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Opinions....rebuilding a 500 H.O...

2K views 9 replies 4 participants last post by  lateburd 
#1 ·
Hey guys, i got an 2001 500 H.O sportsman and recently it started smoking like a 2 stroke...

Im gonna change the valve seals and rings, it still runs flawlessly but obviously something is on its way out...

My question is, when i do the rings would i be better off replacing the piston and rings with weiscos? Or keeping the original OEM piston with new OEM rings?

The motor is staying stock and does mostly trail riding and some work duties.
 
#3 ·
There are no noticeable advantages to using Weisco. They do make good products but a little expensive.
If the OEM piston measures out ok just rings should be fine.
Namura is another low-cost alternative. I've built several engines using Namura kits with no complaints.
 
#4 ·
I have used Namura kits multiple times with no issues. As long as you are going inside anyway, While you have the cylinder off, I would have it measured. You might need to go oversize and now would be the time to do it. Before your tear down, check compression. That should give you some indication as to how far you need to go. If compression is still really good, maybe valve seals will be enough. If compression is low, then get it all done at once. The last few I have done were less than $200 for the piston kit with all the gaskets and machine shop to bore the cylinder and fit the piston.
 
#5 ·
I actually did check compression.

First time i checked it i got 130.

Second time i got 70.

The second time was after the motor was hot. Im not sure if maybe the decompression lever was stuck the first time??

It starts easy (as in one rip on the recoil and it fires) and runs amazing, but smokes like crazy under load or if you rev it, it also puffs slightly at idle.

I should add this all started after it sat a few months while i did a reverse chain. Before that it was fine.
 
#8 ·
Better to remove the exhaust and intake - inspect the ports closely - remove the spark plug and inspect the top of the piston - if the piston is wet and oily it's probably a worn out oil ring but the compression rings are obviously fine - if the piston is dry and black but the exhaust port is wet and oily, then it's a bad valve seal or guide or both - if the intake is wet and oily - then probably the intake seal or guide or both is bad.
 
#10 ·
Some engines do not use a seal on the exhaust valve - the old Kawasaki Z1 900 did not have seals on the exhaust valves - when the engine got to smoking, but started fine and ran normal, but the hotter the engine got the worse it would smoke and it never fouled a spark plug it was a sure sign the exhaust valve guides needed replaced.

Many motorcycles and ATV's Don't get the oil changed and the dirty oil will wear out the oil ring while the compression rings don't exposed to dirty oil until the oil ring fails. Dirty oil will also cause premature failure of the starter clutch on those engines that run the starter clutch in the engine oil.

On certain Honda quads that have electric shift (the 05 650 Rincon is one that comes to mind) electric shifting is performed using hydraulic pressure - engine oil pressure is used in conjunction with solenoid valves and a hydraulic operator to facilitate shifting. If the oil gets dirty enough, the hydraulic operator may lock and shifting fails. The vehicle has a manual shift option and it will shift normally manually - just not electrically.
 
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