Understand how a 2 stroke works before looking into this guide, it isn't here to explain how a 2 stroke works. Have a good fundamental of 2 strokes before attempting any of this.
Compression:
Compression is a RPM killer in 2 strokes, so take that in mind. There are multiple ways of increasing compression:
Milling down the gasket surface on the bottom of the jug/cylinder. Take in mind, you can only mill SO MUCH before you: effectively "drop" the exhaust port, and kill RPM's, and lose torque because you drop the intake excessively. All this is an indirect connection to the removal of the gasket or the grinding down of the gasket area.
If you have a CYLINDER, and a separate head (high performance/more sophisticated 2 strokes), you can swap out domes.
One thing to note, you cannot "hear" knock in 2 strokes. It will be prominient everywhere else, however. Running hot, high EGT's, crappy power, ect. Watch your fuels, compression, and timing.
Timing:
Timing works in harmony with everything else. It affects low end, AND top end. I'll also discuss why MSD is so **** beneficial to these 2smokes.
The flywheel key is where most tuners modify their timing. A general 20-30 degrees BTDC is followed (In Zenoahs at least). The earlier the timing, the "more" the low end. Fuel has to be ~90% burned by the time it reaches TDC.
One thing to note, advancing timing TOO much will result in detonation, not good. Compensate with higher octane fuel, or just don't touch timing at all.
"Rockit" keys (in general, ~10 degrees advanced timing) are out for Zenoah, Chung Yang, and China scooters. Basically, all this does is advance timing for a tad more low end.
BUT, the MORE you advance the timing, the MORE the 2 stroke top end suffers (as in revs). In the last section we mentioned that compression in 2 strokes affect them rather dramatically.
Since the fuel is preignited earlier, it creates HIGHER compression, EARLIER and FASTER than whatever your stock timing was (assuming it was advanced). This in turn, means slightly less revs. Your butt-dyno may not pick up the RPM loss, but it's there, although probably not too prominent.
MSD. What is it? Google it. Don't make me do it for you
. MSD adjusts timing "on the fly". Why is it great for two strokes? Why it's perfect.
Imagine 30 degrees BTDC, a general mark for 2 stroke timing. As the revolutions from the motors increase, the timing DECREASES. What does this do? Ignites the fuel LATER, and more SLOWLY. Obviously, you won't be getting MAX power after the retarding of the timing starts, but it will be retarded enough to make crazy amounts of revs.
A MSD kit on a Zenoah G23LH starts from ~30 degrees (set with timing light), and actually lets the motor hit up to 20,000 revs (as it is firing 5 degrees ATDC). Brilliant, think about it! Only downside is, you need a live power source. AKA rechargeable batteries.
Pistons:
2 stroke pistons are a rather tricky part to talk about. Multiple designs are made, and for different purposes. Some delibretely have a large slope up to aid the transfer scavenging of the cylinder, some are standard domed pistons.
2 rings increase compression, the second ring acting as a "Secondary defense" mechanism, and reduce blowby. However, these pistons suffer large drag from the friction of two rings.
One ring pistons, albeit a slight compression loss and a possibility of a lower life (depends on material, lubrication, thickness, ect, ect).
Lightening pistons... yes, it does make a difference. HOWEVER, do not lighten the skirts in EXCESS. Not only do you weaken them (and since the skirts prevent side/side movement, it may cave in slightly, and instead of keeping the piston straight in the bore, may whack around the bore and destroy the bore itself - and NiKaSil or industrial chrome plating is NOT cheap).
Balance the piston out afterwards, to ensure equal amounts of material removed. You can lighten with anything from a lathe, to a manual mill, to a dremel.
Another trick is to window the pistons, which I will discuss later.
Crankcase:
People love stuffing. What is that? Decreasing crankcase capacity, and thus increasing how much pressure the air/fuel mixture is under before it is shot up the transfers. This "in theory", is said to increase torque.
People do this with anything from JB weld to other epoxies, sometimes even with added ingredients such as cork or bits of aluminum or steel.
Watch out though, almost all contents of gasoline contain ethanol now. 10-20% generally. JB weld is NOT ethanol soluable... it WILL slowly erode away. I wouldn't be using large chunks of metal or abrasive bits if you decide to stuff (I am completely AGAINST stuffing, but mainly depends on stock crankcase volume).
JB Kwik uses a different formula, nobody has tested that yet, so, dunno. Can probably use some modern gas-tank sealing epoxy to stuff if you wish.
Full circle crankshafts also increase crankcase volume, effectively. Some are only "Half moon" (think about it). Some use plastic stuffers (which, are usually melted and glued in).
Another trick is to replace your bearings and SEALS, with SEALED bearings. Sealed bearings are your standard bearings with two dirt/dust seals on BOTH sides.
Take in mind, these seals were NEVER meant to take pressure, at all, (which the piston creates as it moves to BDC). Keep both seals on, and lube with the right grease.
Keep the ABEC rating above 3, 3 being the absolute minimum. If it does not list the ABEC rating, do not buy it. No china bearings, at ALL. Buy from known Japanese brands, NTN, Koyo, ect.
...Gotta go for now. Will write more on porting, pipes, transfers, dome... blah later. Mebe sum pix
Compression:
Compression is a RPM killer in 2 strokes, so take that in mind. There are multiple ways of increasing compression:
Milling down the gasket surface on the bottom of the jug/cylinder. Take in mind, you can only mill SO MUCH before you: effectively "drop" the exhaust port, and kill RPM's, and lose torque because you drop the intake excessively. All this is an indirect connection to the removal of the gasket or the grinding down of the gasket area.
If you have a CYLINDER, and a separate head (high performance/more sophisticated 2 strokes), you can swap out domes.
One thing to note, you cannot "hear" knock in 2 strokes. It will be prominient everywhere else, however. Running hot, high EGT's, crappy power, ect. Watch your fuels, compression, and timing.
Timing:
Timing works in harmony with everything else. It affects low end, AND top end. I'll also discuss why MSD is so **** beneficial to these 2smokes.
The flywheel key is where most tuners modify their timing. A general 20-30 degrees BTDC is followed (In Zenoahs at least). The earlier the timing, the "more" the low end. Fuel has to be ~90% burned by the time it reaches TDC.
One thing to note, advancing timing TOO much will result in detonation, not good. Compensate with higher octane fuel, or just don't touch timing at all.
"Rockit" keys (in general, ~10 degrees advanced timing) are out for Zenoah, Chung Yang, and China scooters. Basically, all this does is advance timing for a tad more low end.
BUT, the MORE you advance the timing, the MORE the 2 stroke top end suffers (as in revs). In the last section we mentioned that compression in 2 strokes affect them rather dramatically.
Since the fuel is preignited earlier, it creates HIGHER compression, EARLIER and FASTER than whatever your stock timing was (assuming it was advanced). This in turn, means slightly less revs. Your butt-dyno may not pick up the RPM loss, but it's there, although probably not too prominent.
MSD. What is it? Google it. Don't make me do it for you
. MSD adjusts timing "on the fly". Why is it great for two strokes? Why it's perfect.Imagine 30 degrees BTDC, a general mark for 2 stroke timing. As the revolutions from the motors increase, the timing DECREASES. What does this do? Ignites the fuel LATER, and more SLOWLY. Obviously, you won't be getting MAX power after the retarding of the timing starts, but it will be retarded enough to make crazy amounts of revs.
A MSD kit on a Zenoah G23LH starts from ~30 degrees (set with timing light), and actually lets the motor hit up to 20,000 revs (as it is firing 5 degrees ATDC). Brilliant, think about it! Only downside is, you need a live power source. AKA rechargeable batteries.
Pistons:
2 stroke pistons are a rather tricky part to talk about. Multiple designs are made, and for different purposes. Some delibretely have a large slope up to aid the transfer scavenging of the cylinder, some are standard domed pistons.
2 rings increase compression, the second ring acting as a "Secondary defense" mechanism, and reduce blowby. However, these pistons suffer large drag from the friction of two rings.
One ring pistons, albeit a slight compression loss and a possibility of a lower life (depends on material, lubrication, thickness, ect, ect).
Lightening pistons... yes, it does make a difference. HOWEVER, do not lighten the skirts in EXCESS. Not only do you weaken them (and since the skirts prevent side/side movement, it may cave in slightly, and instead of keeping the piston straight in the bore, may whack around the bore and destroy the bore itself - and NiKaSil or industrial chrome plating is NOT cheap).
Balance the piston out afterwards, to ensure equal amounts of material removed. You can lighten with anything from a lathe, to a manual mill, to a dremel.
Another trick is to window the pistons, which I will discuss later.
Crankcase:
People love stuffing. What is that? Decreasing crankcase capacity, and thus increasing how much pressure the air/fuel mixture is under before it is shot up the transfers. This "in theory", is said to increase torque.
People do this with anything from JB weld to other epoxies, sometimes even with added ingredients such as cork or bits of aluminum or steel.
Watch out though, almost all contents of gasoline contain ethanol now. 10-20% generally. JB weld is NOT ethanol soluable... it WILL slowly erode away. I wouldn't be using large chunks of metal or abrasive bits if you decide to stuff (I am completely AGAINST stuffing, but mainly depends on stock crankcase volume).
JB Kwik uses a different formula, nobody has tested that yet, so, dunno. Can probably use some modern gas-tank sealing epoxy to stuff if you wish.
Full circle crankshafts also increase crankcase volume, effectively. Some are only "Half moon" (think about it). Some use plastic stuffers (which, are usually melted and glued in).
Another trick is to replace your bearings and SEALS, with SEALED bearings. Sealed bearings are your standard bearings with two dirt/dust seals on BOTH sides.
Take in mind, these seals were NEVER meant to take pressure, at all, (which the piston creates as it moves to BDC). Keep both seals on, and lube with the right grease.
Keep the ABEC rating above 3, 3 being the absolute minimum. If it does not list the ABEC rating, do not buy it. No china bearings, at ALL. Buy from known Japanese brands, NTN, Koyo, ect.
...Gotta go for now. Will write more on porting, pipes, transfers, dome... blah later. Mebe sum pix
