Repair/improving top transfer openings?
- Thread starter BikeBuilder43
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D
Deleted member 12676
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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)?
BikeBuilder43
Member
Need to make a degree wheel and do what you said
D
Deleted member 12676
Guest
print one from google images
HeadSmess
Well-Known Member
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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!
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!
Steve Best
Well-Known 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.
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.
gary55
Well-Known 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.
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.
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.
Steve Best
Well-Known 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
