1972 HONDA CT70HK1 CANDY YELLOW SPECIAL 108 CC STROKER BUILD

lukelaw1

Active Member
I cleared some duplicate model Honda CT70s this summer. With that said, I have some extra cash burning a hole in my pocket. I have really been reaching a 108 stroker motor build. I have a really good candidate. I have; fair conditioned, titled, and complete 1972 Honda HK1 that ran and drove well when park, floating around in storage. I have compiled an excel spreadsheet of all the parts I can think of to complete the build. I need additional sets of eyes to look over the parts list and please advise of any changes.

Here are some pics of the candidate. I have since replaced the torn seat with another OEM tear free seat from another K1 model. Look closely at the exhaust it has been modified, via the end cut off and possibly the inner baffles taken out. I will need to research this prior to purchase of an exhaust.
 

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I cleared some duplicate model Honda CT70s this summer. With that said, I have some extra cash burning a hole in my pocket. I have really been reaching a 108 stroker motor build. I have a really good candidate. I have; fair conditioned, titled, and complete 1972 Honda HK1 that ran and drove well when park, floating around in storage. I have compiled an excel spreadsheet of all the parts I can think of to complete the build. I need additional sets of eyes to look over the parts list and please advise of any changes.

Here are some pics of the candidate. I have since replaced the torn seat with another OEM tear free seat from another K1 model. Look closely at the exhaust it has been modified, via the end cut off and possibly the inner baffles taken out. I will need to research this prior to purchase of an exhaust.


Hi Luke,
Are you building the engine yourself?
Stock transmission not an option?
What carburetor are you using?
 

lukelaw1

Active Member
Hi Luke,
Are you building the engine yourself?
Stock transmission not an option?
What carburetor are you using?

Yes, I was planning on rebuilding the motor myself.

I am not sure of the condition of the stock transmission, as the bike is not even out of storage yet. I was thinking that the bike had some miles on it. IMO $150 for everything new; ie shift forks, gears, shift drum, and etc. is a "good deal". Also from what I have read from Darrel Gunderson, the AHP tranny will configure with the HD kick start shaft upgrade.

I'm not sure on the carburetor setup yet, the stroker kit from TBolt comes with a 26mm Mikuni. I have read that carb setup is a little big and the Minuki 22mm rejetted works better. I may try to contact them and see if they will sell the kit with the 22mm.
 
Yes, I was planning on rebuilding the motor myself.

I am not sure of the condition of the stock transmission, as the bike is not even out of storage yet. I was thinking that the bike had some miles on it. IMO $150 for everything new; ie shift forks, gears, shift drum, and etc. is a "good deal". Also from what I have read from Darrel Gunderson, the AHP tranny will configure with the HD kick start shaft upgrade.

I'm not sure on the carburetor setup yet, the stroker kit from TBolt comes with a 26mm Mikuni. I have read that carb setup is a little big and the Minuki 22mm rejetted works better. I may try to contact them and see if they will sell the kit with the 22mm.

Yes, I believe Darrel has done quite a few of these. I use a VM20. Not sure what Darrel uses. I think it was Racerx that said the VM22 was hard to tune.
 

lukelaw1

Active Member
I would hate to switch the thread title at this point but I do have another candidate. I have this titled CRR HK1. The paint is a little rougher and if I remember correctly there and from what I can see in the photos the area around the air box on magneto side has some good rust. I do have the magneto, magneto cover and chain guard floating around somewhere. Also as you can see the magneto has been removed. When I bought the bike many years ago, I got the bike running and took it for a quick short spin. I wanted to replace the points and condenser. Long story short I took off the magneto cover, magneto nut wasn't very tight, but magneto was taper locked on. I got the magneto off to find that the previous owner had stripped the crank threads for the magneto nut. To get even better the top motor mount bolt is seized in the motor. I couldn't beat it out with a hammer and didn't want to twist the bolt off so I parked it.

There is also a third option here as I was fishing around in storage. I have what I believe is a parts HK0 motor. So I could build the HK0 motor and keep the original motor to the bikes stock, stored on the shelf.
 

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lukelaw1

Active Member
If your building a stroker motor you could use a 3 speed engine if you weren't worried about using the original engine? Just a thought......

That thought had crossed my mind as I should have a 3 speed motor on the shelf, but there is just something about grabbing those gears with a clutch.
 

kirrbby

Well-Known Member
What Darrel is saying, is to build your 4 speed stroker in a random set of cases...3speed, Z50, ATC70 whatever. Save the original motor that belongs in your desirable CT70H.
Byt the time you replace the... trans, crank, kicker, clutch, cylinder, there wont be much left anyway. Basically all you need is a stator setup, and a head. Maybe even build it as a, 12v cdi, stroker-manual-4-speed-with a race head.
 

OLD CT

Well-Known Member
It's not recommended to use the stock throttle for a VM20. Pick any remote pitbike throttle assy with the cable and grips on ebay cheap. They run around 10.00 to 20 bucks shipped.
 

lukelaw1

Active Member
Update:
I got around to taking the motor out of the Red HK1.As I thought the motor mount bolt was seized and broke off. I got both sided to break off and drill the bolt back to get the top mount free. Once got the motor out I started to split the cases. I had to drill the top motor mount bolt down to where the cases split and I got them apart. I had to even drill the motor mount bolt out of the other case half. I didn't do to bad only got into the case a little bit.

Here is the issue now the right case half on the rear mount split out. Check the photos.
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And there is also damage to the left case where someone tried to pry the magneto off and broke the case where the timing mark is. Check the photos.
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Anyone have a case close to that serial number? I though I may try to JB weld it back into place and hope that the magneto cover will help hold it on too????
 

lukelaw1

Active Member
I also split the HK0 cases and determined that I just can't bring myself to build a stroker from it. I want to bring that motor back to stock or an 88cc big bore upgrade. As Darrell and Kirrby recommended I am going to source another set of cases to build the stroker from. I was thinking about buying these cases.

https://www.ebay.com/itm/1979-79-HO...ash=item1c6cb38ae5:g:VRMAAOSwawpXrkPX&vxp=mtr

Can I use these cases with the tbolt 108 kit p/n TBW9111?? Description says ATC70 years 81 and up
 
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kirrbby

Well-Known Member
I think it would be worthwhile to have a pro weld up the LEFT side case of your engine...save the matching # for your bike. Depending on the price and time to repair the right side case...might be better to just buy a good used replacement.

I think the ATC cases should work just fine to build your stroker. Not sure why Tbolt would call out 81 up. Maybe the shape of the combustion chamber changed in 81 or something like that. I don't think the cases changed significantly tho.

Those cases that you linked...it looks like the bottom rear stator cover mounting hole MIGHT be broken out..? I don't see a good pic of it tho. You might need to ask the seller to check it or send you a picture.
 
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