My 2000 400 Scrambler recently developed a rattle or knock that matches crankshaft speed, but does not change pitch or tone with engine load. I haven't pulled the reeds out to look at the piston skirt, that's tommorow afternoons project.
Any body have any problems with the counterbalancer on the 400's?
The counterbalancer had oil on the dipstick in the safe zone.

 

Capt...
I don't know how many miles/hours you have.. but I know that I had to put a top end in a Sportsman 400 because it got a little loose...
From what I was told, when the Factory Cast Polaris Piston get a little loose from normal engine wear, they are EXTREMELY PRONE to Cracking/breaking... So if you suspect piston slap... you might want to go ahead and swap pistons... WISECO and PRO-X both make Forged replacements that will last much longer and give extra horsepower...
Good Luck..

 

I pulled the reed cage and spacer off and looked through the port at the piston. The piston is scored up pretty badly, it's not cracked, but it looks like it'll have to be replaced. The Polaris Dealer is trying to help put a Wiseco forged piston back in the engine, so I'll keep everyone informed.
I'll probably have the cylinder ported while it's off the engine.

 

Other than the piston thing going on? how do you like your mods. I have basically the same in the works for my sport. Currently I have K&N, DG ATVXtreme Pipe and Alloy silencer. But The Delta V-Force Reed Valve and the HPD Aggressive clutch Kit are on the way, along with a Wiseco Forged Piston. They should arrive by Next weekend. I was just wondering How you liked Everything. Also, I only went up one size jet on it for my pipe, to 240 from 230. Do You know what size jet you used?
It seems 240 is still a bit Lean. I just know it is a B!tch to change them (over 2hrs) so i figured I would ask. Also did you change the Pilot Jet up or down or at all? Ive been told not to change by one dealer and to change it by another.

 

Two hours to change a main jet? Are you doing it with your feet??? LOL It should take about 15-20 minutes to change a main jet. The pilot jet takes a little longer since you have to remove the float bowl.
It sounds like you need to invest in some hand tools. Here's my must haves:
A LONG #2 phillips screwdriver for the carb to mainifold clamp
A LONG 1/4" drive extension for about everything
A 5/16" universal ( flex ) socket, 1/4" drive for the airbox to carb clamp
A 3/8" socket, 1/4" drive to remove the airbox
A 6mm socket, 1/4 drive for the main jet
and , if memory serves me correctly, a 17 mm wrench or socket to remove the plug below the main jet.
I'm running a 250 Main Jet, 30 Pilot Jet, and love the combination.
Since I'm going to have to pull the cylinder, it's going to be ported and bored .040" over before it goes back on.

 

20 over should clean it up . Notice your new wiseco piston pin , I recieved a new batch of pistons that have wrist pins that are to short. Most were correct , others were incorrect . Just take a close look at it before installing .

 

Capt,
Have you looked at the piston out of the quad yet.
I'm wondering if you had a lean condition or did the piston just quit,As you know I'm running the same mod's as you but I went back to stock pilot jet to get rid of a low end ping.
After seeing what happened to you I'm thinking of a 260 main? I'm dealing with a 1997 not a 2000.

 

Two things, thanks for the wrist pin info Rick,( how much endplay is considered correct? ). Second, the plug is still sooty black, and not even brown, so I don't belive that the motor leaned out.
From discussions with the mechanic at the Polaris dealer, he said that not allowing enough warm-up time before riding could be part of the cause, along with cast pistons.

 

Scarring on the intake side can be attibuted , (in my experience) with improper lubrication . Oil dribbles in on the injector line , to be met with raw fuel , which can have a washing affect on the piston , removing lubricant . Premix allows the fuel to be a lubricant in itself . Stock quads get allong pretty well with oil injection . Highly modified ones with huge jets can see damage often if still running total oil injection . This is because of the large amount of raw fuel washing oil off the piston skirt .

Cold seizure to can start a small abrasion that just keeps growing as the quad is run , but I think you know how to warm up a quad . I really can not pinpoint the problem , but these two possibilities may bear some of the blame .

Honestly , most 400's just break a piston skirt on the intake side .

The short W-pins I saw were almost 3/16 to short . a proper pin only slides back and forth about 20 thousandths between the clips .

 

I should have it torn down this weekend, so I'll have a better idea of what's going on. It looks like pre-mix is in my immediate future (once it's fixed).
Rick,whats the turn around time on boring and honing and putting a trail type port job on a cylinder, normally?