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Thread: 73' cb450

  1. #11
    Senior Member tbpmusic's Avatar
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    I have no idea - just that I've seen it before and it actually happened to me under similar circumstances, sustained high speed/rpm operation.
    When it happened to me, I had been riding at about 70mph or so for about an hour - then white smoke from the breather and blotto engine.........
    I'm not sure either of us did anything "wrong".
    Bill Lane
    No advice, just info

    '75 CB200T, '71 CB450 K4 Half-Breed, '72 CL350 (Sold), '81 CM200T, '72 C70M

    http://www.bikeexif.com/honda-cb450-restoration

  2. #12
    Senior Member jseconds77's Avatar
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    holy cr**p! Just read this. I am sorry to hear this and a shame since we all complimented your ride. I, too am very curious as to how this happened. Are we concluding that 70mph for a prolonged period of time is too hard on these motors that wind out at 10k rpm? Sounds hard to believe as I know in 5th my rpms are low as they should be,not that a lot of power is present but mine would roll along with ease.

    So the oil just pissed out the breather and you were unable to notice? Obviously motors burn oil if they have too low compression or worn piston rings but if your motor did not exhibit those signs before...

    Please keep us posted on this.

  3. #13
    Senior Member tbpmusic's Avatar
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    I was just indicating that I've seen it happen on 450's, not that they're overly prone to it.
    I've ridden 450's from coast to coast at hiway speeds in the past, with no issues at all.
    But sometimes.............
    When at 70 mph, you generally won't actually see anything except the road in front of you (if you want to stay alive).
    When it happened to mine, it was a good solid engine, no issues at all till that happened. I knew what had happened because it left a real mess on the back of the bike, where the breather tube exits.
    Needless to say, it suffered catastrophic damage.......
    Bill Lane
    No advice, just info

    '75 CB200T, '71 CB450 K4 Half-Breed, '72 CL350 (Sold), '81 CM200T, '72 C70M

    http://www.bikeexif.com/honda-cb450-restoration

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  5. #14
    Senior Member krinkelfish's Avatar
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    Just a quick update, I have yet to open her up yet to see how bad it is, but like mentioned above, I had noticed no oil anywhere on or below the bike, so it must have happened all st once?!

  6. #15
    Senior Member JamesPal's Avatar
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    Clean and regularly changed oil is the most important maintenance item on these bikes. Like mike said, it could blow out the breather. I did this to a fairly new CB750F2 back in the day. I would change the oil and go run it. You may get lucky. Otherwise pull the engine, pop the top end off and see what happened. The last time I did that it took a three day weekend and I'm 63YO.
    Jim Palmer
    '85 GL1200I (Garage Find)
    '81 GL1100 STD (Project)
    CB450 K5 Done
    http://www.hondatwins.net/forums/1-p...s-cb450k5.html
    "If everything seems under control you are not going fast enough" Mario Andretti...

  7. #16
    Senior Member krinkelfish's Avatar
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    Sweet video! I love the creeper stand, I am going to steal that idea.
    its getting too cold here and I don't have time to pull the engine, I did put in new oil and it has no compression barely at all on the right side, hoping it's just the rings.

  8. #17
    Senior Member krinkelfish's Avatar
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    Well it's finally warm enough and I had the time today to pull the engine.
    popped off the top and this is what I get:
    73' cb450-2dfea2b7-84db-4787-bad3-4edb8538020c_zpsb9bjcykk.jpg
    UGH
    73' cb450-6fa1e064-d84f-46ef-b818-22c7fa3be2ef_zps6lo3npgt.jpg
    Guess I get to see what the inside of a 450 engine looks like!

  9. #18
    Senior Member 76TWIN's Avatar
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    ouch.
    '76 CB500T Frankenbike

    Carpe narem.

  10. #19
    Senior Member krinkelfish's Avatar
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    There are couple of local guys with complete motors, could I just swap parts?
    Or, what is the best way to replace? re bore? Best place for parts? I see a wide swing of prices for parts, and some on Ebay as well..?

  11. #20
    Senior Member 76TWIN's Avatar
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    Depending on the extent of the damage (possibly more damage down the crank) it may be better to get another complete motor and rebuild that.

    At the very least you will need new pistons, rings, possibly oversized ones even and have the cylinders bored and honed accordingly.
    Are the valves still good?
    Last edited by 76TWIN; 04-21-2017 at 11:18 AM.
    '76 CB500T Frankenbike

    Carpe narem.

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