Derbi metrakit porting

So I just grabbed this metrakit/airsal from treats. Casting looks good as well as the porting. I still plan on doing some light work to it: Open the exhaust port and polish it, knife the bridges and match third transfer to my case. Being that Airsal made it with metra porting they didnt put the boost window in the piston... Lazyness haha. My question is where should I line the piston up at in the cylinder to make my marks so I can cut the window in the piston. Do I line it up with the edge of the skirt or line it up with the edge of the cylinder bore of nikasil where the side cuts in the piston line up with the side cuts in the skirt. When lined up with the skirt edge all windows are clearly seen within the cylinder. When lined up with the nikasil edge and side ports, the inside ports are covered up about 1/2 way maybe a mm less than. Any and all advice or help would be greatly appreciated. Thx

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Re: Derbi metrakit porting

Re: Derbi metrakit porting

Wow. That's some piston choppin

Re: Derbi metrakit porting

I have done the same thing on quite a few of those kits and it worked out great.

Re: Derbi metrakit porting

So it looks like by your pictures I should line it up with the bottom of the cylinder skirt not the nikasil bore correct?

Re: Derbi metrakit porting

Dan, the fine details on that cylinder are awesome. The brass stud hole inserts and the decomp plug are a really nice touch.

Re: Derbi metrakit porting

What are you people that have done this using to cut the cylinder skirt and piston?

Re: Derbi metrakit porting

dremels 'n stuff. my cylinder is ported just like that one. i used some cut off wheels and a tile cutter. then i cleaned it up with a small file and emery cloth.

i didn't cut my piston yet. gonna save that for later. i imagine leaving it un-cut for now will help keep it cool during break in. my imagination is usually pretty good.

Re: Derbi metrakit porting

I would think more lubrication and cold intake mixture on your small end bearing would be a good thing during break in.

Re: Derbi metrakit porting

line it up with the piston at BDC

Re: Derbi metrakit porting

If you want to plug the decomp.....did this with a drill press...step bit and a Dremel

Re: Derbi metrakit porting

I mean the decamp hole in the cylinder, but that looks super good too.

Re: Derbi metrakit porting

Thanks...I made a threaded plug for that as well...you have good eyes.

Check out the piston internals...I feathered them out to hopefully improve flow into the transfers...have to wait and see if it's worth it :)

Re: Derbi metrakit porting

That head decomp plug! A++

Re: Derbi metrakit porting

Is that jbweld in the decomp channel in the head? Nice work!

Re: Derbi metrakit porting

looks cool, but starting without a decomp is bullshit sometimes. like if your belt or starter shoes are a little wet, or if either are just worn out.

Re: Derbi metrakit porting

It's not going on a derbi....not worried about starting it.

That is JB weld in the channel...I know you shouldn't use it on a head but it's just there to take up the space...no chance for any leaks.

I was going to tig it but this was a cleaner(and easier) application :)

Re: Derbi metrakit porting

@Dan ott

Nice work!

Have you coated the squish band? With what? Ceramic?(edited)

Re: Derbi metrakit porting

Dan did you spin the head in a lathe to polish it?

Re: Derbi metrakit porting

No ceramic...just dremeled and buffed out...I wish I had a lathe :)

I do like the flexible wet sanding paper from 3M though

Re: Derbi metrakit porting

that's the best decomp plug i've seen yet, but i like decomp. i valve seat compounded mine. hope it doesn't leak....

Re: Derbi metrakit porting

if you knife-edge the bridges

don*t they become hotspots?

i have seen pistons drilled just

to lube the bridge, especially

exhaust bridge

Re: Derbi metrakit porting

campeona del mundo /

had this done by a local machinist for rally/party fun. came out pretty decent and dropped temps significantly

Re: Derbi metrakit porting

On the hobbit variant after matching the top transfers there isn't match space left for the gasket about 2-3mm. Anyone run into this? What can I do to minimize airleaks? I'm just not sure if it would hold up or not

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Re: Derbi metrakit porting

2mm is fine for sealing

Re: Derbi metrakit porting

jesus christ, clean up your tooling though.

Re: Derbi metrakit porting

What kind of RPMs are people hitting on their metrakits? Either on a derbi or a hobbit.

Re: Derbi metrakit porting

My metra ^ is hitting about 11.5 +

But my tach is going wacko when I go higher....so I'm not sure...h95 slow climbed up top to 63 before I had to slow down...if I shorten the header I should get more rpm

Re: Derbi metrakit porting

With tall gearing on 17" (17x33) - 9.8k (ran tach) @62MPH

Stock gearing on 10" (17x33) - WAY HIGHER (no tach) @66mph

Both unported, untouched big muff, stock intake, sha16.16, points

Re: Derbi metrakit porting

On my track bike I did some transfer porting (enlarging and kife edging bridges), ex raised to 180* and the aux ports widened to like 1/3 the way up the side transfers, stock decompless head milled to match Puch Gila squish at 1mm, HPI mini, stock length big muff, geared 14x37 was doing just shy of 12k.

revving great, but the power just wasn't really where you'd want it for a dual variated bike with all that transmission in the way. mellowed out the port timing a few degrees and increased compression by removing a base gasket and I'm getting a lot more usable power without having to have wacky clutch springs.(edited)

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