Minarelli Builders Thread

[Cannonball3]

So heres a “junk” Mina build, I named it Scraps cause thats what it is I had the cast iron parts left from the Athena build and thought why not build a low
key bike around them. The basis is a good running GT5 bottom end, cast jug and its stock head, 38mm spacer, and a horizontal Mina piston. I had the piston as an extra and it was much lighter. They are basically the same other wise.

It breathes thru a stock Bofeng and G2 reeds, a crappy restrictive stock muffler and gasket, and a stock ignition. Nothing port matched.
Well Im surprised, but not surprised. Its a Mina in every sense. Easy starting, spookily low idle, good linear power and really quick considering how stuffed up it is. I believe it will easily reach 40 as is with a bit of carb tuning.
Im very glad I threw it together, its less hyper than the Athena, and promises to be a lot of fun as an errand runner.

If one orders the cast kit from China, a build like this is fairly cheap. I know, I know about the chain idler, it will have to do until the arch type gets here.

 

[Cannonball3]

So been riding this thing constantly, figure its accumulated 40+ miles. Its just a perfect little runner. Totally consistent
in all aspects. The idle is amazing, has never stalled. After a bit of tuning on the Bofeng its a solid runner. I knew it topped pretty well but was surprised that it hit 44! Got and calibrated the computer yesterday and just got a run in. This is on a 40t also. The Athena runs a 38. I couldnt be more happy with this thing.

Also I found that the Mina horizontal piston is much lighter than the vertical. 3.1 oz including pin vs 3.7 Its running one in this build. You can buy these for $13.02 shipped from The GY6 Store on ebay.

 

[Cannonball3]

After building 2 different Mina hybrids I have to say Im very happy with my experience. To be able to marry
2 different components to come up with such a good little engine is amazing. They are easy to build, though not the cheapest. I have an Athena Sport version and the common cast iron version. They are kind of apples and oranges in comparison.
The Athena is a nice high end component. Its forte is top speed. Easy mid 50s. What it lacks is low end snap. It not bad but really comes alive in the mid 30s and the afterburner lights around 40.
On the other hand the little cast iron build is snappy from the bottom to the top. Its a blast, and throttle roll on is immediate. Thru a jog pipe it bands around 40 with a bang and 48-50 is immediate.

The cast build I am riding now uses the stock/modified muffler to restrict it. I decided I didn't need two high end rockets, but a more usable daily rider. The cast build is a winner there.
If I were to do it all over, I would build the cast version as the base. In either form its fun and quick. For low end builders
you can build fairly cheaply using a stock modded muffler, a G2 reed, and a Bofeng carb. You will have a snappy, quick bike that tops in the low 40s, cruises nicely in the mid 30s, has a rock solid consistent idle, and mine at least has been totally reliable. Not knocking the high end builds but the Athena tend to collect dust while I enjoy the cast iron daily rider rocket.

Just my thoughts.

 

[Nickt919]

I’ve had the same results with my engine by copying your engine CannonbalI. I just turned 500 miles a few days ago. It’s been worry free except for one issue this morning.
Curiosity got the best of me. I went out on the highway to see just what this engine has. Never did do this until today. If I had an ounce of common sense I wouldn’t have done it. When I got to 52 mph it was still pulling hard but I think I ran out of spark. It momentarily stuttered or cut out until the rpm’s dropped some then picked back up. It happened 2X’s so I didn’t push it. I slowed down.

When I set up my engine I used the catnip or super charged CDI and made a magneto magnet key to retard the timing one half key. I’ve never actually measured the effect of that half key with a degree wheel because it ran fine until I tried pushing it to the limit today.

I’m not too concerned about over coming this short fall because I really have no business trying to reach a speed of 60 mph on a bicycle. At 52 it still had no physical signs of topping out or reaching its limit.
I’ll probably just let it go unsolved becuse it runs great otherwise. It would be nice to know what the actual cause of the cut out was. The rpm’s were well over 10,000 when it happened.

Edit: I did this on a 4 lane, deserted highway. I was good with the speed limit and traffic laws….correct helmet..and clothes,gloves, eye protection…. but… I was on a motorized bicycle.

 

[Cannonball3]

Be interesting to know, but as you say nerve wracking to figure out at those speeds. Maybe a connection?
At those rpms maybe a vibe caused an intermittent connection? If you are running the stock Chinese connections
check em for tightness. Mine on the throttle kill harness double terminal open up over time. I should replace em.

. Last time I did a mid 50s run
in the back of my mind was the carnage to this old 72yr body if a tire blew, chain threw etc. When I was younger the thought would never cross my mind. Maybe wisdom does come with age.

 

[Nickt919]

Be interesting to know, but as you say nerve wracking to figure out at those speeds. Maybe a connection?
At those rpms maybe a vibe caused an intermittent connection? If you are running the stock Chinese connections
check em for tightness. Mine on the throttle kill harness double terminal open up over time. I should replace em.

. Last time I did a mid 50s run
in the back of my mind was the carnage to this old 72yr body if a tire blew, chain threw etc. When I was younger the thought would never cross my mind. Maybe wisdom does come with age.

I have all the bullet connectors hardwired…soldered and heat shrink.

 

[Chainlube]

I have all the bullet connectors hardwired…soldered and heat heat shrink.

I buy the small heat shrink tubing in a 25' roll.

 

[Cannonball3]

I have all the bullet connectors hardwired…soldered and heat shrink.

Thats a smart move! I do that on all my boat wiring. Seems like I am always changing my MBs around, so I stay with the connectors.

 

[Nickt919]

Thats a smart move! I do that on all my boat wiring. Seems like I am always changing my MBs around, so I stay with the connectors.

I already had bullet connector problems on the bike with intermittent power failure.

Soldering is a bit more than the plugs… But then..I soldered so much with RC helicopters for years…it became second nature.
I have kits of all sizes of heat shrink tubes, different solders, braid for wicking old solder, and a few different irons n guns.

With the high amp motors and speed controllers on the rc aircraft it’s important to get the joints right. A cold joint causes all sorts of havoc that’s sometimes hard to run down. I had to learn how to solder after a few receiver shut downs and subsequent crashes.
These few bike wires are a cake walk.

 

[Nickt919]

Santa Claus made an early drop…I’m Santa Claus.
Planning on pairing this with an RDM crank(thanks to Cannonball3), PWK 28 carb, and suitable pipe if it all works out.

The exhaust port has 2 smaller ports from the bore into the exhaust port.

The intake port is odd shaped and big.

The piston is flat topped and the cylinder
bolts down like the one piece CG.. like the NR80…4 hex bolts down by the case. No stud through the length of the cylinder.

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