Hi,
This is a bit long winded, but here goes.

About a week ago I obtained a 2000 Polaris 325 Trail boss for FREE. It was given to me, as the prior owner felt it needed a rebuild, and didn't want to fool with it. This is my first Polaris, but I am adept with anything with an engine

Got it home, and got it started. The top end is SUPER noisy, especially on the timing side. Its worst @ idle, and slowly goes away at RPM.
I've heard on some other forums and such that "Its a Polaris, they just sound like that". I don't buy it. Its REALLY loud and concerning. Bad enough that the prior owner gave it away for free.

So I started to tinker with it starting from the top down. Valve clearances are at spec. Pulled rocker cover. Everything looks almost new. VERY little wear. Rockers are tight, cam bearings are perfect. Timing chain is tight and being tensioned well. Guides are in great shape. Checked valve guides, they are perfect. Pulled cam out, pulled head. Piston looks great and is tight. Cylinder walls still have factory crosshatch. Pull cylinder. Piston looks great with minimal scuffing. No slap. Wrist pin and rod bearings are tight.

Well what the hell is wrong here?

I started to wonder on the compression release lever. Its in perfect shape, but it seemed odd to me that it was in loose, and just flops around. Noticed the tiny spring. Lets look at the diagram:



OK, the diagram (#10) shows the spring has legs. I must have a busted spring. Go to order a "Return Spring" part #3086804. The NEW springs DON'T have legs?! Very weird. Maybe Polaris made a design change late in development? Even the service manual calls it a "Return spring/spacer". Why does Polaris call it a return spring if it does not have that function?

So I made this:


and now it does this:


I haven't installed it yet. I'm waiting for a new base and head gasket to arrive so I can reassemble.

I'd like to get your input. If I ruined this spring for no reason, then I don't mind grabbing another for $3. But my gut tells me that Polaris originally designed it to be a "Return spring".

Thanks for your time!

-JJ

 

For some reason the youtube tag isn't working. Try this:

 

Only problem I see with this spring is if it's too stiff the centrifugal force when the cam turns counter clockwise when starting may not be enough to lift the lever allowing the decompression ball on the cam to work properly. It may take more "umph' to crank the engine where the oem spring allows rapid movement to decompress the exhaust valve quickly then spring back to the stop. But again it might work okay.The early 2000 325 models did have a few problems as the first run of these had some weak rod bearings.
I had a few thrown rods and destroyed cranks. Again this was the very first batch,but if you've eliminated the cam chain,have measured the piston clearance against the cylinder and it still has a loud metallic noise,I'd do some rechecking on the bottom end.Item 14 on the rod bearings,plus make sure the nut holding the lower cam sprocket in place(item #11) hasn't backed off and rubbing against the back of the stator plate. This was another problem area and could make some noise and shear woodruf keys.http://www.cyclepartswarehouse.com/f...2000&fveh=5491 Plus if you notice on this parts breakdown the cam was changed three different times until they got it right! http://www.cyclepartswarehouse.com/f...2000&fveh=5491

 

I think you've nailed it! I looked down their with a flashlight, and noticed the bottom sprocket can easily be rotated back and forth about 10-20 degrees on the crank! I'm surprised this thing still ran without slamming valves in to the piston.
Any suggestion on keeping it from happening again? Loctite red on the nut?

Thanks again!

 

Here's the evidence:

 

If this slotted nut is loose then by all means loctite the crankshaft threads!! On this one I'd use red not blue because of what damage can really happen to the engine if the sprocket or key shatters.This nut has reverse threads and you would think that the engine revolutions would keep it tight,but they have worked loose. Just inspect the key and sprocket to see if any damage. You don't have to have the special socket,just use a good punch and tighten this nut securely after you locktite the crankshaft threads. Something that should have been done at the factory,but wasn't. Same thing on the 500 and 350 and 400 2 stroke that use these nuts. Just saw the video!! Probably need to replace the woodruff key plus if the sprocket is worn in the key way slot,replace it too! Plus might just be shadows on the video,but looks like some wear on the intake side of the piston!!