Silver Tag Z50

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

  1. Texan

    Texan Member

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    Well, I decided to tear into the engine, first time btw. I bought the clutch tool and flywheel puller. I've had this Cummins Mack impact driver that came in a box of misc tools in an auction, but never used it until now. Also got an old Clymer manual to help me out. I just bagged and tagged everything for now along with taking a ton of pics. I plan to (slowly) start cleaning up the individual parts and see what is salvageable, and of course more reading and learning. Enjoy the carnage.
    eng.jpg clymer.jpg impact.jpg cyl.jpg head.jpg piston.jpg clutch side.jpg stator side.jpg
     
  2. Texan

    Texan Member

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  3. racerx

    racerx Administrator
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    Looks like you know what you're doing and are off to a great start. Vintage tools oftentimes are top quality, especially when it comes to impact drivers. That shop manual is, imho, THE reference source to have, for these motors. One day, I'm going to scan mine and post the entire thing as downloadable PDFs.

    The cylinder shouldn't be a problem. It may to be taken out two, or three, oversizes if the pitting is really deep; there should be plenty of metal. Those hex bolts holding the oil pump are worrisome; there should be JIS screws, of different lengths. Gotta wonder wtf would've replaced them with hex bolts and if they're the correct lengths. As long as the block threads are intact, or at least repairable, no big deal, even in a worst case. Not liking that maimed spanner nut, holding the clutch in place; I'd replace it, along with the lock-tab washer. The real pain is going to be that crankshaft. I'd have it taken apart to inspect the rod journal & bearings...and probably just rebuild it, after going that far. If the journal or/and needle bearings are even a little rusty, they'll fail rapidly...at 8000rpm. Might be worth sourcing a new crank, either standard stroke or 51mm. There's not going to be much cost spread between rebuilding this crank, or new TB 51mm arm.

    That last pic is confusing. Looks like the reverse side of the stator plate. If that's what it is, please explain what that broken aluminum piece is.
     
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  4. Tripod

    Tripod Member

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    Is that an early k1 motor? I noticed the 8 bolts on the oil pump. Both my k1's used philips head screws. My k0 had the 8 bolts.
    The inside of the motor doesnt look too bad. The oil hasnt turned to sludge. Once you knock the rust off of the head you will be able to see if the pitting has eaten away too much material.
     
  5. OLD CT

    OLD CT Well-Known Member

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    The head looks like toast from here.
     
  6. racerx

    racerx Administrator
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    Oh yeah, though the appearance is closer to "muffin" (and partially digested, at that :poop:) imo.:whistle: There is yet a lot of this opera remaining before the fat lady takes the stage. The worst of it is the intake side. Two-to-one odds on the intake guide cleaning-up with honing. Even if it's D.O.A., guide replacement is simple enough. IMHO, it's going to come down to the intake valve seat...specifically, how deep the pitting has gone. Remember CJs HK1 head, as-received? It was on-par with this one. It took one helluva deep cut to reach solid metal, still turned out well.
     
  7. Texan

    Texan Member

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    Here is a pic of where it was located before I cleaned it off. It was on the inside of the stator plate, I don't know what it is. I'm just getting familiar with the internals, but didn't notice anything broken where it could of came from,I believe it is steel.
    20181114_201350_LI.jpg

    The cylinder is dead.
    20181104_173629.jpg

    Your guess is better than mine, still pretty new to all this. I was hoping somebody could give me a build date based off the VIN.
     
  8. red69

    red69 Well-Known Member

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    The way things are going, it looks like you will be able to salvage a left and right and crankcase cover.

    Bob
     
  9. cjpayne

    cjpayne Well-Known Member

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    Yes it did turn out well. Sounds like a sewing machine and runs great!!!
    When I first saw it, it did have me pretty scared.lol

    A.jpg 1.jpg 2.jpg 3.jpg
     
  10. racerx

    racerx Administrator
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    IDK about that broken piece. Looks like cast aluminum, to me. Steel rarely breaks like this - flat, with a jagged edge that resembles broken ceramic. If it's part of the stator plate casting, then it may have left the production line looking just as you see it, now. Seems unlikely, imho, but unlikely isn't the same as impossible.

    As for your cylinder, looks like it's already been overbored well beyond mechanical limits. Last time I saw a cracked cylinder, it was a steel sleeve (aluminum jug) that had been overbored so large that wall thickness was just over 1mm. First time I can recall seeing a cast iron, CT70 cylinder cracked. Dunno its actual wall thickness but, even with my aging vision, I can see that the internal end-taper is gone(!). I'd describe its present condition using a word beginning with the 6th letter of the English alphabet, that also rhymes with "duct". Here's your perfect excus....ummm...practical justification for sourcing a new 52mm cylinder & piston kit. 88cc, using new aftermarket parts, costs roughly the same as overboring an OEM cylinder and sourcing a new piston to match.

    IDK, could turn out cheaper to build this into a 108cc stroker than bringing it back to as-new mechanical condition using stock, OEM, parts.

    Next step, glass bead blast the head, with everything removed, except the valves. Just stay away from the cam journals. Those, along with the valve guides, must not be bead-blasted, or they'll be ruined. Guides can be replaced. Cam journals, which are part of the casting itself...not so much.
     
  11. Texan

    Texan Member

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    I checked over the weekend, and the broken piece is steel. It's 1/8" thick and looks like the same material as gear shift. Next time I open the box of parts I will look more closely to see If I can pinpoint where it came from.

    Thanks for the guidance on bead blasting. I bought the HF Blast Cabinet a month or two ago but had yet to set it up until this weekend. Just messed around on some random things to practice and test it out. Before I start blasting engine parts I am going to do some of the "mods" / "upgrades" to the cabinet that everyone on youtube recommends. I researched before I bought and knew that going in. When I was testing it out, most of the complaints people have on these sure showed up for me, leaking cabinet, gun clogging, no light, etc.... When the gun did feel like working the bead blasting seemed to work great and cleaned up some aluminum parts pretty good. I'm also going to read up more on the specifics like the media, air pressure, prep, do's and don't.
     
  12. racerx

    racerx Administrator
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    Two possibilities come to mind: a transmission-related part, or a foreign object. Since you're doing a piece-by-piece teardown & reassembly, it should be fairly easy to see anything that's been broken.

    As for dialing-in your blasting cabinet setup, that small, benchtop, cabinet is an ideal starting point. I don't recall noticing many significant differences between the HF version and others, such as Clarke. There really aren't many places where it can leak. The one issue you will face, if used without a dust collector (vacuum) is the inlet airfilter. It will clog rapidly and cleaning it with an airgun, the only real option, creates a huge dust cloud.

    If you go with soft media, like crushed walnut shells, or corncobs, you can use a glass window, or protector for the installed plexiglass window, and it will last virtually forever. Soft blast media also won't destroy motor bearings, allowing use of a shop vac for the dust collector. There's also no silica content, so a dust collector is optional.The tradeoff, of course, is the seriously reduced cutting power which makes rust removal a lot slower. The only engine parts I ever subject to hard abrasive (glass beads, ground glass) are cast iron cylinder jugs and, in rare cases, head castings...but carefully & sparingly. Bead-blasted aluminum surfaces are profiled and magnetically attract dirt. The lower end, and any internal engine parts should not see hard abrasive; the chances of tragedy are high. If you can, make a choice between soft or hard abrasive and stick with it.

    I do realize that, for most, a dedicated cabinet is going to be too specialized. There is another possibility, changing-out abrasives. If you're going to do that, then I'd suggest either removing the pleated filter element, or sourcing another and modifying the cabinet so that they can be changed along with the abrasive. A minuscule amount of hard abrasive, contaminating the softer media, is all it takes to cause serious problems. So, be prepared to spend some time creating a lot of dust (outdoors, or you'll have a more time-consuming chore cleaning your shop afterward) as every nook & cranny is carefully air-gunned. There's also no such thing as a blast cabinet window that will remain clear for more than a handful of of hours, not even glass, so you'll need to stock-up on window protector sheets. Shop vacuums are also not designed for this kind of use so, with glass, or any other media that's harder, service life will be shortened.

    Sound like I'm trying to discourage you? I'm not. Having your own blast cabinet will allow you do get a lot of things done, effectively & efficiently...not to mention inexpensively. I'm trying to help you avoid the pitfalls, from the get-go. FYI, if a dedicated dust collector doesn't fit your situation, the cabinet can be run sans vacuum with soft abrasive. Just run an exhaust vent hose, or drag the cabinet outdoors, if possible. A shop vac can be augmented with the addition of external pre-filters. Go to youtube and type "cyclonic dust filter" into the search box. I don't want to recommend one person's setup over another, at this time. Some exceed the price of a plug & play dust collector(!). If you're handy enough and have a creative imagination, it is possible to build your own 2-stage pre-filter using two Home depot buckets, a few PVC pipe fittings (for the first stage) and a big, pleated, shop vacuum filter for the second...all-in and under $50.
     
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  13. Texan

    Texan Member

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    Excellent info as always Racerx! One of the reasons I finally made the cabinet purchase was because I previously scored a Dust Deputy setup complete with hoses and custom made stand thru a local auction. I got it pretty dang cheap and I had seen most people recommend them for blasters. The leaking I was talking about was when media was visible underneath and outside near the door. Most people say the factory caulking isn't good enough, so I'm gonna give it another bead all round and add better weather stripping around the door.

    So is glass bead out of the question for hubs, brake plates, fork guides etc...? I'm gonna have to clean the cabinet anyways when I re-caulk it, so it would be a good time to switch to the softer media then.
     
  14. Gary

    Gary Active Member

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  15. racerx

    racerx Administrator
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    If memory serves, Z50 hubs of this era were brushed/polished, plates were polished. Hitting those with fine glass bead, ~120 grit, will create a mess. You'd have to level-out the surfaces, i.e. metalfinishing from scratch (no pun intended) then polishing & clearcoat. Dunno what parts you're referring to as "fork guides".

    The cabinet mods are on-the-money. You might try adding thin, closed-cell, foam weather stripping the the door gasket. It'll be a lot easier than removing the factory foam and all the residue it'd leave behind. Go for the thin, dense, type. As I recall, it's available in 1/8" thickness and 1/2" width. If your cabinet has the low-density foam door gasket I think it does, it'll easily compress to accommodate another ~1/8" of foam...and that extra foam will stick really well to the factory gasket, if applied before the cabinet has been used.
     

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