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

[Chimpo]

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.

http://spookytoothcycles.com/compon...page=vmj_ace.tpl&product_id=580&category_id=6


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?

 

[spad4me]

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.

 

[cobrafreak]

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

 

[retromike3]

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.

mike

 

[motorpsycho]

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.

 

[Old Bob]

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.

http://spookytoothcycles.com/compon...page=vmj_ace.tpl&product_id=580&category_id=6


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?

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.

 

[Skyliner70cc]

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.

 

[wheelbender6]

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

 

[Chimpo]

That clears it up. Thanks for the responses.

 

[HeadSmess]

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.

mike

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....