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Thread: Have you Decked the cylinder

  1. #41
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    Dec 2000
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    I have been reading this post when I can, Good info guys! Any way I have a question that nobody can seem to answer for me. I am wanting to run as close to 11:1 as I can in my 440. How do I check to see what compression I have right now? Do I have to take the head off and measure where the piston is?
    Thanks for the help....
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  2. #42
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    oynot

    To figure your true compression you need to measure the cc's of your cyl volume at tdc.

    there was a very good explanation in the curtis sparks q&a but basic what you need to do is bring the cyl to TDC and fill the cyl with oil or another suitable liquid and measure how much fluid it takes in CC's (cc is easier as this is the unit used for your bore as well) add this figure to your bore (eg 440cc + 50cc) and then divide by the same volume number.

    The example above would yeild a 9.6:1 which is about what I am expecting from mine.

    Hope that helps.

  3. #43
    Join Date
    Jul 2001
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    OXFORD, CT
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    That's probably the most accurate - and the best way to get covered in oil! Don't use alcohol, a light motor oil works best. Also use the correct "engine size". I believe the IMS 440 kits usually come with a 88.5 mm JE piston (431 cc's) and the Wiseco kits are 89mm (435 cc's). Have fun getting the oil out after you're done.
    Mods: Big Gun FS w/MM quiet core, no lid , K&N, FCR41, 11.3:1 440 and Web 479 cam, porting, no choke. Works TRS fronts & Ultracross rear shock, a few other goodies
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  4. #44
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    Thanks 440EX4me, I will try to do that tonight. I have another question for you all then. If these companies are advertising a 11:1 compression and it is only accually 9.5:1 or so. Has anyone looked at a higher compression piston to get closer to 11:1?
    It was just a thought that I had...
    2002 KTM 400 EXC, this bike is awsome!

    Quads I use to own:
    FDO 463ex, Gas Gas 300, Gas Gas 450, Rancher, Yamaha Warrior, ATC Big Red.

    If you can't afford to fix it or replace it, don't ask to ride it!

  5. #45
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    Jul 2001
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    I'm hoping for everyone's sake it's only the Wiseco 440 piston that's advertised wrong. I've tried numerous times to get some info out of Wiseco about this and.................still holding.

    Does anyone know if the JE 11:1 440 pistons have a dome?
    Mods: Big Gun FS w/MM quiet core, no lid , K&N, FCR41, 11.3:1 440 and Web 479 cam, porting, no choke. Works TRS fronts & Ultracross rear shock, a few other goodies
    450R,250EX, Blaster, Banshee

  6. #46
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    Oct 2001
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    INDIANAPOLIS
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    99
    so if i run an xr headgasket and no base gasket with a weisco 440 piston do i get 11to1 or do i need to deck the cylinder some?

  7. #47
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    I remember something about the JE 416 piston having a dome...ask knighttime..(i think thats who...) or vwvr6, they will probably know
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  8. #48
    Join Date
    Dec 2001
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    Visalia, CA
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    While I can't vouch for the JE, the Ross ones I ordered just showed up (ye haw)-and they do have a dome. Since the same guy that designed the JE ones also designed the Ross pistons, I'd suspect they do have a dome.

    BTW, the top of the Wiseco 440 piston I have in my hand sticks up .030 higher than the stocker. I pushed a wrist pin through both pistons, and used the end of my dial calipers to check.

    The Ross piston's dome starts from the stockers height and rises up .190

    Hippy, I think the consensus is that you should end up at about 10:1 with a .010 base and a .025 head gasket... You won't get to 11:1 without visiting the machine shop.

    Mike, I don't see any signs of welding on mine either.

  9. #49
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    Yes, the JE "10.8:1" 87mm piston has a dome - I believe I have the specs at home if anyone is interested.

    I assume that the 89mm JE is also domed, as the catalog I have shows it to be. I believe they use practically the same dome on all their "off the shelf" pistons, which also reflects in the compression rising as you go up in bore size with JE off the shelf pistons.

    Great news on the Ross pistons Matt.... Have you weighed the assembly yet?

  10. #50
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    Dec 2001
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    You're quick Gabe, I was in the process of e-mailing you...

    The pistons weigh 302 grams, a little more than I was expecting. This is off Ross's spec sheet, I have not taken the assembly down to the machine shop to have everything weighed. Do you want piston A or D?

    They look great! Nice big valve reliefs, and the machine work appears to have been done on the skirts, not the pin boss area. They have oil galleys going to the wrist pin, the stocker and the Wiseco don't have this. Good stuff.

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