Honda HKO '72, Upgrades (Head, Piston, Cylinder & Crankshaft from a Honda NICE 110)


Without displaying a great deal of ignorance...
I would like too "Upgrade" my "H" (4-speed), 'Very Tired' Honda 70cc motor using Honda NICE 110cc motor "Parts" !
Swapping out the (Rebuild), Head, Piston, Cylinder & "Pin & Weld" the Honda NICE 110cc (Rebuild), Crankshaft...
Is it possible to use Genuine Honda parts from a Honda NICE 110cc motor & "Transplant" those parts onto my '72 "H" motor?!?

One of the BIG reasons, I am told that the VIN number, (frame & engine case), match my California DMV Title...
I'm 60 years, 5 ft., 10 inches tall...230lbs.!
I believe I 'Need' the "Extra" Hp & Torque to get me around town!

(I would Really like too impressed my boss at a "National Defense Contractor" in Poway, CA)
Showing Her...(and sometimes Him...Them), that I possess the ability to rebuild and "Upgrade" a machine...

Any information that Anyone would care to share...Your input would be most helpful !

Cheers, Donald


Well-Known Member
I don't think the Nice internals will swap into your 70 crankcase.

Why don't you get a 108cc stroker kit? Everything will fit your case and you will see a great increase in power. Racerx could probably confirm my thoughts on the Nice swap.


Well-Known Member
You might be able to adapt a Nice head, that's about it. It's a very efficient design and a high-quality part but, nothing special in terms of gross airflow. It'd be a helluva lot easier to just source a TB race head. The cylinder is way too tall and the lower end architecture is radically different. The longest stroke crank that can be stuffed into 49cc cases is 54mm; the stock Nice crank is 55.5mm. It's also waaaaaaaaaaaaaaaaaaaaaaaaaaaay too wide, at both ends. The Nice oil pump is gear-driven, no driveshaft to interfere with the crankshaft, making cranks as long as 66mm possible in that engine.

It's possible to go as big as 124cc with stock 49cc cases. Nothing increases torque, and with it seat-of-the-pants-dyno readings, like increased stroke length. You can go as big as 52mm stroke with a stock 63mm cylinder height...if you're dead set on retaining an outwardly-stock(ish) appearance. (The carburetion changes and oil cooler will kinda "give away the store".) 54mm stroke requires a 69mm tall cylinder, longer cam chain & cylinder studs. You also have to match piston compression height to the crank & cylinder, as well as the head. A 52 x 54 undersquare will be a high-compression torquer with a broad, flat, power curve. I'd stab-in the hairiest 6v cam profile available. You can't get all that wild with 6v cams, it's not physically possible. All you want to do is balance the tune. Undersquares tend to produce high static CRs and the bigger the displacement, the smaller the cam "acts". 60mph+ should be easy.

If you don't mind having the cases bored, you can go as big as 54mm bore.

Possible combos:
  • 52 x 41.4...88cc
  • 47 x 51...89cc
  • 52 x 51...108cc
  • 52 x 52...110cc
  • 52 x 54...115cc
  • 54 x 51...117cc
  • 54 x 52...120cc
  • 54 x 54...124cc


Not real concerned about how this machine looks... Carburetor size & Oil Cooler!
I wanted some of the parts off a Honda NICE 110cc motor, to "work" on my HKO, 4- speed and keep the 72cc motor ('Cases'), because of the VIN/Engine case numbers & the frame numbers to get a California DMV Title...

I am NOT opposed to a "TB" Race Head...
I was hoping to keep the Original Honda Quality in the Larger displacement I'm hoping too achieve !

There are a few "Motorcycle Salvage" shops here in "North San Diego County, California", so I have access to many different parts from many different types of motorcycles !

Perhaps, I should look into just what I can "Interchange" with the particular mini trail?!? I read "72cc" on the engine cylinder...
So, the actual case us the base for 49cc Honda motorcycles?

Would some/any of the 'Other' Honda Motorcycles (under 200cc), be a better place too start? (There goes my engine/case VIN number) !

Oh...Thanks for the "Possible Combination chart"! I will study this...(I really like the "54 X 52" = 120cc..) !


Well-Known Member
The CT70 engine, like all other 72cc horizontal singles, is based on the 49cc lower end, as used in the Z50 models. It is, essentially, a Z50 motor with an OEM big bore cylinder/head/carb kit installed at the factory. The Honda Nice 110 has little in-common with any of the 49cc-based engine family, up to and including the C90, which never reached US shores. In terms of quality, the 110 Nice and Wave 100 are as good as it gets for these bikes; they are silky-smooth and bulletproof. The one characteristic they do share with the 49cc engines is the motor mount configuration, it's identical. So, these engines bolt-in directly...though the exhaust, footrest assembly and brake pedal must be modified to fit, or replaced outright. That said, the only practical way to get a Nice motor is to source one, complete.

Comparing engines is a huge topic, best left for another time.

As for the various tunes possible with 49cc cases, 52mm is the bore limit above which the cases have to be machined to fit a 54mm cylinder. The biggest you can go without any machining is 52 x 54, which will give you a good torquey motor. Torque is what you want for street riding, that's what gives a machine that feeling of pulling itself along with effortless ease and makes it less sensitive to hills and headwinds.

Much of the time, choices are shaped by budget constraints and what's most readily available as a complete kit. This eliminates the need for research and any guesswork. In 108cc & larger, that would be the TB108 & 117 tunes, which can be sourced as complete kits...everything but the exhaust, oil cooler and dipstick oil thermometer. TB is the only supplier of 6V-type stroker cranks (51mm flavor only) that work with the old `69-`81 breaker point ignitions. 3-speed & 4-speed motors had different flywheels and the cranks were made specific to each type. It is possible to convert a 6V motor to 12V/ you a wider variety of crankshafts from which to choose...including one of the aforementioned 54mm arms. I'd suggest doing some homework. Get an idea of what-all a few different setups require, including clutch, tranny & electrical mods. Some can be a bit confusing, at least initially. The parts can add-up, it's not hard spending north of $1K to build a tuned motor and you get what you pay for. Some guys have difficulty accepting that reality.

If you're dedicated enough, it's amazing just how far these little machines can be upgraded...into real road bikes, capable of covering 200+ miles in an afternoon...enjoyable miles. If you're after more of a suburban runabout, as opposed to a mini grand-tourer, that's fairly easy to accomplish. Be advised, going in, there are LOTS of possible combos, of various parts. It can be a bit overwhelming, at times. Thus, I usually recommend starting with as clear a goal as possible. That'll help set your list of priorities. From there you'll have enough of a focus to begin, without running yourself mentally ragged before you really get started.


Thanks so very much for All this information !
I have been interested in these "Honda CT-70 Mini Trails" since I was a kid...
A few years ago, I helped a family friend move from Escondido, CA (behind San Pasqual High School), to Las Vegas, NV !

When I brought his Big truck back to his 'Former' resident...I quickly called him to remind him that we did NOT clean out the shed in his back yard!
He asked me too do that and that's when I "Found" 2 Honda CT-70's!

He told me I could keep them...Maybe get them running!?!
Bob, on a side note...You helped be (back in 2008)...
I purchased a few parts off Jamie...I sent him the money...took a few months for him too send me the parts !?! I believe that you spoke too him..Asked me too be Very patient...It All finally worked out!!!

I had an "Opportunity" (at that time), to go back too college, finish my "Bachelor's Degree!

I took advantage of this opportunity, paid for by my employer ( "Giant Defense Contractor"), and moved up a lot within the company!

Also, Bob...a "Friend of a Friend" had 'Anthony' ("Primedup 1816"), on eBay contact me regarding the "Honda NICE 110cc"... Used or New engines, with wiring harness, controls on the handle bars, etc.!
Used: $750.00 to $850.00...New: $1950.00

I'm still "Pondering" this offer...

I like the idea of "TB Big Bore Kit" (108 cc or 117cc)!?!
There's a bike shop in Escondido that can "Source" a Bigger Piston & Cylinder...
"Re-Locate" the connecting rod at the Crankshaft, and "Found" a Bigger head...around $390.00...

Thanks again, Bob...For All your knowledge, helpful insight, and information !

Cheers, Donald


Well-Known Member
avoid Primedup ebay seller.

dont bother redrilling a crank and moving the pin. a tb crank at 51mm is only 165 bucks and proven reliable.

buy a tb 51mm crank, 52mm piston and cylinder and a vm20 carb and put it together. more than double stock power


Fatcaaat, Thank you for the "Heads up"...
Again, on eBay..."HondaProducts 7890" sells a number of kits from "TB" !

I looked at & Like the "12 Volt CDI Cylinder & Piston with a crankshaft...The "Race Head" looks Wonderful & Pricey !

I also like the "Roller Rocker Rebuild"...


Well-Known Member
contact vince at tbolt usa to buy your parts. youll get the right ones and he will provide product support. youll find there wont be a price differential.


Thanks Fatcaaat...
I believe I will wait until next week (or later), before I do anything...

My "Lovely Wife"is getting ready to go too Europe...(Prague, Czech., Hungry, I'm Not sure where else), 4 Countries in 3 weeks!

Cheers, Donald