Silver Tag Z50

Discussion in 'Honda CT70/Z50 Registry' started by Texan, Oct 1, 2018.

  1. Texan

    Texan Member

    Joined:
    Jan 31, 2018
    Messages:
    46
    Likes Received:
    4
    Snatched up this little gem last weekend for $60. The seller said it has sat for at least 30 years. He also said the engine was bored to 70cc, the cylinder is marked 68cc. It’s rough, every nut & bolt is rusted and the wheels are rotted thru, but the frame looks straight. Doing a little research, I found/believe it is a Z50AK1. It does have a Silver Tag. Can somebody give me a little info on it & the year/manufacturing date. I keep seeing that the serial numbers are 6 digits, but mine only has 5. Also any other info/advice would be appreciated.


    Frame: Z50A-13575

    Engine: Z50AE-136038

    20180923_142817.jpg 20180923_142831.jpg 20180923_142909.jpg 20180923_142900.jpg 20180923_142607.jpg 20180923_142932.jpg
     
  2.  
  3. racerx

    racerx Administrator
    Staff Member Administrator

    Joined:
    Jul 10, 2005
    Messages:
    13,034
    Likes Received:
    1,156
    Nice score, congrats! For $60..."ya done good, kid!!!";)

    I've not seen a cylinder marked "68cc". IDK if it's aftermarket or from another model, such as an S65. No big deal, either way. There are plenty of 49cc cylinders available...used originals with the proper markings for this model/year, NOS, and aftermarket in 49, 72 and 88cc flavors. The OEM cast iron jugs had cylinder wall thickness that'd do justice to a top fuel engine, lotsa meat for overbores.

    Yes, that 5-digit SN is a bit enigmatic. According the the Honda ID guide, this model began with SN Z50A-120088. Almost seems like someone "forgot" the last digit. That said, I am anything but a trivia expert when it comes to the Z50. Hopefully, one of our Z50 guru members will have the answer.

    BTW, very good snapshots. This kind of detail makes life easier. thumbsup.png
     
    Texan likes this.
  4. Tripod

    Tripod Member

    Joined:
    Jun 23, 2013
    Messages:
    551
    Likes Received:
    19
    Looks like a nice score! Early z50 K1. You can tell on the frame from the mounts for the battery box, a k1 only item. You have good bones there, with the headlight shell being one of the more difficult items to source oem. You also have a longtail points cover, which is $$$.
     
    Texan and kirrbby like this.
  5. Gary

    Gary Active Member

    Joined:
    Jan 17, 2006
    Messages:
    952
    Likes Received:
    108
    It will be interesting to see what the piston and head look like once it's apart- please post a pic. No big deal as you say Bob but it's not S65 either,they are marked 63cc. I got a great deal on a nos S65 head that I could not pass up. Found out they are not interchangeable easily with a CT70. A 70's head has a taper machined into it as seen by these following pictures. I took it to a machine shop to have them cut it but he said it could not be done,I think he just didn't want to be bothered. Also pictured is a 70 piston next to a 65, the 65 piston squishes into it's head differently than the 70's into it's,don't understand what the advantage/disadvantage of one over the other is or why they would add another machining step to the newer/more popular model. Any thoughts on that Bob?

    003-1.jpg 004-3.jpg 008-2.jpg
     
    Texan likes this.
  6. kirrbby

    kirrbby Well-Known Member

    Joined:
    May 28, 2009
    Messages:
    8,676
    Likes Received:
    1,062
    $60 hardtail with "good bones" is a great deal.
    It's funny that you have a very clear 5 digit vin stamping. Factory boo boo...it's missing the 6th digit. So I guess you get to pick one :) you have 10 options...I'd pick lucky #7.
     
    Texan likes this.
  7. Texan

    Texan Member

    Joined:
    Jan 31, 2018
    Messages:
    46
    Likes Received:
    4
    Thanks for the info everyone. I know I got hell of a deal. I've been keeping my eyes peeled for mini Hondas for the last year or so. I actually got this one on OfferUp. The guy was only asking for $60 so that is what I offered. I was ready to jump in my vehicle and pick it up ASAP, but the guy had to leave soon and I was 45 minutes away so he said the next day would be good to pickup. I would be lying if I said I didn't doubt the deal would go thru, but he kept his word (y)

    I was banging my head trying to figure out the 5 digit serial number. Guess it was stamped on a Friday afternoon :LOL:

    I rechecked the cylinder last night, Gary is right, it is a 63cc.


    20181001_203330.jpg 20181001_203347.jpg
     
  8. cjpayne

    cjpayne Well-Known Member

    Joined:
    Jul 26, 2012
    Messages:
    5,589
    Likes Received:
    473
    Will it be possible to find new piston/rings for that? I think its cool that it has more cc's, but that would be a concern to me.
     
  9. racerx

    racerx Administrator
    Staff Member Administrator

    Joined:
    Jul 10, 2005
    Messages:
    13,034
    Likes Received:
    1,156
    IDK...even if it is, the choices will be very limited and we all know what that means. 49 & 72cc heads (6v flavor) are easy enough to find. For that reason, alone, I'd opt for stock 49cc, OEM 72cc or aftermarket 88cc configurations over what it has as-received.

    The bigger the piston dome, the bigger the impediment to smooth, rapid, combustion. Efficiency suffers, big time....just not as much as it would if CR fell too low. Can you imagine the lawnmower-like power curve the would result from, say, 6:1? Ideally, a flat top, or dished, piston allows for unimpeded flame front propagation, depending upon port flow characteristics and combustion chamber shape + volume. Dished pistons have come on strong over the years; having that squish band forces the air:fuel charge toward the center without interference. It's one parameter that engineers have used to increase efficiency and reduce octane requirement.

    Going by the running changes we've seen over the years (decades), it appears that Honda engineers did a lot of ongoing R&D. The running changes have been subtle, but significant. The 12v bikes not only got CDI (a big improvement all by its lonesome), they also got a longer connecting rod(which improved rod/stroke ratio...in terms of higher rpm) and a revised head (smaller combustion chamber) paired with a smaller piston dome (more efficient combustion) with the impact being increased efficiency, including more top end power. The new-gen motors have retained the long rod configuration...and gone to an undersquare configuration - small bore, very tight combustion chamber (less valve shrouding) plus dished piston to maintain reasonable (~9:1) static CR. It's safe to assume that they also included port design, to induce swirl and tumble inside the combustion chamber; the result being engines that "punch above their weight class". By extension (working backwards through the timeline) the S65 was just the first iteration of what became the 72 & 89cc (C90, not sold in North America) motors. They started with a large combustion chamber, to allow large valves & ports, that required a big piston dome to get reasonable static CR...a system/balanced assembly approach. It was a decent first iteration of what would become the most successful engine family in history. That they continued refining/improving the basic design is, imho, classic Honda. The short answer: "they had to start somewhere"...
     
  10. Gary

    Gary Active Member

    Joined:
    Jan 17, 2006
    Messages:
    952
    Likes Received:
    108
    As of a few years ago,yes usual suspects on fleebay had them,I imagine NW vintage could dig them up too. I might add it probably is not worth it with all the other available kits
     
    #9 Gary, Oct 2, 2018
    Last edited: Oct 2, 2018
  11. cjpayne

    cjpayne Well-Known Member

    Joined:
    Jul 26, 2012
    Messages:
    5,589
    Likes Received:
    473
    It would be worth it to me to keep it original, if possible. 63cc's original on a Z50 has got to be rare, as is its serial number. Pretty collectable in my book.
    I'm wondering if it does out perform the usual 49cc version too.
     
  12. Gary

    Gary Active Member

    Joined:
    Jan 17, 2006
    Messages:
    952
    Likes Received:
    108
    Doubtful it's original CJ. Someones thrown together parts. You would see an improvement if they used the head,carb,cam and a better exhaust.
     
    racerx likes this.
  13. cjpayne

    cjpayne Well-Known Member

    Joined:
    Jul 26, 2012
    Messages:
    5,589
    Likes Received:
    473
    Aww....too bad.
     
  14. racerx

    racerx Administrator
    Staff Member Administrator

    Joined:
    Jul 10, 2005
    Messages:
    13,034
    Likes Received:
    1,156
    Absotively and it wouldn't be the first time we've seen a weird combo. It'd be easy enough to replace the cylinder & piston with something bigger than the stock 39mm assembly. Most of them are marked "49CCM" anyway. Dunno that you'd get a whole lot more horsepower, with the tiny ports and tiny Z50 carburetor but, there'd be some increase. What would be really noticeable is the added torque. OTOH, with a CT70 head any bore-up (47mm/72cc up to 54mm/95cc) would perform the same as it would on a CT70, CL70, SL70, C70, etc. Then, the question becomes can you live with a different carb , intake, exhaust and the idea of going 40-50mph on a hardtail Z50?:):eek: It wouldn't be dull, for sure...
     
  15. Texan

    Texan Member

    Joined:
    Jan 31, 2018
    Messages:
    46
    Likes Received:
    4
    With the one wheel falling apart and the other frozen up, this bike was awkward to move around. So first thing to do was get them off. As the pics show in the first post, all the fasteners are rusted up pretty good. I starting soaking them with penetrating oil before attempting to remove any. The axle nuts came off pretty easy, but the axles wouldn’t budge. I kept soaking and tapping with a hammer every so often, but no luck. I read some tips on here how to get them out, but nothing worked and I was getting to the point of damaging the forks or frame if I applied anymore force.

    I went ahead and cut them off with a cut off wheel on an angle grinder. I sacrificed the chain tensioners on the rear, they were crusty anyways, then gently pried the assembly out of the frame. The front was similar, cut against the washer on one side, had to be a little more careful on the head side, but no damage was done. As one pic shows, the axles are rust welded to the hub brake panels. It didn’t get any easier breaking apart the hub & panels, but I managed to get them separated. Currently both panels have a chunk of axle still stuck in them. I tried to pound them out, but didn’t want to crack them.

    At least the big 8 wheel and hub bolts didn't give too much trouble, all came out ok.

    20180926_201253.jpg 20180927_184725.jpg 20180927_185829.jpg 20180927_192102.jpg 20181001_190248.jpg 20181001_190305.jpg 20181001_190356.jpg 20181005_192622.jpg
     
  16. Texan

    Texan Member

    Joined:
    Jan 31, 2018
    Messages:
    46
    Likes Received:
    4
    Nasty wheels off, ready to break down the rest.
    20180927_193128.jpg 20180927_193144.jpg 20180927_193152.jpg

    The muffler is solid on the outside, but pile of rust poured out.
    20180929_193417.jpg


    With a lot of PB blaster and patience, I managed to strip the bike with only breaking two screws. Both were on the battery box which has the back end of the threads exposed, but they should drill out fine.
    20180929_222449.jpg 20180929_222510.jpg 20180929_222513.jpg
     

    Attached Files:

  17. Tripod

    Tripod Member

    Joined:
    Jun 23, 2013
    Messages:
    551
    Likes Received:
    19
    Are you going to be able to save the hubs? That is some gnarly rust. If you dont have one already, a small propane torch will be your best friend.
     
  18. Texan

    Texan Member

    Joined:
    Jan 31, 2018
    Messages:
    46
    Likes Received:
    4
    I have a Bernzomatic torch, I did use it some but maybe now with the panels separate I can really focus the heat on the axle chunk. I haven't measured the hubs, yet but I think they can be saved. Will need bearings and seals. They are polished correct? I already sourced a whole front wheel assembly with a hub that came polished, but I would still like to refurb these.
     
  19. Tripod

    Tripod Member

    Joined:
    Jun 23, 2013
    Messages:
    551
    Likes Received:
    19
    The finish on the hubs is just polished as far as i know. If you plan on doing a restoration of that bike you will definately want to keep the hubs. They are early k1 hubs and hard to come by.

    I love my Benzomatic.
     
  20. racerx

    racerx Administrator
    Staff Member Administrator

    Joined:
    Jul 10, 2005
    Messages:
    13,034
    Likes Received:
    1,156
    The axle stubs should come out. Best method would be an hydraulic press. A deep well socket could be used to support the brake plate. Once the rust bond is broken, it'll put up far less of a fight. FYI, unlike CT70 hubs, some Z50 hubs, of similar (maybe this) vintage are retained with C-clips, so proceed with care. No sense damaging an otherwise usable hub.

    You are correct, the brake plates were polished & clearcoated. The hubs were brushed-polished & cleared.

    As long as you can drill straight, those broken M6 bolt fragments won't be a problem. Cut them down to near-flush, or at least flat. Center punch, then drill a small pilot hole, follow that with a ~4mm drill and you should be able to just tap the holes...good as new. Worst case, it's steel, so it can be welded & re-drilled if something goes pear-shaped.

    BTW, looks like a P.O. did a decent job replacing the TL bracket. I think you hold the new record for most-rusted rim half.:geek:
     
    Gary likes this.
  21. Gary

    Gary Active Member

    Joined:
    Jan 17, 2006
    Messages:
    952
    Likes Received:
    108
    That rim half- It'll buff right out :LOL:
     

Share This Page