2 stroke technology as compared to 4 stroke

[RIDE-RED 250r]

Still haven't got your quad back eh Joe?? That sucks! Here's still holding out hope for ya... BTW, good post...other than the stolen quad part...

[yaegerb]

Maintenence is more expensive on the new 450s, that is true for sure. I got a ridiculous deal on a full mx ready 08 yfz this year with a motor in a box. I bought it because I have a rebuilt yfz motor that has been stolen from me along with the rest of the quad, and I hoped that I would be getting it back this summer. I haven't gotten it back yet, it's a whole other story, so I took the mx motor in to my shop to get it checked out. It came with a new piston and top end gasket kit, I was hoping it could just be put back together and I'd be good to go. Well, it was a race motor and even though it didn't blow up it needs practically everything. The timing gear on the crank was getting wore into or something so it needs a new crank. Needs a ton of bearings, all the valves are out of spec, it came out to around $1500 in parts and like 250 for labor. I picked it up and payed for disassembly, I couldn't swallow that bill. And thats not including the price for a new piston because I had one! They said a yfz came in last month that needed a a rebuild and a new head, that guy ended up doing the same thing I did. I still think the 450s last longer than 2 strokes though, there are examples of each motor that have been together for many years with good maintenence and still run good. But I would like to know where you guys are getting cylinders replated for 140, that's a really good deal

Agreed, that is a CHEAP nikasil price.....spill the beans guys

[oldskool83]

Agreed, that is a CHEAP nikasil price.....spill the beans guys

powerseal in PA and eric gorr racing. just email or go to their web sites. eric gorr did my last motor and it was about 140 for welding rebore and replate.

[yaegerb]

powerseal in PA and eric gorr racing. just email or go to their web sites. eric gorr did my last motor and it was about 140 for welding rebore and replate.

Wow, that's competitive pricing. Is that nikisil on any size bore or is it more for bigger bores?

[86T3]

You must be better friends with him than I am, it says $180 for 50-150cc and $250 for 175cc and up on his site. I still think 250 is a reasonable price though, and he does quality work

[86T3]

Power seal is $184 for a replate. http://www.powersealusa.com/prices/

[oldskool83]

I had other work done so maybe that's why I got it cheaper not sure. All the dealers around me use power seal but I like EGR due to him being able to port and redone the heads also in 1 place, kinda nice he was factory yamahas engine builder thru the good years too.

[JesseA420]

great thread.

21st century 2 stroke technology is easily obtainable now on our 30 yr old bikes thanks to cp cylinders and the amount of knowledgeable builders specializing in 250r and banshee based motors today. to the folks that prefer 4 strokes with the argument "they simply can do everything, compared to 2 stroke" has never rode a properly setup 70+ hp 250 based bike with a broad power curve. along with the power to weight ratio and the power per displacement ratios, they are just as capable, just as reliable, and light years more fun. if you're not riding for the fun and the thrill, what are you riding for? for clarity this is excluding work purposes.

[RubberSalt]

Unfortunately, Jesse, It's not as simple as that. Forced oiling and fuel injections are a couple things we can't easily adapt to our old machines. When oil is being pumped through the crank, and into the bearings, that's something we can't easily adapt. Once you switch to this set up, you also can't switch to any off the shelf 2 stroke oil. Viscosity comes into play now.
Fuel pumps alone also require more power than most stators can put out.

Many of the cylinder's arn't offset either, but this can be corrected with the CP Cylinders.

I'd love to see direct injected 2 strokes. There's plenty of room in the dome. Think of how much the pollutants would drop then!. Next to nothing due to the oil injections, and incredible efficiency due to direct injected fuel. Gasoline would no longer be pulled into the pipe. Just air and exhaust gases.

We can reach the same power levels, but pollute a bunch more.

[JesseA420]

i obviously was talking about modern port tech, not direct injection.

[RubberSalt]

Even our port work hasn't changed drastically. We're a little more refined, but that about it. Our 125's hit a pinnacle in 98. KX250s were pushing 50+ hp from the factory in the mid 80s. The difference, is manufacture's are consistently producing the same power from machines. We've got better metals.

Powervalves originated in the 80s. Pipes made good power then. Pipes make better power today. Our head's have gotten better designs since the 80s, more refined today. Almost every aspect is better today, but not astronomically better than it was 30 years ago. We're not making much more HP, but more usable power now.

Lets take a look at the YZ125. The older information is more difficult to find. This should be fairly accurate though. It shows how we still use similar technology in one of the ever evolving engines introduced.

1974 - the OG, the YZ125 - air cooled Used a 7 port design
1977 - 56x50 bore x stroke - 32mm carburator
1980 - 33hp - air cooled
1981 - 33hp - liquid cooled
1982 - Power Valves added
1985 - 9 port design
1986 - 10 port design
1989 - plated cylinders - 9 port design
1990 - Stroke increased to 50.7mm
1994 - Stroke increased to 54.5mm, new powervalve design
1996 - 36mm tmx carburator - decreased crank case volume - redid the intake tract and air filter. - 7 port design
1998 - 34HP
1999 - 38mm tmx carburator
2000 - 30:1 oil mixture - Oldest manual I could locate.
2001 - 7 port design
2005 - Got a constant mesh gear box
2006 - 34HP
2013 - 30:1 oil mixture
2014 - 34.01 HP

The HP are claimed levels. The port designs are the number of ports. It doesn't reflect the shape, but you can search cylinders and see how they slowly evolved over the years.

[oldskool83]

Yep, reason next seasons bike for me is a fully built 1987 YZ250 vs a 2002-2004 because it's gonna do the same darn thing, just look cooler lol

[RIDE-RED 250r]

We certainly can greatly reduce emissions with different porting. Look up "stratified" porting for chainsaws. Along with Auto tune found on Husqvarna, and Mtronic on Stihls (both are electronically controlled carbs) these newer saws are more fuel efficient, and put out less emissions. These saws run faster and stronger to boot because the auto tune carbs keep them tuned for peak performance in terms of emissions which gives the side effect of peak running performance. They will adapt to any altitude, temperature, and pressure. Pretty cool stuff really. But i suppose that direct injection 2-strokes probably don't need strato porting as the fuel is introduced directly into the combustion chamber if I understand it correctly.

[El Camexican]

There must be a millions opinions on this subject, but along with them come a million variables as well. My thoughts (which may not be facts) are as follows.

Cost to Power Ratio

Power output plays a huge role in determining the life of an engine. Compare an XR400 to a SX450-F: One makes 30hp and the other makes 70+. Depending on the way either is ridden these next estimated numbers could vary a lot, but generally speaking one will run for hundreds if not a couple thousand hours on a few oil changes and the occasional valve and cam chain adjustment and the other has 15 hour oil change intervals, 50 hour (or less) valve adjustments and will need a piston and rings before the 200 hour mark as well as fancy valves, seats and many other parts soon after. And even if both engines were to wear out at the same time the cost of rebuilding the racer is much higher due to the exotic parts that are required to achieve the power levels it makes.

Now compare the air cooled 125cc two strokes still sold down here and used to deliver pizza with a 125 MX bike. Again, the racer makes more than double the power and wears out a lot faster due mainly to the RPM levels it’s used at and the MX bike will be needing a piston and rings well before 100 hours if run hard.

What doesn’t vary as much in the 4 stroke comparison is the cost of the engine rebuild between the two stroke examples. It’s just a piston, rings, wrist pin and 4 bearings every time. The cost of properly rebuilding race version of an “F” engine is outrageous. They’re also much more complicated and require tools and equipment that many of us don’t have.

As far as the rule of thumb about a 4 stroke needing double the displacement to match the power output of a 2 stroke I think that’s outdated info. A modern 250-F race bike makes more power than a 125 pinger and a 450-F race engine will tear the decals off a 250 two stroke as it wheelies past it. Reliability and cost be damned, modern race four strokes are impressive beasts.



If I weigh the benefits of either design as it applies to my riding situation it's like this...

My outdated KTM 300EXC 2 stroke makes about 50hp and 40 pounds of torque.
The sister four stroke of the day, the 450EXC made 42hp and 38 pounds of torque.


On the 300 I can get up to 150 hours on a set of rings and 300 on a piston. The crank and rod on my oldest engine has seen 3 pistons come and go over the last 7 years of use and is still good.
I see the 450’s smoking by 400 hours of moderate trail/endure riding and then they get sold off for $2,000 rather than rebuilt.

So a top end on my 300 engine costs me about $300 and 3 hours working at a leisurely pace while watching a hockey game and sipping on rum. If I needed to do the crank it would take a day and add another $300.
If I owned the 450 and wanted to do just a piston and rings the cost would be about the same, but I’m sure the time would go up and I may have to lay off the rum to make sure I don’t screw the timing up. Now if the valves and crank were spent things change a lot. Cost would be in the $1,500 to $2,000 range and I’d need to ship the head to the US. My riding time would be diminished as would my bank account, but the engine would likely last me another 400 hours and even more if I would do the rings somewhere around the 200 hour mark.

So up to this point the 2 stroke looks a lot cheaper and has a better bang for the buck, but there are other factors to consider. For example, the cost of the fuel & oil. The following is based on 100 hours of riding at an average speed of 20mph.

300
Fuel @ $2.00 per gallon = 100hours X 20mph = 2,000miles/25mpg = 80gal. X $2.00 = $160
2 Stroke oil cost per gallon = $1.25 X 80gal. = $100
Transmission oil = $10 X once per 100 hours = $10
Total cost to ride for 100 hours is $270

450
Fuel @ $2.00 per gallon = 100hours X 20mph = 2,000miles/30mpg = 67gal. X $2.00 = $134
Engine oil @ $7.00 per liter = 1.5 Liters X 20 hours = 7.5L X $7 = $52
Filter(s) $16 = 5 X $16 = $80
Total cost to ride for 100 hours is $266

So much for better fuel economy and not having to mix gas equating to lower four stroke operating costs. That fancy synthetic 4 stroke engine oil and frequent oil and filter changes the high power thumper needs eats it up.

Consider this as well:

You're stuck in a swamp and overheat and seize your engine. If it’s a four stroke you’d best start walking back up the trail to look for a quad to pull your broken bike out of the mud. If you have a 2 stroke you can just wait 15 minutes for the piston to cool off and kick it loose. Depending on how you ride you may not even notice a power loss and you could keep riding it until your next planned rebuild.

Now let’s say you’re a “ride till it breaks” guy. If you do that with a high powered 4 stroke the moment it “breaks” it will may take the head and cases with it, so your best bet is to part out what’s left on eBay when it happens. If you do this with a 2 stroke odds are the only additional cost to fix it that you’ll incur over a normal full rebuild when it “breaks” is to get the damaged cylinder plated, or sleeved.

Here are a few more comparisons:

The 300 starts first or second kick hot or cold. Kick starting a hot 4 stroke can lead to suicidal thoughts
The 300 weighs less that the 450
The weight of the 300 engine is situated much lower in the frame

So when I add up my two cents of opinion and calculations I think I’m better off spending them on a 2 stroke for how & where I ride and for my level of mechanical aptitude.

[Hurley250R]

There must be a millions opinions on this subject, but along with them come a million variables as well. My thoughts (which may not be facts) are as follows.

Cost to Power Ratio

Power output plays a huge role in determining the life of an engine. Compare an XR400 to a SX450-F: One makes 30hp and the other makes 70+. Depending on the way either is ridden these next estimated numbers could vary a lot, but generally speaking one will run for hundreds if not a couple thousand hours on a few oil changes and the occasional valve and cam chain adjustment and the other has 15 hour oil change intervals, 50 hour (or less) valve adjustments and will need a piston and rings before the 200 hour mark as well as fancy valves, seats and many other parts soon after. And even if both engines were to wear out at the same time the cost of rebuilding the racer is much higher due to the exotic parts that are required to achieve the power levels it makes.

Now compare the air cooled 125cc two strokes still sold down here and used to deliver pizza with a 125 MX bike. Again, the racer makes more than double the power and wears out a lot faster due mainly to the RPM levels it’s used at and the MX bike will be needing a piston and rings well before 100 hours if run hard.

What doesn’t vary as much in the 4 stroke comparison is the cost of the engine rebuild between the two stroke examples. It’s just a piston, rings, wrist pin and 4 bearings every time. The cost of properly rebuilding race version of an “F” engine is outrageous. They’re also much more complicated and require tools and equipment that many of us don’t have.

As far as the rule of thumb about a 4 stroke needing double the displacement to match the power output of a 2 stroke I think that’s outdated info. A modern 250-F race bike makes more power than a 125 pinger and a 450-F race engine will tear the decals off a 250 two stroke as it wheelies past it. Reliability and cost be damned, modern race four strokes are impressive beasts.



If I weigh the benefits of either design as it applies to my riding situation it's like this...

My outdated KTM 300EXC 2 stroke makes about 50hp and 40 pounds of torque.
The sister four stroke of the day, the 450EXC made 42hp and 38 pounds of torque.


On the 300 I can get up to 150 hours on a set of rings and 300 on a piston. The crank and rod on my oldest engine has seen 3 pistons come and go over the last 7 years of use and is still good.
I see the 450’s smoking by 400 hours of moderate trail/endure riding and then they get sold off for $2,000 rather than rebuilt.

So a top end on my 300 engine costs me about $300 and 3 hours working at a leisurely pace while watching a hockey game and sipping on rum. If I needed to do the crank it would take a day and add another $300.
If I owned the 450 and wanted to do just a piston and rings the cost would be about the same, but I’m sure the time would go up and I may have to lay off the rum to make sure I don’t screw the timing up. Now if the valves and crank were spent things change a lot. Cost would be in the $1,500 to $2,000 range and I’d need to ship the head to the US. My riding time would be diminished as would my bank account, but the engine would likely last me another 400 hours and even more if I would do the rings somewhere around the 200 hour mark.

So up to this point the 2 stroke looks a lot cheaper and has a better bang for the buck, but there are other factors to consider. For example, the cost of the fuel & oil. The following is based on 100 hours of riding at an average speed of 20mph.

300
Fuel @ $2.00 per gallon = 100hours X 20mph = 2,000miles/25mpg = 80gal. X $2.00 = $160
2 Stroke oil cost per gallon = $1.25 X 80gal. = $100
Transmission oil = $10 X once per 100 hours = $10
Total cost to ride for 100 hours is $270

450
Fuel @ $2.00 per gallon = 100hours X 20mph = 2,000miles/30mpg = 67gal. X $2.00 = $134
Engine oil @ $7.00 per liter = 1.5 Liters X 20 hours = 7.5L X $7 = $52
Filter(s) $16 = 5 X $16 = $80
Total cost to ride for 100 hours is $266

So much for better fuel economy and not having to mix gas equating to lower four stroke operating costs. That fancy synthetic 4 stroke engine oil and frequent oil and filter changes the high power thumper needs eats it up.

Consider this as well:

You're stuck in a swamp and overheat and seize your engine. If it’s a four stroke you’d best start walking back up the trail to look for a quad to pull your broken bike out of the mud. If you have a 2 stroke you can just wait 15 minutes for the piston to cool off and kick it loose. Depending on how you ride you may not even notice a power loss and you could keep riding it until your next planned rebuild.

Now let’s say you’re a “ride till it breaks” guy. If you do that with a high powered 4 stroke the moment it “breaks” it will may take the head and cases with it, so your best bet is to part out what’s left on eBay when it happens. If you do this with a 2 stroke odds are the only additional cost to fix it that you’ll incur over a normal full rebuild when it “breaks” is to get the damaged cylinder plated, or sleeved.

Here are a few more comparisons:

The 300 starts first or second kick hot or cold. Kick starting a hot 4 stroke can lead to suicidal thoughts
The 300 weighs less that the 450
The weight of the 300 engine is situated much lower in the frame

So when I add up my two cents of opinion and calculations I think I’m better off spending them on a 2 stroke for how & where I ride and for my level of mechanical aptitude.

You forgot the most important part. Two strokes are fun as hell to ride!!!