok, so I'm part way I to the teardown, and now I'm stuck...hoping to get some advice. I can't figure out how to separate the bottom end from the rear driveshaft. I've got the axleshaft out of the rear, and unbolted the four bolts holding the diff to the axle tube, but now I'm stuck. I need to disconnect the pinion yoke from the rear driveshaft, but there's a ujoint right after that I can't get to. Do I need to disassemble the rear diff? Here's a few photos of where I'm at right now. The service manual has been as helpful as a pet rock so far.

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Dennhop

Discussion Starter · #10 · Dec 15, 2017

Do I need to disassemble this, and if so, what all do I need to know before I take it all apart?

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dezz

· #11 · Dec 15, 2017 (Edited)

Not much to taking that apart. Just start unbolting parts. I like to do that on the bench though.

Remove the 2 swing arm pivots using a very large Allen key (after you loosen the lock nut). Unbolt the shock lower bolt, brake cable and drum vent tube, rear diff vent tube, then pull the complete rear end assembly from the frame. The driveshaft is just splined together and will slide apart when you pull the assembly.

Dennhop

Discussion Starter · #12 · Dec 15, 2017

So I are retarded...lol. took a few minutes, sat back and looked at everything, and figured it out. Rear end is off, I think I did a few extra things I didn't need to, but oh well. Just need to get either more acetylene or sawzall blades to cut the front ujoint out and the motor can come out after that.

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dezz

· #13 · Dec 15, 2017

Why would you cut the u-joint out? Just take it apart. It's not hard.

Dennhop

Discussion Starter · #14 · Dec 15, 2017

Popped the c clips out, and started trying to drive the end caps out to separate. They don't want to move at all, they're seized. Figured I'd cut it out and separate it, then get the caps out when I have a bit more access to them.

Dennhop

Discussion Starter · #15 · Dec 15, 2017

Just found out that pulling the motor out will separate the front driveshaft. So motors out, heads off. Aaaaaand progress comes to a screeching halt. Exhaust valve tagged the Piston. Gonna have to replace it before I go any further.

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dezz

· #16 · Dec 16, 2017

Replace the valve guide too. It might be cracked or bent.

Dennhop

Discussion Starter · #17 · Dec 16, 2017

Thank you for reminding me...forgot to order that.

Dennhop

Discussion Starter · #18 · Dec 18, 2017

Anyone know where I can buy the valve guide driver and installer for less than $100?

Scoundrel

· #19 · Dec 18, 2017

Dennhop said:
found the gear on the crankshaft assembly for the timing chain was cracked, allowing it to slip on the crankshaft when trying to turn over. My issue now is the only reference to that part is as part of the entire crankshaft assembly, which is around $420 or so.
I'll see if I can upload a picture.

OK dumb question time, and possibly this ship sailed a long time ago, but...
Are you sure that gear is cracked, and is not a two-part gear with maybe some sort of key that sheared off?

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Dennhop

Discussion Starter · #20 · Dec 19, 2017

It's definitely cracked...the line isn't a clean straight machined line, and when I got my new motor in, the gear on that one has no cracks or separation lines in it at all. I'd be a little upset if it wasnt cracked, with how much work I've done so far, lol.

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