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Old 02-09-2008, 13:51   #1
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crank-starting a diesel engine- Safe or Unsafe

A qustion regarding a diesel engine. How unsafe would it be to crank start an engine. Theoreticly, because we can only crank at around 60rpms a minute, when the engine catches, it would be a rapid acceleration to 8000rpms potentially breaking an arm or wrist. Is this true or is there a safe guard built into the motors. Any help or tips would be greatly appreaciated.

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Old 02-09-2008, 14:02   #2
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Firstly, it depends on the size of the engine as to whether you will hand crank it at all. If you have a decompression lever you have a good chance, if not you will have no way of cranking anything big. A single cylinder should be OK. A twin would be getting harder but possible. A three cyl is closer to the too hard basket. If there is no decomp lever, then a single would be about the tops. You would not get enough swing up on a twin, unless you are a hell of a lot stronger than I am.
As to RPM, you don't need the throttle wide open. So it shouldn't run up to full revs anyway. However, the crank point of the flywheel is a dog at pushes the crankhandle away once it over runs your crank speed. If you are using flywheel only to crank, then a pull cord of say some spare line would work, but it is getting dangerous. The most dangerous part of starting any engine is having it fire without getting over TDC and it spins back the otherway. this can break arms and wrists or wind in lines. Beware.
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Old 02-09-2008, 15:36   #3
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Most of the Scandinavian engine makers used to make their small marine engines with starting handles. Also came standard with decompression levers. As Alan says a backfire could cause some physical damage, though I havn't heard of that happening with a diesel.
I have a memory of a Greek engineer on a local work boat of around 60 feet starting its very large single cylinder engine by first heating a glow bulb with a blow torch then rotating the flywheel back and forwards by hand, (around 6 foot dia) bouncing against compression again and again until he built up enough momentum to get it over top dead centre whence it fired with just enough power to get over the next compression then slowly increased revs until the whole boat was shaking with each ignition. It probably did around 300 rpm. It was an impressive piece of very basic machinery that is probably still running today.
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Old 02-09-2008, 15:38   #4
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Had a Volvo that was hand crankable. Well, almost. Could hand crank start it if it was warm. But cold now way. Cold, however; I could hand crank it if I had some battery assist. That is, the batteries couldn't turn it over alone but I could help. Needed to use the decompression levers.

BTW: Hand cranks are designed to not catch when the engine fires.
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Old 02-09-2008, 17:39   #5
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I tried like heck one day to crank our Volvo 10hp - spin it up engage the compression lever - No way...

I can't imagine cranking anything bigger.
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Old 02-09-2008, 18:58   #6
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I had a Volvo MD2B for many years. Hand starting was fairly easy. You released the two decompression levers and cranked the removable handle (having turned on the ignition switch). It saved me, several times, when I had overdosed on the Rolling Stones late into the night, followed by lots of reading. My Yanmar 3GM30F doesn't have a provision for hand cranking, but it DOES have decompression levers if the battery is low.
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Old 02-09-2008, 20:31   #7
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Hand Cranking

Decompression levers are the game. Without them it is not likely Early Yanmars had hand cranks. Many Diesels do. I had a 2 cyl Volvo years ago I could hand crank. The trick is to decompress and spin for a while untill you think all the air is out of the system. Here is a picture of one in the Bahamas that can only be started by hand (Lister Diesel) I think it was built before electric starters! Muffler is a 55 gal drum full of conch shells. Works incredibly well.
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Old 02-09-2008, 20:42   #8
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.......yep...to the point of blistered hands and bruised knuckles. It helps to have a second person! The second person operates the decompression lever (s) and the can of "start you bastard". The reason for this is the most important stroke is just after the lever is thrown and you need two hands on the crank to "pull" it through. Without it, as you get tired it can just end up bouncing and as wheels suggested come back on your knuckles. Worse still is if it fires just before TDC and comes back hard. With two (or more) cylinders you start it on one cylinder only. Once it is running for a minute and has a bit of heat you then throw in the other (s) one at a time. Using the starter to assist is a trick worth knowing. The extra power can help you get over the hump. It is no use doing this once the battery is completely shot though. It works better on the early dynastart type starter/generator units.

Final suggestion dont....I have spent a full day and a half getting a single going by hand. It wrecks the back and the mood !!!
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Old 03-09-2008, 00:16   #9
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Hi Mike
The short answer is if the engine is set up for it then you can do it if not you cant. At the least this requires a decompression lever and crank handle.
Different manufacturers have different systems for the decomp some you set the lever and after a certain number of turns the decomp lever closes automatically others you have to close the decomp once the engine is "wound up " .However the most important thing here that hasnt been mentioned is that its potentially Very Very dangerous.
People have been killed , jaws smashed, fingers? thumbs broken.
As a diesel fitter ive hand cranked the odd small diesel in my time.
Here are the rules
1.Keep the crank handle in good condition and any moving parts clean and well lubricated.Lister and some other manufactures have a spring loaded ratchet pawl in the handle if this jams look out!!
2. Its harder and feels weird but dont wrap your thumb around the handle lay it on top, this way if it kicks back or the handle jams it pulls out of your hand and doesn't break/tear your thumb off in the process.
3.Make sure your footing is good dont have any body parts in the plane of the arc of the handle.
Ive seen a three cyl lister fire up and jam the crank handle luckily the guys hand wasnt broken just very sore, but you should have seen all of us bolt out of the work shop with an angry unbalanced engine hopping around the shop floor, im sure it was funny to see! Just not verry funny at the time the damn thing was possessed.
Cheers Tim
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Old 03-09-2008, 00:20   #10
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Oh and its not going to be spinning at 8000rpm more like between 600 and 4000 rpm depending on type still fast enough.
Tim
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Old 03-09-2008, 02:04   #11
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Old 7 hp yanmar...

I bolted an old single cylinder 7hp Yanmar into the ferro Hartley 32' that I built a while ago.

It was easy to hand start. Set hand throttle, lift decompression lever, crank, and drop. Started every time.

I can see how as engines get bigger it could get harder and more dangerous.
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Old 03-09-2008, 02:45   #12
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When I was a Kid, our first Diesel tractor was a Fordson Major. No alternators in them days and the Generators were useless. So batteries never kept charged properly for long. The only way to really start it was to use the decompression lever, spin her over and then pull the lever slowly down and keep a balance of almost firing and yet maintaining the revs so heat could build up and then finally you could close the lever and away she would run.
But the best story of all was having at a place I worked, an Old Bulldog Tractor. Enfeild was another similar tractor. These where old vintage classics with a big single cyclinder banger and an enormous solid cast flywheel. She was crank start and you cranked the snot out of the thing getting it up to speed so the momentum of the giant flywheel would push the Piston over TDC as you closed the Decomp lever. These things had the bad ability for the engine to run in reverse. So on this particular day, one of the guys started to crank the thing up. I must say I couldn't. I was a wee weed way back then and simply didn't have the weight to get the thing up to speed. Anyway he got the thing to speed and pulled down the lever. The wheel slowed and went to go over top and Bang, she was off in the wrong direction. So here is this big tractor and they really are big. Like a big steam engine tractor that had an enormous single banger fitted. When the engine is upto speed, it will literally bounce the entire tractor on the ground. So here is this thing now spinning in reverse with the huge crank handle spinning around and absolutely no one would go near it. It was left runing till it ran out of fuel.
But I just have to finish with this story. There is an old Tug in Picton. She is a real old beaut. Way more work than I would ever want to take on, but the owner loves her. Now she doesn't have a gearbox. She is from the era when the engine could be stopped and started in reverse. So this guy comes into the Warf and he lines her up, runs down to the engine room back and below the Pilot house, stops the engine, re-starts it in reverse, runs back up to the Pilot house and applies throttle to slow the boat, hoping he has timed it all just right to come up alongside the warf. Glad he isn't coming into a marina berth.
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Old 03-09-2008, 03:01   #13
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first heating a glow bulb with a blow torch then rotating the flywheel back and forwards by hand,

Sounds like the Petters Hot Bulb Engine. How that translates into Scandinavian is up to you. These things were designed to hand start, had lousey efficiency, and would run on anything oily. Because the bulb can be heated and retains it's heat really well it doesn't need high compression or nice diesel fuel.

Your real answer is a small genny to recharge the batteries, or on of those charger things the AA (Road Rescue) bring when you've left your lights on all day.

It's nice to know if you could actually start you iron by hand, but it's not nice to have to when you need to. Adding a little genny to most boats won't hurt the performance, takes hours off the main engine life, and is still portable for beach / marina work. Diesel ones get a bit heavy but there are domestic style petrol ones too.
Plus when the batteries are awash with sea water the genny will still drive the pumps! Woops, Is this a Challenge' thread?
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Old 03-09-2008, 05:18   #14
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Had an old hand crank SABB once. (Not Saab) It came with a tin of what looked like small cigarette butts you lit and inserted in the head.

Flywheel weight is improtant. The more the better. The old Volvos and Buke had good heavy flywheels and you coud hand crank one.
The modern Japanese diesels have light flywheels and will turn up real fast so hand cranking is not even considered. Anything over 2 cyl is asking for a broken hand if you are not careful.
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Old 03-09-2008, 07:22   #15
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Yanmar 1GM 6.5hp. Hand starting is a cinch. Left hand holds the decompression lever down, crank with the right hand. Once it's spinning like a top, release the comp lever and she fires right up. Just one of the many reasons why I love my little 1GM.

The engine can't kick the start lever backwards as there is a one way notch in the lever that engages a cross pin on the engine pulley in one direction only.

Must be a 'racing' diesel to pull 8000 rpms!!
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