Engine weight

[SADLOTUS]

Sorry chaps, can't find the recent thread with engine and gearbox weights.

Following on, would a 4x4inch x8foot piece of wood support the above for an engine in/out?.... and is doubling up, ie 8x4ins x8foot twice as strong?

Any building engineers out there. I don't want to find out the hard way.

Thanks

[handi_andi]

Ok, the simply answer is no 8" x 4" is not twice as strong as a 4" x 4" it is around about 4 times stronger, assuming the 8" side is upright.

In structural terms:

Bending stress = Moment / Section Modulus (Z)

For soft wood:
4" x 4" Z=166.7 E03 mm^3
8" x 4" Z = 666.7 E03 mm^3

According to BS 5268: Part 2 which is a structural design code for buildings, alowable bending stress varies between 5.3 & 16.0 N/mm^2 according to the strength class of the wood.

So taking 5.3N/mm^2 (C16 strength class) as the worst case scenario and assuming a 2metre length of beam then:

mass = bending stress x Section modulus / span

for 4" x 4" case: mass = 5.3 x 166.7 E03 /2000 = 441.75N or 45kg

for 8" x 4" case: mass = 5.3 x 666.7 E03 / 2000 = 1767N or 180kg

According to http://www.woodknowledgewales.co.uk/page.jsp?id=33 C16 strength class would be attributable to UK grown scotspine.

The ultimate strength capacity of the wood is likely to be alot more as these are allowable loads under a building code and therefore will have a factor os safety in them. How high that is I honestly don't know, if it were steel then it would be 1.3 but I can see that because of the uncertainty that comes from using a nature product it is probably higher.

Also the shear strength of the wood needs to be considered. The allowable shear strength for C16 is 0.67N/mm^2, which means:

for 4" x 4" case: mass = 100 x 100 x 0.67 = 6700N = 684kg

for 8" x 4" case: mass = 200 x 100 x 0.67 = 13400N = 1367kg

Which means the bending stress case is dominating as you would expect.

The calculations can obviously be altered for a different span just change the 2000 in the bending calculations to what ever your span is between supports in millimetres.

Hope this helps.

Cheers

Andy

[john.p.clegg]

As they say......"ask a silly question.........?"


John

[handi_andi]

It may not be concise but it is mathematically correct!!!!!

[SADLOTUS]

Thanks Andi, interesting stuff and takes a few reads to even begin to understand. I suppose it's obvious it's to assemble a frame in the garage to put the engine back in.

Found the engine weight thread: http://www.lotuselan.net/forums/viewtopic.php?t=13918

Weight is 100kg engine and 38kg for box.

Did the calcs using your figures and a 3metre length of 4x8. came to 120kg.

The wood looks strong enough but the calcs say not. Time for a rethink. Maybe an RSJ instead.

[handi_andi]

Sorry, was having a mental blank spot and worked it out as a cantilever instead of a simply supported beam.

For a beam supported between two points and the load in the middle, the maximum bending moment would be load x span / 4. Hence the two cases become:

for 4" x 4" case: mass = 5.3 x 166.7 E03 x 4 / 3000 = 1178N or 120kg

for 8" x 4" case: mass = 5.3 x 666.7 E03 x 4 / 3000 = 4711N or 480kg

OK, now they are mathematically correct!!!!!

Apologies for the confusion, and I know my creibility as an engineer is now completely shot as if it wasn't already for having been a civil service engineer!

Andy

[SADLOTUS]

Hi Andi, strange how the brain says 'That should work' even when the calcs say otherwise. thanks for reworking them.
Paul

[handi_andi]

Paul
My brain was saying "That seems low" but didn't ring any bells for why until I started reworking it with 50x30 rolled hollow steel section as that is what I took my Spitfire engine out with and that's when it struck me. With good clear knot free wood you could probably get away with the 4"x4", however, I personally would go to a slightly larger section. I take it you have the 8"x4" handy as something like 6"x4" should do the trick although haven't re-run the calcs.
Andy

[bill308]

SADLOTUS,

I took a quick look a handi_andi's methodology and calc's and I have some concerns. I did not acutally repeat the calculations, so I'll assume they are correct:

1. It appears the calc's assume a simply supported beam. This is OK. Where I have my problem is the assumption that stacked 4x4's act like a uniform 4x8 beam. This would only be true if the 4x4's were solidly bonded to each other with and adhesive having a shear strength at least equivalent to the wood's shear strength. If this is not the case, the joint between the two 4x4's will slide relative to one another under load. This joint is at the geometric center of the beam. If this were a solid piece of wood, the geometric center (height wise) would be under no bending load but it is the axis of maximum shear. A better arrangement for a simply supported beam would be side by side 2x8's, a common size in the US. Incidently, 2x8's in the US are really a misnomer. This may be the rough cut at the saw mill, but after planing they are finished to 1.5x7.5 inches, much less.

2. Assuming full wood dimensions, even if the 4x4's were stacked and properly bonded, or you were to use side by side 2x8's, I'd still feel a little uncomfortable unless the wood were a better spec than assumed and there were no significant knots in the center third of the beam, where bending loads are highest. Also one has to consider how the chain fall or block and tackle will distort (indent) the wood under load. This point or line load is likely to dent the surface of the wood causing an additional minor loss of strength at the point of maximum bending load. If the gear is fixed by a thru bolt, you are removing a plug of wood presicely where you don't want to and again leading to a weaking of the beam.

3. The last issue is the actual lifting gear. It weighs something. If one has to pull down on the rope or chain, some portion of this force also needs to be added to the lifting force. An electric winch does not have a pull down load problem but its weight would likely be more, again an additive load the beam must support.

I would be hesitant to use any wood beam of true 4x8 dimensions over an 8 foot span. You may get away with it, but it will likely bend more than desired. You really want something stiffer to begin with, closer to a 4x10, or two 2x10's (again a common cut in the US but really 1.5x9.5 inches) fastened together (ideally with a spacer between them) allowing a central lift point (or channel) and a little more lateral (side) stiffness. The 10 inch dimension would of course be vertical. A beam of this dimesion might be good to 3 meters, but you'd have to do the calcs to be sure. Again, no significant knots in the central third of the beam. Otherwise, you should have enough margin not to worry about getting everything perfect.

Except for cost, a proper engine hoist is likely a better solution. It's made to do the job and is likely more mobile.

Bill

[pmallinson]

Wow this seems really complicated way of lifting and engine !

Whatever the calcs say 1 KNOT in the wood or and internal 'shake' (a crack down the grain) can dispel all your load / strength calcs !!

My biggest fear of having a engine or engine and box from any wood would be that IF it did decide that enough was enough the the resultant failure would be more than likely very quick not much creaking before a load SNAP and your engine and box embedded in your garage floor or worse in your car !

IF you have to use a wooden frame the uprights should be fine as wood reacts well to compression but for the cross member i would recommend at the very least screwing some lengths of 2X2 angle iron to the top and bottom of it, at least then you will get BEND and hopefully NOT SNAP

Just my thoughts

PS: I have portable (on wheels) a hydraulic engine hoist which is great

Cheers

[handi_andi]

Bill

I would agree with some of what you have said but not with all of it. The calculations are done on the basis of solid wood not jointed wood. They are also done to the Britsh Standard that takes into account the strength loss due to knots up to a point, so assuming that the wood fits within the visual characteristics of C16 as dictated by the standard then there should be adequate strength especially as the code includes a factor of safety.

I would also agree that avoiding knots around the critical support points is of fundamental importance.

What I can also tell you is that I safely lifted a Triumph Spitfire Engine using a home made gantry built out of the steel frames of two old desks, which consisted basically of four uprights with horizontal side braces and diagonal corner braces on the front and back and a central lift beam along the middle running fore and aft. It worked just fine, was wider than the car and was made from about 50mm x 25mm x 1.5mm steel.

If one is going to go to the complexity of making up a compound wood and steel section, then one might as well sandwich the 8x4 between two lengths of steel U section with the flanges point upwards on top and downwards on the bottom with bolts through both the web of the U section and the wood. That way the overall Z value would be massively increased and the wood would be simply acting as the web for the compound section and woudl take very little of the actual bending stress.

As for the deflection of a 8x4 over a 3m span with a 138kg plus load on it:

Elastic Modulus for Scots Pine: E = 10 GPa = 10E09 N/m^2 = 1000 N/mm2

Moment of Interia: I = 666.7E03 x (200 / 2) = 666.7 E05 mm^4
where 200/2 is the distance from neutral axis to further most fibre

For a simply supported beam with a point load in the middle:

maximum deflection = load x span^3 / (48 x E x I)

Assuming our load is 138kg x 2 to account for dynamic amplification etc:

maximum deflection = 138 x 2 x (3000)^3 / (48 x 1000 x 666.7e05) = 2.33mm

As for the overall safety of an 8x4 beam, the allowable loading according to the Britsh Standard is 3.5 times the proposed load and that is excluding the safety factor already built into the code. A typical lift of a several thousand tonne offshore oil platform being lifted by a floating crane that is continuously moving would not typically require such a high safety factor as that.

Whilst agreeing that a hydraulic engine crane might be easier and handy, if one doesn't already have one they are expensive, even to hire, for a one off job. Where as if one has the wood already available and suitable block and tackle or similar then there is no real reason why it can not be safely utilised. In fact I think it shows great sense coming on here in the first place to check out the minimum beam size.

Andy

[elandoc]

HOLY SHIT!
In Australia, we just hoik a rope over the nearest beam, and if it cracks, we bolt an angle to it next time. My advice is give it a go, and see what happens. What...do you want to live forever?
Patrick

[bcmc33]

What isn't clear is how the beam is being supported. Until you know this you can't do reliable calculations.

What I did was to screw (with coach screws) three pieces of 4x2 across the garage ceiling into the bottom of the first floor joists at 24? centres. A piece of 3x3 was screwed to the 4x2 with a nice big hook in the centre for the hoist. It took two hours to complete which included going to the wood yard for the timber. Very basic, very cheap, very quick and very strong for what I wanted. The words brick and shithouse come to mind when I look at it.
I acquired a piece of 4x2 RSJ to replace the 3x3 for future improvement, but this is still in the corner of my workshop ? and will probably be there forever.

Brian Clarke
(1972 Sprint)

[freddy22112211]

4x4inch is easily good enough! Mine is only 2 1/4 x 2 1/4 inch. Works perfectly. Ordinary wood. http://www.lotuselan.de/tech/hoist1.jpg
Gordon

[denicholls2]

Real-world experience: A 2x4 on edge is adequate, a 4x4 is comfortable overkill. Any more and you're seriously into the wastelands.

A 4x4 over an 8 foot span will easily deflect over six inches before snapping unless it is made of dry rot. A deflection of 2.3mm under load is NOTHING for softwood like spruce or pine, which is what they make dimensional lumber out of. (It would be significant for an iron beam.)

I lifted a 600-pound sailboat from beam system made of a 2x6 in the 1.5" dimension. Bent a bit but worked fine. A 2x4 in the 4" direction would take the load without bending.

A 4x8 beam will easily support the entire Elan.