How do you "tune up" a hard-to-start Craftsman 18" chainsaw

Worth noting. There are actually two sparks, per fire. One spark is at
TDC when the gasses are compressed. The second spark is also at TDC at
the end of the exhaust stroke. The second spark is wasted, but does no
damage.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"Steve B" > wrote in message
...

> The spark ignition happens at the top of the compression stroke TDC
> (valves closed). When fuel/air is compressed and fired piston drops
> to BDC ready for the exhaust stroke (valves open). No?

No. Spark happens, piston travels to bottom, on the upstroke, the
exhaust
valve opens, piston comes up, pushes out spent gas, at TDC, intake
valve
opens, piston drops pulling in air, comes up on compression stroke,
and a
few degrees BTDC, fires again. One spark per two full revolutions of
crank.

Steve

Thanks for the link, that's fun.

If you want to talk with other mechanics, it would be wise to call the
compression and power strokes different things. The compression stroke
is the one before the power stroke.

Intake
Compression
Power
Exhaust

(in that order)

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"Oren" > wrote in message
...


The four strokes of a four stroke engine in living ASCII art

http://www.repairfaq.org/samnew/lmfaq/lmtfsofse.htm

I still call the compression stroke the power stroke --even if firing
at BTDC or TDC. I think we get it.

"Steve B" ) writes:
> "Oren" > wrote
> .
>>>

>>
>> The spark ignition happens at the top of the compression stroke TDC
>> (valves closed). When fuel/air is compressed and fired piston drops
>> to BDC ready for the exhaust stroke (valves open). No?

>
> No. Spark happens, piston travels to bottom, on the upstroke, the exhaust
> valve opens, piston comes up, pushes out spent gas, at TDC, intake valve
> opens, piston drops pulling in air, comes up on compression stroke, and a
> few degrees BTDC, fires again. One spark per two full revolutions of crank.


Simple small four stroke engines (lawnmowers etc.) spark every crank
revolution. The spark is usually triggered by the crankshaft on small
four stroke engines. Larger four stroke engines (automobiles) spark
every second crank revolution per cylinder. The spark is usually triggered
by the camshaft on large four stroke engines. The camshaft rotates
at half the speed of the crankshaft.


>
> Steve
>
>

"Smitty Two" > wrote in message >
> Here's what I remember from building the "Visible V-8" model when I was
> a kid: intake, compression, combustion (power), exhaust. I count power
> on every fourth stroke.

Yes, what I said was somewhat misleading. On a two stroke cycle, you get
a power stroke on every stroke. There is a power stroke integrated with
an exhaust stroke (going down) and intake and compression integrated
on the upward stroke. But these are two strokes...down and up.
On a four stroke cycle, you have two downward strokes and two
upward strokes, only only one of which is a power stroke.

So for one revolution of a two stroke, you get a power stroke: for two
revolutions of a four stroke cycle, you get a power stroke.

"Tegger" > wrote in message >
> You're all mistaken.
>
> A "four stroke" is a teenage boy. That's how many strokes it takes him to
> "fire" when viewing online female-anatomical matter.

Yeah, that is what Cuhulin was talking about with his 6 stroke
situation.. It gets that way when you get old.

"Oren" > wrote in message I think we get it.

Maybe.. You still get twice as many power strokes with a two stroke
cycle engine as you do with a four stroke cycle engine, RPM being
the same.