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With taller gearing, can a cr250 handle 60 mph for 30 minutes

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question is in the title. lets say I do that once every day. How many days do you give the motor? does it even care?

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Well think of it as these bikes are more for motorcross, getting too speed quick for jumping and tight corners. Not meant for wide open throttle for miles. Not that they cant handle it which im sure they can and people do sometimes. But with taller gearing you should beable to maintain a consistant speed with out winding it out, give your gearing a try and see how it feels to you.

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Yes that's not a big deal.

What year cr250? The 1992-2001 (cylinder reed) model doesn't have as good piston life as the 2002-2007 (casereed) model. The intake port on the 1992-2001 (cylinder reed) model is large which doesn't offer much support for the piston skirt. Not a big deal just something to know if trying to run a piston beyond its intended life.

In regards to how long the engine would last, it could easily go a summer on a topend if it is a street driven machine.

If it is a race scenario & you are after top performance, the topend should be serviced when there is a drop of 10psi in the cranking psi.

Something like 15/48 gearing running at 60mph in top gear wouldn't be a big deal.

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I'm sure he is looking to convert the bike to being street legal. The 60mph for 30 minutes could be his commute to work.

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Think of supercross and moto-cross bikes as relay runners, or sprinters, quick burst of speeds and then pulling back on the throttle, a enduro 2-t is close to supercross and moto-x bikes, but can be run in longer burst of speed, If you choose to go this route, port the engine accordingly, buy some radiator fans, and hope to god you dont melt that piston.

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Think of supercross and moto-cross bikes as relay runners, or sprinters, quick burst of speeds and then pulling back on the throttle, a enduro 2-t is close to supercross and moto-x bikes, but can be run in longer burst of speed, If you choose to go this route, port the engine accordingly, buy some radiator fans, and hope to god you dont melt that piston.

going at 60mph the fan will be pointless. I won't run the cr250 on the highway as I learnt there isn't a way to make it do that reliably.

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Yaps at it again! [emoji57] what happens when you gear it for the road, then you get in the woods and stall everywhere? Just a thought im sure u kno tho.... Just a thought.

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Let me clairfy that yap, yappers. You will need the fan for traffic, or after that run you will cook your engine, im talking about the complete operating span, from when you start that puppy up, until you switch it off.  I know dam well that engine is not for highway use, its for close course off road competition, a quick side note,,,,,,,,A kx-80 was run at bonniville salt track, and it ran sucessfully wide open, read up on it!

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The bike can reliably be run on the highway. The highway has a surface with an easy rolling resistance, plenty of airspeed to cool radiators & is driven in a more tamed fashion than moto. Ofcourse being geared & tuned properly also matter. Sitting in a traffic jam at 90° is going to be an issue but that is rough on pretty much anyyhing.

A mud race is WAY worse for potential problems on an mx bike. Low speed, high rpm, heavily loaded engine with a mud fouled radiator adds up to a heavily taxed, hot running engine.

Edited by KPRacing
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Yaps at it again! [emoji57] what happens when you gear it for the road, then you get in the woods and stall everywhere? Just a thought im sure u kno tho.... Just a thought.

I wont gear it for the road, I will restrict my riding to 10 miles distance using back roads at 40 mph

 

Let me clairfy that yap, yappers. You will need the fan for traffic, or after that run you will cook your engine, im talking about the complete operating span, from when you start that puppy up, until you switch it off.  I know dam well that engine is not for highway use, its for close course off road competition, a quick side note,,,,,,,,A kx-80 was run at bonniville salt track, and it ran sucessfully wide open, read up on it!

Good point, but where I am there is not much traffic, and most of the time no traffic at all. For city use I see your point. I wont use it for the highway and I wont gear it higher or detune it.

 

The bike can reliably be run on the highway. The highway has a surface with an easy rolling resistance, plenty of airspeed to cool radiators & is driven in a more tamed fashion than moto. Ofcourse being geared & tuned properly also matter. Sitting in a traffic jam at 90° is going to be an issue but that is rough on pretty much anyyhing.

A mud race is WAY worse for potential problems on an mx bike. Low speed, high rpm, heavily loaded engine with a mud fouled radiator adds up to a heavily taxed, hot running engine.

I am getting confused now, what you are saying makes a lot of sense in my head, but my head isn't qualified.

I don't know jack shit about what a cr250 engine can and can't do. If there are ways you can 'tune' it to run reliably on the highway then please share, I would be interested to revisit the idea of a cr250 dual sport, I can carry 2 countershaft sprockets, no problem.

There isn't a traffic jams where I am at, worst case scenario you get a tractor going 40 mph and cars line up behind it.

It makes sense that an engine running at 4000 rpm getting wind at 60 mph should run reliably, but others say that you can't run a two stroke at a constant rpm and it can't cruise??. I don't know if they are talking about 2 strokes in general or about the cr250.

I have owned a honda dio scooter when I was 12 and kept running it at max rpm at 60 mph for very long distances without problems.

 

 

Those are the roads over where I live

070807_32_USA_PA_-_Roads_of_Pennsylvania

Edited by Yap Yap
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There is lots to consider with reliably putting a motocross bike on the street. Two strokes by their nature are far more fussy to ambient temperature than 4 strokes.. You can warm up the engine and have everything expand to operating clearances, then run it through 4 gears down the road on a cool morning and have those rads quench the coolant so fast that the cylinder will shrink and cold seize the piston... That is why dual sports have thermostats in the cooling system. Oil injection is also used for engine longevity, and have direct oil feeds putting straight oil right to the bearings. This system gives much more residual oil to the races than premixing does, which works better for long periods of high engine speeds.

Also the transmission will take a pounding without a cushion drive rear hub, seeing as the drive chain will "whip" constantly from the positive traction on the road. It would be like constantly beating the gears back and fourth against each other, and beat the clutch cushions up. Sure it will work, but don't expect it to last for years without wearing out parts. And stock aluminum rims will fatigue quickly causing spokes to come loose often.

Edited by HRC4
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For roads like that mr yap yap, you only need one bike, nothing else, become a man! Ride this, and stop messing with single cylinders!📎easy_rider_bike_auction-1.jpg📎South_Park_Harleys.jpg📎Jennifer01_03.jpgChic not included on the last picture!    Nuff said!

I almost fall asleep on those roads, and I mean literally fall asleep. I only use them to get to the interesting stuff. I would love a Husqvarna Nuda 900R for the street. I got my first real bike at 16, it was the Hornet 600, I crashed and broke my leg less than a week after I got the bike. My stupidity and street bikes don't get along well. I get bored on the street so I tend to go really fast to stimulate myself. Twisties are fun though!

Edited by Yap Yap

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Thermostats are to get the water temp up quickly so the engine internals get up to operating temp quicker. Once the coolant is to temp (with or without a thermostat), the coolant is stabilized at that temp. The only exception would be if the bike was stopped & let idle for an extended period. Driving down the road will not cause a sudden drop in coolant temp & cold seize the engine. If that were the case, it would happen to an mx bike too.

The reason race bikes have premix is because it is a way more effective way of oiling the engine. A premix will lube an engine much more thorough than an oil injected engine. Anywhere the premixed fuel goes, oil goes. The entire internals of the engine are much more saturated with oil in a premix setup. This is why all high performance high stressed engines are premix.

Oil injection is added to street & trail machines because it is easier for a consumer to pull up to the gas station & simply add gas & go. Oil injection is not fast enough to accurately keep up with engine rpm. It is a good system but not as good (in terms of oiling the engine) as a premix.

Basically get the gearing correct. This would be around 15/48 with an 18" or 19" rear wheel.

The next thing would be to get the jetting correct. If the bike is just cruising on the street, the jetting will be a touch leaner (one or two sizes on the main) than if the engine is being run hard (extended full power pulls).

Run a good high performance transmission fluid & you will he fine. If you are installing the engine in a duel sport bike, it may have a cush drive rear hub. If not, it wasn't a big deal anyway. The transmission will hold up fine.

Edited by KPRacing
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Thermostats are to get the water temp up quickly so the engine internals get up to operating temp quicker. Once the coolant is to temp (with or without a thermostat), the coolant is stabilized at that temp. The only exception would be if the bike was stopped & let idle for an extended period. Driving down the road will not cause a sudden drop in coolant temp & cold seize the engine. If that were the case, it would happen to an mx bike too.

The reason race bikes have premix is because it is a way more effective way of oiling the engine. A premix will lube an engine much more thorough than an oil injected engine. Anywhere the premixed fuel goes, oil goes. The entire internals of the engine are much more saturated with oil in a premix setup. This is why all high performance high stressed engines are premix.

Oil injection is added to street & trail machines because it is easier for a consumer to pull up to the gas station & simply add gas & go. Oil injection is not fast enough to accurately keep up with engine rpm. It is a good system but not as good (in terms of oiling the engine) as a premix.

Basically get the gearing correct. This would be around 15/48 with an 18" or 19" rear wheel.

The next thing would be to get the jetting correct. If the bike is just cruising on the street, the jetting will be a touch leaner (one or two sizes on the main) than if the engine is being run hard (extended full power pulls).

Run a good high performance transmission fluid & you will he fine. If you are installing the engine in a duel sport bike, it may have a cush drive rear hub. If not, it wasn't a big deal anyway. The transmission will hold up fine.

Cold seizing is a common issue with motocross 2 strokes, especially where I'm from. Thermal expansion happens fast with aluminum engines, and that goes both ways. Air cooled bike are notorious for it, and a liquid cooled bikes that are drawing in huge gulps of cold air into the crankcase and radiators that blow out tons of heat at 60mph definitely are subject to a cold seize because of it. I've also personally seen pitted transmission gearsets on street converted super moto bikes that always had ritual trans oil maintenance because of chain whipping at high speeds... Do what you want, it's not my bike.. 

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This is the internet at it's best. You can't learn something because people are arguing and saying the opposite of what the other person says.

I appreciate all the comments though.

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