weight limits of a span

[drewactual]

I've constructed a gantry to pull an engine.

the engine weighs 1k even pounds... a fully dressed SBC... well, okay, 997lbs... digitally weighed.

both sides of the gantry are duplicate- Inverted T's, with 4x4x10 upright, attached to a 2x6x12 base plate (laid flat), supported on side by 2x4's @ 45* either side...

the beam is 2 2x6x12's, screwed together on end... the span is the full 12'...

Should I add a couple 2x8x12's on either side of the 2x6's?

I feel after bouncing on the center the beam as it is now will hold, evidenced by me (all nearing 300# of me) bouncing on it using a tow strap... I 'think'... I want to KNOW.. 1k# is a lot of weight and I don't want to drop it... more worried about what I'm dropping it 'through' than the engine itself... I'm repowering my boat- which I figure this is an odd place to ask such a question, but- you guys seem to know more than most so I figured it wouldn't hurt.

 

[drewactual]

oh... and all lumber is pressure treated. I got plans for it afterward...

 

[drewactual]

yup.. forgot about those... 45* beam braces using 2x4's screwed together on both sides- approx 3' long...

 

[WUzombies]

According to my civil engineer wife "he'll probably be fine, it'll probably deflect a bunch though" also that "the span is the issue, not the supports."

So there ya go, the engineer said it might be ok. How's that for a good hard answer?

 

[drewactual]

nice!!

adding a couple more 2x6's or 2x8's should make it a certainty, then...

 

[rayra]

The diagonal braces will greatly increase the load capacity of the span, as they shorten the unsupported portion a good deal. Wood in compression is quite strong, you don't have to worry about the vertical posts (just brace diagonally as you have done to limit wracking).
Do not drill a hole thru the center of your span, instead wrap chain around the beams, to suspend whatever you are using for a hoist.

 

[drewactual]

zombie- thank you, and tell your wife thanks as well... my wife is an attorney.. shall we vow to never get them together? they could engineer on helluva nasty divorce, no?


rayra- good point and well received... the mechanism I'm using is an engine hoist rated to 1400#, which I will likely double back on anyway... it runs on a trolley, and should grip the top- hence why I was using 2x6's to begin with.. I still yet may attach 2.8's outside the 2.6's, just to increase the strength but also to ensure that trolley hoist doesn't budge...

 

[rayra]

Trapping it would be a good idea.
I just recalled that a woodworkign guy I follow on YouTube has made something very much like you are describing, and he's lifting very heavy loads with it.

Frank Howarth is his name-o and his videomakign artistry is as good as his wood projects

https://www.youtube.com/watch?v=PtPU1pOTLH4

 

[drewactual]

many thanks, Sir!

 

[Ozarker]

Ha, 2- 2x6s 12 foot span? I darn sure would not put a 1000# in a 2" concentration in the middle or at 6'. What type of lumber is it?

Floor joists (pine #2) on a 12' span take a 2x8 on 18" centers, 1/2 or 3/4 TG over that.

You'd be better off building a boxed lam-beam put 2 more 2x6's above that and scab 1/2' ply on both sides to the pitch of the roof (sounds like) if you need to trim the ends down. Glue and screw. Fill it full of screws, 2" above the bottom, 2" below the top for two rows every 12". Then you can hang a chain hoist in the center.

IMO!
'

 

[IdaSHO]

He said its treated :Wow1:


First thing Id do is swap out the treated for doug fir our pine.


Most treated is junk hem-fir.

 

[drewactual]

it's a bit more substantial, now...

the top beam is a 2- 2x6x12 sistered in the core, and 2-2x8x12 sistered to either outside 2x6x12... there is a 2x4x12 in the gap across the top with a center notched, which is a snazzy way to lock the center... total build-up on the beam is 8x8x12 minimum. there are four 2x4x5's braced into the beam and the other side braced to the uprights... the two inner ones are toed in, the outer ones into the face of the upright support with 4" x 3/8" lags.

the beam sits atop a 4x4x10 sistered on either side with 2x4x10's, allowing the beam to rest atop, not screwed to the top or side of the upright supports... the 2x8'12's with the little 2" overlap are lap bolted to the 4x4x10's and using 4"x3/8" lags. there are four 2x4x8's, two on either side, bracing the uprights to the bottom plate. they both toe into and lag into the face of the upright, and into the floor plate..

the floor plate is three 2x6x12's- two edge up one face down, allowing the braces for the uprights to toe in as well as lag into the floor plate.

I purchased an 1100# electric hoist, which allows me to double back for around a ton. that ought to be plenty of safety margin.



I was worried about that thing though I was ensured that it was fine, which is why I asked here... I ain't worried about it anymore, except for the fact the wife ain't gonna like it hanging out and I'll have to disassemble it... that's fine, though (and the reason I chose pressure treated) is I have plans for it later.

 

[fog cutter]

usually an 8" - 10" oak branch will do the trick. the neighbors really enjoy an engine hanging by a chain for a few months. usually Memorial Day to the Fourth of July is long enough.

 

[Scoutn79]

Where did you weight the motor? A SBC weights in around 550lb range. Do you have a sm465 attached?
I have rebuilt a few SBC and IH SV motors (345 and 392 CI) and the IH motor is almost 50% more at around 750Lbs dressed.
Heck a 6.9L diesel weights about 1100lbs

You have overbuilt your gantry...which it good.

Just wondering why your motor weights so much.

Darrell

 

[drewactual]

It's a boat engine... Complete with exhaust manifolds (good for 100# ea) risers, y pipe, bell housing and coupler. Everything including starter, alternator, ps pump, 4 way thermostat housing, cooling expansion... Its turn key drop in... It even has mounts dangling off it right now.

I can easily pull the manifolds/risers/ypipe, and coupler/housing, and lose an easy 300# off the total, and lose likely another 50-75# by removing the accessories... but dang.... It will be SO much easier to shove in there whole... Ya know?