first av10 build

Justin Caswell /

I know this has been beat to death 50x over, but i have a 50v that i picked up and i am looking to make a reliable street machine. I live in a more rural area and would like to top out around 50mph (most roads cruise at 40)

im going to run the av7 for a little while to get the drivetrain back into shape and work out any safety issues (brakes, wheel bearings, lighting etc.) and to give porting a try.

at the same time i would like to put together an av10 that will give me the results above. im willing to spend what i need to to achieve them.

i would start with this bottom end

https://www.treatland.tv/ProductDetails.asp?ProductCode=mbk%2Dbottom%2Dend%2Dadventure&CartID=1

pair it with a doppler 50cc kit and doppler o-ring head.

currently have a sha 15 carb that would go on it and this pipe

https://www.treatland.tv/motobecane-AV10-simonini-CIRCUIT-chrome-p/motobecane-simo-circuit-clear.htm

I want to keep my pedals at this point in time so stock variator as i cant seem to find a way to pedal start with an aftermarket variator, and the pull start kits on treats are out of stock.

stock ignition for the time being as well, though a le partie may get thrown in when i hit checkout.

is this a reasonable expectation or am i missing something huge?

thanks

Re: first av10 build

Justin Caswell /

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

Re: first av10 build

Port a stock AV10 jug and clean up the carter a bit and she can spin to 8500rpm while staying reliable

Re: first av10 build

Justin Caswell /

> Rebel Moby Wrote:

> -------------------------------------------------------

> Port a stock AV10 jug and clean up the carter a bit and she can spin to

> 8500rpm while staying reliable

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

Re: first av10 build

rick ziereis /

I built from scratch an av10 with new case, new crank, doppler 50cc kit, doppler o-ring head, $220 doppler pipe, CDI electrics and alot of time. This was a very spendy project. I am not real happy with the bike at this point because it takes a bit to get it into the rpm range where the pipe and porting turn on. And excess heat is becoming a problem. The next thing I am facing is at 50+ mph my tires, brakes, and suspension are not good enough to handle the roads near my house.

If I were to do it over I would get a 70 or 74cc kit that does not need to spin up over 8500 rpm to get some horse power. For me 40 to 45mph is fast enough on my little Moby.

Re: first av10 build

Justin Caswell /

> rick ziereis Wrote:

> -------------------------------------------------------

> I built from scratch an av10 with new case, new crank, doppler 50cc kit,

> doppler o-ring head, $220 doppler pipe, CDI electrics and alot of time.

> This was a very spendy project. I am not real happy with the bike at

> this point because it takes a bit to get it into the rpm range where the

> pipe and porting turn on. And excess heat is becoming a problem. The

> next thing I am facing is at 50+ mph my tires, brakes, and suspension

> are not good enough to handle the roads near my house.

>

> If I were to do it over I would get a 70 or 74cc kit that does not need

> to spin up over 8500 rpm to get some horse power. For me 40 to 45mph is

> fast enough on my little Moby.

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?

Re: first av10 build

Justin Caswell /

are these worth buying? or is it some type of clone that will take just as much work to clean up as building a bottom end + a kit?

https://www.ebay.com/itm/Engine-Full-MBK-51-AV10-With-Variator-Clutch-Motobecane-Club-Dakota-Motor/352035845634?hash=item51f6f8b602:g:tqEAAOxyBvZTS7w5

Re: first av10 build

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.

Re: first av10 build

Justin Caswell /

Thanks. This is the info I'm looking for. Not new to wrenching, just new to French mopeds. I'm not afraid to experiment, just trying to avoid mistakes that have already been made by others.

So when it comes time to split the av7 cases for new seals and bearings, the ones in there right now sound neglected, I'll be putting in the race crank from the kit linked in the OP, and maybe a 47mm kit tuned conservatively, or just another stock cylinder with some port work. Thats a decision for another day.

Re: first av10 build

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

Re: first av10 build

Justin Caswell /

> Graham Motzing Wrote:

> -------------------------------------------------------

> 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

Did you have to do a lot of shimming to get the ports lined up with the stroke, or did you just install it as shipped and that gave you enough of a hp gain?

I understand they all require a bit of a case match, but seems to be a mixed bag when it comes to exhaust port alignment.

Re: first av10 build

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.

> Justin Caswell Wrote:

> -------------------------------------------------------

>

> Did you have to do a lot of shimming to get the ports lined up with the

> stroke, or did you just install it as shipped and that gave you enough

> of a hp gain?

>

> I understand they all require a bit of a case match, but seems to be a

> mixed bag when it comes to exhaust port alignment.

Re: first av10 build

Justin Caswell /

Wow, thank you. I think I should have plenty to keep me busy over the summer with this info.

Today I did a quick test run for a baseline of the condition of the ped from the previous owner. Topped out at 25 in my small neighborhood, still running the 68 jet that the dellorto ships with. Completely twisted and torn motor mounts, and a really worn belt.

Tomorrow I'll be fighting the motor mounts out and replacing some wheel bearings and chains. It's always fun undoing years of neglect

Re: first av10 build

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

Re: first av10 build

Justin Caswell /

So my hand was a bit forced (enabled) today when i was torquing the flywheel nut and it stopped getting tighter but just kept spinning before even making 30 ft lbs. Its holding good enough to get the other things set up properly (brakes etc) but i am reasonably sure the threads on the crank finally shit themselves (steel treats nut)

SO i took the opportunity to order

treats budget racing crank with new seals and bearings

av7 gaskets

Airsal 45mm 70cc kit

aluminum 70cc head gasket (metal fiber one in the kit looks iffy at a glance)

variator roller guide with adjustable weights

and a voltage regulator

Will get some pics up when i start pulling things apart if anyone cares. Hoping the ports match up enough that i dont have to mess with the port timing and can just get away with some light case matching/smoothing

Can i get away with a stock modded blunderbus for this? or would i benefit from an expansion chamber pipe?

Should re-title the thread "another av7 kit" (edited)

Re: first av10 build

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

Re: first av10 build

Justin Caswell /

yeah i was going to soak the head in oven cleaner then drop it in an ultrasonic as long as theres no rubber seals on the stem of the decomp, before lapping it in. curious to see if ill need to do any work on the squish band, or if the stock head will match up well enough. I did some reading in the tuners handbook, and a friend has a lathe and mill in his garage. We were both machinists for a brief time so i think we can get ourselves into some trouble.

If the piston matches up to the stock head well enough without any weird clearance issues i will just leave it as is to lower the C/R a hair and hopefully mitigate the heat issues.

Re: first av10 build

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?

Re: first av10 build

Justin Caswell /

4 jaw was the plan, but if that doesnt work a plate with some standoffs to pick up the stud holes maybe? I cant imagine the cast aluminum from 1980 is that hard so i have some leeway for rigidity as far as the chuck jaw on fins.

If i didnt need to be able to pedal start it id just buy a head with no decomp and turn the chamber on an arbor.

Re: first av10 build

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.

Re: first av10 build

Justin Caswell /

will knocking the bumps on either side of the plug down remove enough material to adversely effect the combustion chamber volume? I planned to at least smooth all the non machined surfaces down to 400 grit.

Re: first av10 build

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)

Re: first av10 build

Justin Caswell /

thats pretty cool keeps a stockish look but wont choke out the bigger cylinder. I will definitely look into that after i play around with modding the blunderbus

Thanks for the tip

Re: first av10 build

Justin Caswell /

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.

Re: first av10 build

Yeah looks perfect to me!

Yeah doing a squish band always helps, the more eveen and predictable the combustion process is, the better your bike runs no matter what setup. Is just not as big of a deal on a more mild tune. The moby always get hot because the fins are small and blocked so it's just extra important with the higher output setups to have even combustion or you will get detonation and spiking temps.

Re: first av10 build

Justin Caswell /

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?

Re: first av10 build

Justin Caswell /

got the head cut today, was surprised how well it went.

Had to make a fixture as the 4 jaw chuck was a self truing chuck (no independent jaw adjustment)

cut the head at 14 degrees (just slightly more than what i measured the piston at)

bore is now at 45mm with just under 50% area used as squish band in the combustion chamber.

I have to check the new volume of the combustion chamber and will take some more material out of the dome if need be to keep the C/R under 10 but otherwise shes ready to go together.

Edit: does anyone know where i can find the angle that the factory decomp valve is cut at? the seat in the head looks square cut and id like to hit it with an angle before lapping it in for a better seal (edited)

Re: first av10 build

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.

Re: first av10 build

Justin Caswell /

new combustion chamber volume is 9cc+/- .5cc

thats a stock 50cc head, with a 14 degree squish band cut until the outside of the band is at 45mm, id of squish band is about 32mm=~50% of bore area

Stock compression ratio was around 8:1

New compression ratio is around 8.8:1-9:1 depending on how much the gaskets squish down.

These measurements and volumes are approximated and im probably wrong with most of them but so far everything seems to be playing well together

Re: first av10 build

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.

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