preparing for war

[JanBros]

new short-term project, going to prepare this for moped-wars :



bought it for 75 euro and it is a runner.
Moped-wars is MX with mopeds . chose a h***a Sky for different reasons :
* big wheels
* straight up hidden cylinder, so the cooling fins can not get full of dirt/mud
* belt driven with vario in closed case so nothing can happen to it
* front disc brake
* youth doesn't like it, so prices are cheap

planning on opening up the frame at the rear in front of the cylinder, so the expansion pipe can go straight to the front and follow the frame upwarts so it is protected and can not get dented. and the at the end, make a 180° U-turn back down for the can. something like this :



next race is mid september.

[Luders]

Good luck, keep us updated

[garye345]

Class Jan .
Bet there's some"head the ball's" in that class .

[JanBros]

took an extra engine I had appart today. found a "bad thing" in it's design the intake is shit.



going to cut it out, mill a new housing for a read cage with 4 reads and weld that in. I can gain some space at the bottom because I'm gonna dith the electric starter, and am looking for a longer con rod to gain an extra cm at the top.

[maccas]

I did my cbt on a h***a sky. 33mph flat out. Quite frustrating haha. How else are they restricted Janbros?

Dan

[JanBros]

we have 2 versions in Belgium :

class A which is only permitted 25Km/h and you don't need any license : restricted electronic by cutting the ignition with the revs, and to keep it at 25 it cut's early.
class B which is permitted 45km/h, but you need a moped license.

you need to be 16 for both.

I have a B but don't know if/what else is restricted. It has a different CDI, so possibly it just rev's higher. If the rev's are limited, I still have a complete ignition of a MB50 and will put that on.

[JanBros]

made a jig today to (dis)assemble the crank, but sadly my home-made press isn't strong enough.
guess I will need to find a stronger pump from a forklift at work

crank fits just inside, so that after pressing it together again, it should be (almost) straight




this crank is an old rusted, just for testing, I'm not going to use it.

[JanBros]

double post

[JanBros]

ordered a MTX/MBX80 con rod. is 91 mm (original 80mm), but will need to mill the width of the big end a small bit as it's 1.5 mm wider (but uses the same bearring, figure that out )

made plates to raise the cylinder 11.6mm. the one on the right is upside down to show the grove I've made that will be filled with JB weld to make sure there are no air-leaks through my far from perfect aluminium welds



unfortunatly ran out of welding gas yesterady (off course just before a WE )

so started on the cylinder. It already has 5 transfer ports, so decided for now to keep it. timings are small off course : exhaust 156.5 °, transfers 107°. cylinder/transfers are too small for my tools to work on, so just raised the exhaust. As it's a cast iron cylinder, I did the rough work on my mill :



wanted 190° for the exhaust, but not enough meat on the cylinder, so it's arround 182° now

[ozzy1]

Regarding restrictions- a lot of times on belt driven scooters there is a washer on the drive end in the vee pulley which stops the belt climbing down to achieve a higher speed.Its easy to take off the engine side cover and undo the large lock nut with a rattle gun and then you can just remove one half of the drive pulley and the washer is there on the shaft-usually about 5mm thick and about 1 inch diameter.

[JanBros]

put the crankcases to the side (more work than I thought - what's new ) and decided to complete the bike first with standard cases, and if there is still time, I'll do the crankcases.

piston surface was a lot above bottom transfer ports, so raised the cylinder with extra seals (over 1mm) to make them even. gained about 17° in transfer timing on the way now up from a misarable 107° to +/- 124°.

combustion chamber was already way too big, so skimmed 2mm of the cylinder.

[JanBros]

made a new combustion chamber today.

first skimmed couple of mm's off the head on the mill, and than on the lath. Was pain in the ass to get it on, as the spark plug is centered, but inclined, I couldn't use that.

made a plate on which I could bolt the head, and then had to use feeler gauges to get the head perfect in line and at the same time trying to center the combustion chamber

[jarno]

love the tread Jan =D> =D>

[James P]

Looking good Jan. How efficient is the forced air cooling system on this bike? The cylinder head heatsink area seems a little smaller (in relation to the bore size) than bikes with ambient air cooling, so the existing cooling system may be overtaxed with the massive performance increase!

I'd tend to limit the geometric compression ratio to about 10:1 for pump fuel, at least to start with. Does the ignition have a retard function, or is it constant timing? When your modifications are complete, I suppose there will be only one engine speed - maximum ! With that in mind, it may pay to start conservatively with the ignition timing as well; say about 17-18 degrees BTDC. What do you think?

Regards,
James

[JanBros]

Looking good Jan. How efficient is the forced air cooling system on this bike? The cylinder head heatsink area seems a little smaller (in relation to the bore size) than bikes with ambient air cooling, so the existing cooling system may be overtaxed with the massive performance increase!

I'd tend to limit the geometric compression ratio to about 10:1 for pump fuel, at least to start with. Does the ignition have a retard function, or is it constant timing? When your modifications are complete, I suppose there will be only one engine speed - maximum ! With that in mind, it may pay to start conservatively with the ignition timing as well; say about 17-18 degrees BTDC. What do you think?

Regards,
James

I think you are thinking way too big. this is just for fun, not to pour money in
is forced air cooling, big fan on the flywheel with a cover that goes from the fan from one side of the cylinder over the head to half the other side.
my main goal for the first race is to have my engine opened up for inspection, to make sure it's a 50cc, than I will have done a good jod and you would be right about the massive performance increase
I even don't have a clue about the compression ratio (too lazy to calculate ). I stick to 10cc heads for my KR, so that makes 4cc for a 50cc moped.
about the ignition : first need to find out if the rev's are limited or not, than I'll thinck about the rest.