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400 Scrambler Compression & Noise

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  #1  
Old 05-02-2003 | 09:01 AM
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Default 400 Scrambler Compression & Noise

Well, I tested my compression last night - it's at 145 psi. So, can you still have good compression but have a piston that is loose in the cylinder? I have a tickiing noise that started inside the cylinder a year ago, it has since turned into a loud rattle. It is not an intake leak. I thought for sure that the original piston was just getting loose in the bore. But now after the compression test, I'm not so sure.
 
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Old 05-02-2003 | 01:46 PM
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Default 400 Scrambler Compression & Noise

I am very surprised your stock piston lasted a year with your mods. I would swap that out very soon! The stock piston doesn't like higher RPM's, which your pipe gives you, and it REALLY doesn't like the higher compression from the machined head. Ritter sells the wiseco pistons with a Swaintech coating . The noise could be coming from the piston pin, and you could still get a decent compression test. I would swap it out no matter what, you don't want pieces of the piston destroying the bottom end of your motor, its not cheap!
 
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Old 05-02-2003 | 06:12 PM
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Default 400 Scrambler Compression & Noise

Yep I agree on the piston. You may be hearing detonation. Keep a good eye on your plug. The pistons are known to have some rattle though.
 
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Old 05-03-2003 | 06:44 AM
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Default 400 Scrambler Compression & Noise

I just had a similiar problem, piston started making noise, so I did a compression test and it was good. So I figured everything was okay. Two weeks later motor died. Took it apart and the piston skirt broke. And it was on the exhust side. I guess the 400 are known for OE piston skirts breaking. Save yourself some agravation and rebuild it now. I only spent 150, thats with wiseco piston reboring and top end gasket kit.
 
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Old 05-03-2003 | 01:56 PM
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Default 400 Scrambler Compression & Noise

Had the same problem with the piston myself, except mine broke on the intake side. [img]i/expressions/face-icon-small-smile.gif[/img]
 
  #6  
Old 05-05-2003 | 08:56 AM
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Default 400 Scrambler Compression & Noise

Where's the cheapest place to buy a piston and gasket set?
 
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Old 05-05-2003 | 09:10 AM
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Default 400 Scrambler Compression & Noise

Give Rick Ritter a call.
 
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Old 05-05-2003 | 06:07 PM
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Default 400 Scrambler Compression & Noise

I found my piston and gaskets cheapest at Rocky Mountain ATV.
 
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Old 05-05-2003 | 06:57 PM
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Default 400 Scrambler Compression & Noise

Like the others said, get that stocker out of there! Before you install the Wiseco, HPD has a little oiling mod they came up with. Measuring up from the bottom of the piston skirt, at the centerline of the ports, make a mark 1/2" up. Then measure 1/2" up further from that mark, and make another. Using a small square double check your marks to make sure they're in a straight line. Gently centerpunch those two marks. Now taking care to drill straight through, use a 1/16" bit and drill through at both marks. You can use a larger size drill bit to debur the holes after you're through. They add just a bit of an extra squirt of lube....and it's free. [img]i/expressions/face-icon-small-happy.gif[/img]
 
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Old 05-06-2003 | 09:11 AM
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Default 400 Scrambler Compression & Noise

I took my quad apart last night. There was alot of freeplay between the piston and cylinder. Definately the source of my ticking noise. I ended up ordering the piston from Carbides Motor World - $10 cheaper than Rocky Mountain and closer too me so less shipping charges. The cylinder is on its way to Bubba today to get ported. Hopefully I'll be up and running by next weekend!

Ken, I don't quite understand where you want the holes drilled. Does it really help alot? Do you or anyone else have pictures of a piston with the holes drilled in it so I can visualize it better?
 


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