Hi all

I have a 2001 Sportsman 500 exhibiting all the usual signs of a worn exhaust lobe: idles ok but above idle it backfires through the carb, loses all power, smells of unburned fuel, runs really rough.

I've stripped down and cleaned the carb twice but not replaced any jets/needles - they looked fine.
The cutout switch on the electric throttle control is working properly.
Valve clearance is spot on 0.15mm (0.006in)
The exhaust and inlet cam lobes are all worn below spec but are all exactly the same size and are not misshaped.
All lobe heights are 31.79mm (1.251in) and service limit is 32.426mm (1.2766in)
The ball bearing is missing from the manual compression release valve.

As the exhaust lobes are the same height as the inlet lobes I'm not convinced the cam is the only problem. Can anybody suggest anything else to check before I spend money on a new cam - yes, I realise I need a new cam, but could something else be going on here?

Regards

Damien

 

Small detent actuator ball missing from the cam is a good sign excessive wear is happening on the cam.Found plenty of these on worn cams too.Yes you need to replace the cam since the lobes are below the service limit, but you can also do a leak down on the head to see if any valves are burnt,leaking and need to be lapped or replaced.Could be another part of the problem. Getting so cheap now(compared to oem parts) that you can replace the whole top end with aftermarket cam,rocker arms,sprocket and gasket. http://www.ebay.com/itm/POLARIS-SPORTSMAN-500-2X4-4X4-CAMSHAFT-CAM-ROCKER-ARM-GEAR-KIT-SET-1996-2012-/261472878394?pt=Motors_ATV_Parts_Accessories&hash=item3ce0ff7f3a&vxp=mtr

 

That's great advice, thanks.

 

That's why the Fuji dry sump motor is fussy with its oil.

Only Use Full synthetic 0w-40 or the new Polaris 2w-50 . That oil with circulate on cold starts much faster then 10w grades that are dinosaur based.

 

Didn't really matter as to oil as I had plenty of customers that only used Polaris 0w40 only,changed it regularly and still had cam failures. Again not all had problems,but many did. Just a bunch of soft heat treated cams mixed in the batch and I had one Polaris engineer tell me that Fugi admitted using a couple different suppliers on cams during the early years.If you've got an old model and it still runs great,you got a good heat treated cam.

 

There never was a 2W-50 oil...it was a marketing ploy by polaris since you will never find that oil any where....viscosity index is in increments of 5 ....i was told by a sop manager at polaris ..thay they got called out on this and had to change it to 5 W...it was some oil institute who scolded polaris...

any good synthetic 5-40...0-40...5-50 works fine....most 50 weight oils shear fast...

also adding 3 oz of moly to oil keeps parts coated till your oil pumps up..moly bonds to metal surfaces...there is some in oil but not much...its an expensive additive...

 

Just a gimmick to bolster oil sales as Lubrication Technologies is the one that makes Polaris branded oils.We were forced to take it,at least for stocking the shelves for people that absolutely wanted it,BUT didn't buy the 50 gallon drums of the stuff.We still had a couple drums of 0w40 we used in the shop.We knew something was up with the PS4 2w50 and then the PS4 Plus 5w50 replaced it.http://www.lube-tech.com/products-se...brand-building Plus their services offering."If you’re an OEM looking to increase customer satisfaction and your profits, use the power of your established brand to boost your bottom line. Let Lube-Tech experts show you how."

Kinda like the guy that took his Harley in for an oil change and wanted Amsoil. The Harley tech said he absolutely wouldn't use Amsoil until they started making motorcycles! The customer replied that he wouldn't use Harley oil until they actually started making their own oil.