How to smoothly bump start / clutch start an engine

[Blue07CivicEX]

Originally Posted by JJW

By the way, one of my favorite "stupid Metro tricks" was that I could push start the car by opening the door, kicking off like a skate board until it moved, and then smoothly letting out the clutch

You mean you can't do that in the Yaris? oh come on!! :-P

Thanks for the info, when I get my SG2 I'll see what the engine is up to while downshifting and I'll work on throwing it into neutral when i coast rather then holding the clutch in with my luck the throwout bearing would go 30miles over the warranty.

[NoCO2]

Another point about riding on the clutch pedal rather then throwing it momentarily in neutral to coast.

I have no proof to back this up, but a buddy of mine (the kid with the mini) is the guy who taught me to drive a manual transmission car and he always stressed that you should never leave the clutch in because when you do that, the plates aren't touching, but they are still spinning which could cause them to generate more heat and warp because they are not designed to spin for long without being pressed together. What he said makes sense and I've driven a car with a warped clutch pad and it can be very difficult depending on the degree of warping that has occurred. He also stressed that you should engine brake whenever possible to save your brakes (he is a race car driver where brake wear and heat are a major concern) and like was mentioned here, it also saves fuel if your car has the fuel cutoff system in place when decelerating.

[ttoyoda]

you should never leave the clutch in because when you do that, the plates aren't touching, but they are still spinning which could cause them to generate more heat and warp because they are not designed to spin for long without being pressed together.

That makes a lot of sense too. The plates certainly CAN be touching, they just don't have pressure on them. The fricion disk can move freely between touching the flywheel or touching the pressure plate, there is nothing to keep it in the middle where it touches neither.

[ttoyoda]

Originally Posted by JJW
By the way, one of my favorite "stupid Metro tricks" was that I could push start the car by opening the door, kicking off like a skate board until it moved, and then smoothly letting out the clutch

You mean you can't do that in the Yaris? oh come on!! :-P

I just run along next to the car with the door open. When the car is going fast enough, jump in. Doubtless I will run myself over some day.

[ebacherville]

Originally Posted by Blue07CivicEX

You mean you can't do that in the Yaris? oh come on!! :-P

Thanks for the info, when I get my SG2 I'll see what the engine is up to while downshifting and I'll work on throwing it into neutral when i coast rather then holding the clutch in with my luck the throwout bearing would go 30miles over the warranty.

He he.. the difference in 1700 and 3200 lbs id pretty big..lol

Hell in my ninja 250 motorcycle I had a bad battery.. and you could push start it and drop the clutch to start it as the magneto woul d start making power to fire the ignition off... but even that was pretty hard work if it didn't pop off instantly...


When ever i bump start my car i do it in 4th or 5th gear as it prevents a jerk when i do it as the gear ratio is so high.. then i select the gear i need to drive in.. makes for smooth bump starting.. all it takes it that motor barly turning and it should fire up if its warm.

In my truck i do some nutral coasting and idling and some engine off coasting also depending on the situations.. like.. curves or other situations that may need good control of the car I idle it.. as its power stearing is very hard to turn when there is no motor running..

[Twerp]

Originally Posted by ebacherville

Hell in my ninja 250 motorcycle I had a bad battery.. and you could push start it and drop the clutch to start it as the magneto woul d start making power to fire the ignition off... but even that was pretty hard work if it didn't pop off instantly...

I once had an old, crappy Honda CM185 Twin Star with a weak electric starter and an idling problem. It would stall out at a stop light and I figured out that bump starting was much easier than kick starting it. I would just have to put it in second and rock it forward while dumping the clutch. The thing would fire up like it was meant to be started that way. I kinda wondered why they ever put two other starters on it. As cheesy as that thing looked, I really do miss that bike. It got more ugly stares at bike week than a morbidly obese wedding crasher wearing a speedo.

With the Tundra, push starting is a little more difficult but that's prolly due to the 4,000 pound difference between the two vehicles. So unless I already have the momentum, I'll have to rely on ol' sparky to fire up the beast. When I do bump start it, it seems to fire up right away, but it's not very smooth. The dormant engine gives a lot of resistance, even in fifth, so it does jerk a little. I'll have to practice a little, but I'd like some more reassurance that the cat isn't going to go up in flames. You know, especially with the manual specifically telling me not to push start it and all...

[Twerp]

Just to illustrate my fear here...

Flaming cat:

[ttoyoda]

When I do bump start it, it seems to fire up right away, but it's not very smooth.

The correct gear for you to choose would be the one that produces your rpm at idle or just a little higher for the velocity you are moving when you bump it.
I usually bumpstart in second when rolling down a driveway.

[KJSatz]

Catalytic converter damage just scared me away from EOC again...would anyone like to explain this more?

:-X

[brucepick]

Originally Posted by KJSatz

Catalytic converter damage just scared me away from EOC again...would anyone like to explain this more?

:-X

I think it's a bogus reason against EOC.

A modern engine will start burning fuel nearly instantly when started, even when cold. So the air-fuel mixture is burned before it gets to the cat. Even more true for a warm engine. Remember, there's no fuel being injected after engine cut-off so it's not pooling anywhere. Spark and fuel both begin when you spin it up by letting the clutch out.

I think the bogus caution likely dates back to the days of carburetors and points-plugs-condenser ignition setups, where miscellaneous starting issues would end up flooding the engine. If you THEN get the idea to roll it down the driveway and bump start it, all that flooded fuel gets dumped into the cat and would burn there as soon as the cat gets hot enough. Depending on exactly when and how the engine starts, of course. But the cat is designed to get mostly 'combusted' air-fuel mixture, not mostly raw fuel plus air. So the dumped fuel would be bad for the cat.

But that scenario is not likely in your modern computer-controlled car. If the fuel management and ignition are in bad enough shape that raw fuel continually gets to the cat, the car is going to be very tough to drive if you can keep it going at all. In that case, continued operation would likely ruin the cat converter with or without bump starting.