The Phantom.

[Theon]

This is a bike I built a few months back,

My Wife and kids were a way for a few weeks, and although I already had a couple of quite fast bikes, I saw this tiny little 24" 'Teenagers' bike at a Pawn shop for $100 and it looked in good nick and had a three speed hub on the back which I wanted for my FTC tadpole trike.
I doubted I'd be able to squeeze a motor in it, but just 'fell for it'.
Got it home and realized if I tried hard enough, a motor would just fit!
I got a '70cc' motor of Ebay, to find it had a 40mm crank, but a 45mm piston and 6mm head studs.
So I redrilled the cases for a set of M8*1mm head studs, Stuffed the cases with 3mm alloy 'street sign'. Got a good 47mm piston and barrel which were then ported, polished, lightened, and match ported, and reshaped the chamber on a 'chromed' angle fire head, made copper gaskets for everything and gave it a coat of black after filling as many casting flaws as I could be bothered.
I had her running real nice with a speed carb , fairly standard exhaust, and a 36t sprocket, letting me take off from a dead stop with out pedaling and getting to and holding a bit over 60 Kph. It didn't want to do any more than about 8000 Rpm as I remember, But got there quick.
Then I had an idea for an expansion chamber for her, and made a manifold for a'16mm' Walbro rep, that I had bought for a pocket bike motor that is going in the FTC Trike. Which are much better to try and tune to a pipe than the speed carb. And is a much neater fit also. I had her doing 70 Kph and 9000 Rpm when I blew the head gasket due to using recycled head studs and nuts.
So I got a 'new' set today, and When I get a chance I'll pull her down and give you all a look inside.

 

[Greg58]

How does the exspantion chamber work for you? I read your other posts, you will find lots of good ideas here and from your bike we are probably going to learn from your Experiences.

 

[Theon]

The Pipe seems to work as I had hoped,
But have only got an hour or so run time on the motor yet and is not really even close to being run in.
I found a lot of trouble getting my Delorto Rep to work with the pipe, but may have just been my carb? The Speed carb went O.K. but the $10 Walbro Rep is my favorite for WOT. as well as having an Idle mixture adjustment, and gives reasonable Mid range.
The Pipe is much Quieter than the Raliegh's, but was designed to Limit the top end a little, and gives a nice broad Band from say 4000 to 8000 ? With a pipe working properly it 's a lot easier to distinguish when your 4 stroking and therefore easier to get a perfect mixture if you know what your doing with a 'Walbro' or similar. That's been my experience.

 

[Theon]

A nice wet day here today, and I decide not to go to work!
So I strip the top end on the Phantoms motor to install some new head studs and get a look at how she's wearing in.
So as promised a few photos of the insides.
This is a "70cc" motor, 40mm stroke and originally with 45mm piston (now 47mm).
Compared to the "80cc" 40mm stroke cranks I've seen it is lighter and narrower.
Which may not help top end, but In my opinion gives better low to mid range response than My other "80cc" with the heavier crank.
It does however leave a lot of spare room in the cases, so as I have already mentioned they were 'Stuffed' using old street sign that was made to fit neatly between case and crank, and glued in with 'liguid metal' or some such epoxy after carefully dremeling a grove that it 'clips' into. I won't be splitting the cases this time round so you'll just have to visualize.
Theres a photo showing the match porting of the cases, which also shows where the case stuffers were blended to the transfers.
There's a 'tapping' for a pulse tube which was 'scavenged' from a pocket bike carb.
The base gasket is hand made, .5mm thick and rests on a .2mm paper gasket.
The original head studs were 6mm, threw them in the draw and used an old set of m8*1mm studs, which is why I'm now installing new ones.
They are awaiting a spot of Thread Locker before being set.
While the head was off I gave it a Quick polish up to show off how shiny I got it!
The piston has been getting too hot! I Knew she was pinging, and was running the Mix a little rich to try and cool her down, But no signs of ring bypass, and I'll give her a clean and polish and back in. The piston was 2nd Hand, from my Raleigh, and has a few hours on it, has been lightened a little, matched around the transfer ports and trimed a little on the inlet skirt to give 120 deg duration, or 60 deg BBDC.
All my motors are set up with a $2 kids plastic protractor, which is carefully 'drilled' (A Dremel and bur is less likely to brake it) and gently tightened under the Magneto Nut.
But I'll give photos of that one day.
I can only fit 5 photos to a post, so to be continued.
I'm having trouble with my computer reading my memory card so photos as they come?

 

[Greg58]

A lot of work goes into one of these engines if you get it to run like you want, I run the 48cc engines so to pull my 210lbs around I have to make changes as well. I did the porting and piston skirt trimming on a eBay engine, also made a pipe. On mine I found a 16 inch head pipe was best for both low end and top end power.

 

[Theon]

I was a little limited in the length of my pipe design, and would have loved to have made it longer in every section. However I read somewhere a header wants to be 6 to 8 times the Diameter in length? My header is 9" long, and starting at approx. 1" in dia. It was made to Taper a little by using chosen pieces of two different fork sets, starting at 28mm OD and tapering to 32mm OD, the divergent was given a slight trumpet shape, and I would really be guessing at the angles I ended up with, but did put a little math in to the design, and from what I read my sharper baffle should limit my top end alittle, but was not trying to get this motor to 9500 Rpm instead have a strong mid.
I admit it had a bit better low down with the standard pipe and long ( custom 4" * 22mm) inlet manifold to a speed carb, But goes a lot better from 4000 upward now , and with me only weighing in at around 60 Kg (150lbs?) It pulls me off the line without pedals running a 36t sprocket and 24" wheels, then does at least 65 Kph, But still tuning,
Does not want to Rev far above 8000, but does it smoothly, It was pinging a bit around 8000 though and I need a better Cdi with more Retard to get this motor to run it's best.
It seems to have a little more advance than my other 40mm stroke motor as It seems stronger down low and pings up top with a similar compression ratio. I'm next to try an offset key that I made for the Mag to give her a couple less deg.
But will be building my Own Cdi's at some stage from info I have collected here, Thanks Guys, I'm a bit rusty with my electronics but was once an Electrical Instrument Fitter by Trade so have a good understanding.

 

[Greg58]

I have built a couple of the cdi's using info found in the roll your own cdi thread as well, if you read through the post some people had trouble with resistors failing. I used higher wattage resistors and had no problem, finding a scr that would open at idle speed proved difficult. I built mine from used scr's and capacitors from other projects.

 

[Theon]

Cheers Greg, On to the High Watt Resistors.
I had a mate recons he knows ...
But said he had to get his SCR from the states?
But curious to give this a go, I'm suppose to know all about this stuff with my Trades but never needed to look at electronics other than a bad solder joint for 20years!
Throw 'em a way get the new model!

 

[Theon]

As covered in the expansion chamber thread, I have given the Phantoms Pipe a polish up.
I am quite proud of the way it has come up, and will fix a few slag intrusions and take a few close ups of some of the more complex shapes and lines.
The motor is back together and back in the bike, and just awaiting me to finish the pipe.
This is a really fun bike to ride as it feels like a BMX did when I was a kid, turns quickly, nimble and light but also built strong!
It's been running a 36t sprocket to a 24" wheelchair tyre, And the gearing is probably Ideal. On the other side of the flip flop hub I have a 44t, but havn't tried it yet, It'll likely pull wheel stands! But have a 39t sprocket to go on as this is probably all I need on her for a 'tighter track'.
Was curious to try her on a 33t but can't seem to find one.
Still she's fast enough for that short wheel base.
I need to find some better tyres for her also, 24 x 1 3/8, so she won't take fatty's, nor will the frame.
But I need something a bit stickier than what I have.
Better get back to welding.

 

[Theon]

I put her on 'wet' and took her for a spin.
Still pinging a little, but just hit 9000.
Will try the 'retard' key on the magneto next.
I know she's getting a little hot, and am running 98. octane in her but will try some AV Gas. I must get on to that CDI.

 

[Greg58]

Theon I am building a grubee at this time and noticed my crankcase area is much tighter than yours in the pictures, I wish I had took pictures but the crank weights almost touch the case sides. This is on a 48cc , there is no where to stuff anything in it!

 

[Theon]

I guess they are all different, but that sounds good, Mind you I believe you want to have a bit of side float. I never stuck the feeler gauges in there but it should be around .006" I was told.
We don't get to many real Grubee's here, I'm just going by what I've been told, maybe they've lifted there standards, maybe I've been misled.
All my motors have plenty of room for stuffing if running the 3pc crank.
The Phantom motor was my second attempt at case stuffing, my first was a little rougher, hence I havn't put up photos.
But I've been trying to get around to doing another set for one of the motors still apart on my bench. Waiting for RSE to get back to me with a new balanced crank, I'll give him a call today.

 

[sublunacy]

ogh man the 40 by 45 is so sweet. what are u doing changing it to the 47? i was jealous besides the 5pc crank. change it back please for me and wich seller?

 

[sublunacy]

will u sell me that 45mm topend please cheap cheap? 30or 40 mm intake? 3pc or 5pc crank?

 

[Theon]

It runs a 3pc crank, really the 45mm bore motor is sweet?
Hard to get parts for though.
I don't need it, postage would be the killer, But I'll get a Quote if you PM me your address.
It turned out a good motor with the 47mm piston, has very nice balance, I was a little sus on the 6mm studs, and have damaged the head, using it as a drilling guide. but the piston, rings and barrel are in unused condition.