What happened to my crank?

[Octanee]

Hey guys, So I picked up a pro rmk that went down last weekend, guy said cruising the trail and it started to sound bad and he let it idle down then it shut off. I pulled the jugs, the pistons had some scuffing, i was hoping for it to be a piston issue, but I see one of the connecting rod mains on the MAG side perhaps lacked oil, It got hot enough that its dry like theres no oil at all, however the wrist pin feels ok and the bore has that sticky oil feeling to it. the clutch side is OK. Sled has only 1700km on it.


Would Could It be that the "infamous" oil cap issue occured? but I'd think both would look dry? and oil pump, well it should be dry both sides again right? Maybe a plugged oil spray jet? or 2 somehow?. or maybe just a literal rod main bearing failure which caused it to get hot enough for the oil to just disintegrate? It still spins over just fine however its STIFF, no chunks or looseness otherwise.


Also that cylinder has some sidewall scuffing from the fine particles, but doesn't feel like any roughness, maybe some muratic acid and a re-honing to fix that?


Sorry for big picture size, I tried to shrink them down but it wouldn't let me.

 

[BILTIT]

Lack of oil or bad rod bearing. Get a vent on that tank and start replacing some engine parts.

I have had two rod bearings go and they are always on the trail at part throttle.

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[Vance Matheson]

Thats exactly what happened to my 12 pro. I knew it was going to happen just never know when. Same bearing also.

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[Vance Matheson]

New crank is about 650

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[Octanee]

Thanks for the replies guys, so when you had a similar failure.. It was just a bad crank and not a oil issue? Id hate to invest 1500 to find out it was an underlying issue! But I probably am over thinking it a bit.

I know I'll deff be fixing the cap vent, maybe make it vent all the time? And at that increase the oil pump for extra lubrication.

 

[Vance Matheson]

Turn the oil pump up 3 turns for sure. I believe its common for that bearing to fail. Mine always used oil so i dont think it was a vent issue.

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[Octanee]

Alright, well I ordered a reman crank, How about my cylinders? Should I use some muratic acid to scrub the aluminum off then give it a quick re-hone? Doesn't look like the nikasyl layer s hurt or any cracks in the cylinders.

 

[HotShotHarry]

Hey Octanee. Gave up on turboing that RT?. Sold my RT too. Welcome to the Polaris world. Also helps keep the dust of the tools. I have 2. An 11 Pro NA and a 14 Turbo... Loving it. Good to see you here.

 

[Teth-Air]

I bet it was clutch side bearing? (PTO) All failures seem to be on that side. Also have your dealer confirm the oil pump is working to feed that side.

 

[Rhodesie]

the mape crank wasn't the best quality. fuji's seem to have less issues. hopefully the rod never hit the lower case.

 

[Octanee]

Hey Octanee. Gave up on turboing that RT?. Sold my RT too. Welcome to the Polaris world. Also helps keep the dust of the tools. I have 2. An 11 Pro NA and a 14 Turbo... Loving it. Good to see you here.

Geesh I barely remember your name haha, and yes long ago I gave up on it. Rebuilt the engine, drove 2pkm, faulty cylinder repair, engine grenaded, company claims its my fault, and I was looking at another 1500, ontop of 1500 for 20km. I called it quits. I bought a yamaha apex with the 310 kit on it, love the sled, now selling that and looking to buy for my self a 13 pro with a boost it turbo kit. Figure try light weight but I still want some power! The sled I got the bad crank in, I bought it last weekend for cheap so it'll be a spare sled for family and friends haha.

But yes I'll have to dust off the ol tools, I'm a bit rusty on the 2 stroke world now!

 

[Octanee]

[crank failure happened on the mag side

 

[rmk600700]

Turn the oil pump up 3 turns for sure. I believe its common for that bearing to fail. Mine always used oil so i dont think it was a vent issue.

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Yep some dealers turned them up during pdi and others didn't. Either turn up oil pump or add oil for premix, both seem to work OK. Since your doing the motor anyway turn that pump up!

 

[neilsleder]

What year of pro? I think 13 and up had Fuji cranks that were better. I would replace with a Fuji crank.


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[Octanee]

I thought it was a 13, its actually a 12. Getting a re-man from CVt-AAB, so I'm sure it should be stronger than a new crank per say using good bearings.

 

[Beels]

What year of pro? I think 13 and up had Fuji cranks that were better. I would replace with a Fuji crank.


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They started using Fuji cranks sometime during 2012 MY.

 

[Lund]

Hey Octanee. Gave up on turboing that RT?. Sold my RT too. Welcome to the Polaris world. Also helps keep the dust of the tools. I have 2. An 11 Pro NA and a 14 Turbo... Loving it. Good to see you here.

Haha, was going to say the same about the RT.
Octanee, before putting together post pic's of your pistons, crown and exhaust sides.

 

[tstams]

I had 3 reman cranks all lasted less then a thousand k, everyone we took out was a bearing failure. I ended up putting a axys crank in a 2012 pro rmk motor, was well worth the 1500.

 

[flying frenchman]

Mine just did it too. What a piss off. Drive 12 hrs to ride 1.5 miles up the trail.
Mag side.

 

[Octanee]

Haha, was going to say the same about the RT.
Octanee, before putting together post pic's of your pistons, crown and exhaust sides.

It's sure been a while lund! you still got the ol RT? what do you ride these days?

I'll get some pics after work of the pistons, I'm replacing them anyways with that "fix it kit"

Mine just did it too. What a piss off. Drive 12 hrs to ride 1.5 miles up the trail.
Mag side.

Wow that really is no good after a long drive!

I had 3 reman cranks all lasted less then a thousand k, everyone we took out was a bearing failure. I ended up putting a axys crank in a 2012 pro rmk motor, was well worth the 1500.

Good to know, I sure hope I don't have those issues, I'm going to turn the oil injection up lots,