Middle Gear Catastrophic Failure - Yamaha Rhino Forum - Rhino Forums.net
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post #1 of 23 (permalink) Old 03-31-2009, 09:58 AM Thread Starter
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Unhappy Middle Gear Catastrophic Failure

Had a great weekend with the usual antics until my Rhino let off a loud bang, pop, and grind. No movement in gear, but the engine revs fine in neutral. We attempt to tow it back to camp only to learn the rear driveline is locked. After some creative winching, we tow it back - wrecker style. The next day, we replaced the rear axles with just the stubs so I can at least push it into the trailer. When I unload the Rhino at home, I notice about a quart of engine oil on the trailer floor. So, I'm fairly certain it's the middle gear and a windowed case, but I have not begun to tear into it yet. Am I looking at a complete engine tear down to fix this? Is there any chance that gear shrapnel can get into the engine?

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post #2 of 23 (permalink) Old 03-31-2009, 11:01 AM
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I am sure you broke the ears that hold the gear. I have seen many pics of the busted middle drive gear. I hear that make a billet one that will be stronger and make this hard to break next time. So you will have to pull the motor crack the case clean it all up with the shrapnel then place everything back in the new case and install. Once again i not do it personally but spoke to those who have. Sorry for the bad break.
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post #3 of 23 (permalink) Old 03-31-2009, 11:19 AM Thread Starter
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Yeah, this is a tough break for sure. I will definitely add a billet support for the middle gear during the repair.

I have no experience splitting the case on the 660. Does the cylinder need to come off, along with the crank, etc. to fix this?

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post #4 of 23 (permalink) Old 03-31-2009, 11:21 AM
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Yeah, this is a tough break for sure. I will definitely add a billet support for the middle gear during the repair.

I have no experience splitting the case on the 660. Does the cylinder need to come off, along with the crank, etc. to fix this?
Yes. And do yourself a favor while you are in there. Replace that stock rod with a good falicon rod and weld the counter balancer drive gear.
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post #5 of 23 (permalink) Old 03-31-2009, 11:36 AM Thread Starter
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That sucks. I hate tearing into an otherwise perfectly running engine...

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post #6 of 23 (permalink) Old 03-31-2009, 01:07 PM
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Yeah, this is a tough break for sure. I will definitely add a billet support for the middle gear during the repair.

I have no experience splitting the case on the 660. Does the cylinder need to come off, along with the crank, etc. to fix this?
Yes. And do yourself a favor while you are in there. Replace that stock rod with a good falicon rod and weld the counter balancer drive gear.
Weld the counterbalance drive, can you give more specific info? maybe some pictures or a link?
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post #7 of 23 (permalink) Old 03-31-2009, 01:31 PM
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Yeah, this is a tough break for sure. I will definitely add a billet support for the middle gear during the repair.

I have no experience splitting the case on the 660. Does the cylinder need to come off, along with the crank, etc. to fix this?
Yes. And do yourself a favor while you are in there. Replace that stock rod with a good falicon rod and weld the counter balancer drive gear.
Weld the counterbalance drive, can you give more specific info? maybe some pictures or a link?
On the crank there is a gear that presses on that drives the counter balancer. It needs welded so that it does not spin and wreck your engine.

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post #8 of 23 (permalink) Old 03-31-2009, 01:44 PM
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Yes. And do yourself a favor while you are in there. Replace that stock rod with a good falicon rod and weld the counter balancer drive gear.
Weld the counterbalance drive, can you give more specific info? maybe some pictures or a link?
On the crank there is a gear that presses on that drives the counter balancer. It needs welded so that it does not spin and wreck your engine.

This should be done especially if you have had the crank apart for any reason



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post #9 of 23 (permalink) Old 03-31-2009, 01:46 PM
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Weld the counterbalance drive, can you give more specific info? maybe some pictures or a link?
On the crank there is a gear that presses on that drives the counter balancer. It needs welded so that it does not spin and wreck your engine.

This should be done especially if you have had the crank apart for any reason
Rog, That end had never been apart on my crank until it moved. Then I had my last motor problem and found that it had moved. BUT ABSOLUTELY...it should be welded if that end has been taken apart
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post #10 of 23 (permalink) Old 03-31-2009, 02:00 PM
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we will see if mine holds, April 11th Perris, Flying banana!!!



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post #11 of 23 (permalink) Old 03-31-2009, 02:21 PM Thread Starter
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Thanks for the tips. I want to make the rebuild as reliable as possible:

1) Middle Gear Billet Support
2) Quality Aftermarket Rod (Falicon, Carrillo, etc)
3) Weld Counter Balancer Drive Gear to Crank

Anything else?

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post #12 of 23 (permalink) Old 03-31-2009, 02:52 PM
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Thanks for the tips. I want to make the rebuild as reliable as possible:

1) Middle Gear Billet Support
2) Quality Aftermarket Rod (Falicon, Carrillo, etc)
3) Weld Counter Balancer Drive Gear to Crank

Anything else?
CP piston and DLC pin from Benchmark performance



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post #13 of 23 (permalink) Old 03-31-2009, 03:00 PM Thread Starter
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1) Middle Gear Billet Support
2) Quality Aftermarket Rod (Falicon, Carrillo, etc)
3) Weld Counter Balancer Drive Gear to Crank
4) Quality Aftermarket Piston (CP, etc)
5) Quality Aftermarket Wrist Pin (DLC, etc)

What about the cam chain tensioner? I thought I read about that little piece causing problems.

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post #14 of 23 (permalink) Old 03-31-2009, 03:55 PM
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What kind of riding is the cause of this stuff breaking, rocks, speed, rockcrawling???????

08 Rhino(hers)
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Las Vegas, NV.
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post #15 of 23 (permalink) Old 03-31-2009, 04:17 PM Thread Starter
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What kind of riding is the cause of this stuff breaking, rocks, speed, rockcrawling???????
Don't forget sand and jumping...

When it broke, I was testing a jump. I was on the third try before letting it fly, just before the jump - BAM!

I was at Johnson Valley - Boone Rd last weekend. There's a little bit of everything there. On Thurs night, we were on one of the Hammer trails. I'm lucky this did not happen on that trail. It would have been a real ***** to get back to camp...

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