Breaking engine mounts

[Samuraicato]

Hey guys..Norway calling
My 01 rmk 800 keeps splitting the pto front engine mount?
4 times this has happend now.
Any ideas why?
Stock engine.

 

[retiredpop]

Engine torque stop not adjusted properly. It requires an air gap of .010" to .030".

 

[Samuraicato]

For crankcase torque stop the manual says .100" 2.54 mm

 

[retiredpop]

Better go with the .100" then. There seems to be a lot of confusion about this and the spec changes depending on the year.

 

[sled_guy]

Check clutch balance and crank run out. How many miles? Has it broken a crank pin yet?

sled_guy

 

[Samuraicato]

It has about 5000 miles/8000km on it.
When i bought it the left front mount was broken so it was replaced.
The guy i bought it from said crank bearings and pistons had been replaced just before i got it.
regarding the crank pin and crank run out?? what is that

I have changed the mount 4 times now in about 1000/1500 km.
Could bad rear mounts cause the front one to tear apart?
There has been alot of oil and gas on these ruber mounts so they feels soft.

 

[sled_guy]

Yes, if one mount is broke then the others can fail.

But to tear that front one apart every 250km is pretty severe.

Crank run out is measuring the crank end to make sure it is spinning true, not wobbling. The 800s have a reputation of breaking the PTO crank pin which holds the PTO crank lobe to the center lobe and the PTO rod is mounted to. When they are starting to fail you will start to see crank runout numbers go up.

Heck, just for grins, take the belt off, open the clutch guard up and start the engine, letting it idle. Look at the clutch and see if it looks like it's wobbling. As I said, if the other motor mounts are ok then it has to be some wicked wobble in the crank or the clutch is way out of balance.

sled_guy

 

[Samuraicato]

That's exactly what i've been thinking when looking at the clutch at idle.
it sure looks like it's wobbeling..gotta messure that crank tip

 

[FEZ]

i went through 3 PTO fronts on my 00' 700 until i discovered when I set the motor in the left front was not touching the mount so when i tightened the motor mount bolts it pre-tensioned the mount.

i put a thick washer under the PTO front mount to raise it and that solved my problem. I never broke another mount in the 6000 miles i put on it after this fix.

i suspect either the motor plate or the bulkhead is slightly bent or not quite matchy, matchy with each other from the factory.

Some never tear mounts some do.

 

[go high fast]

Shouldn't happen. Remember Henry Lee at the OJ trial....."something wrong". I recommend closely inspecting the torque stop as sometimes the rubber degrades to the point where you are not getting any benefit whatsoever from the torque stop. I would also recommend using the SLP torque arm to further secure the motor from twisting under load. A motor plate can also be helpful as it is better than the stock Polaris motor straps. And while you're at it I would just simply replace all four motor mounts and call it good to make sure all four are of the same stiffness to avoid using some soft and some stiff. I would also inspect the female threads for the front PTO motor mount to make sure it is actually mounting properly and securely into the chassis. Put it on a stand and rev it a bit to confirm both primary and secondary work in unison because if the secondary isn't opening up all the way it will put major stress on the twisting of the engine under load. Regardless of the Polaris specs and I tighten the torque stop up against the crankcase as tight as I can get it finger tight and call it good. Final chore is to check alignment and parallel measures and then let it rip.

If you have an iPhone please post a 10 second slow Mo video with sound of the clutch at idle to see if it isolates crank wobble....i wouldn't have thought of this one.

 

[Samuraicato]

Back with a update on this engine
Checked the crank and we found out it had .0044 runout on the pto side.
Added a slp single & holzman atacc at the end of last season and it was strong as hell this old sled
Had the engine out and everything looked ok. Changed all off the mounts now so will se how it does.