Just curious.

[2strokesrock]

I have heard conflicting ideas about what type of engine overheats the easiest. I used to think that Two strokes ran hotter which is why the old ones had such long fins compared to the old four strokes, but I read in post not too long ago that four strokes run hotter then two strokes, making them less suitable for heavy trail use.
Dose it depend opon the bike? Or is it the cooling system?
or Dose one type tipicly run hotter?

Its not an important queston, I'm just curious.

P.S sorry about the spelling.

 

[jsantapau]

I am guessing that since a 2 stroke fires every revolution it will it will have less time for heat to dissipate(sp?)and be more prone to a heat related problem than a 4 stroke if you can get them to be on an even comparison.

modern fourstrokes will tend to boil over quicker because they have twice the displacement for a given class compared to more than likely an overly rich two stroke never really getting hot enough.

an x amount of fuel will only produce so much heat when burned properly after that you have to look at what there is to carry the heat away a four stroke will have oil to help carry the heat away while a two stroke will have a lot of its heat dissipated thru the exhaust pipe

being able to contain as much heat as possible in the combustion chamber to push the piston down without any thermal problems is the whole quest for horsepower

 

[2strokesrock]

Thanks! I understand now :)

 

[jsantapau]

don't go by what I think because I wish I truly understood it :think:

 

[jason33]

2 strokes have more friction, rev quicker thats why they needed the big fins they used them to kool the steel/iron cylinders,and steel rings
otherwise you can seize the piston/rings in there /possibly until it cools again, yea i did that lol , i have found a few things out the hard way

 

[2strokesrock]

I have done that too :) on a hot day in tight trails running a little too lean on a extreamly underpowered air cool 125

 

[aaronnaland]

I dont think they have more friction because my nabors crf250 runs the same compression as my bike and that means the rings are pushing about the same on the cylinder or else it would be leaking more on one. I could be wrong it just seems like they would have the same friction but also older 2 strokes might be different my bike is an 03 with liquid cooled. And for the answer to the original question. Yes 2 strokes run hotter being that they fire 2 times as much at the same rpms. some four strokes are getting hotter tho now they make the motocross fours with liquid cooling.

 

[holeshot]

The early two strokes had fins because this was the day before water cooling. When water cooling arrived, the fins went away.

A water cooled four stroke runs hotter than a water cooled two stroke for reasons that run deeper than anyone has gone so far in this thread. Someone that understands the dynamics that cause this, probably won't post in this thread, because there are too many Albert Einsteins here. :laugh: I sure won't try to explain, because it's deeper than I can go.

 

[_JOE_]

The biggest factor in 90% of modern liquid cooled MX bikes is air flow. At very low speeds there isn't enough air moving through the radiators to pull the heat from the coolant allowing to boil. 4 strokes seem more prone to this boilover than most 2 strokes. I'm sure there is a good reason for this but I don't know what it is for sure, so I'll sit back and hope one of the more informed members can get into it a bit deeper.

 

[XRpredator]

it's not so much air flow (although that's a big factor) as it is surface area. The reason for big radiators is the same reason there were big fins on air cooled bikes.

 

[Patman]

Considering that the greatest trail bikes of all time, the ones that could be ridden for years on end with no more than an occasional oil change happened to be Honda's XR series which are air cooled 4 strokes and the second best might be Kawasaki's KDX which is a 2 stroke of either air or water cooled varity the question seems answered. It doesn't matter. :)

 

[holeshot]

Considering that the greatest trail bikes of all time, the ones that could be ridden for years on end with no more than an occasional oil change happened to be Honda's XR series which are air cooled 4 strokes and the second best might be Kawasaki's KDX which is a 2 stroke of either air or water cooled varity the question seems answered. It doesn't matter. :)

Yeah..but the XR's were "lower performance" four strokes...if my CRF were air cooled, it'd probably end up as a pile of glowing goo. Water cooling allowed engines to be more radical in terms of performance without overheating problems.

Anyway, the reason four strokes retain more heat than two was once answered in some forum here.

But I don''t remember the answer...

Let's not confuse these kids ... :rotfl:

 

[Patman]

Yeah..but the XR's were "lower performance" four strokes...if my CRF were air cooled, it'd probably end up as a pile of glowing goo. Water cooling allowed engines to be more radical in terms of performance without overheating problems.

:laugh: Folks might believe that until they have experienced my Rich Rohricherized XR284. Grady rides the biggest of the water cooled pumpkin thumpers and was quite impressed.

 

[2strokesrock]

If any of you feel like typeing it up I would really like to know why 4 strokes are more prone to boiling over?
Evan if you don't know it all, a little more info would be nice :)

P.S its ok to confuse me :)

 

[dirt bike dave]

My guess is 4 strokes produce more pressure and heat on the power stroke due to much higher effective compression ratios. Plus the lube in the 2 stroke oil helps cool the cylinder.

 

[Vic]

The excess fuel used by a 2t helps to cool it.

 

[holeshot]

:laugh: Folks might believe that until they have experienced my Rich Rohricherized XR284. .

Old thread..but the XR284 was probably a sweet motorcycle ... too bad I couldn't have taken a spin on that baby... :cool:

 

[Patman]

I still have it and it's available to ride anytime. Heck I might even be making a trek to Stillwater this summer :)

 

[AJ Waggoner]

hp=heat

dosnt matter how many strokes.

your XR100 or TTTR 125 is incredibly hard to overheat
in technical trails where there is low airflow over the engine.

a modern 450F isnt that hard to overheat..
even wth its rads ..

the same dispacement 2 stroke with same sized rads typically runs cooler in thoe situations..

(but in those scenerios you are not using all the HP..
and mostly generating heat because of low air flo over the rads)


if both bikes are run at top speed..
where there is plenty of airflow..
then the one making the most hp is going to have to disapate the most heat..

most modern bikes are designed to do that very well with proper airflow over the rads.

get them in the tight trails..
the hi out put modern strokes by design are going to run a bit hotter?

(the off road versions of the MX models typically have larger rads and coolant recovery tanks)