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Free Start

Posted: Wed Feb 06, 2019 11:56 am
by Norman Kling
Richard G says free starts are hard on cranks. Why? and How? I can't see how it would be any harder on it than starting with a crank or starter?
Norm

Re: Free Start

Posted: Wed Feb 06, 2019 11:59 am
by Rich Eagle
I don't see either. It isn't firing under load. Going up a hill would seem to be harder on it but I'm no Fizasist. <;Oo
Rich

Re: Free Start

Posted: Wed Feb 06, 2019 4:03 pm
by Dallas Landers
I think it has something to do with the "shock" to the crank when it fires without revelution started. I think it was discussed last year in a thread. I could be all wet to.

Re: Free Start

Posted: Wed Feb 06, 2019 4:27 pm
by Rich Bingham
Dallas, that's the explanation that was given on that thread as I recall it. Like Rich, I find it hard to believe either that the stock T crank is not robust enough to absorb the impulse of a free start, or that it amounts to a great deal more sudden torque than hand cranking or engaging an electric starter. For one thing, ignition of a cylinder charge of fuel mixture doesn't result in an "explosion" but a radial "burn". When it comes to broken crankshafts, I'd think running for extended periods mis-timed, with intermittent "missing" as might be the case with a bad coil, high compression heads and loose rods may in part contribute to hastening the failure of century-old forgings. JMHO

Re: Free Start

Posted: Wed Feb 06, 2019 5:32 pm
by Colin Mavins
Our 1912 free starts all the time,and has been doing it since 1960, now I did break the crank after 103 years. I think after 103 years it just got brittle, even cold if I pull it over once and then turn it on it starts. So I can't see free starts breaking a crank. Just my opinion Cheers From Winnipeg

Re: Free Start

Posted: Wed Feb 06, 2019 6:15 pm
by 24t
The electric starter probably gives a harder jolt than a free start . just thinking again .

Re: Free Start

Posted: Wed Feb 06, 2019 6:35 pm
by Ruxstel24
I can think of a dozen malfunctions and/or operator errors that I would say are harder on a crank than a free start.

My old man, once in a while, in a parade at too slow a speed, would let the clutch out into high and throttle it up and make the car buck like a rodeo steer !!

I don't think the crank has been changed in 50 some years...

Re: Free Start

Posted: Fri Feb 08, 2019 2:37 am
by Erik Barrett
Can anyone here say they have broken a crank or seen it happen during a free start event?

Re: Free Start

Posted: Fri Feb 08, 2019 3:11 am
by Matt in California
Erik Barrett wrote:
Fri Feb 08, 2019 2:37 am
Can anyone here say they have broken a crank or seen it happen during a free start event?
Erik we have a logical problem here. If the engine breaks it is not free;)

Re: Free Start

Posted: Fri Feb 08, 2019 9:14 am
by pops
Mine broke going up a hill, going from low pedal to high pedal when I pulled the throttle down.(broke the crankshaft,bent the rod and the rod hit the camshaft and bent it)
Pops

Re: Free Start

Posted: Fri Feb 08, 2019 12:29 pm
by Bill Coyle
My thought is "what was happening at the time it broke" was only the final straw which broke the proverbial camel's back. When I Magnafluxed the crankshaft from my '26 roadster's worn out sawmill engine which had been sitting for many years, I found 4 cracks. The other interesting fact was the crank measured .030" runout (TIR) on the center main with the 2 end mains on V blocks. It had probably taken a set over the last 50 years resting in bearings that were likely adjusted for clearance but ended up .015" out of alignment. In this case, I'm guessing rotary fatigue caused by misalignment played a big part in propagating the cracks. Well, needless to say, I did not use that crankshaft.

The Model T crank encounters a lot of stress over it's life, and cracks, if they start, continue growing until that final straw is added. Bill

Re: Free Start

Posted: Fri Feb 08, 2019 1:20 pm
by Erik Barrett
Nothing free about a broken crank.🤑

Re: Free Start

Posted: Fri Feb 08, 2019 3:06 pm
by Rob
This was Ford's position on free starts, in 1907.

Also good advice when meeting a horse:
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Re: Free Start

Posted: Fri Feb 08, 2019 5:36 pm
by Rich Bingham
Rob, thank you much for posting that from the Model K manual.

So, according to Ford, a "start on the spark" (aka a "free start") can break a crankshaft, but then it's stated that "Ford shafts are extra heavy to meet this condition . . ." So they ain't worried ? and so it's up to you ? :o Was this before vanadium steel ? Does that matter ?

(Still good advice regarding horses ! ;) )

Re: Free Start

Posted: Fri Feb 08, 2019 6:25 pm
by GrandpaFord
All the broken cranks that I have seen on the forum were cracked before they broke and all had the signs of fatigue failure. None showed a sudden break because of a heavy load or torque. A fatigue failure is caused by repeated back and forth bending, just like breaking a paper clip by bending it back and forth for a while. The free start is a one time load on the crankshaft and not a back and forth bending. Whether the load from the free start is enough to stress the crank or not, it is not a source of fatigue failure.

There has been lots of speculation on the forum about the source of the back and forth bending that leads to the fatigue failure. Mis-alignment of the 4 main bearings has been brought up over and over. Another possible source of the back and forth bending is the periodic power pulse, especially when lugging the engine. My personal thought is that there is a natural frequency twisting in the assembly of the crankshaft, rods, and pistons. Right around WW II dampeners were added to the front of crankshafts on 6 cylinder engines to keep the torsional vibration in check to prevent the crankshafts from breaking.

If your crankshaft has 40,000 miles on it, the crank has been twisted back and forth about 200 million times.

Re: Free Start

Posted: Fri Feb 08, 2019 10:58 pm
by Scott_Conger
I would suspect that misaligned 4th mains and worn out 4th mains, period, are one of the biggest contributors to crankshaft stress and ultimate failure.

Re: Free Start

Posted: Sat Feb 09, 2019 12:20 am
by Richard G
THANK YOU ROB! you guys can inject all your this and that's on this subject why then is the t the only one born with this problem. I just read ROS post, that says it all, don't it .i'm going to bed with a big SMILE.

Re: Free Start

Posted: Sat Feb 09, 2019 2:25 am
by Raoul von S.
I blame Russian collusion.

Re: Free Start

Posted: Sat Feb 09, 2019 8:20 am
by samuel pine
Things or anything could break or snap caused by shock more so when cold. With its low compression a free
start won't hurt anything. High gear lugging not good for any engine. I have been doing this since I was a kid,
take a ride engine running at its sweet spot. Stop it.> don't retard it put to idle & shut down, turn key to batt then
retard spark then instant start 9 out of 10 times. Even after after days turned key retard it instant start.
The modern new junk snaps cranks too don't ya know. Remembering back in the 70s we had about 60 Gmc
school buses with 350 gas and with their massive crank pulleys they would snap right behind the timing gear,
these were new buses so, gov't motors paid for that.. Told my uncle he should have bought Fords with the
HD 391 FTs....... just rambling again............sam

Re: Free Start

Posted: Sat Feb 09, 2019 2:01 pm
by BobD
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