.003 runout...ride it?

[HotShotHarry]

2014 pro rmk 800. Crank run out is a exactly .003. About 4000 miles on engine. Boondocker turbo. Would you run it?

 

[CJD]

send it.

 

[RXN]

0.003". What's spec?

We deal with much bigger slower turning shafts. So 3 thou is nothing.

I'd probably run it until it grenades and replace the engine then

 

[HotShotHarry]

Spec is .0025

 

[Bnorth]

Send it. That's better than some brand new Doo cranks.

 

[RXN]

Spec is .0025

I'd run it. In my world that's not bad. Keep on eye on it and see if it worsens. Or if vibrations go up

 

[HotShotHarry]

You are right. It isn’t too bad. However, every time I go over the mountain.... Im going to be thinking about it. $676 for a rebearinged crank at Motts. Replace the pistons again and should be good for another couple seasons.

 

[ABMax24]

Sometimes you can have the crank straightened without having it rebearinged. I had mine done, rode it another 2500 km after that, finally a rod bearing let loose after 5500km total because the oil pump quit. Most of those kms were turboed as well.

 

[RXN]

You are right. It isn’t too bad. However, every time I go over the mountain.... Im going to be thinking about it. $676 for a rebearinged crank at Motts. Replace the pistons again and should be good for another couple seasons.

Yeah it's a tough call.
I guess if it is going to pick at you. And you have the cash on hand then go with the old when in doubt change it out

 

[ctd]

It's very close to spec, the problem is you do not know if it has moved. If you would have checked it new or when the clutches were serviced you wouldn't be guessing.

Back together, run it for weekend & re check.

Not a science project.

 

[HotShotHarry]

Thats a thought.Although, would it get much worse in one weekend ride? Not likely. Its one of those things.. what to do? Lol

 

[ABMax24]

I'm assuming you are measuring runout at the PTO end with the crank still installed?

Technically the 0.0025" clearance applies when the crank is pulled from the cases and setup on V-blocks on the center 2 bearings. If it's still in the cases it's possible the runout is actually higher than 0.003". I think mine was a full thousandth more when removed from the cases and on V-blocks than when in the cases.

If it's a true 0.003" runout it's not likely to cause immediate disaster, but that being said if it was my crank and pulled from the cases I'd be having it trued while out. The shop I had mine trued at set it up on v-blocks and showed me it was less than 1 thou out before I took it back home.

Even with a rebuilt crank I'd have the runout checked before I put it in, I wouldn't trust that it's within spec either.

 

[HotShotHarry]

Yes, the engine is still in the sled and running. You are right. The Polaris .0025 spec is when the crank is set up on blocks.
knowing that it is probably more when taking it out of the cases makes the decision a no brainer. Spend a grand or so on a rebearinged crank now or possibly spend twice that getting the sled out of the mountains.

 

[ABMax24]

I guess that's my point, true the crank you have and then you don't need to buy a rebuilt one. At that point your only out your time and maybe $100 on gaskets. Assuming your existing bearings are still good.

 

[HotShotHarry]

Yes that could be done but..... with 4000 miles on it..... for a grand.... and a bit of wrenching... with High Velocity helping me ....Im pulling it out.

 

[Bnorth]

Are Polaris really sensitive to crank runout? I've never seen a Doo tested that had any amount of km on it that was within spec but they still go for a long time afterward.

 

[HotShotHarry]

There is a good chance that their probably not.... but I am. Lol. I like to have as much confidence as possible, that my sled is going to get my butt back to the truck. I checked yesterday, the engine has 3450 miles it. Ive changed the pistons twice. Inplan on keeping this sled for a while yet. Its hard to justify a new when this one is so done up. Intercooled boondocker, Fox shocks, 36” titanium a arms, blowhole, handlebars, etc, maybe when Polaris comes out with a factory installed turbo....

 

[HotShotHarry]

Well, Im glad I decided to replace the crank after all. The pto crank seal was leaking a bit of oil.... imminent disaster soon to happen. Also, the reeds we’re getting quite worn out. Pistons look good- slight markings where the ring locator pins ride. 1170 miles on them. I would have replaced them next spring anyway, so might as well do it now too. Anyway, thanks to Tom at Motts Machining for the same day crank install, I should be up and running soon.

 

[Bnorth]

Well, Im glad I decided to replace the crank after all. The pto crank seal was leaking a bit of oil.... imminent disaster soon to happen. Also, the reeds we’re getting quite worn out. Pistons look good- slight markings where the ring locator pins ride. 1170 miles on them. I would have replaced them next spring anyway, so might as well do it now too. Anyway, thanks to Tom at Motts Machining for the same day crank install, I should be up and running soon.

Sounds like a quick enough turn around you won't even lose any riding time!

 

[HotShotHarry]

Engine is back together.. on the bench. Just for curiosity sake, we measured the run out on the newly installed crank. .0005. Much better.