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Thread: When do you kinow it is time for a top end rebuild and what does it usually consist o

  1. #1
    Join Date
    Sep 2011
    Location
    Hillsboro, OH
    Posts
    384

    Default When do you kinow it is time for a top end rebuild and what does it usually consist o

    How do you know when it is time to rebuild your top end (new piston, rings, polish, etc.)? What all is included in a top end rebuild?

    Especially, for the CRF450X owners out there, but curious about when I need to think or know to start thinking about a top end rebuild.


    Just wondering.


    Thanks.

  2. #2
    Join Date
    Oct 2012
    Location
    Bradenton, FL
    Posts
    565

    Default

    usually its because of some type of problem (road bike) but i'm sure racers do it as part of maintenance.

    If you have low compression or burning oil then you can usually assume that the rings are worn or the valves, valve seats, guides or seals are worn. While you have the whole top end apart you might as well replace all gaskets and seals because it's inexpensive. You can measure cylinder and piston inner and outer diameters and decide if you want to replace them but im sure most people will go ahead and replace them or just bore over with a new piston. valves get measured stem to guide clearance as well as out of round for both. anything worn gets replaced. if one is bad might as well replace all of them. seats can either get cut or replaced, but i'm not sure if many people replace the whole seat anymore.
    2013 Speed Triple SE

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  3. #3
    Join Date
    Jun 2012
    Location
    Canberra, Australia
    Posts
    52

    Default

    I just had a top end done on my 08 CRF450X. Dirt ridden not a sumo though.

    Reason for getting it done was the left hand side intake valve had closed up, thought about shimming it but figured it would close up again the next time I rode it so I got it done.

    Had 2x new intake valves (del west ti for 450R with seats cut, thought about going SS but decided not to) with all new springs etc, piston, rings, gaskets.

    Piston and rings were still in good condition but decided to swap them out anyway to have it all fresh.

    Bike had done 2700kms (1650ish miles) unknown hours. Only symptom was one ride before it had been a bitch to start, went to ride it around to a mate's place (about 2km away) to fiddle with the suspension and on the ride back made it about 200m, it stalled and I was stuck. Ran the battery flat trying to start it and it wouldn't kick either.

    Personally I'd just ride it until it stops, worst thing for the Honda's is that the valves will close and you won't be able to start it as in my case.

    When doing the top end stay away from the OEM ti valves (I probably should have gone stainess but we will see in the future) and go for stainess if you are after reliability and greatly increased periods of time between rebuilds.

  4. #4
    Join Date
    Jun 2011
    Posts
    977

    Default

    I have over 400 hours on my engine, never touched anything except for refreshing the valve train at 250 hours and pouring 12 gallons of oil in it. And a couple dozen valve checks. It starts first kick or press of the button every time. It smokes a little bit on startup, but pulls like a mother and a 1/2 still.

    I've never even considered doing a top end...mainly because you have to split the cases, as the cases make the cylinder. (With a liner).


    Edit- it's a 2005 Husaberg FS650






    Excessive smoke and loss of power is when you need to do a top end.
    Last edited by idle; 04-02-2013 at 08:38 PM.

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