CT70HK0 Restomod - Help/Input Appreciated :)

Alright 'fellers, I have decided to start the build on my HK0!

Its been a while since I've poked around or posted on here, but I'm ready to get back in it! I'm typically long-winded. I've tinkered with some vintage Honda stuff for a while now, but haven't done much lately due to house projects, some dual sport riding, and welcoming our Little Bundle of Joy into the world. I will try keep it brief so I don't lose everyone's attention. Lets get to the details!

Bike Background:
I picked up this Topaz Orange HK0 from a younger kid a few years back. The owner mentioned it needed a new stator and wasn't running, so I got a pretty good deal on it. It has the Mitsubishi stator, so that will be a bit of hurdle. The bike is missing some miscellaneous items, some functional, some not. The frame paint is actually in pretty good condition. Other components, not so great, but not awful. Currently not titled in my state of Ohio, but working on that part. Okay, that's about all I know about the bike.

Build Plans/Objective:
I want this to be a clean stock looking CT70, with a punch! I have no desire to make this a pristine restoration, nor do I want to dump that money in it. I know me, and I will be afraid to ride it if it looks too good or I have too much money in it. What I do want, is something that looks nice and original, but don't mind throwing it in the back of the truck and taking down some trails. I also want it to be street legal, and able to ride on some town roads, mostly 35mph speed limit, but occasional 45mph roads, and rarely a country 55mph road. This will NOT be raced or flogged on the street. It will be used for occasional rides, maybe a couple hundred miles a year if I'm lucky. Based on that, here is my game plan:

• 108cc TB Stroker - I need some help on this one, stock head or go with the kit and get the TB head?
  • I don't need or want a high performance machine. I won't be flogging it. I just want the extra displacement to so I can ride comfortably on the road, and have that WOW factor compared to stock. I think I can save $1-200 by piecing the kit together without the head.
  • So, stock head with cam (I have a mini-monster cam from DRATV that I can use, I believe similar to the SL70 cam) OR TB Head??
  • Stock appearance is important, but it doesn't have to be perfect. I don't think the TB head will detract from the stock appearance that much, thoughts? I DO want to keep the Engine Guard, will the TB head impact that?
  • I will not be running an oil cooler. I know I may be taking a chance, but I want the stock look and I wont be pushing it to its limit. I know the risks. (This decision may impact the stock vs TB head decision?)
• Carb
  • After digging in, I think I have decided on a 20mm (true 20mm opening, so maybe a knockoff would be labeled as a larger size??) carb. I dont mind splurging a bit on a Mikuni, but does anyone have a proven out cheaper substitute?
• Exhaust
  • Going with the CHP Stainless K0 performance muffler!
• Clutch
  • Plan is to keep as much of the current clutch as possible. What basic upgrades are recommended? I've heard the general "Heavier Springs" and clutch plates, but I haven't had luck finding any of those components for the 4 speed. Can someone learn me on this one?
• Swap out Mitsiu Stator/Flywheel for Hitachi
  • I already picked up a Hitachi set, may need some opinions on the condition of the Flywheel. More later.
• Clean up painted bits
  • Frame should clean up nicely. No intent on repainting. I think she will shine up fairly nice. Some items may need replaced. Rpop parts may be used, if they closely reassemble stock.
• Clean up and replace Chrome Parts as needed
• Budget
  • I will spend the majority of the build budget on the engine. I don't mind going quality, but I'm not going to go overkill. Engine budget needs to be under $1k. I've done the research, this should be achievable.
  • Budget other than engine, $5-800.

So there is my outline, hopefully that helps direct the conversation. Too many threads I've read don't clearly state the objective, and I think it causes a lot of "you could do this, or that, or this, but depends on what you want" stuff. Trying to avoid some of that by clearly stating what I want the bike to do!

I just a '74 CL125 to fund some of this build. I also cleaned out some of the garage to prep to tear down, hopefully I will get to some of it this week. I'm itching to start!

Last but not least, some eye candy (Topaz Orange, to be exact )

Perfect beginning to a project thread.
Welcome BACK to lilHonda Streak09!

kirrbby said:

Perfect beginning to a project thread.
Welcome BACK to lilHonda Streak09!

Click to expand...

Thanks @kirrbby ! I have based a lot of my decisions of the info you have provided in other threads. So, thank you for already contributing to getting this thing going again! More input is always welcome

Hi Streak, I really do not recommend you build this to 108 as I am thinking you want to retain the pogo ''no real suspension'' front end. Keep it to 88ccs. One pothole that you can't see at 45 to 55 will be BAD news. If you change the front end to a K1 frontend or the inverted aftermarket you will be ok. The bike will feel like a deathtrap at any speeds over 45 with the pogos anyway. 108 will not cruise on a 55 mph road easily, it will be screaming, that's why folks build to a 124cc. 50 to 55 mph all day capability.

4 speed clutch springs are no longer sold separately.

OLD CT said:

Hi Streak, I really do not recommend you build this to 108 as I am thinking you want to retain the pogo ''no real suspension'' front end. Keep it to 88ccs. One pothole that you can't see at 45 to 55 will be BAD news. If you change the front end to a K1 frontend or the inverted aftermarket you will be ok. The bike will feel like a deathtrap at any speeds over 45 with the pogos anyway. 108 will not cruise on a 55 mph road easily, it will be screaming, that's why folks build to a 124cc. 50 to 55 mph all day capability.

Click to expand...

Understood, I do not intend to cruise @ 55mph. Most (and for me, most means MAYBE once a month) of the time I will be on 35mph roads for short distances. Other than that, it will be in neighborhood 25mph zones. Occasional trot in the woods and yard at a buddy's place. I have zero intention of maintaining 55mph. I really don't even intend on touching 55mph (outside of a "i dare you" LOL). What I do want is the torque to pop a wheelie whenever I feel like it, or cruise comfortably at 35.

I completely understand the death trap pogo front ends on the K0. I had '69 K0, it was actually the first bike I have owned, and sucked me into this mayhem. I've tossed the idea around of going to a k1 front end, but we will see. For know, pogos it is.

Thank you for your concern and knowledge though. You are another one that I have collected a TON of info from while deciding how to build this.

A good 88cc will hit 53 mph topped out. And cruise 40 nicely, with no cooler. A 108cc needs a cooler. I have a nice G Craft cooler that isn't really that big, but does a good job with the finned cam cover on the other side. Webikes has a lot of good performance parts. Check out that site and get a list going.

A Trailbikes head and matching stroker kit will give the most punch. The guard will fit.

Well, now you have me waffling a bit. I was originally going to go with the 88cc and stock head, for simplicity and cost sake. That was until a buddy picked up a beat up HK0 and is building it right now with a stroker. I mean, I can't let that happen can I!?

I think I will go with the TB Head and Stroker, and I can keep the stock head and jug in case it ever needs to go back on. Always nice to be able to return to stock or have a backup.

Streak09 said:

Thanks @kirrbby ! I have based a lot of my decisions of the info you have provided in other threads. So, thank you for already contributing to getting this thing going again! More input is always welcome

Click to expand...

Well... no wonder I like your plan
I do talk a pretty good game. But its risky to actually BELIEVE anything I say.

Like old CT said, the oil cooler is a concern. But enginedoctor ran a 108 with no cooler on his #1 for...ever, without any trouble. I never had a cooler on my 124cc dax.
If you baby it well enough throughout the break in, watching oil temps and all, you might be ok. Keeping the jetting on the rich side will help it to run a little cooler. But keeping the speeds low is the only REAL way to keep the temps down during break in. That's a hard thing to do.

The stroker crank makes a mighty big difference in power. It will definitely get the job done...the job you're describing.

I haven't ever been impressed with 88cc. It's a nice boost for $150. But that's all I have to say about that...(Z50)

The stock head should work...probably as well as a regular race head would.
The V2 race head can stay in your back pocket(wallet). You could do a easy upgrade to the V2+front end, if you start feeling frisky down the road. I've never been fast on a set of pogos. I would not want to be fast on a set of pogos either. I really think it will be a problem for you eventually. I've hit potholes, and roadkill on 90s front shocks, and it hurt!

The mikuni VM20 is a very good carb imo. Can't speak for any others, but someone else might have recommendations.

Tbparts has a complete disc kit for your stock clutch...5 discs. It's a tight squeeze with the stock springs. That should work plenty well for you.

Great info Kirrbby.

So, just the TB Disk kit should work out okay, stock springs are sufficient?

As far as the head is concerned, I suppose a stock head isn't that difficult to come by, so using it wont be that big of loss. I guess I was thinking that i would be risking it a little more by running without an oil cooler. If anything were to happen, I would have the stock head to fall back on. Teh big appeal to me is having the ball bearing cam vs the journal bearing on the stock head. It seems I would accomplish about the same same performance with either, seeing that I do have a hotter cam for the stock head. In the grand scheme of things, it looks like it would only save me $150 to go with the stock head. And at that, I haven't figured in any new components for the stock head other than the cam. No stronger springs or valves... so really, its probably a wash...

I guess I need to price out piecing together the stroker instead of relying on the kit. The 24mm carb seems kind of excessive in their kit...

I think your right. Use the race head and save the stock one. Just in case it does get cooked.

You should be good with the stock springs. Plus, you'll have a hard time finding stiffer manual clutch springs. I've been using the same setup on a 117cc manual clutch engine with no troubles.

Nothing special about the TB head. The CT70 head is better than most realize. That said, it is a 12v style head and that makes parts such as cams and oil coolers easier to source.

Two details that need clarification...

You want a high volume oil pump. That augments cooling (as does an aluminum cylinder jug).

"HD" valve springs are a misnomer. Valves this small are easy to control and I've yet to run across a set of springs that was much stiffer than stock. That's actually a plus...lower spring pressure equals less valvetrain wear. What is needed is wider coil spacing to prevent coil bind with a high-lift cam.

The TB clutch kit is an excellent piece, with the billet basket. It'd be my first choice. On a budget though, the Takegawa manual clutch is a good value at half the price. Dratv lists this kit. You will need to reuse your primary gear; otherwise it's plug & play.

Only way to keep oil temps down is to keep your speed down. Speed equals hp and hp equals heat...basic physics. Source a dipstick oil thermometer and see where your oil temps really are. If they peak above 110-115C you need a cooler.

Unless you're willing to run a 12v alternator, the TB 51mm crank is the only choice...available in 3-speed & 4-speed flavors.

For your objectives, I'd go for the TB top end & crank, oil cooler kit, a dipstick oil thermometer & Takegawa clutch. That's an easy build w/60mph power. Plan on replacing the shift forks while the engine is apart...then you're good-to-go for a long time.

The K0 pogo stick fork is marginal, at best. K1-79 is far superior and not hard to find. Those Chinese inverted front end "kits" are...cheap. You do get a disc brake but it's small diameter. The suspension action isn't as good as K1-94. The one suspension item no one seems to understand...rear shock set. Go for the best shocks your budget will allow. Real valving and correctly matched, progressive spring rates will give you control and comfort. But, real shocks cost real money

Well, racerx, your comments have completed what I had hoped for; the Holy Trinity of CT knowledge chiming in with advice .

Thank you for pointing out my omission of the high flow oil pump. That is a MUST on my list, I just overlooked it in my original posts.
Your clarification of the clutch and valve springs also helps immensely. I've got clear direction now on those items.


Another worthy topic which you mentioned is rear shocks. I know the stock suspension can be down right dangerous. That being said, I am going to sacrifice some handling and spirited riding for the stock look. That pretty much eliminates the real valved rear shocks. What I would like to do is get some heavier springed shocks. It looks like some are available, but not in the Topaz orange... any suggestions, other than getting a different color and painting to match?

I think I am sticking to the plan, given the advice you three have provided. I understand the risks and limitations I will have to live with, given the lack of oil cooler and stock(ish) suspension. I can live with those things, for the time being anyways...

I ran the numbers for the stroker kit vs piecing together. The TBolt kit for $499 seems to be a great deal. Looks like I would get; Race Head, Throttle Cable, Intake Manifold, and Carb (although I wish I could get it without the carb or swap?) for less than $100 difference when piecing together. Seems like the way to go to me. Any thoughts on if Tbolt entertains swapping out components in a kit for others? Who do you guys prefer buying through?

Again, many thanks for your thoughts and input. It really helps boost confidence when tackling things. Im ready to riiiiiddddeee

The oil thermometer will allow you to stop before the oil gets burnt. Keep your speeds below 45-50 and you may not have problems. A good quality 20w50, such as Honda GN4 will give you the zinc required to keep shift forks from
premature wear and a few more degrees of peak temp headroom.

Make no mistake, it's a machine. If you hotspot it during break-in, use anything but JASO-spec oil, burn the oil, or fail to keep clean oil in the crankcase it'll eat parts. It's easy enough to avoid those issues and inexpensive.

I forgot about the carb. Go for a genuine Mikuni VM20. That's all this engine can use. Quality is dependably first rate, parts are easy to find and it's an easy carb to tune. Forget about the cheap & chineezy carbs. There"s maybe $45 price difference. What's your peace of mind...and hours of your time...worth?

And running a carb that's bigger than the intake port is stupidity.

As for shocks, personally I view them as bolt-on parts that can be changed-out at any time...in under 5 minutes. That said, the top priority is prevention of bottoming-out; that breaks shock mounts. Cheap shocks typically have overl'stiff springs and no damping. You'll get a harsh ride but the shock mounts may thank you...by not bending/breaking. The stockers are dangerously soft/weakly sprung.

Ill definitely following this thread. I to am building a stockish 70 with a Honda 4 speed from an xl.I recently bought the tb 108 kit with the v2 head and complete gasket set,carb and intake.I pretty sure it comes with a 24mm mikuni.looking at buying a fmf big bore exhaust for a crf 50.after reading replies to your thread I guess ill be buying a cooler.plan to ride it about like you.in town, occasionally ripping it when I get the urge.I live in florida so I feel cooler wont be optional.cant wait to see how yours comes out.

definitely following along with this build. gotta love all the knowledgeable advise from guys that have actually built bikes and know what works and what dosent. I too am building a 108 big bore ct. got my stuff from tb. ended up ordering complete kit with v2 head,carb,all gaskets.I live in florida so probably be getting a cooler.plans for me are similar to you as far as riding. back and forth to work at city speeds. and a occasional rip.cant wait to follow your progress.

sorry for the double post.no I don't live in moms basement

mark from florida said:

sorry for the double post.no I don't live in moms basement

Click to expand...

.... that’s what all people who live in mom’s basement say

Welcome aboard! Hopefully we can learn together here!

The v2 head is altogether different...a copy of the Takegawa +r head. The "normal" TB race head is, essentially, a copy of the 6v & 12v CT70 heads...the bigger inrake port of the old 6v casting and ball bearing cam of the later 12v.

The v2 can make more power. The other head will likely have a longer service life by virtue of its conventional rockers.

I f you weigh 170 or under the Dratv replacement shocks will get you by and not bottom out, they are the closest looking to stock and have a little better feel. They do have a little bouncy feel at times but never bottomed. Some members have ''red69 '' had CHP shocks, but they wound up leaking. They are not as close looking to stock either.

In the near future, I will be buying a set of rear shocks with real valving to test out.

Major progress update...

The CT is off of the patio and into the garage. I saw a brilliant idea around the forum to use a desk chair base as a work stand. This is gonna work out great. I think I will need an adapter plate of some sort, due to the chair mounting base being just irregular enough to make bolting the engine directly too it a bit problematic. Should be simple, just need to grab some scraps from our lab here at work.