Hey OPT/All,


Have a Cam question for you guys. Long story short, been having some backfiring, popping sounds and power issues on hills. Runs great with full power on a flat surface. Looking at other posts I suspected to find the exhaust lobe worn down. Instead I found parts of the left intake and exhaust lobe have been grinded down (see pictures). The lobe height itself looked ok. Would this cause the same issues as a worn down exhaust lobe?


I suspect this is new cam material but wanted to check with you guys first. If this cam is still under an acceptable range what else can cause it to die on a hill but run good on flat? Float issues maybe?


Also, just FYI, this is the second cam as the first was replaced because it did have a worn exhaust lobe. This cam is about 8 -10 years old.

1996 Polaris Sportsman 500


Thanks!
Craig

 

Does your machine have a manual clutch? If yes, I'd take a look at that (see if the metal plates are blued - overheating)...loss of power could be clutch slipping.


Cam - looks trashed to me...are you noticing metal bits in your oil when you service? And those lobes are both chewed up on the right side...looks like the whole cam is shifted left and not centered...just an observation from the pics provided...

 

Thanks DD! I did notice that it looked like it had shifted. How does that occur? Also, sorry I didn't put the model, this is a 1996 Polaris Sportsman 500 so it is an automatic clutch.

Next question, there are a lot of after market cams out there does anyone have any they recommend with decent price and quality? Probably will not go with OEM for over $200 just for the cam.

Thanks!
Craig

 

Not sure why it would do that...I can't see anything definitive from the fiche...hopefully OPT will chime in...I think any aftermarket cam will do...but I think something else is going on as well...


Ilias - please refrain from hijacking other's threads...

 

Looks like the replacement cam from 10 years ago came from the same lot the original one came from. Shouldn't be chipping like this,but this may not be the source of the popping back. If you can get a pair of calipers or a micrometer, measure the exhaust lobe height.Lobe needs to be horizontal to accurately measure it while installed. 1.276 is the limit allowed on wear.Even if you decide to replace the cam and exhaust rocker arm,pull the black wire from the reverse limiter module at the terminal board also. It can mimic cam problems if the module faults and can cause limiting in forward range.Item#31 on the parts break down. Also Niche talks a good talk on their cams(around 70 bucks or so) but don't know if they're any better than the others offered on ebay and amazon. Finding all sorts of good videos today. Here's a good one on cam timing when/if you decide to replace the cam.

 

Thanks OPT! That timing video is was great. As DD noticed it looks like the cam either wasn't centered properly or fell out of center. Do you know if that is normal or if something can cause that? I would hate to put a new cam and rockers only to have something else cause it to wear the new parts.

Thanks!
Craig

 

Cam can only go so far as the cam plate(where the detent arm is) and cam sprocket won't allow it to move.You can see what I mean if you replace the cam. Cam is inserted from the opposite side of the cam sprocket,when sprocket and chain is in the correct position,you push the cam a little further into the sprocket alignment pin.The right rocker shaft block has a bolt through it that fits in the groove to keep the shaft from moving. Doesn't show the bolt in the support block but it should be there.You can see the groove in the rocker arm shaft. If you need a manual,here's a cheap one that can explain better than I can at times.1996 Polaris Sportsman 500 Service Manual PDF Download

 

Ahh yeah that makes sense. I think my picture is just deceiving since it looks like it has moved back but that is probably where it sits. Thanks again for both of your help! Looks like replacing the cam is my next project.

Thanks!
Craig

 

When re-installing the new cam, make sure those rockers are centered over the respective cam lobes...still baffled by how those lobes got chewed ONLY on the right side...may not be the cam that's out, could be the rocker assembly sitting on it...or could be just coincidence...

 

Should be able to see if there is any scoring on the exhaust rocker arm pad since you've removed them. Complete cam kits with intake and exhaust rocker arms are available also if in doubt on any of them. You can go that way or get the Niche cam and an exhaust rocker arm.https://www.ebay.com/sch/?_nkw=Polar...0rocker%20arms