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Discussion Starter #1
Hi Gentlemen and Ladies. I seem to be having some issues with my old girl. I use it to plow. Just got finished replacing and rebuilding rear axle and joints in no heat outdoor shed. FUN! Now, I have no power at all. Engine starts fine, idles fine but when i give it throttle it seems to bog and has no power at all like there is resistance. I pulled the seat and airbox cover to take a listen and there is air or pressure being blown backwards into airbox? What could cause this? Blocked exhaust? Any suggestions would be greatly appreciated.

We have been getting hammered with snow so far this year and snowblowing a 400 ft driveway sucks! Need my plow. If anyone could give me some troubleshooting advice it would be appreciated. Happy Holidays!
 

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It can be a leaking (not completely sealing) intake valve sometimes if it is coming through the carb itself. Can you tell if that is the case or from some hose connected to the air box (do not know your machine)?

What kind of pressure do you feel coming out of the muffler at idle?

Did the power loss occur all at once or just gotten weaker with each plowing/ride?
 

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Discussion Starter #3
Ive really just noticed today but thought it felt weak for the last couple of rides. Didnt have any response on the throttle. Usually plenty of power. It will still plow in low gear and low idle but when i give her a shot it just bogs and with the air box off i can see the out filter on the K and N blowing up with air and a strong muffling sound. If it is a valve not sealing are replacing them difficult? I have time and patience but i also have winter and non heated shelter. I have basically replaced this entire bike minus the main engine and clutch. There does seem to be a ticking sound that is not familiar to the regular slappy polaris sound. I am starting to wonder if it does indeed have something to do with valves or cams. I dont know enough about the internal workings and usually will rip something apart and figure it out. I hope it is not something difficult. I appreciate any advice.
 

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Some of the older years had weak cams. Might be that the cam is shot. You can pull the cover and check the gap. That would be my first idea.
Do you have a repair manual? It's not really all that hard to check the valve lash. But being outside will make it a pain....esp if the cold is hitting your area.
 

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KaBoom with a Polaris shop manual you should be able to do it perhaps. While we are much warmer we just cleaned out an old three sided garage that is in very bad condition to work on our 2 Polaris 325 Magnum's vs the open driveway. We caught it 60F+ last week for a couple days which was nice but have picked up a silver tarp from HF and plan to tarp the garage opening so we can keep out some of the wind and get a little heat from IR 120v heaters.

The shop manual is for the 2002 Magnum line with the 325 and 500 engines covered. While they are very different (325 oil cooled/500 water cooled) many other things like the heads are similar I read.

The project 325 (guy blew oil line and did not know it) ATV we did get it torn down (top end) and removed the connecting rod to look at the crank damage which was extensive. The 325 has rod inserts like a car engine that can be removed AND replaced without splitting the crankcase we found by trial and error over the past two days.

The head (where the valves and overhead cam live) is the first thing off so you just need a new head gasket and up gaskets wise to put it back together. You can find good used heads on Ebay sometimes but the 500 if idled much can eat the lobes off the cam one shop told me and others state the same here so used can be iffy.

Do you have a Polaris shop manual yet? It is really good for anyone who does not want to take their machine back to the shop for every thing.

Read up the head removable and replacement and get the gas tank off. After that point pulling the head could be like a 15 minute job.

We move slow and take a long time because I am using the Polaris engines to teach the 16 year old engine building. In fact we got the chewed up crankshaft more smooth with strips of roll emery cloth and turning it by hand with the rope starter than I expected and went back with a used rod (eBay) and a new set of standard rod bearings and got it torqued back to 30 fp before we stopped last night. While this is a shade tree mechanic approach with a capital S this is a learning process because I doubt our hand sanding of the crank will last very long. :)

Back to your head question. It is simple as it is setting right on top of the engine. The manual (we have the paper on but some are online free PDF files too) is detailed enough so you can decide if you want to tackle it or not. For the 325 head bolts we did pick up a 12mm spline (universal) socket at Lowes for $3. For 325 owners the rod cap bearing nuts are standard 12mm nuts.

After you review the Polaris shop manual see what you think. This site has very informed and experienced people posting.
 

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Discussion Starter #6
Thank you very much for the detailed responses. I do have a manual and have used it many times. I will get to some studying.

I do have one of those tarp garages with a propane heater that i can use if need be. Just gotta be careful with the air...lol. I guess im getting into some fun. I will do the recommended readings and processes in due time. I may just wait for a buddy down the road with a heated garage to get home from Barbados. I can trade his help and shop for plowing his driveway as his wheeler needs some expensive repairs. lol
 

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First thing I would look at is the cam shaft, take the valve cover off and look at the center lobes on the cam, these are the exhaust lobes, some of the older machines wore them off, also check rocker arms.
 

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Discussion Starter #9
Just an update to this post as i have got to a warm area and did some digging. The exhaust lobe on cam shaft is actually gone. Like, nothing. Intakes are both perfect. I determined this after rebuilding carb, replacing plug and wire, air filter, new gas etc...

I wonder if it is absolutely necessary to replace exhaust rocker as well? I am just thinking that if it is worn completely off, there had to be some significant wear on the rocker that contacts lobe, correct? I am yet to pull rocker assembly which is why i ask.
 

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Discussion Starter #10
I am also wondering if it is a huge gamble to buy a used CAMshaft? I dont have a lot of extra money at moment and need to spread it out. Need rear bearings, front springs, cam shaft...good times..
 

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Look on ebay & bike bandit

for your camshaft, go OEM, not used. Yes, you will need the rocker arm pad also, if the cam is worn down the rocker is eaten up too - they come as a kit or just the cam. I've seen them on there for about 175-225, just shop around.

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 are 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. Once done, make sure to run Full synthetic oil & change often. Lots of this info is from OPT (old polaris tech) at this site: camshaft and timing chain - ATVConnection.com ATV Enthusiast Community

So yes that back pressure you're feeling is the exhaust that can't get out, errrrrr.
 

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Discussion Starter #12
Thanks for reply. I have wondered about the HO replacement but am getting mixed info. I've read that if you go with HO you need to up the carb as well or possibly the jet then eventually increase exhaust size? Based on your reply, it is a near match? Definitely lots of info on that thread. Thank you.
 

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Discussion Starter #13
You say go full synthetic for my future oil changes. Do not use the Polaris change kits? What is the full synthetic 0w brand to use?

EDIT: Found some info in the other referenced post with regards to oil:

0w40,5w40,5w50,etc as long as it's good oil and full synthetic.
 

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Think its ok to use the HO cam but to be sure

why don't you call out 'OPT' on ATVConnection? Just put something like "help me OPT" and he'll respond. If i read the article i referenced correctly he made it seem like you could be the HO cam w/out increasing the carb size or jetting. You won't get more HP w/out a bigger carb/jet but your engine will breathe better is what i understood. If in doubt stick with stock. I've got a '98 and its still holding w/original cam at 3500 miles. Yeah depending on what your lowest expected temp is usually you can use a 5-40. I love Shell's rotella t6-its meant for dirty diesels so excels at keeping carbon out. $22/4 qts at walmart...
 

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Discussion Starter #15
Does anyone recommend using a HotCam aftermarket camshaft? Says its compatible with stock valve springs. If so, would i put in my larger main jet?
 

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why don't you call out 'OPT' on ATVConnection? Just put something like "help me OPT" and he'll respond. If i read the article i referenced correctly he made it seem like you could be the HO cam w/out increasing the carb size or jetting. You won't get more HP w/out a bigger carb/jet but your engine will breathe better is what i understood. If in doubt stick with stock. I've got a '98 and its still holding w/original cam at 3500 miles. Yeah depending on what your lowest expected temp is usually you can use a 5-40. I love Shell's rotella t6-its meant for dirty diesels so excels at keeping carbon out. $22/4 qts at walmart...
well, the bike stays outside in canada during winter. So i get some major temp swings. I use it for plowing and i try to change the oil more. Battery sits on tender. I would assume the 0w would be best if it is staying outside. thanks for the info.
 

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Yeah at zero degrees

I'd say use at least something like mobile 1 0-40. I have placed a bottle of rotella 5-40 in my freezer (set to -10) and it flows, of course more slowly than at 30 or 60 degrees but it flows like heavy sryup. Mobile is still far less costly than polo branded oil too.
 
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