Working on old Honda CM400 (valve seals/tensioner)
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Thread: Working on old Honda CM400 (valve seals/tensioner)

  1. #1
    Registered User Array
    Join Date
    Apr 2006
    Peachland, BC
    1981 Honda CM400

    Working on old Honda CM400 (valve seals/tensioner)

    Decided to keep the bike I bought last summer. Worked perfectly, got my license with no problems, used it to cruise back and forth to work.

    But, smokes on startup. And I tried to adjust the timing chain tensioner and it just got noisier (supposedly self adjusting, loosen off a bolt while it's running and a spring pushes the tensioner out).

    So, thinking of changing out the valve seals and seeing what's going on with the tensioner. Just curious what I'll need to do this?

    - valve compressor
    - valve seals
    - head gasket

    Suggest anything else? Any tips for the tensioner (bidding on some spare parts off of ebay right now)

    Thanks in advance!

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  3. #2
    Moderator Array TeeTee's Avatar
    Join Date
    Feb 2002
    Out to pasture in the 'Wack
    04 Kawi Z1000,
    If the tensioner isn't doing the job anymore it's from about 3 possible causes. The cam chain is worn or "stretched". The tensioner shoe is worn so the spring and ram can't push it far enough or the spring is sacked out. Usually on a really old or high mileage bike it's a combo of all three. To really do the job right you should be replacing the whole chain and tensioner system. But that's likely more than you want to spend. As a bandaid leave the chain and get a new tensioner assembly. I'm not sure that buying off ebay in this case is a really good idea since you're very likely to get one as worn as what you have.
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

  4. #3
    Registered User Array navarcht's Avatar
    Join Date
    Feb 2005
    North Van
    90 VFR
    First thing I'd do is get heavier oil!

    I had a '71CB350 that I rebuilt for the same reason, well that and I really wanted to tear it apart just to see if I can put it back together. Unfortunately I couldn't buy a new cam chain so I had to reuse the old one which was probably stretched. I got the bike put back together and it ran fine for a while but it chewed through the new chain tensioner fairly quickly.

    If you're going to replace the cam chain and tensioner it's going to take a fair bit of work as you have to break open the bottom end just to replace the cam chain.

    Best of luck

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