'72 HK1 Project

Discussion in 'Projects/Builds' started by Clint, Dec 21, 2011.

  1. Clint

    Clint Member

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    A reintroduction: A couple of years ago in September, I was lucky enough to find an HK1 in fantastic shape. Strong engine, great body. Only a tiny dent in one of the upper fork covers.

    P1050350.jpg

    I started a thread on the forums here:

    http://lilhonda.com/webboard/f36/new-member-new-bike-7009/


    My intention was to do a complete restoration so I started pulling the bike apart. I restored the wheels and hubs and mounted new trail wings. The seat wasn't original so I found an HK1 seat on eBay. I sent the seat along with the tail light and the engine guard off to our own Motor City Bob to work his magic. He waged an epic battle with the seat to fix the pan, have new custom triple layer foam made, and reattach the cover and original trim. The engine guard and tail light assembly were straightened, stripped and triple chromed with an initial strike of copper.

    Bob worked on this in the fall and winter. I got busy, Bob had some legendary computer problems and the project got put on the back burner. The bike had been completely disassembled and cleaned (except for the engine) and was chucked into a giant rubbermaid container.

    P1120022.jpg

    P1050621.jpg

    Bob and I alternately lost touch, kept in touch and lost touch again. I forgot about the project and was resigned to just sell it for parts. Money also became an issue. I finally got tired of looking at the engine and the frame sitting in the carport beside my house and tried to sell it early this year, but wasn't able to. I checked out the boards sometimes and saw other rebuilds but mostly lost interest in the bike.

    This fall I saw it again under a pile of stuff, got pissed off, and remembered Bob. I got in touch with him and the parts were still sitting in boxes ready to be shipped. So we finally concluded our business after two years and he shipped the parts back to me. The seat is awesome.

    P1120023.jpg

    The tail light and the engine guard are show quality. I still had the issue of the frame and the engine. I had went back and forth a couple years ago about keeping it yellow or painting it red. Red won. I wanted to keep it the original color, but couldn't love it enough to repaint it yellow. So the frame was shipped off and came back shiny candy ruby red.

    I wanted to do the engine myself so I contacted engine maestro Mark Pearson and he sent me the videos. Now the engine is in a hundred pieces on a spare table in my living room. It's going slowly but his videos are like having Mark right here in the old Morris chair sipping a beer and guiding me.

    I had originally wanted to keep it bone stock but also want to ride it, so I made some concessions. The stock rear shocks looked cool but the ride sucked so I found some YSS gas shocks. I wanted to put an 88cc kit on it also, but the more I thought about it, the more I didn't want to mess with a great Japanese engine. I will probably go with some modifications on the intake and exhaust end to up the power instead of a BBK.

    P1120024.jpg

    I'll add to the thread as I slowly put the bike back together and rebuild the engine. Thanks in advance for answers to the multitude of questions I'll surely have.
     
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  3. racerx

    racerx Administrator
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    Glad to see your project back on line, after an epic siege. For the longest, I had wondered if you'd thrown in the towel.

    If you're going to tear down the engine anyway, a 52mm (88cc) bore-up kit, SL70 (a.k.a. "fast road") cam and an 18mm carb may be worth their nominal added cost. H-motors respond pretty well to these minor mods. With a larger countershaft sprocket to match the increased torque output, I'd expect 50mph+ top speed. Just as the aftermarket shocks were a good idea, so too is more power for road use. And, these are all bolt-on mods. True enough, the engine mods are more involved than a shock change, but still reversible as long as you retain the original parts.

    Here are some details on the seat & tail light asm. restorations. Most of the photos of this project, including the lion's share of the "befores" and all of the engine guard (which was fairly involved, as these go) were lost in "the big crash".

    Here's the ebay K1 seat, as-received.

    Orchuckproject032.jpg Orchuckproject047.jpg
    Looked like a post-modernist sculpture of a meatball sub...rendered in 40-year-old latex foam.

    It turned out to be worse than it looked. Orchuckproject052.jpg

    The booger-welded pan had little structure left, as became obvious, once the paint & bondo was removed.
    Orchuckproject004.jpg seatpanstage211.jpg

    Saving this pan wasn't really practical, just possible. Making it solid took a lot of metal. Once the sloppy, useless, welds were ground away, the metal was left too thin to weld in some spots...so brazing rod was used as filler and to add strength.
    panstagethree6.jpg panstagethree.jpg

    After a ridiculous amount of grinding and metalfinishing, the pan turned out reasonably well. Considering that reusing the cover was part of the plan, to contain costs, show-quality wasn't part of the equation here. The custom foam was cut to give more arch than the OEM profile, in order to get close to the proper spacing at the rear of the cover - and to "hide" as many of the incorrectly positioned holes (created by the P.O. using that cobbled-together foam) as possible. Ultimately, I was able to straighten the stainless trim strip. A good polishing and some stainless bolts capped-off the project.
    DSC08860.jpg seat006.jpg

    The tail light assembly was worth the effort. The bracket had the usual bent license plate backing, dents & rust. The tail light base was quite rusty & pitted. Everything straightened-out nicely. Had this been a K0, sourcing a new tail light base would have made more sense. Unfortunately, new K1s aren't common or cheap anymore. So, while this one cost more than a K0, it's original to the bike and turned out exceptionally well. A light sanding and polishing revealed a near-pristine vintage original red lens, that had been lurking beneath paint, dirt & scratches. A new bulb + 4 new stainless screws later and it was ready for the next 4 decades.
    DSC08840.jpg DSC08845.jpg DSC08846.jpg DSC08850.jpg DSC08855.jpg
     
    #2 racerx, Dec 21, 2011
    Last edited: Dec 22, 2011
  4. Clint

    Clint Member

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    Hi Bob. The engine is all torn down now. I had originally planned to add an 88cc cylinder and piston. Hunting around on the forums here, the consensus seemed to be that it wouldn't do much with out the race head. That's more than I want to spend. I saw a post by fatcaaat that said:

    This is what I'm leaning toward. I can't get a new pipe right now, but the baffle is out of the old one. Can anyone recommend a carb/intake/cam/gearing combo that would work for me? The only other mod I will be doing is swapping out the shift drum and shift star from an SL70 engine so it's one down/ 3up.
     
  5. bullitt

    bullitt Member

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    Nice job on that tailight,ran into the same problem with my K1.Seen one on E bay go for a cool 177.00 plus shipping I will use the old one.
     
  6. OLD CT

    OLD CT Well-Known Member

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    Now is the time to do the 88 kit and consider buying the stroker crank too.I believe the stroker crank is as good or better designed that the factory crank.When see it in person you will know what i mean.I do not run a race head but use the original head that i ported.Matter of fact i never use them''race head''.Faatcaat's particular performance #s does not mean that you will easily be able to duplicate it.If that was the case no one would buy the 88 kits!52 is the norm for a good geared 88 kit and a minimum for street use.build at least a 88 kit,and you will have a hell of alot quicker take off ability than any external hop up on a stocker 72cc.
     
  7. racerx

    racerx Administrator
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    The 88cc kit, if matched with some port work, hotter cam and 18mm carb ought to get you close to 50mph top speed, roughly a 20% increase, over a very healthy stock H-motor. Since these engines have spark advance, they tend to respond more enthusiastically to performance parts than the 3-speeds, with fixed timing.

    ~$225 buys the 52mm stroker crank, HV oil pump kit & hotter 6v cam. If your budget can handle the extra hit, you'll have a 52x52 110cc motor that makes a lot more road power than any 88cc tune. You'd get gobs more torque and that's what equals acceleration. I agree with OLD CTs advice on porting the stock CT70 head, too. The old 6v head was fitted with larger valves than any other 72cc/6v head, except the CY70, which was never sold here. Our own Fatcaaat is a knowledgeable tuner of these engines and has also championed the use of the vintage CT70 head, with some massaging, as well.

    Top-off the stroker rebuild with HD valve springs, a dipstick oil thermometer, VM20 carb and taller sprocket combo and you should realize a bike capable of at least 45-50mph cruising and top speed around 60. Even if you intend to stay mostly below 50mph, you'll be able to easily keep pace with suburban traffic with some reserve power for hills & headwinds.

    Like any other upgrade, it comes with up-front costs. That said, you're going to change the shift pattern, so bone-stock originality will already be somewhat beyond a quick bolt-in reversal (if that even matters to you). One of the nicest aspects of fortifying a 72cc motor is that you still retain a nearly-stock outward appearance, other than the larger, aftermarket, carb setup...a sleeper.

    Perhaps this isn't what you're after. It's still good to be aware of possible options early on. Whatever decision you reach, it's all good as long as you're happy with it. After all, this is your bike...build it the way you want it.:4:
     
  8. Clint

    Clint Member

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    It all sounds good Bob. But the $225 plus the 88 kit, valve springs, oil thermometer, carb, and sprocket combo is going to top out over $500. That plus all the gaskets seals, assorted cam gear, hardware etc. is going to get near $700. Way outside of what I'm considering.
     
  9. racerx

    racerx Administrator
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    I hear you. The ever-optimistic Mr. Enthusiasm has an Olympian disregard for budget...unfortunately, that mean & remorseless Mr. Reality stands at the ready to maintain balance.:68:

    Oh well, it was just a thought. Still, a 52mm bore-up kit is roughly a wash for over-boring the original cylinder...with no waiting for machine work. An SL cam & HV oil pump will add less than a C-note to your project total. Removing the restrictor cone from the inlet air booth and tweaking the carb are virtual freebies. An inexpensive 5-10mph boost, with the potential to reach or exceed the high end of that range by installing a larger carb (down the road, if/when budget permits) might be worth considering, however briefly.
     
  10. Teamfour

    Teamfour Member

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    Can you provide a clearer explanation on this? Also, except for the cam, is the head basically unmolested? Heavy duty valve springs perhaps?
     
  11. OLD CT

    OLD CT Well-Known Member

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    Clint,the dratv 88 kit without the race head and carb is around $128 and all the gaskets are included.You will need the hi volume oil pump though.
     
  12. Clint

    Clint Member

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    Thanks Bob and OLD CT for the input. Regardless of any upgrade I do, I'll need a bigger carb, so I'll start with a Mikuni VM20. They look to be around $75. Another $125 for an 88cc kit. The HV oil pump runs $30 and a fast cam around $50. That sticks me already at about $280 and I still need an intake. That's about as far as I can go.

    I see talk about fast cams, race cams and hot cams. Am I right that a fast cam is an SL 70 cam and a hot cam is a CL70 cam? Race cam? I saw a post by Bob that read:
    "The CL version of the 72cc motor already has spark advance and the hottest stock cam grind Honda used in production bikes of the era. You're starting out with a motor Honda rated at 6.5hp, 1.5-2.5hp higher than any other 6v iteration. That 88cc kit ought to work very well with little more than a minor tweaking of the sprocket ratio and maybe upsizing the carb to 18 or 20mm."

    I would appreciate knowing what the differences are and which is suitable for my rebuild. I see that the three main vendors all offer the 88cc kit. Two of them are around $125 while CHP's is $200. Why the difference? I couldn't find much feedback on CHP's kit but from what I read on the forums, the TB kit is highly rated.

    I studied up on porting. It looks really interesting, but also way out of my league. I would have to find someone who could handle that for me. Does anyone have any recommendations on an intake that would match up well between the stock head and the VM20?

    I finally got the engine completely disassembled today. The valves were the last thing so I went to a buddy's shop and borrowed his spring compressor to get them out. Now it's just cleaning and figuring out what parts I need.
     
  13. OLD CT

    OLD CT Well-Known Member

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    Post up some pictures of the rocker and valve faces to see if they need replacing.The dratv mini monster and hot Honda cam have the same duration specs.I purshased the mini cause at the time they were close to ten bucks less than the hot cam.It turned out to be a great long lasting cam.

    Now that they are so close in price buy the hot cam with HD springs.CL cam is not a option NLA and now the stock #41 cam is extinct so clean of your stocker and put some grease on it bag it and park it on the shelf for safe keeping.
     
    #12 OLD CT, Dec 24, 2011
    Last edited: Dec 24, 2011
  14. racerx

    racerx Administrator
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    Not a whole lot to add to this part of the discussion. X2 on OLD CT's cam & spring recommendation. The "MM" cam has a little more duration & needle bearing on the RH side.

    If the intake port is black, the valve is worn & leaking. Hand a bare head & new valves to a reputable shop and $70 should get both seats cut & lapped as needed. Not much cash to have a key task done right...from the get-go. Worn exhaust valves are far less common than intakes. Thus, the exhaust side may be fine with lapping only.

    Porting a CT70 head for this type of tune primarily consists of re-profiling the short-turn side of the exhaust port and some bowl area cleanup. You don't want to increase port volume significantly, valve size is pretty generous already. Go too far and the valves will become the restriction point(s), plus you'll kill airflow velocity & throttle response with it. The exhaust port walls can be polished (though it's totally unnecessary), the intake should be left rough to aid fuel atomization. It's not an expensive job to farm-out, there's not that much labor involved to get what you're after.
     
  15. Clint

    Clint Member

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    Thanks OLD CT and Bob for the advice. The rocker arms look good. No flat spots. I'm not sure what the valve faces are. I'll post a photo of them if you let me know what to photograph. The intake port looks fairly clean. Just a little black around the edges but not the whole port. I'll post a photo of it also.

    I'll get the Honda hot cam and the heavy duty valve springs. As for the porting, if anyone is interested in doing it, send me a PM. Any input on a carb and intake would also be appreciated. I've looked around a lot and the VM20 seems to be a good carb, but I don't know which intake to get for it.

    Have a great Christmas. It's my first with my 3 1/2 month old daughter and she already gave me a great gift. She laughed for the first time today.
     
  16. racerx

    racerx Administrator
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    Here's a Christmas present for you. Use the info as you see fit...

    So far, you're looking at:
    • valve job...70
    • OEM valves...50
    • bore-up kit...130
    • fast road cam...46

    Total...296

    Alternatively:
    • 100006 Ultra head, complete...200
    • 100012 52mm aluminum cylinder...57
    • 100042 52mm piston kit...30
    • Z40 or TBQ cam...40

    Total...327

    An extra $30 buys you a bore kit, plus a brand new BV head complete with valves installed...and you can use any of the current model ball bearing cams. Nothing would have to be sent out for machining, just assemble & go. The original top end assembly can be stored for "someday".

    Season's Greetings!
     
  17. OLD CT

    OLD CT Well-Known Member

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    For what it's worth the MM cam is non bearing and is exact duration,the cheap 26 dollar bearing cam the DR sells is the cam to be avoided.They usually walk in the bore of a seasoned head and destroy your valve train.Merry Christmas all!
     
    #16 OLD CT, Dec 25, 2011
    Last edited: Dec 25, 2011
  18. Clint

    Clint Member

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    A friend with engine rebuilding experience stopped by today and looked at the head and valves. He said the valves are in fine shape and that I won't need a valve job. So that will save me the $50 on the valves and $70 on the job. I'll throw that cash toward a new carb, intake and HD valve springs. And I'll order the 88 kit and the hot cam from TB. A friend of mine has a motorcycle accessories shop and gets great deals on TB stuff. That's an interesting price comparison Bob. I would have never looked at it like that. Hope a great Christmas was had by all!
     
  19. racerx

    racerx Administrator
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    That answers one question, while raising others. I was kinda thrown for a loop on this one. In the earlier post, I incorrectly guessed that you had meant the cheaper cam, since it also has a more aggressive profile. With a mere $3 difference between the MM & OEM Honda cam, with the same specs, why would you choose the aftermarket part? Second question concerns cam walk. I'm familiar with that term as meaning excessive endplay, i.e. R-to-L movement; however, going by the context of your post, it sounds like you're referring to excessive journal-to-bore clearance, which would allow the cam to rattle around inside the bore. Not trying to be a wise ass, just on the same page.

    FWIW, I've ridden a couple of bikes fitted with the cheapie Dratv cam. One was an 88cc kit, the other a 110 - both peformed well, with no obvious running problems I'd expect with erratic cam timing. That said, I've not so much as seen either bike since the test rides and thus cannot comment on the longterm durability with this cam.

    Frankly (and this is somewhat off-topic) I've never been a fan of plain bearing heads or engine cases. I passed on the Kitaco SE head for that reason and it's a good performance piece.

    Clint...if your buddy is giving you "friend discount" you might look into the TB head. It's another good value item and uses ball bearing cams...which gives you a number of profiles from which to choose. Combined with a VM20 carb, you could see 50-55mph on a light budget.
     
  20. Clint

    Clint Member

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    Even with the discount, it still adds up to too much. I don't even see a TB head for my model, only for the later model CT's. I'm sticking with the stock head, 88 kit, Honda hot cam, HD valve springs, and a HV oil pump. It's enough. I found a kind gentleman who'll help me with my stock head, bead blast it, lap the valves and install the valves and HD springs. It's been a good Christmas.
     
  21. racerx

    racerx Administrator
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    Cool biz...all that matters is that you're happy with the end result. You should easily get 45mph, hopefully more, from your chosen setup.

    It is possible to use the TB head (it's a 12v type, using the ball bearing cams) on a 6v motor...which is academic when you have too much month leftover at the end of the money.:eek:hwell:

    Good luck with your project, please keep us posted.
     

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