The public's return to 2 strokes

Nobody was buying them, they quit making them.

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I would just like to reiterate here... Over half of KTM's total off-road bikes sold last fiscal year were 2 strokes. In case anyone is mathematically challenged, "over half" means they sold MORE 2 strokes than 4 strokes.

Very good point Rich, and well taken. Judging by the lower manufacturing cost of a 2t, and KTM's high price point, I'd wager they make as much or more profit on 2t sales as they do on 4t's though. You're absolutely correct though, without actual numbers it's impossible for us to say with any degree of certainty.

For me and my budget here is a great reason to stick with the 2 stroke.

Below is a quote from a very well respected source talking about 4 strokes.

"We also worked a lot on engine forensics to get a handle on the cause of catastrophic failure in late model MX engines and what could be done to prevent them. Eric has a wealth of data and experience in this area."

I personally hate to think there is a wealth of data to be had in the area of catastrophic faliure of late model MX engines, but there you go :think:

Ok I have re read his post and apparently the author was talking about 6 or 7 years ago. My bad. Do they still have the problems with catastrophic faliure? The cost of running a modern 4 stroke is one of my greatest concerns. Every time I rode mine I just thought about the dollars, and every time I gave it some decent juice I thought about valve stem stretch etc. and it kind of ruined it for me.

P.S. Please don't ban me.

What is the "public" going to do, if there were no more new bikes available, period? What if, what dealers that are left, only get 1 or 2. Sales figure are not readily available? We obviously NEVER had any say so in what goes on in the industry. So what happens when the big 4 go belly up? We have a front row seat with the auto industry, what about the dirt bikes? 2 strokes, how about no strokes? The rebuild industry will soar. Fixing a clapped out 4 sure seems more solid than the 2 strokes. Has anyone else found this to be true, or just me? Vintage Bob

Joburble said:

. . . The cost of running a modern 4 stroke is one of my greatest concerns. Every time I rode mine I just thought about the dollars, and every time I gave it some decent juice I thought about valve stem stretch etc. and it kind of ruined it for me.

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You're thinking too much. Just go ride

Joburble said:

The cost of running a modern 4 stroke is one of my greatest concerns. Every time I rode mine I just thought about the dollars, and every time I gave it some decent juice I thought about valve stem stretch etc. and it kind of ruined it for me.

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I was the same way for the first two years. Now that it has had a chance to prove that with reasonable maintenance a 250f can run very well and still provide good reliability. Just don't try to run it for two years without tearing it down.

My buddy has a 250 2 smoke that has WAAAAAY more problems than my 250f. Might be because he's afraid to work on it?

Why are 144cc two-strokes not allowed to race in the 250F class? This would totally bring back some fun in the Pro Lites and Junior level racing. Pro Lites is quiet frankly dull as ditch water.
It would be a cheap way to keep privateers in the sport and a cheap way again for people who can nay afford an expensive fourer and maintence to start off in the sport.

I ask again why no 144cc twoers in the 250F class? :pissed:

Amateur and pros have different rules. Around here 250fs' race against 250 smokers, ama racing. I am not for sure where the 144 goes. The new 125 rules are just that, 125's! Who and to what end is anyone going to sponsor a pro rider to campaign a 144 on the national circuit$$$? Vintage Bob

Amateur and pros have different rules. Around here 250fs' race against 250 smokers, ama racing. I am not for sure where the 144 goes. The new 125 rules are just that, 125's! Who and to what end is anyone going to sponsor a pro rider to campaign a 144 on the national circuit$$$? Vintage Bob

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144cc, more of a hypothetical displacement to get my point across.

205fs vs 250 smokers? Can you give an average 4st : 2st ratio in a race for my reference?

If I understand your question, a 2 stroke hypothetically makes 2x the power per CC that a 4 stroke would make. Simply because it fires twice as often.

In practice, it's not that good. A two stroke cannot use the full or as long a stroke, as it has holes in the cylinder walls for valves. A four stroke can also positively expel all exhaust gasses before refilling with a fuel air mixture, so it will get a more complete burn as well.

So at a narrowly tuned RPM range, a 2 stroke will probably make somehthing like 1.7 or 1.8 the power a 4 stroke would make (equal CC). At other RPMS, its probably significantly worse, and at low RPM a two stroke probably makes less power then a four stroke. Until the 4 stroke spins a cam bearing ;)

(Thats engineering intuition, not real math :) ).

Its hard to compare, as it changes so much across the RPM range....

Why does everyone act like a 2 stroke is so much less maintenance than a four stroke?

I hunted down a two stroke after blowing up my 4 stroke (KLR-250, as far from high strung as a thumper ever got).

I can to a TOTAL top end rebuild on my KDX-200 for about $150... the cost of a new piston and rings and small end bearing. I probably spent that much on *gaskets* on the 4 stroke...

_JOE_ said:

Why does everyone act like a 2 stroke is so much less maintenance than a four stroke?

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because they're luddites that cannot bring themselves to embrace technological advancement

reepicheep said:

If I understand your question, a 2 stroke hypothetically makes 2x the power per CC that a 4 stroke would make. Simply because it fires twice as often.

In practice, it's not that good. A two stroke cannot use the full or as long a stroke, as it has holes in the cylinder walls for valves. A four stroke can also positively expel all exhaust gasses before refilling with a fuel air mixture, so it will get a more complete burn as well.

So at a narrowly tuned RPM range, a 2 stroke will probably make somehthing like 1.7 or 1.8 the power a 4 stroke would make (equal CC). At other RPMS, its probably significantly worse, and at low RPM a two stroke probably makes less power then a four stroke. Until the 4 stroke spins a cam bearing ;)

(Thats engineering intuition, not real math :) ).

Its hard to compare, as it changes so much across the RPM range....

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Its the pipe that gives the 2 stroke its power and it can only be tuned over a short range. With a straight pipe a 2 strokes swept volume is from exhaust port closing to TDC which makes the effective capacity of a 250 at around 160cc, thats a 160cc of exhaust gas and intake mixed so its less than 160cc of explosive gases.
It could be argued that a 4 stroke is in the same boat because the intake valve closes long after BDC, bigger cam later closing, thats the main reason bigger cams kill bottom end. Where the 4 stroke picks it back up is at higher engine speeds the inertia of the intake air keeps filling the cylinder whilst the piston is coming up.
A 2 stroke is harder to ride because the power is over a smaller range but as with most things worth doing the harder it is the bigger the reward :) .
Worst part about a 2 stroke is the amount of air filter cleaning required because they pass so much more air that doesn't do any work.

Yeah... I love technological advancement.



I'll make you a good deal on a KLR-250 head... only 10,000 miles on it.

(and you shoulda seen the valves!)

XRpredator said:

because they're luddites that cannot bring themselves to embrace technological advancement

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Well Mr Bear fighter, I haven't laughed so much in ages :eek: You're quite a comedian.

Tom68 said:

Worst part about a 2 stroke is the amount of air filter cleaning required because they pass so much more air that doesn't do any work.

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Yea that's a great reason to buy a 4 stroke, so you can save on maintenance by not cleaning the air filter as much.

Damn, I need some more coffee.

reepicheep said:

Yeah... I love technological advancement.

I'll make you a good deal on a KLR-250 head... only 10,000 miles on it.

(and you shoulda seen the valves!)

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yep, and they did that all by themselves, with no help from you.

actually, it probably was with no help from you . . . you still gotta adjust things, change oil, etc. I mean, heck, it's not like it's an XR :nener:

reepicheep said:

Yeah... I love technological advancement.

I'll make you a good deal on a KLR-250 head... only 10,000 miles on it.

(and you shoulda seen the valves!)

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Advanced tech 4 valves per cyl have been around for 100 odd years DOHC similar and Tmodel fords had a cam lobe sliding on a flat lifter pushing directly on a valve. And they could do it with the basic oils available then.
Joburble I reckon the air filter cleanings worth it but I'll pass on the coffee have a beer with mine.

No argument, I did kill it. The backstory is that I bought a $650 KLR-250 in a bucket, fixed everything broken I could find and scrounged a bunch of stuff off of ebay, and got it running pretty well. At 10,000 miles, the valves had already been replaced once by a previous owner, and the bottom end was rebuilt by a different previous owner (big end bearing probably died).

So I rode it around town, no problems, and did a number of off road rides, some pretty challenging. Kept up on the maintenance pretty carefully... put about 3000 miles on the thing with no issues and no oil consumption. Took it on a trailer with the Buell (sniff :() to Deals gap for a long weekend...

Railed up and down Deals gap 5 or 6 times, great fun. Then did the Cherohola by way of the gravel road... also great fun.

3/4 through the Cherohola, the temp gauge was high. I am riding by myself (mistake number 1). I know the bike lacks a thermostat, I had pulled the tubing earlier and found the gutted shell of the thermostat. And of course the coolant temp sensor was burned up... I bought a new one ($60, sigh) when I found the original dead, and that died in about 500 miles. God bless Kawasaki. So the fan was run off a switch. Throw the switch on (it was never needed before for street riding) and keep riding.

Hmmm. I am still in the middle of freaking nowhere, and it's getting hotter. Finally get off the gravel, bang a right on the Cherhola to get back to Franklin, and pin that poor things throttle up and down several mountains.

At this point, it is getting close to dark. And there appears to be one HECK of a thunderstorm coming. And there is NO cell phone coverage. No good options... keep pushing. The temp gauge is right on the edge of red right now.

I figure the previous owner didn't remove most of the thermostat, it must have disintegrated in there. Push on back to the tools before it overheats. Heck, screw that, just get the stupid thing back to the trailer and get on a real bike (the Buell). It was fun to embarass the busa guys for a day, but 65 MPH WFO is getting pretty tedious.

Crap. I'm loosing power. Double crap. It is an absolute frog choker of a downpour, complete with lightning, and I am in the middle of freaking ***nowhere***, and it's getting dark fast.

Puph. Out comes the magic smoke. I *just* get to the gas station, coasting to a stop and trailing oil. Ironically, as I get off the bike, I see the "DOHC" plate fall off my head. She's dead jim.

I then do what I should have done earlier (though I don't know what I would have done when I found it) and check the oil level. I started the day, about 300 miles ago, with a topped off and checked oil tank. Now? Dry as a bone. triple crap. Crawl into the gas station, get two quarts of oil, pour it in the smoking oil fill hole, and kick it over. It runs, but with little power and it sounds like a blender full of quarters.

Limp back to the hotel, pull the cam cover just becuase I am curious, and see the picture above.

I have plenty of guilt. I should have checked the oil at the first sign of overheating. But the bike gets some guilt as well... it never burned oil before and it was topped off *that* morning... less then 300 miles ago. Whoda thunk?

I *think* I had a head gasket failure, that lead to be blowing all the coolant out, which lead to the overheat, which vented all my oil.

No whining... I man'd up and just fixed the thing. But I learned a few lessons....

1) A dirt bike is fun to play with on the street for a while, but it's a novelty that will pass. Between burning up motors and ruining perfectly good knobbies, it's a pretty damn expensive form of entertainment. A good and fun street bike (like a Buell XB9SX) is even more entertaining, and will go 50k miles with only minor maintenance.

2) Thumpers (and two strokes) live hard and die young. My Buell (two 500 cc air cooled engines siamesed) somehow holds up for 30 k miles (and counting) with nothing but a sheared exhaust stud (resulting from a lost bolt that was probably my fault). The KLR-250, a fairly reliable flavor of thumber, had already have valves and crank rebuilt at 10k miles... before I burned up the head.

This isn't a slam on thumpers... its a 250 pound bike going all out to make decent power, and half the time it's crawling up some 50 degree hill side covered in 2" of slimey clay on a 95 degree day. It's gonna have a hard life.

After a season (or three, since I have kids and won't get to ride a lot), I'll drain the coolant, remove 4 bolts from the base of the cylinder, and two bolts from the motor mounts, and pull the whole head and cylinder as a unit. Then I'll pop off the circlips, put in a new piston, rings, and small end bearing, and bolt it back together. Two hours tops, and thats with the kids helping ;).

No valve adjustments. No stretched cam chain. No worn valves. No oil levels to check. No butter soft aluminum cam journals (what were they thinking?).

Nothing against four strokes... my neighbor has a CRF-450 that is an incredible little bike. But my $850 two stroke is awful nice as well, and *so* easy to maintain, and a lot lighter and simpler. So nothing against two strokes either... especially for playing in the woods.

reepicheep,
sorry to read about the death of the KLR. With the effort you put into the bike when the previous owner just left it in pieces on the floor deserves more than that.

PS. Real sad to hear about Buell. Erik Buell seems like a top geezer. He should buy the company back.

I restored it back again to be a solid runner, and sold it to a good home. It was straightforward, but restoring the 4 stroke was too much work, which is why I sold it to buy a 2 stroke for woods riding ;)

Right now, Harley won't allow Buell to be sold to anyone. They are saying it will be shut down and will not be sold to anyone. Ironic, considering the *only* reason Harley Davidson still exists is because AMF allowed Harley to be sold, rather then just killing it.

Hopefully, public pressure, common sense, and angry stockholders get Harley to "rethink" their decision to kill the American dream.

The American dream died when they sold off to AMF. Since then its for the Luddites! I did steal that from Xavira, Thank you!