Transfer port correction results:

mew905

mew905

New Member
Well, I hate to say it but the transfer angles were corrected on my jug and it didn't help at all. I think it may be because I got an old GT5 jug though (the head that came with it was squarer, and the combustion chamber was just a simple dome cut into the porous aluminum, not shiny at all). The intake was tiny (As is the one on my GT5a cylinder though, but the 5A is smaller, oddly), the transfer ports were also significantly smaller, and opened on a taper (for example, they start to open at 125 degrees, then at 132, the whole width is opened, then at 150 they're 100% open, top to bottom).

So I corrected the transfer angles using a small pilot hole, drilling in at a 4 degree angle, then switching to a bigger one, and finishing it off with a round/pointed double cut dremel burr, and finally a small diamond burr. Also I opened up the exhaust port width to 30mm along a chord (so about 32mm arc, or port-map width, which comes to 65% of the cylinder bore. Also chamfered the edges.

In addition, I removed the SBP flex pipe, mostly for cleanliness issues, but I didnt think it gave me any power. Upon reinstalling the stock muffler, I realized... the SBP definitely gave me more low end power, as with the stock muffler I have to pedal much longer than I used to, just to get going.

So stock exhaust (no cap, couldn't gut it though), corrected transfers, wider exhaust and intake ports (no timing changes), and reed valves with an RT carb on a 5" hose = net loss of power. It's not *much* slower, aside from off-the-line, but I'm willing to bet the SBP pipe will be a bit more effective now. Too bad it turned my nice, white, DC shoes black with oil, so I need an alternative.

The solution? Hopefully this thing will help

http://www.motorizedbicycle.ca/exhaust-system/motocross-poo-poo-pipe-muffler.html
 
I know, I know, double posting, but I wanted to add this addendum:

So the jug has corrected transfers. But the head, reeds, carb and intake tract are all the same as the old jug. The only difference is it's a stock timing jug, with corrected transfer angles, the exhaust port is wider, the SBP pipe is gone in favor of the stock pipe, AND I forgot to add the reed booster port. I also need to trim off the little lip on the transfer ports so the corrected angles have more effect.

So in conclusion, the wider exhaust port and semi-effective transfer angles Nearly make up for the lack of a reed booster port and expansion chamber. I'll update tomorrow when I add the pipe back and the booster port.
 
Update: Put the SBP pipe back on (no change in length or position), and cut the booster port... I gotta say... it's significantly faster now. PReviously my bike would slow to about 20mph going up my usual hill. Now it'll crank it at ~28mph. Possibly could be due to the stock ports matching the pipe more closely, but considering I didnt lose much power switching to stock pipe no boost port, I'd say the corrected transfers definitely had a great effect.
 
haha I had that theory for a while ever since I theorized about the reason the HT's four-stroke so commonly (a lot of 2 strokes wont 4-stroke unless severely choked).

But yeah, definitely hits alot better, but I think there's still work to be done, the cylinder I got is apparently for an older Type D motor (hence the angled, tiny transfers), so I gotta order another one. I'll attempt the same thing on my GT5a with 19mm manifold and matching PHBG once I make one (I broke a titanium bit while drilling and now I cant get through it...). and then we'll see what a properly breathing 66cc can do :)
 
Get a nicepick tool like off a mechanics tool truck. One you can hammer on. That drill bit is brittle steel and will break apart in crumbs. Will come out!
 
what's it called? can u find one for me? typing in nicepick or "nice pick" only comes up with FB/Twitter accounts and lockpicking tutorials
 
p25114b.jpg
Always want somthing made of a good alloy for this sort of thing. Not shure what this set is like? Just see somthing I would hammer on and even reshape at the grinder.
 
looks good, but I doubt it'll work, see the problem is the drill bit that's broken is the one I was drilling for a pilot hole so the bigger bit wouldnt slip into the transfer, it's only 1/16" >.>
 
How deep is it? If a tool like this is made of good metal, you can get away with sharpening the tool a bit. Infact it is not uncommon for me to sharpen somthing in this manner a few times. Patience is key.
 
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I'd imagine it's about 1.5 inches deep, it's not far, I figure I could possibly drill right through it with a carbide tip
 
mew905 said:
haha I had that theory for a while ever since I theorized about the reason the HT's four-stroke so commonly (a lot of 2 strokes wont 4-stroke unless severely choked).

But yeah, definitely hits alot better, but I think there's still work to be done, the cylinder I got is apparently for an older Type D motor (hence the angled, tiny transfers), so I gotta order another one. I'll attempt the same thing on my GT5a with 19mm manifold and matching PHBG once I make one (I broke a titanium bit while drilling and now I cant get through it...). and then we'll see what a properly breathing 66cc can do :)
Click to expand...

Aiming is so important yet so misunderstood.
It has EVERYTHING to do with mixture dilution and yet almost NOBODY ever experiments with it.
I've ported motorcycle cylinders and picked up BIG gains without changing transfer SIZE at all.
But it's more magic than science and takes enormous work or blind luck to realize the gains.
 
I agree, with the way our transfers were angled, we were losing a large portion of our mixture, and worse still, leaving exhaust gases in the chamber to be fired again. just a huge amount of wasted power right there. If anything, it means I'll have more bang for my buck.
 
Are you using smoke or something to check the aim as you work? I used to have friends blow smoke through a hose attached to intake to check as I modded the area. It's SO easy to remove too much...be very careful and check often!
 
honestly I just guessed. I measured it months ago but never had the tools or the guts to try it. Now I just gave it a go, and used a 4 degree angle to drill into the transfers so I didnt break through the wall, and used a file, or something else that was straight to check the angle, because I remember it's supposed to aim more toward the intake than the intake side does to form a "scoop" of air. I think it was about 60% of the bore (so the converging points were just behind the center of the cylinder). Worked pretty good IMHO, if I start making and selling these to other members, I'll for sure measure and check, this one was a one-off to see if it could be done with my existing tool set :)
 
So good news, the new 2014 GT5a's have corrected transfers FROM THE FACTORY! Upon inspecting the new cylinder for my green bike, I noticed that while the base of the cylinder is the same shape, following the transfer port all the way up to the piston window, I noticed that it tapers at a steeper angle on the outside than the inside on the exhaust side. It's not an angle that points where it should be for max performance, but the angle matches the intake side of the transfers, in pointing back toward the intake! rejoice! these motors ARE getting better!
 
mew905 said:
So good news, the new 2014 GT5a's have corrected transfers FROM THE FACTORY!
Click to expand...
Is that the gasbike $99 un-assembeled 66cc ones, or the $179 'whole kit' with just the top end in pieces?

I bought a couple of the $99 'engine parts in a box' but haven't even opened them yet.
The last $179 semi-assembled full kit I bought came fully assembled with a big red sticker where the green EPA sticker would go that said:

RACING ENGINE ONLY
NOT LEGAL FOR STREET USE.

Pfftttt...
I liked having the top end in pieces for inspection and modification.
 
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Also .. just as an added note of " F.Y.I " I don't think I will be dealing with "Gas Bike" or "King's " in the future ... I really can't , and really don't want too contribute , or sponsor / support a company that "steals" from the good people of this great sport/hobby / business ... like Fred of CR Machine ( Home and designer of the FRED Head ) , they stole his design ...copied and are "mass" producing them with cheap stock alum .. material , un -measured combustion chambers ...etc. and are selling their "copy-cat" cheap "china-man version at cut throut price to "under cut" Fred !!
I;'m sorry but I try ta support not only 'American' products but also stand behind those who devote their time , patience and heart too this ... and FRED does this .

** Ride with Pride **
 
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