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Honda Express From 49cc To Stroker 100cc In Original Case

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jumps4

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#1
A story in photographs....
I had originally posted about this project at "project of the day" but I have done a lot more and had lot more pics so I'm starting a thread.
http://hobby-machinist.com/threads/...-in-your-shop-today.14637/page-27#post-154852
There is no real good reason to do this except to improve my skills the bike is so mean now it's breaking the spokes and I'm going to have to change the rear wheel.

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jumps4

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#2
The cylinder work from 39mm to 54mm

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jumps4

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#3
Crankcase modifications

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jumps4

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#4
Stroking and modifying a stuffer crankshaft to fit this case

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jumps4

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#5
More crankshaft

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jumps4

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#6
mock up and exhaust fabrication

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jumps4

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#7
transmission and modified gear ratio

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FOMOGO

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#8
Very cool. I do quite a few stroker motors, mostly Harley, and small-block and FE Ford stuff. Like the old saying goes " there is no replacement for displacement". I imagine that little scooter is going to surprise a few unsuspecting souls. Cheers, Mike
 

Cheeseking

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#9
WOW! Thats amazing. :clapping: A "sleeper" moped!
 

jumps4

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#10
everyone gets in the other lane so they are not stuck behind me and I leave them in my dust
It screams...
I just got a go pro I'll try to figure it out and make a video with the GPS for speed
 

woodtickgreg

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#11
That's an insane amount of machining and know how right there! very cool indeed. what is the piston and cylinder from? I have an express that I am building but mine will be mostly suspension upgrades and a 70cc bolt on kit, better reeds and carb, expansion chamber exhaust, lighting upgrades , etc. Anything to make it unique and mine, lol. I briefly entertained the idea of fitting an old air cooled cr80 cylinder to it. I dig what you have done to this bike, interested in what you did to the trans, I have thought about that as well to get a little more top end speed.
Thanks for posting this thread, very cool for the mopeders here!
 

jumps4

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#12
Hi Greg
I originally fit the bike with a 70cc big bore kit and a peoples pipe and a 19mm carb/manifold kit from Treatland.com
most of the parts are for a Honda Hobbit moped. The crankcase is from a 1981 Honda Urban express with the 2 speed automatic transmission.
With all of that the bike will not be able to do more than 35 to 40 mph because the gear ration is to low and rpm exceeds 13,500 rpm.
Extended riding at that rpm is too much for the engine so I had to change the ratio by changing the driven chain sprocket.
The problem here is Honda uses a proprietary chain size and the sprocket could not be purchased and had to be made.
I downloaded a free program called Sprocketeer 2.0 and after carefully measuring the original sprocket and chain I cut out a sprocket on the Cnc mill.
The new sprocket gave me an rpm of 8500 at 50mph and the peoples pipe had a power curve that came in at about 4500.
Jet the carb big and work your way down or you will destroy the cylinder and piston in one pass if too lean.
This explains why I have so many cylinders in stock to modify later....
The bike was great at this point and could cruise at 45 all day with plenty of power left to easily get out of the way if needed.
This is where the rear spokes in the wheel started breaking. I purchased all new spokes, a spoke gauge and rebuilt the wheel.
It was a waste of time and money the spokes are too thin. In 1982 Honda urban express went to thicker spokes and that is the wheel you need or the spokes for it.
A dirt bike shop can fit your wheel with thicker spokes and If I had to do it over I'd do that.
To get to 100cc I used a Honda elite big bore kit (80cc) (allowing me to use the original case to cylinder bolt pattern) a Honda elite piston 54mm from the 125cc kit and a Lasleeve liner for a Honda cr80 big bore kit (100cc) bored to 54mm.
the polished rod is from a Yamaha 100cc dirt bike and because the crank pin is 3mm larger it allowed me to modify a Honda hobbit stuffy crankshaft and add 1.5mm to the stroke. the drive end of the crank was turned down and a sleeve was heated and pressed on, welded, straightened and machined to fit the 2 speed clutch for the transmission.
The expansion chamber and pipe is 28mm id for a Honda elite 125 big bore engine modified to fit, right now my power curve is not coming on in high gear until about 45mph and I should shorten the chamber a bit. Once again it is pulling so hard at 50 it is breaking spokes so I'm going to have to fit another wheel to safely see what it can do.
Steve
 
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jumps4

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#13
The carb (28mm Mikuni flat slide), manifold and parts were all modified from a honda elite 125 kit and an adapter plate was made to get the correct angle and fit for the four valve reed-plate to crankcase. There is also a 100cc boost bottle on the manifold.
The bike was also converted from 6v points ignition to 12v advance curve electronic ignition and coil.
Steve
 

woodtickgreg

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#14
Very cool Steve, If I get 35 to 40 out of mine I'll be happy. Probably going with a treatland kit too. I know about jetting rich and working down from there, I've been playing with 2 strokes for a long time, But I do appreciate your input. Cool mods to the trans, I didn't know they had a weird chain. I'll probably go with a kit, carb, reeds, and call it good.
 
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#15
Steve,
Sorry for reviving an old thread, this is an extremely interesting Honda Express engine mod. I thought the max was 70cc, but apparently not! I, too, have a race Express ('79 NA50 Express II), and am most interested in your sprocket mod in particular. Two questions, if I may:

1.- Being as how the counter-shaft sprocket also has a splined shaft built into it, did you re-use an original by removing the original 30 teeth away and cutting out the 27 new teeth?

2.- Did you have to remove any links from the drive chain or make any other modifications, such as to the chain tensioner?

Thank you for your time, it is very much appreciated.

Rusty
Phoenix, AZ
 

jumps4

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#16
Hi Rusty
The sprocket was brazed to the original shaft so a little heat and it came off.
The new sprocket had to be made because Honda has it's own chain size.
I used a program called "Sprocketeer" to cnc a new sprocket with the correct pitch and size.
Then I shortened the chain and modified the quides.
I thought these mods were on site but I could not find them for you. I'll see if I still have pics.
Steve
 
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#17
Steve,
Thanks for the reply. Your Express is seriously unique, sounds like it'd be a hoot to race around on. Any additional pictures of the chain/sprocket area would be fantastic. I have a couple extra Express countershaft sprockets lying around, I think I'll grind the teeth off and recut the teeth. How many links did you have to remove, and what mods did you perform on the guides? Thanks again.

P.S. What is the top speed on your rig? I'm guessing 55+ mph
 

savarin

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#18
Now that is one serious moped.
Brilliant.
 

jumps4

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#19
This is one of those projects that went crazy over budget. The scooter is beyond it's power limits and breaks spokes every time I exceed 50mph.
I know I have been over 55 but I'm not going there often.
Imagine having a car that only does 100mph and you modify it to do over 200mph, things start breaking.
The fun is the look on peoples faces when I open it up, I'm over 50 in less than a block.
I have put 200 plus miles on the motor now and everything has been fine, but I always feel like it's just a matter of time before something lets go.
I trusted the bike more with the 70cc mods and I had put more than a 1000 mile with no problems, the 70cc would do 50mph but took longer to get there.
I do not remember how many links I had to remove from the chain but you have to reassemble the chain with the original links, you cannot purchase a master link.
The project was more to see If I had the skills to do it, than what the bike would be like after.
At 90 pounds this scooter is crazy mean.
Steve
 

wrmiller

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#20
Your scooter project reminds me of the nightmares I gave myself after building a go-cart and stuffing a friend's 450cc twin into it. Scared myself silly in it at over 100 mph and I'm lucky I didn't die. The stuff a 14 year old kid will think up... :eek:

I took out the motor, sold it, and cut the frame up shortly after that. Dad's orders.
 

crazypj

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#21
Love this kind of stuff, been doing motorcycle engine mods since mid 70's but always too broke to do 'big bikes'.
I was working at Honda dealers in Britain when Express came out. Ours were limited to 2.4bhp and just barely 32~35mph
Last several years I've been 'playing' with Honda CB360's fitting Suzuki GS850 pistons. Only 22cc larger but 10% or more power increase (previously playing with Yamaha XS650's - 800 & 840 conversions, re-phased crank, etc)
BTW, nice boring bar, pity company went bust a few years ago. With correct adjustment they will easily hold 0.0005" over length of a Harley Sportster piston. At one time I was teaching people to use them at MMI. (Motorcycle Mechanics Institute, Orlando Fl.) Did so many cheap 883 to 1200 conversions HD stopped supplying piston kits and forced people to buy cylinder+piston kit for the conversion (pair of pistons with all the gaskets, etc could be had for about $120.00, the 'full kit, from HD, around $800) It did take a while to bore 0.496" though (complete 5 hr period)
 
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