Re: Derbi metrakit porting

Downhill Harvey (OFMC) /

Re: Derbi metrakit porting

Just another method in regards to derbi decomp plugs, the valve hole can be tapped without predrilling to M5x0.8

I picked up a set of M5 aluminum countersunk allen head screws from

OPPracing

and just threaded it in with a bit of loctite... no leaks

I think the aluminum screw will help to avoid hot spots in the chamber, you might be able to run slightly leaner??

Re: Derbi metrakit porting

Dirty30 Dillon /

That's tight ^^^ Exactly what I need to do to run a derbi head on my hobbit

Re: Derbi metrakit porting

1486086823597650796346.jpg

So Boyz feast us eyes on this. Max originally worked in this derby metra kit head for me but lost access to his machine shop. Anyway Nate the great did this for me and naturally it's innovative. So that's a one way bearing he installed in the clutch so obviating the need for a decompression. Plus the head wasn't machined art the way to the Athena 47.6 width. He tigged dat decomp to oblivion before reshaping the head on his lathe.

Yea I want to one day be able to do stuff like this. This is exquisite as is cheeta 's pull stsrts. This one way valve should spin the crank forward and otherwise disengage. Definitely worth a trial!!! I gotta get to work on this stuff but I swore I would do those vespa engines first.

Re: Derbi metrakit porting

on my "race" derb I have found a stock decompless head from some PP/PR bike and had Lucky mill it to Puch Gila Squish specs. Makes a perfect .95mm squish with a 1mm base gasket. Ports dead on at BDC and with a little porting an ex duration right at 185º

IMG_20160627_112212.jpg

Re: Derbi metrakit porting

the stock heads that didn't have a decomp, to my knowledge, were used on the start3/start5 motors. that's the only time i've ever seen them --- but maybe they were used on others? interested in finding out!

this is a cool thread. I just slapped a 47mm airsal kit on my variant yesterday. I cut the boost ports into the piston, cleaned up the casting a little, gapped the rings and spaced the kit appropriately and have amazing power. great for riding around the city. flew down claiborne last night passing cars. weeeeeeeeeeeeeee!

Re: Derbi metrakit porting

Cut her up last night, carbide bit on a dremel eats right through the piston, done in 5 min.

Re: Derbi metrakit porting

grim ripper /

my decomp is lapped and i'm not making any "extra" compression. it doesn't leak now...i freakin like decomp! is it going to blow up my shit? i lapped it good with proper valve lap compound...

i'm running a 12.12, it's fine right?

like if i put the destroyer and a 18+mm carb, maybe i'll get a no decomp head...

Re: Derbi metrakit porting

Ryan N. Wrote:

-------------------------------------------------------

> the stock heads that didn't have a decomp, to my

> knowledge, were used on the start3/start5 motors.

> that's the only time i've ever seen them --- but

> maybe they were used on others? interested in

> finding out!

38mm squish so idk, not start 3 or 5

Re: Derbi metrakit porting

damn dan i was looking at a couple of my reed kits the other day and decided to port out the piston window to match the width of the port. then i was thinking...why the hell cant i just cut out the whole thing? thank you for the confirm here good shit

Re: Derbi metrakit porting

grim ripper /

it's the "puch polini" of '17.

Re: Derbi metrakit porting

Bump this to remember to read up when I get the derb out of storage and on the bench

Re: Derbi metrakit porting

never forget

Re: Derbi metrakit porting

IMG_20170426_204236.jpg

Re: Derbi metrakit porting

^that's almost exactly what I've done with good results. My exhausts aren't quite that wide though

Re: Derbi metrakit porting

Dirty30 Dillon /

Marc Friedman Wrote:

-------------------------------------------------------

> So that's a one way bearing he

> installed in the clutch so obviating the need for

> a decompression.

I've seen this in action and it does work, but it definitely doesn't eliminate the need for decomp. You are still have to spin the motor by turning the wheels, just like starting with starter clutchs.

Re: Derbi metrakit porting

Dirty30 Dillon Wrote:

-------------------------------------------------------

> Marc Friedman Wrote:

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

> -----

> > So that's a one way bearing he

> > installed in the clutch so obviating the need

> for

> > a decompression.

>

> I've seen this in action and it does work, but it

> definitely doesn't eliminate the need for decomp.

> You are still have to spin the motor by turning

> the wheels, just like starting with starter

> clutchs.

It does because you don't have starter shoes that will slip. If you belt angle is right, and gripping correct, you do NOT need a decomp.

Re: Derbi metrakit porting

Not sure if I initially wrote it correctly but yes the Nate one way bearing does work well. It requires some omnipresent belt tension so The belt actually will spin the crank. Also if the bike sits for a while the minute oil on between the bore and the rings probably dissapates making it hard to spin the engine. Two ways to deal with that

1 back out plug and spin for a bit with pedalling. Make sure if u have the plug out the kill switch is on so as to not fry your CDI.

2 haven't tried this seeing I have a cover over the magneto but spinning that by hand a bit should also work.

Re: Derbi metrakit porting

Downhill Harvey (OFMC) /

Marc Friedman Wrote:

-------------------------------------------------------

> the Nate one way bearing does work well.

Which bearing? There's a ball bearing, and a needle bearing in the clutch bell.

Re: Derbi metrakit porting

There is a recent t post on methods to make this. I didn't fab it so I can't say exactly how Nate did the one way bearing. Pedaling directly rotates the crank and it disengages the pedal mechanism when not pedalling

Re: Derbi metrakit porting

Downhill Harvey (OFMC) /

Not a Metrakit, but fun to watch anyway,

Re: Derbi metrakit porting

Downhill Harvey (OFMC) /

Re: Derbi metrakit porting

Derbi metrakit 70cc on a morini m1....modified

Re: Derbi metrakit porting

Brandon Weiss (Detective brandon to you) /

Bump....I have a 65cc cast iron Metra for a Derbi Pyramid reed engine, and the 47mm airsal for my flatreed variant.

The 65 Metra has a 3rd transfer, but neither the piston or cylinder skirt are windowed.

How would I figure out how to make a window in the cylinder skirt in the proper place?

And for the 47 airsal, the cylinder skirt has windows, but not the piston. Figuring out the location of the piston windows is simple, just match em up at BDC. BUT, I see some people here cut away the whole piston skirt, without leaving a bridge at the bottom. Is that safe? I'd be worried about those prongs breaking off the piston.

Re: Derbi metrakit porting

Ummmm. Don't you see that everyone is doing it? Must be safe. Everyone is running it like that

Re: Derbi metrakit porting

Have any of you guys ran closed end wrist pins? I added auxiliary ports on my puch polini and it seems like if I sent them any wider the mix would go out the transfer and into the auxiliary exhaust ports thru the wrist pin hole before the blowdown period is complete.

Re: Derbi metrakit porting

Tommy isn't as much of an asshole as he sounds on the internet.

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