(Re)building a Derbi Flat Reed - What to expect?

Hey all

Picked up a '89 Variant Sport a couple of weeks ago and have decided I'm just going to tear it down, clean it up, slap a kit, pipe, VM18 and intake, crank, and so forth on it over the winter. Currently have a lot of parts (flywheel, variator, clutch, etc.) soaking in evaporust so I'm trying to anticipate what else I should look out for once I get more into it.

Its my first Derbi, and variated ped, so I have my reservations about taking it apart. Have a ton of tools and experience with e50s and tomos', so I'm not completely lost. Also have the repair and parts manuals.

Is there any benefit to the 47mm airsal over the 44mm? Treatland reviews make the 44mm sound like the "easier" of the two to dial in, but I'm hoping the derbi pros can chime in. Thanks!

Andrew

Re: (Re)building a Derbi Flat Reed - What to expect?

Make sure you get the proper case gasket

There are 2 small ball bearings in the transmission, on the sprocket side where it sits in the case wall, watch out for that. The 50cc airsal kit doesn't have that much if any performance gains over a stock kit with the skirt hacked open, I've built and ridden 2 side by side with near identical setups.

Get rid of them starter shoes but be warned that the bearing delete kit from treats needs very regular maintenance.

You'll need some mapp to get cases closed around the bearings for sure.

Other than that it ain't too bad.

As far as performance for real use a large and trim down the sides of the variatior it's fucking awesome that with some black malossi springs and it will be a rocket ship. Also get the intake from Ryan Go (crank pipes) it's awesome

Re: (Re)building a Derbi Flat Reed - What to expect?

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Re: (Re)building a Derbi Flat Reed - What to expect?

Hey Wesley,

Thanks for the tips.

I just wanted to clarify that the kits I'm trying to decide between are the 65cc airsal and the 70cc airsal. Both would be used with the metrakit head that has the decomp. Any insight into which is the better or easier of the two to tune and enjoy with less effort?

I already reached out to Ryan for a vm18 intake and will be getting one as soon as he can make it. If needed, ill pair it with a cranks pipe. Currently have a mlm sidebleed sitting in my garage that I can repurpose for the time being.

I intend on ordering the correct base gasket once I split the cases. From what I can see, there are 2/3 possible variations available from treatland / Dos.

What's the reasoning behind the start shoe delete? Is this where the "one way bearing" I've seen people talk about comes into play?

Lastly, and sorry if I missed something, but what were you referring to here?

"...for real use a large and trim down the sides of the variatior it's fucking awesome that with some black malossi springs and it will be a rocket ship."

Sorry for the many questions.

Thanks.

Andrew

Re: (Re)building a Derbi Flat Reed - What to expect?

I can't speak to the 65cc or 70cc kits but I'm sure they'll rip. It boggles my mind thinking about how insane the jump up from 50cc to 70cc, seeing how 50cc rips dicks.

I'm talking about this

moped-army-6195b2ae71ceacd54c3db812deb5c6af.jpg

my phone autocorrected lathe, my bad.

This thread has great info in it, free speed if you're handy with tools

https://mopedarmy.com/forums/read.php?7,2118298,page=2

Re: (Re)building a Derbi Flat Reed - What to expect?

Brandon Weiss (Detective brandon to you) /

Get the 47mm airsal from dos, and one of the 47mm decompless heads that Treatland just released to pair it with if you want to go with either the one way bearing or a pullstart. If you want to keep the starter shoes, then buy a 47mm decomp head. I don't like the 47mm decomp heads though, there is poor quality machining by the decomp hole in the mating surface, its too close to the combustion chamber and is prone to leaking. Maybe it's just the heads that I've bought, and others have had success with them?

Keeping the starter shoes is preferable for some, because its easy to start the bike. Downsides are you have to make sure your decomp works and seals properly, and generally the bike will run hotter with a decomp. You also lose a bit of performance potential, you'll sacrifice some takeoff to the starter shoes engaging whenever you start moving.

Converting the needle bearing in the clutch bell to a one way bearing allows you to remove the starter shoes entirely, which allows you to finely tune your clutch performance and takeoff. This also allows you to convert to a decompless head, which will help the bike run cooler and better overall, and eliminates a potential source of leaks. Downside is that you want to remove the clutch bell and regrease the bearing every 4 or 500 miles. Starting is a little less elegant if you remove the decomp, you end up having to drag the rear wheel and drop your weight on the bike to turn the engine over. If your tune is dialed in, it will start easily this way.

Pull start is also an option, Ed of Ed'sMopedShop makes custom ones. This will allow you to remove you starter shoes entirely as well, and you will not have to worry about relatively frequent needle bearing maintenance.

Re: (Re)building a Derbi Flat Reed - What to expect?

Oh and the starter shoes drag and slow you down. You can take them out and rope / pull start it or buy the one way bearing kit from Treatland. The downside is that you can't really roll it with the motor engaged and you have to lube the bearing a lot. Mine expanded very quickly when I went too long without lube.

Re: (Re)building a Derbi Flat Reed - What to expect?

Dirty30 Dillon /

The 47mm Derbi Airsal/Metra is the way to go, no doubt about that. I hit mid 50's with the take off of a much bigger moto. Its really an impressive setup.

47mm Airsal/47mm Eurokit head/21 PHBG/Zen Pipe/SLEX CDI

I run the one-way sans decomp, and it starts just dandy if you're tuned right. As far as maintenance, just grease it regularly. It takes SO little time to pull the pedal arm/cover/variator off that it's a non-issue, just know that it has to be done.

You should probably be cleaning and lightly lubing your var that often anyways on a performance setup.

Re: (Re)building a Derbi Flat Reed - What to expect?

Emil Kniemel /

One of the main reasons i didn't like the one way since i have the pedal engage delete and i move my bike around the garage a lot. also i barely weigh enough to get weight down the rear to start it it easily. i was fighting wheel drag a lot.

I went pull-start: first the rope pull start with HPI mini but then upgraded to ed's mopedshop version.

Also OP, i emailed you a pic of the controls, let me know if thats what you want/need.

> Wesley Ambrosini Wrote:

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

> Oh and the starter shoes drag and slow you down. You can take them out

> and rope / pull start it or buy the one way bearing kit from Treatland.

> The downside is that you can't really roll it with the motor engaged and

> you have to lube the bearing a lot. Mine expanded very quickly when I

> went too long without lube.

Re: (Re)building a Derbi Flat Reed - What to expect?

I’m a fan of any kit on a Derbi. They all go about the same top speed with various levels of acceleration ranging from a spanked donkey to a straight up rocket ship. I haven’t used one of those new cranks, the flat reed stock crank usually holds up to mild set ups and is rarely messed up if you pulled it from a stock bike. Also the vm isn’t my favorite carb on a Derbi, they are a little harder to fine tune IMO and you end up leaving a lot on the table or worse not realizing you’re lean on the main and blowing your kit.

Re: (Re)building a Derbi Flat Reed - What to expect?

Emil Kniemel /

I currently have the 43.5mm cast iron metrakit that i got used and sourced a NOS piston. I think the smaller kits you can run a stock head. 47mm airsal youll need a new head for sure.

that being said im running the 47mm decompless head on my 43.5cc and it rips (54+mph). i have a 47mm airsal sitting in a box. 15mm amal right now. crankspipe. waiting on my cranksintake to swap my 17mm amal when i go for the 47mm kit.

the various plates (dos, TJT, treats, stock 6) will affect your tuning immensely. i woudlnt even fuss with the gear ratio or contra spring.

Re: (Re)building a Derbi Flat Reed - What to expect?

Sorry for not replying back to this thread. Been so busy with work, holiday shopping, and tearing into the Derbi...of course :D

Appreciate everyone's input. A lot of good info and things for me to take into consideration for future plans. As of now, I've decided to completely tear the bike down, replace any parts that a good evaporust soak, epoxy, and elbow grease can't fix, and rebuild in a "stock plus" configuration.

Current performance plans - and parts I have are as follows:

Keep stock 6 roller, install Dos ramp plate. Keep stock weights until tuning time begins.

New dayco belt

Removed the variator spacer / restrictor. Believe it was 5mm. Possibly 8mm. Can't remember.

MLM / metrakit pipe

43.5mm airsal with stock head. Keeping decomp. Have a good one from Dos and another from Richard as backup

Keep starter shoes for pedal starting. Upgrade clutch springs. Keep stock gearing 13/33 for the time being.

15sha (came with it) w/ new filter. Get a 15mm sha intake with upgraded reeds. Either gila or the assorted pack on treats.

I'm sure I'm forgetting something but I've still got about a month or so till I see myself being ready to put it back together. Shipping delays are slowing me down so I'm focusing on cleaning everything up and getting it ready for paint. Thankfully all the internals look good. Going to replace bearings and seals as customary with all my purchases. Best to know what state everything is in and to ensure you can ride happy and mostly carefree! Can't understand people that run janky peds/motorcycles/etc.

Here's a few pics of how she currently stands. As a side note, I'm glad I took the plunge and tore it apart. Swingarm is missing 1 of the tabs that mount to the frame / motor!! Looks like it cracked right off. Unbelievable. Have to add that to the shopping cart....

Might start another thread titled "Things you wish you could tell the previous owner(s)". Id like to tell them that mopeds don't belong underwater (RUST!!) and that they shouldn't buy something they can't take care of!!

Anyway. Rant over. Back to tinkering. Thanks again everyone!

Andrew

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Re: (Re)building a Derbi Flat Reed - What to expect?

After soaking in evaporust for 2 days...

Can't wait to soak the rest... (edited)

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Re: (Re)building a Derbi Flat Reed - What to expect?

Brandon Weiss (Detective brandon to you) /

Wow, that swingarm missing a mounting point is whack.

Looking good so far! Just be careful with the drive gear engagement dog, if it pops off it will shoot the 2 detent balls into oblivion. Make absolutely sure it's working properly before installation.

Re: (Re)building a Derbi Flat Reed - What to expect?

> Brandon Weiss (Detective brandon to you) Wrote:

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

> Wow, that swingarm missing a mounting point is whack.

>

> Looking good so far! Just be careful with the drive gear engagement dog,

> if it pops off it will shoot the 2 detent balls into oblivion. Make

> absolutely sure it's working properly before installation.

Tell me about it. At first I was like...uh okay...MAYBE there's some offset mounting thing going on here...NOPE! The more I tear into this the more I realize why the PO might have sold it. Then again, there's also the possibility that he just didn't know anything about this and wanted out. Oh well. Don't hate the player, hate the game, right?

The drive gear assembly appears to be working fine. I took the circlip off but the gear itself just don't want to come off. Weird. Might try a little bit of heat and gently prying it off. If it doesn't work, I'll pull the gear off the resting plate and clean it as best I can before reattached the spacer / shamrock washer and the circlip

Re: (Re)building a Derbi Flat Reed - What to expect?

looks like you’re on the right track. they’re not too bad. keep an eye on the drive engagement ball thing like everyone mentioned. get a blind bearing puller for that drive pulley(?) blind bearing. i did the wet paper towel method + heat to get mine out but i think i got lucky and didnt bust thru the case somehow. derbi is fun, i got to 51 on a stock cylinder with cylinder bridge cut out, hpi, single pedal reedblock mod, 15 sha and blue baffle. it’s on my stand now getting a windowed piston and a little bit of porting. (edited)

Re: (Re)building a Derbi Flat Reed - What to expect?

> ck 🌧🌧🌧 Wrote:

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

> looks like you’re on the right track. they’re not too bad. keep an eye

> on the drive engagement ball thing like everyone mentioned. get a blind

> bearing puller for that drive pulley(?) blind bearing. i did the wet

> paper towel method + heat to get mine out but i think i got lucky and

> didnt bust thru the case somehow. derbi is fun, i got to 51 on a stock

> cylinder with cylinder bridge cut out, hpi, single pedal reedblock mod,

> 15 sha and blue baffle. it’s on my stand now getting a windowed piston

> and a little bit of porting.

Good to know! Taking it a bit slower than I did my Morini M1 and e50 rebuild. Just for the sake of not knowing what to expect. The repair manual is a great tool. The detailed pics are a big help.

What's the paper towel and heat gun trick? Sounds interesting lol.

Re: (Re)building a Derbi Flat Reed - What to expect?

Brandon Weiss (Detective brandon to you) /

> Andrew B Wrote:

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

> > ck 🌧🌧🌧 Wrote:

>

> What's the paper towel and heat gun trick? Sounds interesting lol.

You jam greased up paper towels, bread, or other similar media into the bearings inner race with a snugly fitting shaft, and eventually enough pressure builds on the opposite side of the bearing to force it out. Its a common mistake to leave the casting on the other side of the bearing unsupported, and wailing on it with a hammer and a punch to shove stuff in can cause the backside to blow out. I've used the trick before in a pinch, took awhile but it actually worked!

Its commonly referred to as "the bread trick"

Re: (Re)building a Derbi Flat Reed - What to expect?

Lol sounds hilarious. I'll have to do a search for it and watch some YouTube videos. Thanks

Edit: Just watched a youtube video of some guy doing this on his 350z clutch bushing....mind blown. Time to throw away all my pilot bearing pullers (edited)

Re: (Re)building a Derbi Flat Reed - What to expect?

I couldn't get the bread trick to work on a Za trans cover.. but it did smell nice when I heated it up and slammed it onto a block of wood.. which works fine on those FR cases.

Re: (Re)building a Derbi Flat Reed - What to expect?

> Wesley Ambrosini Wrote:

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

> I couldn't get the bread trick to work on a Za trans cover.. but it did

> smell nice when I heated it up and slammed it onto a block of wood..

> which works fine on those FR cases.

Funny you mention that. When I drained the trans what came out was around 3oz of the greenest and smelliest substance I've ever found on or in a moped. Heating up the cases to split them resulted in gobs of blue RTV.....fun.....and more stink. Can't wait to smell the freshly baked bread

Re: (Re)building a Derbi Flat Reed - What to expect?

Steven Whitright /

this is super minor... but just FYI for posterity... every one of these i've gotten into has had ONE detent ball. seen multiple posts on MA mentioned detent ballS. shit got to the point i was paranoid that i'd just always received motors where someone lost all but one ball coincidentally, then saw in the manual there other day there IS only one (#34 in attached diagram)

> Brandon Weiss (Detective brandon to you) Wrote:

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

> Wow, that swingarm missing a mounting point is whack.

>

> Looking good so far! Just be careful with the drive gear engagement dog,

> if it pops off it will shoot the 2 detent balls into oblivion. Make

> absolutely sure it's working properly before installation.

Screen Shot 2021-02-27 at 10.53.35 PM.png

Re: (Re)building a Derbi Flat Reed - What to expect?

Brandon Weiss (Detective brandon to you) /

> Steven Whitright Wrote:

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

> this is super minor... but just FYI for posterity... every one of these

> i've gotten into has had ONE detent ball. seen multiple posts on MA

> mentioned detent ballS. shit got to the point i was paranoid that i'd

> just always received motors where someone lost all but one ball

> coincidentally, then saw in the manual there other day there IS only one

> (#34 in attached diagram)

>

> > Brandon Weiss (Detective brandon to you) Wrote:

>

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

>

> > Wow, that swingarm missing a mounting point is whack.

>

> >

>

> > Looking good so far! Just be careful with the drive gear engagement

> dog,

>

> > if it pops off it will shoot the 2 detent balls into oblivion. Make

>

> > absolutely sure it's working properly before installation.

That's the detent ball for the pedal shaft, which is on the outside of the engine. The detent balls i mentioned and that you read about are inside the engine, on the output shaft/dog mechanism.

Re: (Re)building a Derbi Flat Reed - What to expect?

Yeah if you have those parts just do yourself a favor and toss them in the trash. The detent balls that are important are the ones that sit in the collar on the output shaft.

Re: (Re)building a Derbi Flat Reed - What to expect?

Steven Whitright /

ohhhh - that clicked - remembering now yeah

> Brandon Weiss (Detective brandon to you) Wrote:

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

> That's the detent ball for the pedal shaft, which is on the outside of

> the engine. The detent balls i mentioned and that you read about are

> inside the engine, on the output shaft/dog mechanism.

Re: (Re)building a Derbi Flat Reed - What to expect?

Steven Whitright /

(this bullshit)

24F915C0-BCB7-443B-99DA-77E75F204E36.jpeg

Re: (Re)building a Derbi Flat Reed - What to expect?

Downhill Harvey (OFMC) /

> Andrew B Wrote:

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

> Id like to tell them that mopeds don't belong

> underwater (RUST!!)

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