I picked up a nonrunning 98/99 SP500 HO for $175 mainly for parts because the previous owner did not know what the problem was, turns out it needs a cam and a carb,I got it running but it will not rev up past mid throttle.The carburetor is body is cracked near the diaphram housing and the cam has a bad exhaust lobe"checked"but the engine is sound as well as the drive portion.I do not want to put alot of $$$ in new parts,I know the 400 cam will interchange as well as the scrambler according to the polaris parts site but will the carbs dispite the jets? I asked the dealer about a 2002 SP 500 cam and he said it would work but the Polaris site shows a different part #,is there a difference? I shop Ebay alot and plan to go used,just need to know what will work.I have a 02 SP500 I ride all the time so this is just a no rush budjet fix

 

In 2001 polaris went to the 500 HO, they put a different cam and a 40mm carb on them, it really helps in the power dept, If you want to stay with the stock carb I have a good one I'll sell for 100 bucks.

 

Hmm must be a 01,found a cam.I may try it first to see if it solves the no rev issue.I still may be a player on your carb,I'll email you if I decide.Thanks

 

79 Hugger. I see where you had a problem with the 500 Polaris engine not reving past mid throttle. I'm having the same problem. What did you find was the problem? Thanks, You can e-mail me at R-Stout@hotmail.com

 

The Polaris 500 engines are known for the exhaust lobe on the camshaft to wear drastically - The original design did not allow for enough oil flow on startup. "Solution" was ... make a camshaft with a larger diameter oil passage. This is part of the reason for Polaris specifying 0W40 engine oil. Thinner "cold" oil pumps faster. Even with the larger diameter oil passage, the camshafts (even on the HO's which came later) will still wear over time, especially for the people that want to save a buck and use a heavier oil like the 5W40 and 10W40.

Reason for the "story" - when the exhaust lobe wears past a certain point, the exhaust valves do not open all the way, so the piston cannot expel all of the exhaust, which means that the intake stroke cannot "suck" as much air and fuel because there is still "volume" in the cylinder - therefore causing the higher RPM levels to cut out.

Pull your valve cover off and take a look at your rocker arms - pull the recoil starter rope and watch the rockers move up and down - you will notice the lack of "stroke" on the exhaust rocker compared to the intake rocker if your cam is going south. With the removal of 4 more bolts, you can take the rocker assembly off and "see" the condition of the lobes, and any wear that will be on the exhaust rocker.

The camshaft is replaceable without removing the cylinder head.

 

Good discussion on the cams on the 500. Tell me if this is the same engine as the 500 ranger 2005 carabureted. Dad is having a problem with the no compression but the valve clearance was tight. he backed them off and now gets 30 # but of course it still wont go and blows back through the intake. can it be out of time? How is the timing set. The timing chain seems tight he tells me. I cant get there till friday but he is chomping at the bit to get in the field and needs it for running back and forth. At 81 you can't walk to the tractor all the time. Any ideas would be helpful.

Rocknchair

 

All the Sportsman/Scrambler 500 Fuji motors are the same. They changed the Cam and carb and added a throttle body (efi) but the engine core itself is the same as it always was.

<div class="FTQUOTE"><begin quote>I asked the dealer about a 2002 SP 500 cam and he said it would work but the Polaris site shows a different part #,is there a difference?</end quote></div>

The 02 has the H.O's high duration cam that was first used in the Sramblers in 98 and later in the 500 Sportsmans in 01.

 

the 500 ranger is not a 500 HO motor it has a bst 34mm carburetor and the original 500 cam. if you have cam problems, you might as well put the bigger cam and carb on there, you will notice the difference right away

 

I wonder if the H.O cam on its own with the original 34mm carb would be a noticeable power upgrade?

BTW Good info to know "Ujoint".[img]i/expressions/face-icon-small-smile.gif[/img]

 

You can drop an HO camshaft into a regular 500 - my sister has a '98 Sportsman that dad did this to. There is noticeable power increase, but I think he had to make a jetting change in the carb as it was running richer and fouling plugs - I can't really remember, he did this to her quad about 4 years ago.

Upgrading to the cam AND larger carb is a little more involved than just replacing cam, carb and adapter - the 500 exhaust pipe is a smaller diameter than the HO ( if I remember right 1 1/4" vs 1 1/2"), so you actually start choking the cam & carb upgrade if the exhaust is not changed as well.