MOPED ARMY

Alternatively would i be able to achieve the same results by putting a better crank, and porting a stock cylinder for the av7?

would i be better off just getting an av10 crate motor? or would the "race" crank linked above still be a benefit with the higher rpms

thanks

those speeds are all that im after. just so im somewhat flowing with traffic.

i will build a "stock" 50cc jug on the bottom end linked above, play with some porting and go from there.

also looking at the roller guide for the stock variator so i can tune it a little bit.

Any insight on a pipe for the stock 50cc jug with some porting?

If you want a reliable daily stick with a mildly modded AV7.

I have a Doppler 50cc AV10 engine setup w/Doppler pipe, 19mm PHGB, CDI with retarding curve box and kickstart vario, it honestly needs a clutch pulley to get the stall I need for it to run well on the street. It's a lot of money for something that isn't what you say you want out of an engine.

If you're bent on running an AV10 go with a milder kit and pipe, you'll be happier in the long run.

I've built a couple 45mm airsals on AV7 and they are very nice, stock pipe (de restricted) and a 15 Sha. They will get over 45 and pull really nice in midrange. They aren't blazing fast but they are very nice cruisers

Airsal had core shift problems in the past which had the exhause and transfers higher or lower than desired which created a shyte show on the consumers who were trying to just slap on a kit and go. You can set datum and index for these deviations from norm. I use the extra fine sharpies for the piston marking, I can get those at a dollar store in a 5 pack (blue red green 2xblack ) but any permanent marker that is extra fine is good.

To check if you might have gotten a core shift old cylinder somehow, you can set datum but putting the piston on the conrod, add the gudgeon pin (no need for fighting with clips or rings to measure), introduce cylinder without a base gasket and put piston at TDC. Do not use any lube on the cylinder, as there are no rings it should slide easy enough dry and any lube will erase or blur any sharpie marks you draw. Set the datum by shimming the cylinder up using feeler gauges until the periphery of the piston crown is level to the deck of the cylinder. Note how much shim thickness you need for datum and also use a sharpie and draw on the piston where the floor of the exhause port is on the side of the piston.

Rotate the crank to put the piston at BDC and check that the periphery of the piston crown alignment with the floor of the exhause port. Use feeler gauges to make these two points in alignment. That is the thickness of base gasket you would need to have free flow of exhause and transfers gasses into the cylinder. Make note of the thickness you need for this index mark. Leave that thickness at the base and rotate to TDC and mark to the piston where the floor of the exhause port is on the side of the piston.

Any extra that you need to shim up the piston to go from datum to index will be a slight loss on compression. You can correct that by using a thinner head gasket. This is where copper gaskets of different thickness is handy. Otherwise you will need to decide of you want to have a machine shop shave a little off the deck for you, or a little off the head, to restore compression ratio.

Any less shim from datum to get index is a different issue as you would want to maintain datum, so the piston does not pop up out of the cylinder at TDC. You need to gauge this within reason though, if it is minor then you can just use a thicker head gasket (again copper ones are handy) to avoid contact between head and piston crown. Or you can leave it to the thicker datum thickness and shave the floor of the exhause port and the transfers to align the floors of the ports to the periphery of the piston crown. HOWEVER before you shave, remove the cylinder and check on the skirt of the piston for your sharpie mark(s). If shaving the floor will give less than a 2mm margin between the future mark and the bottom of the skirt, to not shave. That 2mm margin is your guarantee that the hot gasses of combustion will not be migrating into the carter and cause more than just a bit of a issue.

Yeah great start, I think Reb pretty much covered it, I would say that the newer 45 airsal have always been good for me, the 47 (or maybe it was parma?) was the one that back in the day was really wackadoo.

I've always been able to get them to line up pretty good with just a thick base gasket, the heads pretty much all suck for moby and keeping them cool is always a challenge, so don't be afraid to leave it spaced up a little bit on top, it will hurt the bottom end compared to a properly setup squish, but you can tune the variator to make up for it

Yeah go for the stock pipe just make sure you get the threads really clean (no grease/carbon) and go back and re-torque the nut a couple times after you heat cycle... Eventually it will stop getting tighter.

Rebel has a good write up on drilling out the baffle plate, it's not obnoxiously loud and it will rev out nicely.

Also clean/lap your decomp valve in your head, this is very important

If you can cut the head go for it, just surface it and cut a squish band. It's hard to hold... I have some really fancy jigs I made but maybe you can do it in a 4 jaw?

Open the head to 45mm and cut 7-12° from the angle of the piston crown so the gasses are forced to the center of the head. Stock closed chamber (higher compression) head has a issue with spark plug being very shrouded, so you want to dress the bumps that deflect the flow, and also unshroud the spark plug, so the fresh charge can fill where you want to have the flame kernel start right at the spark plug.

Run the ignition at 1,5mm BTDC (or 1,2mm if you have CDI) to get the heat of the combustion down the pipe and still have the piston take a lot of the power from the expansion.

Hey in france when on these small stock or small 50s or small 70cc builds (not like polinis and Malossi's ) lots of people tend to use what we call a Turkish pipe, its a little longer than oem, but fits fine and it's not got any baffles so its a little noisy, but it works great especially in the mid range to the top of a litlle 70cc. U c them in Turkey with one of these and a 15mm carb going 120kmh down masive hills sucked in behind semi trucks on stock av10s!

heres a video of an airsal 45 stock av7 bottom end and variator with a "Turkish" exhaust.

If u order one from Turkey theyre about $5-$10.

But otherwise Ebay one guy sells em with some markup.

https://www.ebay.fr/itm/POT-D-ECHAPPEMENT-CHROME-MBK-51-MOBYLETTE-MOTOBECANE-881-av-7-av-10/352616601478?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D7de98c356eef4b9c88ad2be380f17849%26pid%3D100675%26rk%3D3%26rkt%3D15%26mehot%3Dpp%26sd%3D233755369137%26itm%3D352616601478%26pmt%3D0%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A421cbb6b-4b53-11eb-b090-ba748d472e1c%7Cparentrq%3Ab859aa5f1760a9cb216b9562ffd6ee08%7Ciid%3A1 (edited)

Well the kit looks to fit really well.

I dont have any pics of the port matching but im happy with how it came out, bottom end is assembled and im starting to fit up the cylinder and see what, if any machining will get done.

With base gasket

Without base gasket, though it doesnt make much difference.

With no head gasket, the piston clears the head with no reworking. I may shove some play dough in there to see just how much clearance there is, but my main question is:

Is there a point where adding a squish band will yield no benefit?

Im also an idiot and broke one of the rings when removing it, and while i was ordering a new one i tossed in the le-partie. basically a decomp-less head, variator, and pipe away from going whole hog on this thing.

I think ill cut one on the head, then get some play dough or something and check the clearance on the squish band. Trying to avoid decking the cylinder unless absolutely necessary.

Also, the factory combustion chamber looked like it was somewhat polished already? Is this normal?

Perfect! That looks fantastic!

I just lap them with some compound, never actually re-cut one, can't help you there but it's not a bad idea.

no that all looks perfect, i usually shoot for a little bit less than 50% bore and a 7 degree taper divergence but thats using a cnc lathe so i can actually interpolate the curve of the piston.

https://www.doscycles.com/products/moped-factory-av7-av10-47mm-cylinder-head?_pos=1&_sid=7da50dfc9&_ss=r

i actually had to quit making these because we couldn't find good aftermarket heads to machine, the decomp holes were too sloppy and kept breaking through to the bore, but you can see from the profile its real close to yours.

when i used to be able to get real french MBK heads these things were really really nice. I have been thinking about going back and redesigning it for 45mm because it would be that much farther from the decomp and might work, but i have a lot of other irons in the fire.