Repair/improving top transfer openings?

Discussion in 'Performance Mods' started by BikeBuilder43, Oct 17, 2016.

  1. BikeBuilder43

    BikeBuilder43 Member

    Recently I did some port work and raised the transfer openings which exposed them more to the exhaust opening. Not good!! Never do that. I worked with a 2 part putty that hardens like metal...harder than jb weld. Could I use it to lower the transfers below the exhaust, even lower than factory and redirect them away from the exhaust. I know I'd have to put another gasket on the bottom of the cylinder to expose more of the transfers again.
     

  2. jaguar

    jaguar Well-Known Member

    yes you can but don't do guesswork. use a degree wheel on the magneto with the head off to observe the total number of degrees the port(s) is open.
    Exhaust port can be as much as 160 and the transfers shouldn't exceed 120 degrees.
     
  3. BikeBuilder43

    BikeBuilder43 Member

    The degree wheel determins the height of the openings?
     
  4. jaguar

    jaguar Well-Known Member

    360 degrees in one crank rotation

    as piston goes down the port begins to open. mark the degree on the wheel and keep turning the crank. note when the port starts to close.
    the total number of degrees the port was open is what is important.
     
  5. BikeBuilder43

    BikeBuilder43 Member

    What about the width?
     
  6. jaguar

    jaguar Well-Known Member

    I made the width of mine less in order to direct the transfer flow more toward the intake so that less is lost out of the exhaust port. That improved its power.
     
  7. BikeBuilder43

    BikeBuilder43 Member

    Thats what I'm gonna do. Just wondering if lowering the ports so the top of the transfers arent in line with the bottom of the exhaust would yeild any power gain. Or maybe I could fill in the bottom of the exhaust port and take some metal off the top. It would raise the port and the transfers wouldnt be lined up with it.
     
  8. jaguar

    jaguar Well-Known Member

    you are talking nonsense.
    It is all about the degrees that ports are open.
     
  9. BikeBuilder43

    BikeBuilder43 Member

    I know that. I was just thinking of changing the exhaust port location because I already raised the transfers too much.
     
  10. jaguar

    jaguar Well-Known Member

    How do you know what is "too much" if you don't know the port duration in degrees?
     
  11. BikeBuilder43

    BikeBuilder43 Member

  12. jaguar

    jaguar Well-Known Member

    What are the port durations of the transfers if you consider when its open that all of it is open (as if that horrible notch wasn't there)?
     
  13. BikeBuilder43

    BikeBuilder43 Member

    Need to make a degree wheel and do what you said
     
  14. jaguar

    jaguar Well-Known Member

    print one from google images
     
  15. HeadSmess

    HeadSmess Well-Known Member

    that IS a horrible notch!

    you could, maybe, possibly reclaim that cylinder with some judicial use of a DENTAL DRILL rather than using a dremel or die grinder. they actually get into the ports, and allow you to do things. would you let a dentist stick a dremel in your mouth? well, how do you think your poor little engine feels about it?

    the problem youre suffering from isnt necessarily from having raised the port too much, its from shaping it BADLY, with no regard to how the gas will flow when it enters the cylinder. will it purge all exhaust gases out the exhaust before it itself starts to exit? or does it actually cut the exhaust in half, leaving this great big pocket of dirty, burnt gas at rear of the cylinder, whilst half your fresh mix goes out the exhaust?

    the degree wheel simply attaches to the crankshaft and lets you know when ports open and close. very important. but what it doesnt help is determining the way gas FLOWS. thats mostly just trial and error, guesswork, and the application of LOGIC.

    said it before, ages ago...whats really required is a smoke machine/fogger, and the use of spark flash photography to really understand what changes can be made, and what affect changes have on circulation in the cylinder, as you spin the engine up at operating speed. sort of like a flow bench, but they do not let you see how the piston, constantly moving, also affects the gas flow.

    dont stick any type of putty epoxy filler near the walls of the cylinder. one, its nothing like chrome plating, two, its prone to fall off, three... um...it makes a mess when it does fall off. use it further back in the port for redirecting/smoothing gas flow, but not for rebuilding cylinder walls!
     
  16. Steve Best

    Steve Best Active Member

    Yup, what Jag and Headsmess said, only more so.
    You could rescue it by leveling the top of the transfer and aiming it right like Headsmess described, then taking a degree wheel (saves a lot of trig math) like Jag suggested to get the exhaust port in the proper relationship again, then drop the cylinder (no base gasket, mill the cylinder or case or taller piston) to get everything back in perspective. For as cheap as these cylinders are, I'd start with a new one.

    You seem to be under the delusion that taller ports make more power?
    Sometimes a taller exhaust port will make more rpm but you are usually trading off more peak rpm power for less mid-rpm torque.

    I've used a lot of epoxy in motors over the years, follow Headsmess's advice. It won't work in an exhaust port. It >might< be possible to fill in the top of the transfer with epoxy but I highlight the >might<. It would take a very careful procedure and I don't think you are there in the skills and theory department yet. Like mentioned above, catastrophic failure is more likely. These cylinders won't take welding anywhere near (6mm-12mm) the cylinder bore. Start with a new cylinder.

    Want more power? The formula is simple, Sir Harry Ricardo had it 100 years ago - PLAN - Pressure in the cylinder, Lenght of stroke, Area of piston and Number of power strokes per minute. Average burn pressure, displacement, rpm. That is what it takes to make pressure. Cut the exhaust port higher you are reducing the average burn pressure for higher rpm. It is possible and advisable to increase both.

    Gordon Jennings had a wonderfully simple plan, figure what the maximum mechanically tolerable rpm is, and work backwards from there. Read his book to find how.
     
    FurryOnTheInside likes this.
  17. gary55

    gary55 Active Member

    Click on Jag's mods for porting. It will explain how to modify the ports in terms of distance in mm's from top of cylinder. It's been in my bookmarks for years.
     
  18. BikeBuilder43

    BikeBuilder43 Member

    Well I used the 2 part epoxy in the transfer ports. First i lowered them way too much. Went back and raised them a bit and it worked...sort of. I made sure the inside of the transfers were cleaner than they were before...the epoxy helped with that. I started it up and barely had power. I got off the bike and reved it a bit. At first it vibrated like crazy and ran really rich then it almost backfired and reved really fast while barely vibrating at all. When i took it for a ride it had a little better power but still not enough to get to half speed. It's like its running way too lean. I have the needle set to the richest setting. I have the thrust expansion exhaust and the "upgraded" NT carb. Also it is a lot louder now than it was a few minutes ago like something was restricting flow inside the pipe then vibrated loose...idk. There are no exhaust leaks.
     
  19. BikeBuilder43

    BikeBuilder43 Member

    I have the jet black "80cc" coming in at the end of the week. Might leave everything alone minus shaving the bottom of the piston on the intake side.
     
  20. Steve Best

    Steve Best Active Member

    I wouldn't even do that. How will you know if it is an improvement unless you run the engine stock?
    Break it in, 3 tanks of fuel, then experiment one step at a time.
    I'd buy a spare piston to cover yer a$$ if it is not an improvement.

    I tried it and was not pleased with the result. More rpm but less power.
    Buy a spare piston and try it, after break in. Find a way to accurately measure results.

    Steve
     
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