What are the mechanical effects of a manual transmission equipped car rolling backwards while a forward gear is engaged and the clutch is fully out? Does being forced to rotate backwards cause engine or transmission damage?
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Rolling Backward in Forward Gear - Damage?
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On anything with a timing belt its not good but would usually not result in damage. But it could! I've seen some engines equipped with a spring loaded "floating" tensioner that could cause the T-belt to slip if rotated backward.
The engine in question is equipped with a timing chain (Ford Duratec 30 in a Mazda 6).
It was likely forced to run for less than 5 seconds somewhere between 5 and 30 mph in reverse while 3rd gear was engaged. After the "event" it started right back up and seemed to run as if nothing had happened.
Does it sound like there's nothing to worry about?
It was likely forced to run for less than 5 seconds somewhere between 5 and 30 mph in reverse while 3rd gear was engaged. After the "event" it started right back up and seemed to run as if nothing had happened.
Does it sound like there's nothing to worry about?
I hadn't thought much about it until you mentioned it was more than a few feet. 5 sec isn't long, But if it had been towed a long way like that I could see it getting a rod or main, or even a cam bearing. Due to the fact the oil pump would be running in reverse.
I wouldn't worry about it. How many un-tuned vehicles used to diesel on hot summer days back in the 70's?
Do they pump gasoline back into the tank? (kidding)
Joel
Joel
When a gas engine diesels, it is still running in the forward direction. Not relevant to the discussion here.
Joel, No a mechanical fuel pump will still pump fuel in the correct direction. I had an elder friend once admit he hooked up his little Toyota carbed pickup to the tow bar of his RV... he had forgotten to take it out of gear. It was empty when he got to the campground. I'd guess the oil had a LOT of unburned fuel in it as well.
Although it was being towed forward it wouldn't matter since every stock fuel pump I've seen just strokes on an eccentric. Whereas oil pumps are rotor/gears.
Although it was being towed forward it wouldn't matter since every stock fuel pump I've seen just strokes on an eccentric. Whereas oil pumps are rotor/gears.
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I had a Honda come in on a hook because it had a flat rear tire. Tow truck guy pulled it backwards and left it in a forward gear.
By the time it got to me the cam was siezed in the head and there was smoke coming out of the oil fill cap when I took it off.
A few feet and a few revolutions backwards shouldn't be any problem but a trip across town will burn up the engine.
By the time it got to me the cam was siezed in the head and there was smoke coming out of the oil fill cap when I took it off.
A few feet and a few revolutions backwards shouldn't be any problem but a trip across town will burn up the engine.
Originally Posted By: George7941
When a gas engine diesels, it is still running in the forward direction. Not relevant to the discussion here.
I've seen it happen. A 225 odd fire CJ5 stopped in gear after a hill climb and dieseled, causing the Jeep to jump backwards a few feet before it stopped. He was in first gear! Yeah, it shouldn't happen, but it does.
When a gas engine diesels, it is still running in the forward direction. Not relevant to the discussion here.
I've seen it happen. A 225 odd fire CJ5 stopped in gear after a hill climb and dieseled, causing the Jeep to jump backwards a few feet before it stopped. He was in first gear! Yeah, it shouldn't happen, but it does.
Originally Posted By: George7941
When a gas engine diesels, it is still running in the forward direction. Not relevant to the discussion here.
That's not always true. I'll never forget an old 78 Horizon (VW block engine, carbureted) that would diesel roughly forward, then occasionally kick backwards and run ridiculously smoothly, BACKWARD, blowing bluish smoke out the air intake. The only way to stop it was to go clap your hand over the tailpipe (which was indeed SUCKING air in). It was an automatic and the transmission wouldn't engage with the pump being spun backwards. I didn't believe it until it did it to me one day. I think it was dieseling on engine oil being drawn in past the exhaust valve guides.
When a gas engine diesels, it is still running in the forward direction. Not relevant to the discussion here.
That's not always true. I'll never forget an old 78 Horizon (VW block engine, carbureted) that would diesel roughly forward, then occasionally kick backwards and run ridiculously smoothly, BACKWARD, blowing bluish smoke out the air intake. The only way to stop it was to go clap your hand over the tailpipe (which was indeed SUCKING air in). It was an automatic and the transmission wouldn't engage with the pump being spun backwards. I didn't believe it until it did it to me one day. I think it was dieseling on engine oil being drawn in past the exhaust valve guides.
I've had my truck off in gear before on a steep enough incline to turn the motor over and creeeeeep backwards. Always makes you feel wonderful...
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