Oh, no worries! I would've assumed it was identical or at least very close. As it turns out, there are more differences that I wouldn't have thought of.
What caused this piston failure? 340 fanner
- Thread starter TurboSportTSi
- Start date
So, the primary had weights for 0-2000' elevation.....just ordered ones for 6-9000'.
That might explain why your top speed was so low. The clutches may not have been able to shift out fully with the heavier weights.
Makes sense. I kinda want to leave it the way it is as a governor of sorts...I don't necessarily want maximum performance until my 6 yo gets more experience, but if it will cause engine problems, I'll set it up per the manual.
I guess the only negative would be the engine revving high with a relatively low ground speed and thus less airflow/cooling. Does anyone see this as a problem or would the motor be cooled adequately from the fan?
I guess the only negative would be the engine revving high with a relatively low ground speed and thus less airflow/cooling. Does anyone see this as a problem or would the motor be cooled adequately from the fan?
G
Running the motor at WOT and well below the rated rpm will contribute to your overheating.
I would run the correct weights for your elevation and would use the secondary and ignition timing to control performance.
The better governor might be retarding the timing by a couple degrees which will lower tq/hp and send a lot of the heat load down the exhaust pipe instead of retaining it on the piston crown. Heat down the exhaust is waste heat (ie: It is energy that isn't contributing to making power) and on a two stroke as the exhaust temps go up the power band moves up m (ie: the power band will be higher rpm than the rated rpm is). Timing can be changed with an offset flywheel key or rotating the stator plate.
If your concern with the little one is speed, the better way is to use a heavier spring in the secondary. This will slow up-shift which lowers speed while allowing the engine to build more rpm before shifting out. If your concern is throttle response then using a lighter spring in the secondary will speed up the up-shift resulting in a situation like running your car in too high of a gear; The down side of the light spring is the lowered rpm and fan function.
For CVTs the simplistic approach is the primary senses engine torque and rpm and the secondary senses driveline resistance/torque; Use the primary (spring/weights/ramps) to control engine rpm and the secondary spring/helix to control shift out and down shifts.
Building a restrictor plate and placing it behind the carb boot might also work better than over weighting the primary clutch.
I would run the correct weights for your elevation and would use the secondary and ignition timing to control performance.
The better governor might be retarding the timing by a couple degrees which will lower tq/hp and send a lot of the heat load down the exhaust pipe instead of retaining it on the piston crown. Heat down the exhaust is waste heat (ie: It is energy that isn't contributing to making power) and on a two stroke as the exhaust temps go up the power band moves up m (ie: the power band will be higher rpm than the rated rpm is). Timing can be changed with an offset flywheel key or rotating the stator plate.
If your concern with the little one is speed, the better way is to use a heavier spring in the secondary. This will slow up-shift which lowers speed while allowing the engine to build more rpm before shifting out. If your concern is throttle response then using a lighter spring in the secondary will speed up the up-shift resulting in a situation like running your car in too high of a gear; The down side of the light spring is the lowered rpm and fan function.
For CVTs the simplistic approach is the primary senses engine torque and rpm and the secondary senses driveline resistance/torque; Use the primary (spring/weights/ramps) to control engine rpm and the secondary spring/helix to control shift out and down shifts.
Building a restrictor plate and placing it behind the carb boot might also work better than over weighting the primary clutch.
This may help understanding the clutch operation relationship to rpm.
There is no wash on that piston, exhaust side seize, intake mostly clean, I don't see any detonation (will erode the exhaust edge if that's the cause). For an overheat condition, I would expect intake to be seized up much more than that, I'd expect oil to be burnt onto the underside of the crown (it's clean) and you usually see minimal to no oil on the wrist pin bearing (it has a ton of oil). So not oil shortage either. It burned down lean (unfortunately I have experience on lean burn downs...).
How did the other piston look? Any pics? Was the wash good? Etc? That will tell you how your jetting is. If the other piston has minimal wash, that could do it. Also, mag sides often require more gas as the magneto runs them a bit hotter...and sometimes one cylinder just likes a little more gas due to variation in manufacture.
That said, I am suspecting a leak of some type on that side. Intake boot? Intake gasket? Exhaust gasket? Crankcase seal? Crankcase gasket? Something made that side run too lean. Was it "loud" due to bad exhaust donut?
And a tip for your first time back out, watch the pre-mix. That actually leans you out a bit because the fluid/gas is more viscous. Yes, you have more oil...but oil is not your issue here. And it's a good idea to run a bottle of octane booster just to keep temps down a little more when breaking it in...I use Royal Purple after many trials. Is available everywhere and works well. Is just an added safety measure.
How did the other piston look? Any pics? Was the wash good? Etc? That will tell you how your jetting is. If the other piston has minimal wash, that could do it. Also, mag sides often require more gas as the magneto runs them a bit hotter...and sometimes one cylinder just likes a little more gas due to variation in manufacture.
That said, I am suspecting a leak of some type on that side. Intake boot? Intake gasket? Exhaust gasket? Crankcase seal? Crankcase gasket? Something made that side run too lean. Was it "loud" due to bad exhaust donut?
And a tip for your first time back out, watch the pre-mix. That actually leans you out a bit because the fluid/gas is more viscous. Yes, you have more oil...but oil is not your issue here. And it's a good idea to run a bottle of octane booster just to keep temps down a little more when breaking it in...I use Royal Purple after many trials. Is available everywhere and works well. Is just an added safety measure.
OK, gentlemen, I just made a bonehead move. Well, technically Polaris made the bonehead move, but I sure didn't help. Got it back together and was anxious to get it at least mostly broken in while there is a still a skiff of snow; this way I would be confident that it'd be ready for next season.
Well, I realized that I never did clean out the check valves on the outlet side of the oil pump, so I popped the feed line off and tried to flush it with carb cleaner the same way I did with the oil injectors. I put the feed line back on and proceeded to go break in the motor.
Anyway, the motor was smoking pretty good when I first fired it up, which was expected since I adjusted the oil pump arm to be correct @ WOT and liberal @ idle. I loaded it onto the trailer and drove off. It stopped smoking during break-in and I had a hunch, so I pulled the exhaust and looked up the y-pipe. Sure 'nuff, the PTO side piston is scuffed up and the mag side is a tiny bit scuffed. The pistons had break-in coating on the skirts, but it was more than just worn off...there are vertical scuffs in line with the exhaust port. Son of a B. Both pump to cylinder oil lines were empty. So much for pre-mixing...didn't help much at all. Maybe delayed the inevitable. I think I had it around 100:1, roughly.
Why the heck would Polaris make an oil pump that is not self-bleeding? Actually, I found out that they do make a kit to convert it to self-bleeding, due to the burn down issues with the old 550 fans...definitely going to be buying one of those because this is a stupid problem to have and is 100% avoidable. Remember, I'm a car guy and totally new to 2 strokes, so this is a paradigm shift to some degree.
Compression test shows about 80 psi on the pto and 110 on the mag. Adding a bit of oil brought both up 5-10 psi. I only drove a couple miles....2 or 3, maybe. Hoping the rings aren't fully seated yet and will improve with more running, but the damage is already done and more running isn't likely to improve anything. The question now is: Should I just run it until it gets hard to start, then rebuild or just do another rebuild over the summer? It's not like the rebuild process on this motor is difficult or time consuming, and isn't terribly expensive either, assuming the jugs are still OK.
Also, I never did pressurize the motor and check for leaks. I will do that when I get some free time. Hoping my existing kit is the correct size.
I had high hopes for this thing, with a fresh rebuild, clean carbs, corrected jetting, and adjusted oiling. Perhaps we will get there someday, though the track is still pretty hard to turn by hand, at least compared to my '07 M8 163 and '08 Summit Adrenaline 144. On the bright side, the sled took my not-so-small self a bit over 40 MPH on mashed potato snow, so it's at least better than it was!
Well, I realized that I never did clean out the check valves on the outlet side of the oil pump, so I popped the feed line off and tried to flush it with carb cleaner the same way I did with the oil injectors. I put the feed line back on and proceeded to go break in the motor.
Anyway, the motor was smoking pretty good when I first fired it up, which was expected since I adjusted the oil pump arm to be correct @ WOT and liberal @ idle. I loaded it onto the trailer and drove off. It stopped smoking during break-in and I had a hunch, so I pulled the exhaust and looked up the y-pipe. Sure 'nuff, the PTO side piston is scuffed up and the mag side is a tiny bit scuffed. The pistons had break-in coating on the skirts, but it was more than just worn off...there are vertical scuffs in line with the exhaust port. Son of a B. Both pump to cylinder oil lines were empty. So much for pre-mixing...didn't help much at all. Maybe delayed the inevitable. I think I had it around 100:1, roughly.
Why the heck would Polaris make an oil pump that is not self-bleeding? Actually, I found out that they do make a kit to convert it to self-bleeding, due to the burn down issues with the old 550 fans...definitely going to be buying one of those because this is a stupid problem to have and is 100% avoidable. Remember, I'm a car guy and totally new to 2 strokes, so this is a paradigm shift to some degree.
Compression test shows about 80 psi on the pto and 110 on the mag. Adding a bit of oil brought both up 5-10 psi. I only drove a couple miles....2 or 3, maybe. Hoping the rings aren't fully seated yet and will improve with more running, but the damage is already done and more running isn't likely to improve anything. The question now is: Should I just run it until it gets hard to start, then rebuild or just do another rebuild over the summer? It's not like the rebuild process on this motor is difficult or time consuming, and isn't terribly expensive either, assuming the jugs are still OK.
Also, I never did pressurize the motor and check for leaks. I will do that when I get some free time. Hoping my existing kit is the correct size.
I had high hopes for this thing, with a fresh rebuild, clean carbs, corrected jetting, and adjusted oiling. Perhaps we will get there someday, though the track is still pretty hard to turn by hand, at least compared to my '07 M8 163 and '08 Summit Adrenaline 144. On the bright side, the sled took my not-so-small self a bit over 40 MPH on mashed potato snow, so it's at least better than it was!
The mag side piston is pictured in post #6. Only 1 picture, but it had a narrow scuff, off-center.
As for the potential air leak, I will check that out and report back. I didn't do it before teardown, so now that it's back together, it would be good to know if I have a seal in the lower end that is leaking. The gaskets and boots all seemed good to me when I was pulling it all apart.
The exhaust is quite loud, actually, but it does not use a donut. I verified this with a parts diagram. Kinda odd.
G
Don't run it with 30psi difference between cylinders.... hard on the crank and primary. 10psi max is the rule.
Assume around 10hrs run time to fully seat the rings. On the compression gauge don't expect to see more than a couple psi difference between brand new rings and rings with 10hrs.
Premix at 50:1 for that first tank; for the reasons you have unfortunately discovered. If the oil pump is easily accessible I tie wrap the arm in the WOT position and heat cycle the engine at an elevated idle a couple of times while the sled is still on the stand. After the first heat cycle the oil lines should be air bubble free and the shop full of smoke. I do this any time I open the oil system up or to do an end of season fogging.
Most oil pumps have a manual bleed screw or bolt. The few auto-bleed pumps I have seen rely air bleeding back up the supply line to the oil tank, which requires the supply line to be short as possible and routed so it is near vertical through it's entire length.
Assume around 10hrs run time to fully seat the rings. On the compression gauge don't expect to see more than a couple psi difference between brand new rings and rings with 10hrs.
Premix at 50:1 for that first tank; for the reasons you have unfortunately discovered. If the oil pump is easily accessible I tie wrap the arm in the WOT position and heat cycle the engine at an elevated idle a couple of times while the sled is still on the stand. After the first heat cycle the oil lines should be air bubble free and the shop full of smoke. I do this any time I open the oil system up or to do an end of season fogging.
Most oil pumps have a manual bleed screw or bolt. The few auto-bleed pumps I have seen rely air bleeding back up the supply line to the oil tank, which requires the supply line to be short as possible and routed so it is near vertical through it's entire length.
Yeah, in retrospect, 50:1 makes much more sense than 100:1. If the 100:1 isn't enough to keep the engine from having problems, then there really isn't much of a point outside of 'extra insurance.'
The bleeding system won't be an issue on this machine, in terms of routing. I could see it being problematic for others though.
The bleeding system won't be an issue on this machine, in terms of routing. I could see it being problematic for others though.
On the 800 Polaris rmk, the piston ring pin is on the intake side because the cylinder is tilted so the gap in the ring would want to stay at the higher end of the ring channel, which is the intake side. The first pictures of the piston show piston ring failure on the piston ring pin side / intake side. Which confirms a lack of oil injected into the air stream in the carburetor. You can prime the oil pump by using holding it in your hand with all exit tubes disconnected, (but plugged elsewhere with a 16 penney duplex nail), then hold the lever at wide open throttle and then turning the drive blade by hand. It takes about 5 minutes of this to get oil to flow out the 4 exit tubes. As for the oil lines, you definitely would want to prime those fully by sucking oil out of the oil jug and then quickly plugging into the oil pump. Once all of this is installed, you let it sit overnight and the naturally gravity action of the oil tank being higher than the engine, slowly pushes the tiny air bubbles out. But a couple of small bubbles does not hurt anything. Use compressed air to clean out the 2 oil injector ports in the carburetor. The oil should be consumed at a 40:1 ratio, with half of that being injected into the air stream in the carburetor and half being injected into the 2 outer bearings. The PTO end crank bearing should be changed every 2500 miles, along with all other outer loose crank bearings.
Since the pictures showed the failure on the ring pin side of the piston, and the owner reported the failure to be on the exhaust side, when the pistons are supposed to be installed with the ring pin on the intake side because otherwise the piston ring ends will get hung up on the exhaust ports, THEN THE PISTONS WERE INSTALLED BACKWARDS. Which resulted in rapid heat build up on the exhaust port side of the piston due to excessive friction that was created as the piston rings kept grinding away at the exhaust port.
<=<= That is an actual picture of a Bigfoot hiding behind blackberry vines.
<=<= That is an actual picture of a Bigfoot hiding behind blackberry vines.
The arrow on the piston should point to the mag side of a Polaris, yes?
Yes it should.
Just a recommendation after fighting the 550 engines. Remove the oil pump and mix your fuel at 40:1. They love oil.
If you are running ethanol fuel you will need to jet up as well.
The oil boils/air entrains at the pump from engine heat. The 550 Polaris fix doesn’t work well. Pre-mixing your fuel is the best answer.
Check those pilot jet, make sure they aren’t plugged.
If you are running ethanol fuel you will need to jet up as well.
The oil boils/air entrains at the pump from engine heat. The 550 Polaris fix doesn’t work well. Pre-mixing your fuel is the best answer.
Check those pilot jet, make sure they aren’t plugged.
No. The MAG side and the PTO side are right and left side references. The Exhaust side and Intake side are front and back side references. There obviously is a MAG side or PTO side piston, but that does not describe where on the piston that the ring failure occurred.
The problem with removing the oil pump, is that the critical PTO end crankshaft bearing does not get oil directly injected onto it. Instead, it is blocked from receiving oil from the fuel stream, by the bearing that occurs next to it. In the Polaris model years after 2000, Polaris thought that they would save a few bucks by eliminating the oil drip hole from the upper crankcase half, that again drips oil directly onto the critical PTO end crankshaft bearing. With the oil pump left as installed by the manufacturer, the total oil consumption is 1 part oil to 40 parts gasoline. However, half of that oil is injected directly onto the two end crankshaft bearings, with the other half being injected into the air stream in the two carburetor venturi tubes.
Understood, but what it does describe is that the pistons were installed in the correct orientation based on the arrow markings on the crown...
Are you saying the factory pistons are defective? Arrows on the wrong side and therefore ring locator pins are 180* out?
You can drill the hole out and machine a grove.
In reality the oil is pushed through the bearing and out the hole.
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