CT70HK0 Restomod - Help/Input Appreciated :)

[69ST]

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.

The difference between optimally dialed-in shocks and everything else is "night & day". So too is the price tag. The most frustrating aspect of this is the obscene markup. With so few options remaining, truly good shocks now start around $450/pair (and rapidly increasing) up to $800/pair for top-line, 4-way adjustable with correct spring rates. If you want Ohlins, it's 4-digit purchase.

One other possibility would be sourcing a pair of used Ohlins, from a fullsize bike, then ordering different springs, new, from Ohlins.

 

[Streak09]

Alright gurus, I'm about to throw a wrench in my plans...

Came across a couple threads that made me ponder building my 108 using ATC70 cases as a base. It sounds like I could get the benefit of CDI ignition, and maybe better parts selection? Am I off base here?

Here is why I am considering...

• I have a mitsubishi iginition
  • If I understand correctly, using the ATC cases would allow me to keep my Mitsu flywheel, but run a late model CDI ignition?
    • I am pulling this from bits on info found in this thread -- https://lilhonda.com/index.php?thre...low-special-108-cc-stroker-build.21518/page-2
• I've already got the 4 speed trans, can I just swap from my H cases to the ATC cases?

Please tell me if I am misunderstanding or missing some big pieces here. What would I need to source to build a 12V CDI "CT70H" 108 stroker motor? Are the ATC cases the big piece I need? It looks like those could be sourced easily. And I already am planning on replacing the crank and flywheel/ignition plate. Are there many other things I need to source and consider, or is this fairly straight forward?

My CT70H motor isnt cherry by any means, so I don't mind building a Frankenstein out of it. As long as it appears stock and doesn't put a dent (bigger) in my budget

 

[Tripod]

Im following along too. In the process of a sort of unrestomod HK0. Debating on sticking with the H motor and spending money building/rebuilding it or slapping in the 140 i have sitting.

 

[69ST]

Okay, this could take a lot of verbiage by the time we're done detailing various possible combos. Let's take this in easily-digested pieces.

Transmissions can be used in any cases, with any clutch type and with any alternator.

Shift linkage goes with tranny...3sp or 4sp.

Clutch linkage goes with clutch type.

GB4 (12v) cases differ, mainly, in that they use needle tranny bearings on the non-thrust sides.

Cranks go with alternators (3sp, 4sp, 12v types) to fit the 3 flywheels, each with a different taper.

Pistons have to be matched by compression height and combustion chamber configuration (dome).

Given my druthers, I'd start with a CRF or XR 50/70 core engine. That gives you the GB4 cases and CDI alternator...I'd wind my own lighting coils and use a full wave 12vdc reg/rec unit. That allows just about every 12v style performance part to be used...and 12v stuff is the most varied & plentiful.

All of that having been said, there's nothing wrong with using a 6v style lower end. Anything up to 124cc (54x54) is possible. The limit of outwardly-stock appearance is 54x52mm. Anything over 52mm bore requires case boring. Anything over 52mm stroke requires a 69mm tall cylinder...stock is 63mm tall.

Hopefully, this installment doesn't cause on digestion

 

[Streak09]

Thanks racerx, I think that clears it up for me. It seems I had read all that stuff before, but never in the same spot and concise enough for me to follow .

The main thing I came away with there is that I would need to source a 12V flywheel and figure out a lighting coil. That seems a bit too involved for me, I’m thinking I need to stick with something “plug and play” (plugging, in this case, still means splitting the cases and doing a major overhaul LOL).

Appreciate the clarification.

In other news, I cobbled together a supporting plate to mount the CT securely onto the desk chair base. It’s ugly, but is rock solid. I can spin the thing like a top!

 

[vintagehondatrailbikes]

"My intent is a Stock Sleeper 108. My base is a ‘70 CT70HK0 that is pretty worn out.". Hi Streak. I received your message. In reading this thread it appears that you are drifting away from a stock look and also a low budget. You also indicated that you won't be driving much or at speeds over 50mph. Aside from going to a 12v CDI conversion I think the Tb88cc race head with a Mikuni VM20 and the CHP performance pipe would be sufficient for how you plan to use it. Stock carb and air cleaner with a 65 main jet and even a stock pipe will work but will limit your performance a bit. The 108 stroker race head kit is a different ballgame. Now you will need to move away from a stock looking "sleeper". HD oil pump. IMO an oil cooler isn't necessary for what your usage will be. VM20 is still plenty. K&N air filter. Not sure the CHP pipe will give you the flow necessary to get the full power from the build. I have used the K1 108 CHP pipe but not convinced with the same narrow pipe as the stock pipe. I have used Over Racing and also the Tb oversized pipes and they absolutely provide the flow but are not stock looking.

 

[vintagehondatrailbikes]

 

[vintagehondatrailbikes]

This a pair of 72 HK1. Stock matching engines with the Tb108 race head kits as described in the last post. As mentioned, the stock front suspension with heavy duty rear shocks. Over Racing pipes with down under mounting (saves leg burn but you need to change the kicker). That's it. Still 6v and all stock.

 

[vintagehondatrailbikes]

 

[vintagehondatrailbikes]

This also is 108 kit on original engine. This one has the "stock looking" CHP 108 performance pipe.

 

[vintagehondatrailbikes]

You can also go "stock sleeper" 88cc with larger piston, HD oil pump, high lift camshaft, SL/XL crankshaft and head with larger cooling fins. All OEM Honda except for the AM cylinder.

 

[vintagehondatrailbikes]

You can also go "stock sleeper" 88cc with larger piston, HD oil pump, camshaft, SL/XL crankshaft and head with larger cooling fins. View attachment 63174

Carb is stock w/65 main. Stock air cleaner and pipe.

 

[vintagehondatrailbikes]

This is an 88cc Custom pearl lime green 72 K1 4 speed semi-automatic with the same setup VM20, K&N filter and the Tb parts performance exhaust.

 

[vintagehondatrailbikes]

This one is close to what you are doing Stock original paint with the same setup. 88 cc and VM20 with Tb pipe

 

[Streak09]

@vintagehondatrailbikes, Wow! Those are some awesome examples! Thank you for taking the time to explain and post.

Now my gears are really turning (or maybe screeching to a halt LOL)...

Here is my thought process, and I know you guys can't make the decision for me, but I like thinking out loud and hearing all my options and others opinions.

• I will spend AT LEAST $150-200 swapping out my Mitsu stator/flywheel for a Hitachi Setup
  • Instead of spending that dough on a used stock setup, I could spend that dough on a 12V CDI setup
    • If I go to 12V cases, I will be buying a new crank, so why not go stroker?
      • I've already figured that it makes little financial impact to go to a TB Race head if building a 108. In reality, I probably come out ahead because I wont have to clean up and rebuilt the stock head. That is a big factor for me, time savings.

So that's my justification for going 12V + stroker...

That being said, you bring up a pretty good argument for just going to 88cc. In all reality, you are right, I don't need the 108 for what I want to do, but man it sounds fun...

Looking back at my parts list, I'm looking at a $300 delta between building an 88 with stock head and cases vs a 108 with race head and stock cases. For me, that is a considerable chunk. Now, that $300 really goes a long way... stroker, race head, etc, but is it necessarily for what I want to do? Doesn't sound like it...

Its easy to get caught up and blow a project out of proportion.

Sounds like I need to decide what I want to do. Right now, I think my options are

• Build a modest low(er) cost 88cc, stock head, no splitting cases, and leave the 108 stroker upgrade for down the line
• Build a 12V 108, and get some major bang for a bit bigger buck... (I think going to 12V makes sense in my situation, given I will be spending $150-200 on ignition parts either way...)

Okay, feel free (anyone) to throw in some more $0.02! Maybe if we keep this up, all the cents will pay for my stroker!

 

[Streak09]

View attachment 63181 View attachment 63182 This one is close to what you are doing Stock original paint with the same setup. 88 cc and VM20 with Tb pipe

How does this setup run? Speed, torque, etc. Very nice looking bike, very comparable with what I would like to do.

 

[69ST]

For an outwardly stock appearing sleeper, you can eliminate anything that prevents using the engine guard...the signature part of K0-78 models...or/and buddy pegs.

Most aftermarket pipes won't clear the engine...not even close. Low-mount types are totally impractical, costing ground clearance on an already low-slung bike. The oversized headpipes look the biz...but that's only part of the story. They absolutely kill low-speed scavenging...and torque...not what you want for anything other than top speed runs. Biggest exhaust port I've seen on any head for these engines was 25mm, most are smaller. The TB pipe is a decent product. I run the Kitaco pipe it copied, on an ~80mph bike. It's good for ~6% at peak power...which translates to 2mph. Oh...and it's LOUD. No doubt, the OEM muffler becomes a restriction once you have 50mph+ power. Still, no need to go with something that's marginally practical.

IMO the biggest draw of big pipes is the look. Same goes for wheels & tires. There are a lot of 70mph bikes out there with more invested in the muffler & wheel assemblies than the rest of the bike...because real brakes & suspension are "too expensive". My point...there's more to be gained by focusing on a specific goal and what is practical. That is usually unglamorous stuff.

You have some reasonable goals and a pretty good handle on the basics. For example, you aren't talking about a $700 dollar exhaust on a $300 Chinese engine. Keep doing your homework, asking questions and following your gut. You're headed in the right direction already.

Winding a CRF stator isn't difficult and there's an easy 50w of full wave power to be had.

There are also at least 4 engine combos that won't "give away the store" visually...88cc, 89cc, 108cc, 117cc that can be had in 6v/4sp flavor.

$300 is a modest amount circa 2019. May as well start with a fresh base...which means splitting the cases; the shift forks are probably well-worn. HV oil pump installation is easy while the cases are apart...now you'll have a solid lower end, for any top end you choose, even if you change your mind later.

88cc is the most popular tuning upgrade.
But, it's not going to register a big boost on the seat of the pants dyno. Expect enough torque to allow one more tooth on the c/s sprocket and usable road speed going from the mid-to-high 30s into the low 40s. If you're expecting to keep pace with 45mph+ traffic, this isn't going to do. That's where the longer stroke makes all the difference, even with restricted top-end breathing.

 

[Streak09]

Racerx, you hit the nail on the head with your comments on “stock appearing”. That is exactly where my head is at. The big items that make the HK0 stand, they are what I want to keep. Like you said, engine guard, exhaust, headlight/speedo combo, paint, decals. I am alright with some minor tweaks like head fins or intake. Most of us here on the forum will know that it’s not stock, but the general public, even those familiar with CTs probably won’t pickup these subtle differences. They will be drawn to all the things listed previously that make the HK0 what it is.

So, non-negotiables are the engine guard and “stock” exhaust. Pretty much stuck with the CHP knockoff performances exhaust for that. And I’m okay with that.

I’m really getting interested in this 12V conversion...

@racerx, can you direct me to a good how to on winding a lighting coil? I really am starting from zero here. I wouldn’t say I even know the basics when it comes to stators and coils (at least the details of these bikes, I get the concept in general).

I would like to price out this 12V conversion with stroker.

Here’s what I understand I need:

• CRF50 Stator - Wind the lighting coil (per above, i need some guidance here)
  • $40???
• CRF50 Stator Plate - I’m assuming other models will work, is it safe to say just a “12V” stator plate?
  • $40???
• 12V flywheel - many models to choose from??
  • $30
• Can this be used in place of all the above components??? - https://tboltusa.com/store/gold-flywheel-and-standard-ignition-stator-br-with-lighting-p-5325.html
• CDI unit - I have no idea what I am looking for here, but know I need it.
  • $20??
• 12V Full wave reg/rec - again, no idea what I’m looking for here
  • $20???
• 12V cases - sounds like a lot of options here
  • $40
• 12V stoker Crank Kit - TBolt

If that’s all I need for this “conversion” then it makes sense for me to go that route. Like I said before, I’m already spending $150-200 just to get my H motor stator/flywheel sorted out.

I’m assuming the CDI unit uses spark advance, right?

 

[kirrbby]

The 12v conversion is awesome after it's done. You'd basically be doing the electrical the best way, using the most up-to-date parts. racerx is recommending the BEST of the best with the full wave setup. More-better power for your lighting. He would be able to guide you thru that full wave setup. I'm not familiar with how it's done.

But swapping to 12v adds some challenges for sure. And, I'd not recommend using your matching H engine case if you're going 12v. It would require notching the engine case. You'd definitely want to start with a different case.

There are lots of 12v stators available that would not require you to wind your own. Probably 50 bucks and up. You pick it. You buy it. You make it work. There are more than one variation of these stators.
Then you buy a good used or new flywheel. 35 bucks is cheap, and up.
Then you pick and buy the CDI...coil...reg/rec...etc and make them work. Maybe 20 bucks each for cheap Chinese, and up. Squeeze in a 12v battery and box...probably $60+

It's really no about the money...for most of us. It's more about making the commitment to put in the work. Most of us also need someone who will commit to helping us sort it out...via lilHonda.
It's all worth it in the end.
But in comparison, repairing and bolting up the original parts, is easy.
Every single modification, away from stock, poses some challenges. Stock parts bolt up and work, period.

For you...I'd recommend the 108. In 12v cases. With 12v power.
Might as well build it right...the best way...the first time around.

I'd also recommend leaving your H lower end whole. Buy a atc70 4speed trans to build from.

 

[69ST]

Kirrbby just gave you a really good bit of perspective. It really isn't about the up-front cost. It IS about the longterm value. Coincidentally, a little more up-front cash, to do things right from the get-go, usually does end up being less money over the longterm. Even if it weren't so, how would one quantify the satisfaction of a project that meets or exceeds expectations...versus one that falls short?

I can't really see there being more than a $300 bill difference here. What"s the annualized "premium" after 2,3...or 5 years. Imho, those are inexpensive grins circa 2019.

You could start with a used CRF/XR 50 or 70 lower end, then replace the tranny with an AHP 4-speed. That'd take care of the tranny, HD kickstarter asm. & 12v CDI and on the cheap.

There are any number of ways to piece this together...that's part of the fun, i.e. the "treasure hunt" aspect.

And...you've come to the right place to sort things out.