Me and a couple of others used to argue about the term compression start and i was WRONG!!! I had allways maintained there was a little compression left and i thought i could prove it but i was WRONG!!! Today i changed spark plugs from champ X's to H-14 champion primer cup spark plugs.After sitting at least 4 days and the spark plug change Lizzie started when i switched to batt no cranking involved!! While it was running i thought i would check for a leak so i passed my hand close to the top of the plugs and Lizzie showed me not to do that again.I was WRONG and now i think there is no such thing as a [compression start] Bud.

The old story was to speed up the engine slightly then kill the ignition to leave an explosive charge in the cylinders. I have also pulled the crank afew times (w/choke),pulled to just past compression and hit the switch to Batt.It will kick and sometimes continue to run if all's set perfect. But you can hear compression bleed off when you do this. So I agree the term "compression start" may not be quite accurate but it's been around for so long I doubt it'll change.

Some motors will give you a "free one" almost every time. Some seem never willing to do it. Gasoline inside a somewhat sealed compartment will not evaporate for a very long time and though not under pressure, if there is a sparking device in that same compartment and there is even a small amount of gas residue in there, you have the fixings for an explosion even if small. Since a T is low compression anyway and another firing of another cylinder is only 1/2 turn of the crankshaft away - you can get a free start pretty much anytime. One must always assume it to be possible to thus be on the safe side. I have had my T in gear with the brake lever forward and sitting in the lot at a tour when I turned on the key before pulling the brake lever back. The T didn't start but it sure lurched forward a short distance and if anything was in front of me that was close - I could have bumped into it. I have routinely stopped at a filling station, shut it off, filled the tank, and then hopped in and turned on the key and had it start without using the starter. Funny car.

We always used the term ‘compression start’ for a push
or downhill start with a car, or a ‘bump’ start with a motorcycle.
Get it rolling and let out the clutch. The bump start with the
motorbike involved running with the bike and jumping on.
The inertia of your body when your butt hit the seat (bump)
timed with the letting out of the clutch helped with the start.

I think they use the term compression start because a cylinder has to have stopped a bit after TDC on the compression stroke. This leaves gasoline in the cylinder, the piston in the correct position to rotate the crank shaft, and the the valves closed.

At or just after TDC there is little or no leverage arm for the piston to act on.

Ever since I came to Ca. I hear folks refer to push starts as "starting on compression".
When you hand crank an engine or use the starter are NOT starting it on compression???
I have heard Engishmen mention "bump start" many times. Thanks Art for explaining the meaning of that.

Aaron
On high compression racing bikes it helped with the traction on the rear wheel when you let the clutch out,
and made sure you were 'on board' if and when it started. <g>

If the engine stops after TDC it is on the power stroke. The compression stroke is over at TDC.

Yes, it's a compression stroke on the cylinder behind it in the firing order that causes it to stop but it's the cylinder well past TDC on the power stroke that starts the engine. In other words, if it's #2 that's on compression, it's #1 that fires and starts the engine.

It's the dwell of the timer that allows this cylinder to fire. If the coil on time was only 30 degrees of crank rotation instead of the almost 90 degrees, free-starts would be well-nigh impossible.

The new car manufacturers are trying to incorporate free starts in their cars. They use the computer to tell which cylinder is in the right position, spray fuel from the injector and then fire the plug. Funny, how technology seems to come back around in time.

On the first Monday of each summer month there is a cruse for any type of car that you can get running and drive in Golden CO. I go whenever I can. I drove the stock 14 Touring car last month. The 14 drew quite a crowd. I left the cruse well after dark thirty and had to light the acetylene headlights. The crowd that was around my car was clapping as I lit the headlights. Then I choked the car and pulled it through twice. The folks were wanting to see me crank start the car. When I turned on the ignition switch the car roared to life. It was the first and only tine that has happened to me with the 14. The crowd seemed to be disappointed that I did not have to crank the car to start it. I tried to repeat this at home. I can’t get it to do it again. Model T's have a sense of humor.

Paul

Over this weekend I read an old post where someone stated instead of giving the T some throttle as you turn off the car to get some extra gas in the cylinders advance the spark. On the “old” method I rarely every got a free start.

With advancing the spark all the way as the engine shuts down. When I was ready to start the T again I would then retard the spark and turn the key to bat, it would start maybe one out of three tries.

Jason,The best for me is to retard the spark at semi fast idel count to 5 and shut off the switch.As a safty i think the spark should always be retarded so you never forget and with a Anderson timer sometimes you cant retard the spark unless the engine is running? Bud.

Your right Royce & Seth-- Old age got me --

4 stroke motors - intake/compression/power/exhaust strokes.
It has to be on the power stroke so I haven't a clue where the name compression starts came from.

Bump start was where you pushed the vehicle and let the clutch out to get the crankshaft rotating-
Jump was where the battery was low and you connected a second one with "jumper wires" to get a bit more electricity to run the starter.

Does that mean when I connect wires to my pacemaker for more power and I crank the car I'm actually jumping it?

Just a thought. the term "compression start" has been around a long time. Could it have come from the air starters that some companies (like Pierce Arrow) offered before electric starters were offered. They had a compressed air tank that fed air under pressure into the power stroke cylinders to turn the engine till it started. The problem with the system was that if an engine was cold and hard to start, usually it ran out of air.
Drive safely, W2

This pretty much shows the basics of the “Compression Start”

http://s3.photobucket.com/albums/y91/bandr3w5/?action=view&current=100_2751.flv

(or perhaps shows the gullibility of recruits being taught how to start
their chop saws if the starting rope is broken and the saw is needed)
Perhaps a ‘Snipe Hunt’ as the next lesson !!!

Wayne,With so much tire trouble many of the expensive cars had built in air compressors and the air starters soon followed.I think i saw one on a 1906 National and i also think it was a two stroke? Bud.PS,I shure havn't seen that before Art!! Bud.