350 exc-f top end

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Thread: 350 exc-f top end

  1. #1
    Fetus Moto
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    350 exc-f top end

    Hi all,

    is it OK to lap in the original valves on this? will I destroy any hardened coating on them? The seats are basically OK but I,m doing the stem seals while I,m in there for piston change and minor decoke.

    Doing the piston change at 150 hours , Teflon pad almost gone piston skirts slightly polished but barrel OK.

    When would you consider changing the cam chain? Book suggests same time as piston but I think this maybe on the cautious side?

    Thanks

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  3. #2
    The "Moto" nickr's Avatar
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    What sort of use did the bike get for that 150 hours if you don't mind me asking. Mines on 160 hours, green lane use. I feel I should have it apart.

  4. #3
    Fetus Moto
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    It a 2013 6 days and I bought it with 80 hrs on the clock, believe it had done a few enduros, since then its done 5 or 6 enduros / H&H's plus some trail riding. It ran OK didn't seem to smoke or use oil, but as the book says take it apart by now I decided to do it. Chassis parts were getting a bit tatty , plus decided to send the forks and shock away for some TLC as we cant do them at home but can do most other stuff. Bore still has honing X hatches on it and feels OK, piston and cylinder were probably a bit sootier that they should be and Its probably been running a bit rich since the airbox seems to fill with crap on any muddy enduro. Popped the valves out for a look and cleaned them up, will do valve stem seals as theyre only £2.50 each Still not sure if its OK to lap them? Would consider doing the cam chain at next piston change ( 300hrs total) what do you think?
    nickr likes this.

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  6. #4
    Teenage Moto Rob James's Avatar
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    Top end - 78.7mph
    2017 350 EXC-F

    Previous, 2009 CBR600rr, 2008 SX250, 2004 CBR600SP2, 2002 CR250, 2001 CR125, 1996 CR125, 1989 YZ125

  7. #5
    The "Moto"
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    Quote Originally Posted by nickr View Post
    What sort of use did the bike get for that 150 hours if you don't mind me asking. Mines on 160 hours, green lane use. I feel I should have it apart.
    I did mine at 200 hours similar to DRZ, maybe a bit more worn by the sound of it, pads gone, but bore still good, would not have wanted to leave it any longer. usage was mainly rally's and hare and hounds in sportsman class, I am an over 50 rider who is quicker the more knarly it gets and gets left behind on the WOT parts of the course, so I wouldn't say it was hardcore riding but not green laning either. I would leave the cam chain until it started sounding rattly but I am no mechanic, don't think it is like a piston which can be a silent killer of bores with no signs until smoking and piston slap when you are well and truly into a rebore by then! I also ignored the crap about changing all the other bearings in the manual!
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  8. #6
    The "Moto" eveshamhardcore's Avatar
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    If you have the head off I'd do the cam chain.

    I would give the valves a light lap with fine paste. I don't think there's any coating on the mating faces and you won't remove any heat treatment until you've ground a mil or two off!

    Do it right once and ride it another 200 hours.

    I'd be interested to see some pics, my 350 is on 140 hours and I don't plan to take anything apart for a while
    nickr, Taffymoto22 and sidecarbod like this.
    "Chop your own wood, and it'll warm you twice"
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  9. #7
    Fetus Moto
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    I have some pics of piston but don't seem able to attach them from my PC. They were taken on my digital camera not smart phone as I,m still DumbPhone 1
    On the Reply form it says You may not post attachments!

  10. #8
    The "Moto" nickr's Avatar
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    Put the pictures up on a hosting site like photobucket and then paste the link using the "insert image" icon.

  11. #9
    Fetus Moto
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    350 top nd

    350lower_zpswypymhhl.jpg Photo by DRZdave1 | Photobucket

    350head_zpsmsyo1psd.jpg Photo by DRZdave1 | Photobucket

    350inlet_zpswgd4rvow.jpg Photo by DRZdave1 | Photobucket

    350exhaust_zpsykat31nq.jpg Photo by DRZdave1 | Photobucket

    350crown_zpsc6vj6hyq.jpg Photo by DRZdave1 | Photobucket

    Links above should take you to pictures of Piston underside, crown, exhaust side, inlet side and head.

    The ring end gaps were all within spec, valve springs were good, 41.75mm, piston diameter was 87.961 ( 87.96 size1 piston) Inlet valves were .03 below min ie .07 instead of .1mm, Ex valves were in mid range. Teflon squares just about gone on both sides of piston , exhaust side of piston had polished up and machining marks were no longer visible.
    Also in barrel there is a corresponding polished patch on the exhaust side at top of stroke, and a couple of vertical scores on the inlet side ( crap thru the air filter) but otherwise you can still see the hone x hatch quite clearly. this was difficult to photo, I don't have the kit to measure the inside of the barrel.
    Valves, Ex valves had a thin coating of hard light grey /brown deposits on them which would gently scrape off with an ally scrapper, then polished up lightly with a stainless steel dremmel brush. Inlets had an oily sooty deposit on the stem sides which was quite soft and polished off easily with dremmel.

    overall I think it was ready for a strip and replace of piston, replace valve stem seals , lap in the valves and its good to go.

    The cam chain I'm happy with and there is very little wear on the cam sprockets, so i'll leave that till next time ie another 150 hrs.

    hope this helps any other engine anoraks!
    Dibbs and Rob James like this.

  12. #10
    Teenage Moto Rob James's Avatar
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    350 exc-f top end

    Good work. How many hours did it take you to complete?
    2017 350 EXC-F

    Previous, 2009 CBR600rr, 2008 SX250, 2004 CBR600SP2, 2002 CR250, 2001 CR125, 1996 CR125, 1989 YZ125

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