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Discussion Starter #1 (Edited)
My 15 year old son and I are doing our first engine tear down together on our 2003 Grizzly 660 after it developed a very pronounced engine knock. We have found the source of the knock... the balancer is striking the connecting rod, but I don't know why or how to correct it. I thought for sure we'd find the balancer gears out of alignment (though I don't know how that would happen), however, they appear to be good from what I can find in the service manual and from the forums. To my knowledge this engine has never been apart. Was running great until it developed the engine knock. Where do we go next?

Thanks for any suggestions/info!

Here's a picture of the connecting rod and balancer contact:
IMG_0777[1].JPG

And here is a picture of the balancer gear alignment:
IMG_0770[1].JPG
 

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Discussion Starter #3
Thanks for the reply!

I took a couple more pictures of the rod and attached them below.

It seems like the balancer is contacting the rod no matter what position the rod is in, laying on the base of the opening, held to the top of the opening, or centered. The contact is right at the base of the rod where it widens to attach to the crank. If it were a bent rod, it seems like moving the rod to different positions in the opening would effect the contact from the balancer, yet no matter what position the rod is in, the level of contact from the balancer seems the same, and is pretty solid (notice the mushrooming of the balancer edge in the initial pictures).

Just trying to make sure I'm going after the correct part before tackling removing the engine completely and splitting the case (already feel like I'm in over my head :) ).

Thanks again for any responses.

IMG_0783.jpg IMG_0784.jpg IMG_0785.jpg IMG_0788.jpg
 

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I guess I'm not familiar with the actual balancer, but is it possible for balancer sprocket to spin on the shaft, or for that matter the crank shaft gear, therefore going out of sync?
 

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@Type10 Welcome to GC from Wisconsin.

Unfortunately it is time to pull the balancing gear set for inspection.
It appears that one or both of the gears has moved.
The balancer driven gear is keyed to the shaft. Never heard of it but it be the key is sheared. Allowing the gear to creep around the shaft. The timing makes will always be proper as they are mechanically sync'd to each other.

Get a factory service manual from GC member oleblue22 site www.501parts.com
 
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Discussion Starter #6
Thanks for the additional suggestions.

I'll get the balancer gears pulled and report back with what I find. Might be a couple days before I can get back to it.
 

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Thanks for the additional suggestions.

I'll get the balancer gears pulled and report back with what I find. Might be a couple days before I can get back to it.
This will require the crankcase to be split...


 

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no need to split case. take the nut off the balancer shaft and you will find the key is sheared. replace the key and cross your fingers, but some damage may have been done. be sure to flush the engine out well as there is lots of metal in it now.
 

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Discussion Starter #9
Finally able to get back to this and I was able to take the balancer driven gear off with no issues, key looked good. However, I cannot seem to get the buffer boss off for the drive gear. I had a 6" gear puller torqued to the point of nearly stripping the threads on the puller and it wouldn't budge. Tried taping the bolt on the puller while it was torqued down in the hope the jolt would cause it to pop loose... nothing. Any tips on how to get this thing off? Could the tightness be an indication it was slipping and is the cause of the timing issue?
 

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does the dot line up with the keyway on crank? That would be normal and would indicate it has not moved. Was the key good on the balance shaft?
 

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hum.....
Working on the gear key for a rod knock?
Just out of curiosity, did you happen to check the timing before removing the top end?
 

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My 15 year old son and I are doing our first engine tear down together on our 2003 Grizzly 660 after it developed a very pronounced engine knock. We have found the source of the knock... the balancer is striking the connecting rod, but I don't know why or how to correct it. I thought for sure we'd find the balancer gears out of alignment (though I don't know how that would happen), however, they appear to be good from what I can find in the service manual and from the forums. To my knowledge this engine has never been apart. Was running great until it developed the engine knock. Where do we go next?

Thanks for any suggestions/info!

Here's a picture of the connecting rod and balancer contact:
View attachment 98371

And here is a picture of the balancer gear alignment:
View attachment 98372
"striking the connecting rod" is generally a bad bearing or bent rod.
 

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The buffer has a woodruf key. The manual suggest replacing the key and the buffer if it is removed.
Can you see any damage on the balancer?
 

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Discussion Starter #16
I think "reogem" was right when originally suggesting one of the gears must have spun. I still cannot remove the buffer from the crank shaft, but as "tombauer" pointed out, the dot on the buffer does not line up with the key slot from the CDI rotor in front of it on the crank. Assuming the two key slots are in line on the crank shaft, the buffer appears to have rotated about an 1/8th of an inch out of place. I'm guessing that means the key sheared and may now be jamming the buffer on the crank shaft.

IMG_0802.jpg IMG_0801.jpg
 

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Now I see some conflicting info on the boss. It may not have a key. I can't imagination that it is just pressed on.
Here is a member that built a big bore 660 that welded the boss in place.
More importantly is the index mark on the boss aligns with the keyway
98454
 

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Discussion Starter #18
The service manually clearly shows putting a puller on the boss to remove it, but every picture I can find of a crank has the boss already installed. Appears to be pressed on. Which means mine just spun on the crank for some reason.

I might try blocking the crank so it can't turn, then tapping the boss back into place to see if it will move. Otherwise, I can think of two options...

1 - Weld the boss in its current location to make sure it can't move any further (like the previous picture), then install the driven gear off by a tooth to get the balancer back in time so it stops making contact. I did place the balancer driven gear on and it seems to be about right when installed one tooth off. No contact and things move freely.
IMG_0806.JPG

2 - Pull the engine, split the case, and replace the crank and the balancer.
 

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I'm Looking at your boss's misalignment vs your key on the crank in your previous photos. To me simply going one tooth off may not be enough to keep the crank and counter balance shaft in proper phasing.

You may need to go 2 or 3 teeth to rephaze them correctly
 

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More thoughts on your issue. I'm wondering if that amount of movement is enough to cause the collision between the balancer and the rod? Has it moved 180°±? Has the boss stopped moving? Can you rotate the engine by hand to see the actual collision?
Here is info/explanation on the balance system. With a theoretical diagram of the crank and balancer movement.
DansMC site

Would it be better to move the drive gear position on the buffer boss one position rather than the adjusting the drive and driven gear timing.
 
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