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Polish jet pilot

Polish jet pilot

4aces4aces4aces4aces4aces
Location
Warsaw, Poland
yamaha 62T cases have moulded "fingers" in the intake tracts. Filling them up with epoxy reduces the negative crankcase volume, thus icreasing the effectiveness of the combustion cycle...
 
Polish jet pilot

Polish jet pilot

4aces4aces4aces4aces4aces
Location
Warsaw, Poland
there was a question on case stuffers: quite siilar function to the filling of the intake tracts. a case stuffer can be done in a few ways, but basically it is suppossed to decrease the negative crankase volume... back in the old days some folk even used wooden blocks / brass stripes on 2 stroke motorcycles to accomplish that.. Usually the inserts were done on the webs (counterweights) on the crank...
 
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waxhead

wannabe backflipper
Location
gold coast
SuperCarlus said:
View attachment 195245View attachment 195246
what do you think about this case porting? Did I grind to far or it will be good? Need I another case to do the job?
Click to expand...
You didnt go out far enough and you have an angle on the floor the weight of the air will push hard on the floor so make sure it has a smooth radius on it.
I go alot wider, Also look at filling the fingers and building a ramp to send the charge over top of the crank
 
SuperCarlus

SuperCarlus

Location
Québec, Canada
Really thank you waxhead.

1- What angle on the floor are you talking about? The litle curve of the fingers just at the beginning of the reeds?

2- When you said building a ramp, it's like a 'kick' at the end of the intake? If yes, don't fear about the crank lubrification?

3- Is it necessary to fill fingers with epoxy? DASA left them like that and just rough the top. I want bottom end!!! Yess I want...

4- Notch or not the bottom of the sleeves?

I forgot to tell that it's a 771BB with Northwest sleeves, Bpipe and dual 44mm.

The be honest, I just looked pics and took my dremel, but I don't really understand why to grind tunnels from the intake to the transfers. When the piston is going up and create a depression, reeds opens and the f/a mixture is vacuum in, but the transfert ports are closed right? So why do we do that?

If you look at my 2nd picture, you can see that the grinding affected the shape of the 'bottom of the transferts' a little bit, so I'm worry about that because don't know if the f/a mixture can go back to the intake instead of be pushing up to transfert ports and then reduce the air velocity.

Is anybody can light my lantern? (hihihi I know that I should understand before playing boucher with my baby SJ...)
 
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waxhead

wannabe backflipper
Location
gold coast
If you go out side and have a look at your victa lawn mower you will see a two stroke that has air flow that goes in the intake and up to the bottom of the piston then into the transfers when the primary piston rises.
Two strokes that have a pipe actually pull the mixture up the transfers.

I wouldnt normally post pics but I dont do this stuff anymore. Every one just buys billet engines and thinks they are the gun
Here is a set of cases nearly finished
A well set up engine will have great bottom end as well as nice top end as well. Get the blow down right and you will scare your self.
The bad thing about the 62t platform is the really really bad transfers there is alot to be gained in there as flow slightly more than a maccas straw and there angles are all to hell
001-37.jpg


http://s215.photobucket.com/albums/cc79/waxracing/?action=view&current=001-37.jpg
024-1.jpg
 
Last edited:
M

mmprestine

Location
Green Bay, WI
This thread is great, thanks Matt_E. I have been thinking about this for my 6M6 build into a 61x/62T and have a question about jetting/pop off. Where does one begin?

I would assume that with all the porting the pressures have to be considerably lower so the pop off would be in the 20lbs range or less, sound right?

How high would one begin with jetting, 150 & 75?

I have play extensively with the 650 but this is going to be a whole new learning experience that should be fun. I know it is a trial and error black art but any suggestions are generously taken on my side.
 
SuperCarlus

SuperCarlus

Location
Québec, Canada
waxhead said:
If you go out side and have a look at your victa lawn mower you will see a two stroke that has air flow that goes in the intake and up to the bottom of the piston then into the transfers when the primary piston rises.
Two strokes that have a pipe actually pull the mixture up the transfers.

I wouldnt normally post pics but I dont do this stuff anymore. Every one just buys billet engines and thinks they are the gun
Here is a set of cases nearly finished
A well set up engine will have great bottom end as well as nice top end as well. Get the blow down right and you will scare your self.
The bad thing about the 62t platform is the really really bad transfers there is alot to be gained in there as flow slightly more than a maccas straw and there angles are all to hell


http://s215.photobucket.com/albums/cc79/waxracing/?action=view&current=001-37.jpg
Click to expand...

Wow, and with those monster intake holes, the epoxy ramp to the sky and the notched sleeve, does it 'snap' to be terrified? All it incresed bottom or top end?
 
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waxhead

wannabe backflipper
Location
gold coast
It will increase it every where due to the transfers now having the charge more available to them.
It gives great throttle response and good power. The notches are perfectly safe and will not drop off at all
 
SuperCarlus

SuperCarlus

Location
Québec, Canada
I bought JB Weld at Canadian Tire, 2 x 141 mL for 19,99$ and one kit was enought. It took much time to dry than Devcon, but in the 'epoxy world' :), more time to dry meens more solid and that's really true. To do touch-ups, I putted aluminum powder (from grinding) in to create some structure. Just after the putting, I used heat gun 'SLIGHTLY' to make it more liquid and then blow up bubbles.
 
SuperCarlus

SuperCarlus

Location
Québec, Canada
1- ok, I ported exhaust ports and I'm looking at the transfers with my dremel in the hand. I have 62T cylinders re-sleeved with Northwest sleeves. The top of the transfers is not 'fluid', because the sleeve create a lip lower of about 1,5 mm. Can I grind the sleeves, up the roof of the transfers and then tweak the timing, or I put my dremel on the table and back off?

2- About the sides of the transfers, with preservation of all the angles, should I grind the sleeves to fit the casting, or grind the casting to fit the sleeve?
 
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waxhead

wannabe backflipper
Location
gold coast
Gee the exhaust port looks small in that photo.
Yes you can do the transfers a bit to make them flow more. Cases Look ok a couple of sharp edges but they will still work just fine
 
Nimmer705

Nimmer705

Big Bars
Location
haliburton ontario
So ive been building up a 760, i'm doing the cylinder porting and wondering about doing the crankcase fingers, so im thinking about doing it a little different than the above pics, heres my thoughts, 760 engines are top end power and weak on the low end speed, so if filling the fingers will produce more top end why not cut into the middle fingers and make like a trench threw the middle, and still fill the two outer fingers, fingers cut.JPGfingers.jpg so the first picture is what i want to cut out ( lighter grey) 2nd picture is wat it looks like with them filled, so basicly i just would think this might help the 760 with the bottom end,

any thoughts? anyone heard of this?
 
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