Hello Sir,

I have done a lot of research and found other forums where people asked you about backfiring problems and the solution may be the camshaft. I have cleaned the carb and I believe that is okay. I am going to attempt to take the ATV apart to see if the "lobe" is worn. a member by the name TLC said Then buy a $40 Cylmer manual is my sugestion. http://www.themanualstore.com/Polari...al-p/m3654.htm
I purchased that one on ebay since this website is sold out.
My question to you is, should I change the timing change and sprockets? or anything else besides the camshaft and exhaust rocker arm?
The machine is a 1998 Polaris Sportsman 500...
thank you for your time.
Jeff

 

Most of the time chain replacement is not needed. Same for the sprockets.Most of the time I just replaced the cam and exhaust rocker arm. If the exhaust lobe is damaged the rocker arm pad will be also.As far as the chain,just pull the right side rectangle plate on the head and you can feel the cam chain.If it's tight I wouldn't replace it.Here's a free pdf service manual you can look at until you get a hard copy.Index of /ORV Manuals/Polaris/1996-1998 - All Models
Plus shows this diagram in the manual on cam timing.

 

okay cool thank you I will look that over I went to the Polaris website and seen that almost everything is the same from a 2003 to a 1998 except it gives different part numbers for the springs that go to the valves... one other question should I inspect the valves themselves and if so how? I see they do not cost that much, worth replacing?

 

this is what I found while looking up parts, while I have the top end apart should I replace any of these or just check the timing chain like you said and if tight everything else should be okay?

Parts for changing the camshaft

2003 sportsman 500 HO

#14 new camshaft 3085855

Polaris says to include 15-18

#15 Pin, Dowel 3086838

#16 Lever, Release 3085348

#17 Spring, Return 3085076

#18 Pin, Dowel 3084899

Timing chain Parts

#19-24

( Crankshaft & Pistons)

#16 Sprocket 1 3084882

#19 Sprocket 2 3084914

#20 Bolt and washer 3081657

#21 Guide, Chain 3084916

#22 Chain, Timing 3084915

#23 Bolt, Pivot 3084924

#24 Lever 3084917

Rocker Arm

#6 Intake Rocker Arm 3084910

#7 Exhaust Rocker Arm 3084913

#8 Nut (1 intake, 2exhaust) 3084912

#9 screw(1 intake, 2 exhaust) 3084911

Valves

# 11 Collet, Valve 3084908

# 12 Retainer, Spring 3087203

# 13 Spring, Valve 3084906

# 25 Valve, Intake 3085349

# 26 Valve, Exhaust 3085412

Differences between 2003 & 1998

Valves

#12 Retainer Spring 3084907substituted by 3086893

#13 spring, Valve 3084906substituted by 3086892

 

Cam shaft comes as a complete assembly with the spring lever,etc.(15-18) Just replace it and the exhaust rocker arm. You don't have to pull the head to change out the cam shaft! You do if you need to do any valve work.This can get labor intensive,plus lapping valves,valve guide seals,etc. 99 percent of the ones I changed the cam shaft on,the engine would idle ok,but spit and back fire from the flattened cam lobe. Cam shaft,exhaust rocker arm and possibly a cam cover gasket if you damage the old one is usually all that's needed.

 

okay I understand, but ones on ebay I found only show the camshaft they do not show or say they include the dowel pins and lever ect... I guess I will have to email them to find out what comes with the camshaft unless you know a better place than ebay?
thank you

 

Ebay does have some after market cams that are cheaper than most oem online places. I think a couple people have used them with good luck,plus a lot come with the exhaust rocker arm and from what the pictures show the cam is complete..http://www.ebay.com/itm/NEW-ROCKER-CAMSHAFT-POLARIS-SPORTSMAN-500-EFI-HO-RSE-TOURING-X2-96-00-01-02-03-/360496403102?pt=Motors_ATV_Parts_Accessories&hash=item53ef42929e&vxp=mtr

 

okay if I put in the manufacture oem part number in ebay than that will not be an after market correct? I believe the cam part number I want is 3085855. I reviewed the PDF file you gave me and I found the sections about removing and installing the camshaft but I am a little confused... Do I have to remove the gas tank and the front fender? to get to the top end of the motor?

 

You're trying to get too deep in to this! Your actual cam replacement is oem#3086212,BUT you can use the later model HO #3085855 cam. The only difference is the cam duration,all other specs,lobe height,etc is the same. Look close on some of the Ebay ads as they say it's a replacement for the #3085855 cam. They don't actually come out and say it's the oem Polaris cam,but the price of the cam and rocker arm is about $150 cheaper than going online at such places as Cheap Cycle Parts for the cam and rocker arm. Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse And yes it's best to pull the gas tank to have room to work,especially on the left side of the engine where you have to remove the thermostat housing and the cam cover to be able to pull out the old cam and insert the new one.

 

okay I understand now I looked closer and I see where they use their part number and say it is a replacement aftermarket cam... Thank you...