CA77 reassembly - couple of questions before we get started
Results 1 to 5 of 5
  1. #1
    Senior Member the-chauffeur's Avatar
    Join Date
    Nov 2009
    Location
    U.K.
    Posts
    452

    CA77 reassembly - couple of questions before we get started

    So now comes the CA. Given that it's essentially the same layout as the CL, I'm expecting the number of questions I have to be considerably fewer than I've raised in my other post, but I'm bound to come across things I can't quite get my head round . . .

    . . . and I've already found one. It's to do with the factory cam lobe grind. Having disassembled the camshaft to extract it from the head, I've compared the left camshaft with the right and they look remarkably similar. Given it's a 360deg crank, that's not entirely surprising, but there's a couple of things about it that make me go huh . . . wha . . .? This is almost certainly due to a lack of familiarity on my part, but I thought I'd see if anyone could shed any light on the how and the why these things were made the way they were and how they function.

    Since the engine is a 360, I'd expect the left and right sides of the camshaft to be mirror images of each other, with the lobes being the same profile/shape, and that they would exactly line up with each other when the assembly is together. What I've found is that rather than mirror image, the ends look to be almost identical if viewed from the splined ends. Maybe this will help explain what I mean:
    CA77 reassembly - couple of questions before we get started-camshaft-left_big14121259020-01_eff5.jpg CA77 reassembly - couple of questions before we get started-camshaft-right_big14111259020-01_2ce6.jpg


    The image on the left is the LHS camshaft; the image on the right is the RHS.

    If you look closely at the lobes, they seem to have been ground the same way, with the flat on the top and the curve being sharper at the end of the flat than it is on the underside (I realise I'm explaining this badly . . . ). Where this gets strange is when the camshaft is fully assembled, because one of these shafts has to be rotated, which has the effect of orienting one set of lobes upside down relative to the other. I don't quite know how that works. On top of that, the lobes have an offset when the camshaft is assembled. So rather than firing exactly opposite eachother, there appears to be a small amount of delay or advance built in to one side.

    So I guess my question is why are those things the way they are? The only reason I can think of for the former is reducing manufacturing cost, and if that's the case, the reason for the second is probably to make balance the engine performance/response given the oddly shaped camshaft.

    Strange.
    CL77 (1966)
    CA77 (1966)
    SL350 K0 (1969)

    SL350 K2 (1971)
    CB450 K6 (1972)
    CB750 K2 (1972)

  2. #2
    Senior Member mike in idaho's Avatar
    Join Date
    Jan 2012
    Posts
    2,393
    The cam lobes aren't symmetrical, maybe that's what you're seeing.
    '65 YG1
    '65 CB160
    '66 CL160
    '67 CL77
    '68 TR6
    '69 T100R
    '69 T120R
    '72 Commando 750
    '78 XS650E
    '79 Gl1000
    '81 440 LTD
    My company car is a Kenworth

  3. #3
    Senior Member the-chauffeur's Avatar
    Join Date
    Nov 2009
    Location
    U.K.
    Posts
    452
    Nah, I kinda realise that. I've taken some photos but they don't really demonstrate what I'm getting at, so I'll leave that for now.

    Moving on . . . how to interpret the FSM 'repairing limit' figures. According to the FSM, the standard piston ring gap is 0.15-0.35mm, with a repairing limit listed as 0.6mm more. Is it safe to assume that means the actual limit is 0.75-0.95mm?

    I've measured the piston rings and the top ones are at around 0.6mm, with the seconds at a much tighter 0.4mm. This bike is likely to do less than 1,000 miles a year, so I don't need it to be as-new. If my assumption is correct, I'll probably go with them as is.

    Cheers.
    CL77 (1966)
    CA77 (1966)
    SL350 K0 (1969)

    SL350 K2 (1971)
    CB450 K6 (1972)
    CB750 K2 (1972)

  4. Remove Advertisements
    HondaTwins.net
    Advertisements
     

  5. #4
    Senior Member mike in idaho's Avatar
    Join Date
    Jan 2012
    Posts
    2,393
    You must be measuring a set of used rings? Assuming the bore still in good shape, 0.6mm would seem to indicate a fair amount of wear(and a resulting loss of tension). Of course since we don't know what the gap was when the engine was originally assembled, the current end gap measurement doesn't really tell much. Personally, I won't willingly re-use a set of rings unless there are no new ones available. End gap measurements really don't tell much how much tension is in that ring, which is a measure how well it seals against the cylinder wall. Put a new piston ring in a freshly honed cylinder and material is worn off in the process of seating that ring(which is a normal occurrence), now take a used ring that measures"in spec" and introduce it to a re-honed cylinder(as some folks here are wont to do do) then material is worn a second time in an effort to get it to seat. That loss of cross sectional area in the further reduces its tension and ability to seal. I expect I'll be taken to task by some resident experts here for expressing My opinions, oh well, so be it.

    Later: just dug My FSM, the way I would interpret it, the total ring gap limit is .6mm.CA77 reassembly - couple of questions before we get started-dscf0594.jpg
    Last edited by mike in idaho; 09-05-2019 at 02:13 PM.

  6. #5
    Senior Member the-chauffeur's Avatar
    Join Date
    Nov 2009
    Location
    U.K.
    Posts
    452
    Ah - thanks very much, and boy am I glad I asked. My FSM must be a different year to yours (1971). It contains pretty much the exact same table, but as I said, the wording is ambiguous because it's missing the crucial word 'than'. That puts a totally different perspective on the sizing.

    Annoyingly I'm having to take a hiatus until either the cotter valve that launched itself across the garage turns up or the replacement comes in from Holland (yeah . . . I know). Since that's going to take a few days, I'll see about a new set of rings in the meantime.
    CL77 (1966)
    CA77 (1966)
    SL350 K0 (1969)

    SL350 K2 (1971)
    CB450 K6 (1972)
    CB750 K2 (1972)

Sponsored Links

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •