2 stokes need to "cool off" every 30min??!

Discussion in '2-Stroke Engines' started by Chimpo, Jan 11, 2011.

  1. Chimpo

    Chimpo New Member

    I was flipping through the bikes for sale at spooky tooth and came across the following statement that had me going wtf?!

    "A 4 stroke doesn't need to cool off every half hour like a 2 stroke engine does, so you can run a 4 stroke all day long, even cross country."

    Here is the link to the ad I saw it in. Its about 1/4 of the way down the page.


    I've been reading the MB forums and retail sites for a while now. This is the first I have heard of a cooling off period. I didn't see it in my owners manual either.

    What gives?

  2. spad4me

    spad4me Member

    Spookytooth is in a place that gets 120 plus in the summer.
    Very nice in the winter though.
    I have encountered cooling problems in the summer in BHC.
    When I used a happytime 2 stroke
    Use a good brand of Castor / synthetic air cooled engine oil in the summer.
    Blip the throttle to keep the cooling oil flowing in a two stroke.
    Do not let a hot engine idle for long, like at a stop light.
    Coast going downhill, Pull the clutch in to keep the forced revolutions of the engine down..
    I NO longer use a happytime in any motorized bicycle I build.

    All of the engines I use now have an auto clutch and a COOLING FAN built in.
    They still warn you to let it idle for a minute to fan cool the engine before shutdown.
    Last edited: Jan 11, 2011
  3. cobrafreak

    cobrafreak New Member

    The fuel and oil mix cool down a two stroke as well. Run it on the rich side in hot weather for cooler running. A laser thermometer is a great tool to have. Harbor Freight has them for about 10 bucks. 250 degrees or lower on the head and you are doing good. If you are hotter, go up a jet size and take a new reading. The temperature will be lower. High temp = short life
    Last edited: Jan 11, 2011
  4. retromike3

    retromike3 Member

    cooling Why?

    when you first brake in the 2 stroke motor you need to run it at small bits for the first fifty miles or so so maybe that's were you get that Idea. The fact is that there is thousands of detonations going off in your engine and the outside air temp has some but not a major effect on the heat generated by your engine. These are air cooled engines that explode at each stroke so I am sure they do get hot. I never had a problem with any of the other two stroke motors that I have used on a hot day.

  5. motorpsycho

    motorpsycho Active Member

    Yes, when you break in a new 2 stroke, you are supposed to (according to the book anyway) run it for about 30 min. and then let it cool fully before you run it again. This is to allow the cylinder to expand and contract in a certain way so the rings will seat correctly.This only needs to happen for the first tank of gas or so,according to the things I have read.

    On the other hand, if you really think about it, IF this is what you are supposed to do, you should rotate the crank so that the piston is at at b.d.c. every time you shut the engine off during the break in period. This would leave the cylinder "open" to contact all the way while it's cooling down. If the piston is in the center or top of the cylinder, it would not contract "true" because of the piston rings. (in theory)
    This is what you are supposed to do with a nitro r/c car engine every time you finish running the engine for the day. Putting the piston at b.d.c. allows the cylinder to contract "true". The piston could cause the cylinder to become mis-shapen if the cylinder cools with the piston in the middle or top of the cylinder. Yes, I know that r/c pistons do not have rings, but it's the same principle as with a 2 stroke.

    IF it is true that you have to let a 2 stroke cool down every 30 minutes, I have no idea how landscapers can get anything done. They run their 2 stroke weedeaters literally all day long.
    I think the statement has to do with initial break in, and the fact that it gets 120 degrees where spooky tooth is at.
  6. Old Bob

    Old Bob Member

    In general 2 strokes do not suffer from heat build up as 4 strokes do. A 2 stroke with proper lubrication can and will run at max power for hours on end.
  7. Skyliner70cc

    Skyliner70cc Active Member

    If 30 minute cooloff is good then isn't a cooloff every 15minutes better? If not, please apply the same logic to those who insist on running 15-20:1 oil ratios.
  8. wheelbender6

    wheelbender6 Well-Known Member

    I agree with Retromike3. The 30 minute rule applies to the break-in period only.
  9. Chimpo

    Chimpo New Member

    That clears it up. Thanks for the responses.
  10. HeadSmess

    HeadSmess Well-Known Member

    i like this thinking.

    the flame front, combustion, whatever, in the cylinder? in the 800 degree range... a few degrees either way on the outside arent going to hurt the engine.

    a big issue is the change of fuel mixture from the change in air density. bernoulli's principle, and the venturi effect. works to give an overly lean condition that does result in too much heat and a siezed engine...

    this is why small aircraft have head temp guages and easily adjusted mixtures... altitude also affects air density.

    and theres a point. most ultralights use 2 stroke engines and are perfectly happy running all day... sure its cold up there, but hey....
  11. PhoobarID

    PhoobarID Member

    I pushed mowers all summer long at the lawn care biz my roommate has & doing a yard by myself takes me about 1.5 hours of running my mower to get it done...then onto the next yard...usually down the street. Same with the weedeater. The only time I would stop would be to refuel. Didn't think anything of it and they're not traveling at 20-30 MPH like the bike is.

    As for the bikes...got a friend of mine who runs 40 miles one way over small hills...but he's pedaling to get over those hills. Told me his trip takes between 1.5-2 hours...according to how hard the wind is blowing. He's made this trip several times to see if he could. His bike is still running. We can't wait to get mine built next month and for it to get warmed up. ROAD TRIP!!!

    Used to live out in Kingman/Bullhead City and used to ride an 850 in the summer. Was riding one day it about 125-130 and when I stopped...the wheels would leave indention's in the pavement where I stopped. You also find out there they have steel plates where the bikes park to keep them upright. Thank God for Idaho...don't have that worry and it's a pleasure to ride during the summer...but hate not being able to in the winter.
  12. DuctTapedGoat

    DuctTapedGoat Active Member

    Ohh, c'mon Phoobar - Idaho riding is great in the winter... except for when it rains in January like it's been doing all week...
  13. PhoobarID

    PhoobarID Member

    Used to ride a 450 in snow storms and almost froze my fingers off on an 850. I much prefer a a warm cab than a frozen seat. On the other hand...did find my gauntlets...so whenever I get it built/broke in...I'll be ready.

    As for raining...had hardly any all week in the Magic Valley. Just is overcast like it wants to do something.
  14. DuctTapedGoat

    DuctTapedGoat Active Member

    Wow, lucky! Treasure valley hasn't been that way, rain almost every day for a week! Someone should make heated handlebars off the exhaust...
  15. PhoobarID

    PhoobarID Member

    We even had clear skies earlier in the week.:devilish:

    Shouldn't be too hard. Seems like running a small pipe hooked to the air shield on the muffler to the handle bars should take care of that. You could probably re-route a muffler to take the place of your handle bars for winter driving and normal bars for the rest of the year. Or another better way would be to dip your gloves in that chemical that fire eaters use...light up & stay warm the whole trip.

    Of course...I can continue and get more Rube Goldberg-like.:evilgrin:
  16. DuctTapedGoat

    DuctTapedGoat Active Member

    LOL, if you put two and two together, you can have flaming hands AND flames coming out the sides of your handlebars!!
  17. PhoobarID

    PhoobarID Member

    If we were looking for perfect...could always do a reenactment of Nicholas Cage riding the MC from ****.:devilish:
  18. Skyliner70cc

    Skyliner70cc Active Member

    I've done 6 hour rides (about my max before my saddle and wrists tire from the vibration) and in those 6 hour rides have never shut the engine off. I'd typically stop every hour for a break and leave the HT engine running at idle for my breaks, sometimes up to 30 minutes when I'd stop and eat lunch. My rides were often in remote mountains areas and I'd be SOL if my engine died. I'd leave the engine running because I didn't want to risk the engine not being able to start if I shut it off, particularly at the higher altitudes.
  19. PhoobarID

    PhoobarID Member

    That's what my buddy would do on his 80 mile round trip to see his parents. Am happy to hear that others do this as well.

    Thanks for posting. Am getting more and more excited as the time to get my engine comes.