Center of gravity of engine

Magnetoman

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I found a post from 5 years ago by Glenliman saying the center of gravity of a twin engine was about 5/8" to the left of the crankcase joint. Does anyone know how far to the rear of the 'V' it is as well?

I can probably guess as well as the next guy how far to the rear of the 'V' the center of gravity is for an engine complete with gearbox, but perhaps someone has something better than a guess(?). It's not critical, but it would be nice to come as close as possible if making a jig to hoist it.
 

Howard

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As you say the maths is simple, just taking the moments about the RFM pivot (eg). The problem is how much does the gearbox weigh compared with the engine - maybe we need to ask one of those nice people who've wrecked.... sorry that should be modified ... twin motors. My guess at the gearbox and clutch weighing 20% of the engine weight would put the CofG at about 40 mm behind the crank centres - assuming mag and dynamo cancel each other.
 

Howard

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Make a bracket to fit between the head mounting holes with a slotted lifting point, slide the lifting point til the engine is in the normal attitude, and let us know the answer. :D

H
 

Magnetoman

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Make a bracket to fit between the head mounting holes with a slotted lifting point,
Indeed, it's precisely to minimize the length of that slot that I'm hoping someone else who already has done this reports the measurement.
 

vibrac

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wont it vary with the position you rotate the crankshaft to? ie one piston as far up stroke and one 50 degrees behind plus half rod weight to the front or back.
 

Howard

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wont it vary with the position you rotate the crankshaft to? ie one piston as far up stroke and one 50 degrees behind plus half rod weight to the front or back.

Yep. All sorts of reasons it can't be precise, hence my grinning face, above. :D

H
 

macvette

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You're looking for an unnecessary degree of precision and it's bad lifting practice to lift an asymmetric load at a single point. Put the head brackets on, feed load ratchet straps under each bracket, protecting them from sharp edges with a couple of pieces of old inner tube. Attach both to your lifting device and adjust the straps using the ratchets so the engine is at the desired angle. You will need to cut the "loose" end of the straps if you don't want lots of excess length of strap getting in your way.
 

Magnetoman

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Yep. All sorts of reasons it can't be precise,
It doesn't have to be precise to be useful. The position of the pistons and flywheel are small effects compared with the moment arm of the gearbox. Also, one time the engine might be lifted with the magneto attached, and the next without. However, even if an adjustable lift point was used to position the engine precisely horizontal at some arbitrary angle of the flywheel, moving the flywheel to any other angle, or adding or removing the magneto, would still leave the engine reasonably close to horizontal.

Further, the 5/8" offset to the left is unlikely to be precise, and one also could mention the additional imprecision of the gear the bike happened to be in when lifted since those heavy steal gears move left and right so would throw off a precise balance. But, again, those effects are small.

So, 5/8 of an inch to the left and ___ inches to the rear of the 'V' for a reasonable balance. If anyone knows the answer, please fill in the blank.
 

Magnetoman

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You're looking for an unnecessary degree of precision and it's bad lifting practice to lift an asymmetric load at a single point.
The hoist doing the lifting does so using a hook, i.e. always from a single point. I lift heavy, asymmetric loads all the time from a single point, e.g. 60 lb. Kurt vise and 60 lb. rotary table for my milling machine, 95 lb. auxiliary head for my lathe, etc. I've moved my ~1500 lb., asymmetric, milling machine twice, each time lifting it from a single point (and without any additional balancing straps since it didn't matter that it was tilted).

To the extent the lifting point is positioned over a load's center of gravity it means additional straps to do any final tweaking of the way it hangs have minimum stress on them. In fact, I would say it is bad practice to lift a load if there is excessive stress on additional balance straps, i.e. if the lifting point is too far removed from being over the center of gravity.

I could lift my Vincent engine from a bracket attached to the front mounting lugs if I had to, along with additional straps to keep it horizontal. It's just that isn't the best way to do it. Again, I'm in no way looking for unnecessary precision when asking where the approx. center of gravity of the engine is located in order to make a bracket to lift it.
 
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