Over heating!

Hey people
What are the most common problem causing overheating??
Or should i say the worst source that overheats the engine?
I have fittet a new piston an bored out my DT175 engine after i assembled it
i soon discovered that it ran awefully hot. After about 5 min it got too hot
to touch and if i spit on it then it vaporized off right away.
the exhaust system looks like it is leaking but i don't think there is
anything leaking in the intake side of the engine.
There is a small 2 stroke oil pump to mix it up. Im not sure how it should
be set. i have been changing the settings. then bike has been in the garage
for about 2 months.

Andras

 

Lean fuel/air mixture and riding slowly, or running the engine for a
long time without moving air over the fins...

It's an air-cooled engine. It will run about 350 degrees F, so the fact
that spit boils off quickly is no surprise. You can tell if the engine
is really overheating by pinging noises that sound like loose valves on
a 4-stroke engine...

The engine will ping when you try to accelerate. Overheating 2-stroke
engines will rev up very high, but won't feel like they have any
power...

Also, the spark plug might show little black specks like pepper on it.
That's carbon that has flaked off the top of the piston and melted on
the spark plug...

Air-cooled engines aren't just cooled by air flowing over the fins of
the cylinder and the head. Engines are also cooled by rich fuel/air
mixtures. All internal combustion engines waste fuel to cool
themselves, otherwise they'd melt....

To find out if your engine is getting enough gasoline to keep it cool,
you need to do a "plug chop". I just described that this morning. Do a
google search for "spectraltarsier@aol +plug chop"...

One time I helped some guys prepare a 3-cylinder liquid-cooled 2-stroke
motorbike for a 6-hour endurance race. It was very fast, but the
exhaust note sounded strangely *sour*. That's the only way I can
describe it. Our rider went out on the race course to qualify the bike
and it was beating all the 4-stroke motorbikes. Then it didn't come
around again and we saw our rider pushing it...

When we took the spark plug out, it was full of melted aluminum from
running too lean. We took the head off to see what damage had been done
to the piston.
It had a hole melted in it. I pushed on the top of the piston to see if
it was seized. The piston moved, even though the crankshaft wasn't
turning. I knew then that the rod was broken from when the engine
seized. When I took the water pump apart, I found that it was full of
some kind of radiator stop leak compound and wasn't pumping any
water...

I know that your engine is air-cooled, but that story just tells you
how hot an engine can get and what happens when the piston starts
melting...

If you find tiny little silver balls of aluminum in your spark plug,
you're melting the piston from overheating, lean mixture, or advanced
ignition timing...

Two stroke exhaust system do leak often, because they use a labyrinth
seal without gaskets. Excess oil in the exhaust port can be seen
leaking around the
labyrinth seal or you might feel hot exhaust blasting around the
labyrinth seal. If most of the exhaust is going out the pipe, you're
OK...

As I recall, there were punch marks on the oil pump cable drum and you
were supposed to rig the cable so the punch marks lined up when the
throttle was closed...

Did you ever get your exhaust ports chamfered properly so the rings
didn't make a lot of noise?

 

On a two-stroke, instant recipe for a holed piston.

If it's the MX bversion, electronic ignition, so unlikely. Possible on
the older points-ignition engine.

It's air-cooled.

Heh

I don't think there's anyuthing wrong with his engine at all, to be
honest.

 

Uhhhh, oil is important. I have 2 of these bikes. Run the oil hose from
the pump (the hose should be clear platic so you can see the flow) to the
carb.

This hose runs to the brass fitting nearest the cylinder on the right side
of the bike.

If the hose is full of air, start the bike and then pull the cable running
to the pump, you should be able to watch the oil flow to the carb.

Does you tach work? It runs on the same gear as the oil pump.

Good luck, there is excellent help at vjmc.org maillist for DT175s.

Bryan

 

Perhaps not, but he nearly says it's running hotter after boring the
head than it had been. More air into the cylinders, more fuel needed.
Since it's been sitting awhile, the combination of a need for more fuel
+ partially plugged fuel passages sounds like a possibility. I'd put my
best guess on it needs a little more fuel.

If the old piston was holed, that might tend to confirm the guess?
[/QUOTE]
Indeed it would. Doing a plug chop would be the first port of call.

 

Not sure, but I think "too-high oil level" may be on the list.

 

This motorbike is a 2-stroke. It doesn't have any oil in the crankcase,
except for whatever settled out in the very bottom...

You could probably overfill the transmission so that oil was running
out the filler cap, but that wouldn't affects Jimmy Joe's temperature
perception that the engine was running too hot at idle when he touched
the cylinder...

 

Well, I know I am very ignorant about two strokes, but I didn't know I
was _that_ ignorant. I always disliked that 1968 Lawn Boy ...

 

What are the most common problem causing overheating??

Overeating is caused by being too hungry.....or just plain boredom....oh
wait .. you siad overheating.... ah... thats whole nother problem...
How do you know its overheating? Do you have a temp gauge on it? For
example, I have a bike that the oil temp got as high as 250 degrees.... Once
I put an oil cooler on, it now it runs mostly around 180 -190.... and it
seems to run much better too!!

good Luck...

Fwed