Polaris 800BB crank failure help

[Desperado]

I'm working on an 02 800 RMK all stock due to a crank failure. What appears to be the problem is the lower rod bearing went out on the PTO side. This was a recently installed new crank from a local Poo shop. The crank probably has about 600mi on it now. What I'm looking for is possible causes for failure. So far I have not been able to find anything obvious to tag the failure to. I did not see anything wrong with the crank seal, case halves carb boots, oil injection, jetting etc. This was the first ride for this sled this year. We got her up the trail about 8mi before it failed. Elevation starting was 4000 ft and the crank failed at 6500 ft. Any imput would be appreciated.

 

[Ollie]

I'm working on an 02 800 RMK all stock due to a crank failure. What appears to be the problem is the lower rod bearing went out on the PTO side. This was a recently installed new crank from a local Poo shop. The crank probably has about 600mi on it now. What I'm looking for is possible causes for failure. So far I have not been able to find anything obvious to tag the failure to. I did not see anything wrong with the crank seal, case halves carb boots, oil injection, jetting etc. This was the first ride for this sled this year. We got her up the trail about 8mi before it failed. Elevation starting was 4000 ft and the crank failed at 6500 ft. Any imput would be appreciated.

They have a larger bearing that needs to be installed on the crank.
http://www.startinglineproducts.com/catalog.cfm?pageID=detail&catalogID=3&catID=18&productID=153

Also, make sure your clutches are balanced.

 

[johnsodo]

might be a bad cluch and cases that put the crank out of phase when the crank gos out it will move on the rod pin and pinch the rod

 

[cowboysedge]

Its a common failure on the 800 crank, usually the rod pin on the pto side will break because the pto crank bearings have gone bad. I have seen twenty or so break both with the stock bearing and the wide bearing.

There are many factors to why this happens. Case flex, worn cases, unbalanced drive clutch, and the worst part of all. Polaris pretty much just took there old big block 700 crank used a smaller rod pin and moved it out to get the stroke for the 800 top end. Creating more power with weaker parts.

This is only my 2 cents.

Just wondering if you had your cases line bored at the time you relaced your crank? And did your old crank break?

 

[Desperado]

Its a common failure on the 800 crank, usually the rod pin on the pto side will break because the pto crank bearings have gone bad. I have seen twenty or so break both with the stock bearing and the wide bearing.

There are many factors to why this happens. Case flex, worn cases, unbalanced drive clutch, and the worst part of all. Polaris pretty much just took there old big block 700 crank used a smaller rod pin and moved it out to get the stroke for the 800 top end. Creating more power with weaker parts.

This is only my 2 cents.

Just wondering if you had your cases line bored at the time you relaced your crank? And did your old crank break?

I've rebuilt several 800's that had the broken crank issue but I've not delt with one that had the rod bearing go out. As for this crank No the crank did not break it simply siezed up and we towed her home. When I tore her down is when I discovered the lower rod bearing issue. As for what work was done on the engine by the Poo dealer before it was purchased I could not tell ya. I have no clue whether they linebored the cases before installing the new/rebuilt crank. It does not have any upgrades such as the wide bearing mod etc. I've read many of Indy Dans posts describing why the pto crank pin breaks but not many on why a failure like this may happen. Before we rebuild this thing I was hoping to find a reason why it failed so I can be sure that when I put this thing back together I resolve the problem on why this lower rod bearing went gunny sack on us.

 

[cowboysedge]

If the crank was a rebuild and you have checked everything that you think might have caused the lower rod bearing to fail, I would have to say maybe it was a problem before the motor was ever assembled.

I have seen some pretty shabby rebuilds on these 800 cranks. I have seen shops take pieces and parts used some completely wore out and new throw them together and call them freshly rebuilt! The only way to know what you are getting is to see every part before it is pressed together. There are many good shops out there who do a great job but there are a few who are out there putting together junk and selling it for $500 dollars. I have felt the pain of the 300 mile rebuilds a couple times.

As you know lots of things can cause bearings to go bad. You said the bearing went on the first ride of the season right. Where was the sled stored all summer? Was the humidity high where it was stored. Is there anyway moisture could have got to it? Just a little rust and there it goes.

Anyway good luck finding the problem.

 

[badass1000]

I had a buddy that replaced the crank in his 800rmk. When he did it he used all new parts. new rods, pistons, etc.. It was line bored, cases checked, big bearing, etc..
The place that originally did the crank would not warranty it. So he sent it some where else. I can't remember 100%, but I believe the new rods he had instaled were too tight of clearance on the crank. The big end of the rod was blue from heat. Bearings went out. Called the rod place with all the info and they sent him new rods, but wouldn't cover labor. If the guy who originally put the crank together would have checked all clearances on crank and rods he would not of had the problem.

 

[jim]

You need to get with Indydan on here...he has a crank rebuild kit that uses a forged end and beefed up bearings. Believe he puts a one or two year warranty on it. It all makes sense to me from a mechanical standpoint. And, yes, those cranks are fragile.

 

[sled_guy]

Improper summerizatoin of the motor? If there was moisture in the case and that bearing got any rust on it at all then that could cause the failure.

Where is the oil pump set at? If the oil pump is a little "low" then over time a rod bearing will fail.

I've been told by 2 different crank guys that if the rod bearing fails its an oiling problem.

sled_guy