Backstory: Bought used - more abused than I thought. It wouldn't top out when bought, I was convinced carb needed rebuild. I did that. Still ran like crap. Rebuilt top end. Still ran like crap. Tore carb apart again b/c it sounded like it was "loading up". When doing that I discovered that one of those little red caps for the float slides (that I thought the shop lost when I had carb dipped) was actually down inside the fuel inlet. It fit perfectly.

That was done last spring and may not have anything to do with this but I felt it was important to know top end was rebuilt as was carb.

We rode all last year - no problems whatsoever!!! Last ride on last day in October last year the TB died and I couldn't get it restarted. Parked it all winter and now trying to get it fired up again.

While turning over, sprayed some Carb Cleaner into air inlet. Fired right up. Hm, sounds like no fuel. Pulled filter and blew it out. Seemed to clear it up a ton. Fuel was exiting through filter and out right where I disconnected from carb. Tried again and it wouldn't start.

Pulled carb and cleaned it up and reinstalled. Machine was hesitant but fired up!!! NICE!!! Reinstalled all parts. Tried to start and no go!!!

Pulled airbox back off, pulled plug. Has dark oily film on it - wet. Oh, plug is brand new!! BR7ES (should be one hotter than std. BR8ES). Held finger over hole and turned over. Blew my finger off and then tried to suck it back through hole. I would say feels like great compression!!

Has great spark. Tested with a spark gap tester AND holding plug against block. Both had nice blue spark.

Put back together and it was more hesitant but got it fired up again!! Ran a couple minutes and sounded like it was loading up. It eventually died. Checked all hose fittings and look good.

Changed plug gap from .028 to .025 to .035 with no discernable difference. It "wants" to start - it's so close.

I am beyond frustrated!!! We were supposed to be pulling out tomorrow morning!!!

Fuel: check
Air: check
Spark: check
compression: finger test check

I am at a total loss!!!! Oh, now when I put the carb cleaner through airbox it won't fire up!!! It's like it is flooded but holding throttle full while trying to start doesn't help either!!!

About to blow this thing up!!! UGH!!!!!

Would like to attack this in morning. If I can get this figured out we can still get out early!!! Sorry so long winded, guys, but wanted to give you as much info as I could!!

 

First thing I'd do is get a compression checker. Finger test may work, but my finger couldn't tell 70psi from 100psi, but the motor could.

 

And would also do a leak down test too.

 

 

I didn't have a gage to check. got one from a buddy this morning. It wasn't very kind, either!!!

83 psi!!! Surprised it fired at all!!! We did a top-end rebuild this time last year. In fact, almost exactly one year.

SIGH...

 

Don't forget to check out the bottom end! A new top shouldn't go out in just a year if it's been treated right! I've had a bunch like this to where if there is any play in the lower rod bearing or crank bearings along with leaking seals,they would take a high $ top end out pretty quick.It's just good money down the drain when you do a partial engine job and it doesn't last.

 

How does that work? Does the "slop" in the bottom end cause excessive wear on the piston/rings?

 

If you have any play/clearance in the lower rod bearing or even crank bearings for that matter, a rod may not run straight or "true" in the cylinder bore. If this happens it can cause the piston and rings to wear unevenly in the cylinder by the action of the rod. When this happens a lot of times you can pull the rings off (if they haven't seized) and see the difference in wear around the rings.They can end up being oblong on wear. That's why I wouldn't warranty just a top end only on atvs brought into the shop for repair. I took a chance on a couple that I thought would be ok and they ended up coming right back. Even though it's a simple design,fewer moving parts compared to a 4 stroke,all the parts,the crank,rod,bearings,cylinder bore have to be right for an engine to last. We're talking about thousands of an inch clearances here which are critical as the shop manuals point out. Even when truing a crank shaft with a new rod,the max allowable crank run out is .001

 

Ok, I wanted to follow-up on this issue. I pulled the head, jug and piston. The piston was "coined" along the intake side. I guess you could say "scored" but it didn't look like a normal scoring mark.

Dropped it at my buddy's and the groove was caused by the intake bridge heating up and expanding, thereby pushing against the piston!!! the cause: lack of oil!!! Ouch!!! The cylinder walls were also washed down with fuel.

This quad still runs the oil injector...well, it did!!! That will be getting blocked off and we will be using premix from now on!!!

Is it weird that I actually "feel better" knowing that?? I guess b/c I know what the issue was and I can correct it. It's getting another bore/hone and piston kit and I should have that installed by end of next week.

However...the fuel washdown on the cylinder now has me thinking: how much of that got into the crankcase??? Cuz....that's not good for bearings and/or seals!!!

I am leaning toward pulling bottom end out of machine and replacing all the bearings and seals. I have done several but never the Polaris. Anyone have any tips, advice or part numbers one what I need to replace?

THANKS!!

 

Most people think when a piston seizes it's always an oil pumps fault,when in fact most of the time the piston needed replacing before the seizure ever happens. Very easy for a cylinder to get washed down also by fuel if a carb needs a new needle and seat. Just a lot of extra gas and not enough oil. I've seen too many top ends go out on older machines when the bottom end isn't taken care of and just a top end done. If you're going to keep it I would have a new rod kit installed and crank bearings and seals along with a new top end. Always premix the first tank of fuel at a 40-1 to 50-1 ratio.Easy way to check the oil pump is to clean the small line from the pump to the cylinder base so you can see if oil moves through it. You'll have the tank premixed so there isn't any worry.Bleed the oil pump(10mm bolt at the top) crank the engine up after the rebuild, lift the pump lever all the way up at idle,this tricks the pump into full flow. Check that the line fills with oil and pumps to the cylinder. "IF" it doesn't then you can do a pump block off if you wish.