Rotisserie Mounting Points

[Careless]

Hello everyone,

I'm mounting a completely stripped Series 1 chassis to a rotisserie, and it's actually all done, but for some reason it feels like the rear bumper mounts with the M10 bolts are... inadequate?

There is absolutely no frame rot, and the car is being held up right now but I have yet to turn it upside down or even on its side.

Is it normal to look a little... flimsy when suspended?

From what it looks like, the factory bumper mounts are stamped L brackets that are fastened to the underside of the car, somehow on the frame rail above it. How are they tied in? just measly spot welds? I'm afraid to suspend the car upside down with those if that's the case.

I was going to call in to schedule the car for blasting on Monday, but I may take a day or two to adjust the rear mounts. Has me a little worried, but google images searches keep pulling up the same type of fastening locations with no other support. One even on the same brand of rotisserie (which was supplied to me, and is extremely sturdy and should support 1/2 ton truck, never mind a 240z)

 

But then again... the tow hooks and shipping container loops were fastened to the same area- soooo if you could pull out a fully assembled car from a ditch using these locations... i guess it's ok???

Edited October 23, 2016 by Careless

[Careless]

Here is a picture of how I made the mounts... pretty much the same as making flat steel bar, but these box tubes prevent the area around the bumper mount from being marred, since they're only the width of the mounting area itself. inside corners are rounded so that they don't compress against the body and dent it when tightened.

 

and here is what they look like together.  there is a through-bolt to prevent it from sliding off the extension arm, and then two slack bolts & nuts are integrated to the top and the sides so that when its tightened up, the car doesn't wobble around and clunk and make weird noises when operating the rotisserie due to the tubing ID and OD gaps.

 

and this is what has me concerned but not frightened:

note: the droop in the rear... The bolts are tight as can be. I will probably lift the arse end up again and double check tightness once more but it's on there good as far as I can tell.
It may be an optical illusion. Perhaps the slack bolts on the actual rotisserie extension arms have just too much of a gap and is making them twist downwards. Might shove a couple of shims in there and see what happens.

Edited October 23, 2016 by Careless

[grannyknot]

You gotta remember the stripped shell of an early Z is only about 550lbs. Remember this getto contraption I slapped together?  I spun that car hundreds of times over 4-5 months. To get the car truly balanced for spinning either the front or the back needs to be mounted off set 5"-6" higher than the bumper mounting point, the car is a little top heavy.  Now that I look at your rotisserie I can see you have already done that.  Is this car #2? So the first on is done?

[Diseazd]

You guys are awesome....I love your creativity.....grannyknot, I'm impressed....Careless...where is the final shot of your first Resto? I know how you feel....once restoration is done, you're ready for the next.....the fun is in making something ugly beautiful again. How's this for a before and after.....

[Careless]

6 hours ago, grannyknot said:

You gotta remember the stripped shell of an early Z is only about 550lbs. Remember this getto contraption I slapped together?  I spun that car hundreds of times over 4-5 months. To get the car truly balanced for spinning either the front or the back needs to be mounted off set 5"-6" higher than the bumper mounting point, the car is a little top heavy.  Now that I look at your rotisserie I can see you have already done that.  Is this car #2? So the first on is done?

Yeah they're extremely light. I was pushing around this car on the frame dolly while eating a slice of pizza one night, and I began to laugh with my mouth full of food. haha I was just concerned about the actual area that it's bolt to. Is it just spot welded? I'm thinking i'm going to peer around a bit more with a flashlight to see how sturdy it is. The bit of sagging had me concerned. Not sure if it's typical of these cars to do that when suspended. Car #1 is still being worked on, I just want to get the ball rolling on this one so the body shop can have at it.

4 hours ago, Diseazd said:

You guys are awesome....I love your creativity.....grannyknot, I'm impressed....Careless...where is the final shot of your first Resto? I know how you feel....once restoration is done, you're ready for the next.....the fun is in making something ugly beautiful again. How's this for a before and after.....

That car is still in the works. I will update that thread soon. I had been making templates from the car you see above so that I can prepare the sound deadening sheets that the body shop who did the work forgot to put back in the first car before painting it. Really causes a big headache when they do that. So once that is done, I think the interior will come together fairly quickly. There will be a couple of things missing but I'm making note of everything and making sure it's stuff we can change later.

Your white Z looks similar to a white Z i might own soon :-)

 

Edited October 23, 2016 by Careless

[Patcon]

The rear mounts on my rotisserie are not as long as yours so they don't have as much leverage as yours. Mine still droop some. The plate at the rear bumper is double sheet spot welded together with a tube piece welded up behind that runs across the rear of the car IIRC. Your rotisserie is nice and heavy. You should be fine, spin it!

[Careless]

Yeah this rotisserie is pretty well built and beefy, just like the mounts i made for the front and rear too. It was lent to me by the body shop for soda blasting, and I guess this is what they will be using to do some of the under body work. we'll see!

[EuroDat]

The bumper mounts should not be any problem if the rotissorie is rigid. Any flex in the rotisserie will be transferred to the mounting point on the car and like Patcon mentioned, it's made of two pressed metal layers. They will flex and you could distort that area if the rotisserie flexes too much. The connecting brace going to the front section of the rotisserie can help stiffen it up, but the rotissore also needs to be a solid contruction.

[wheee!]

My 280 has the convenient shock mounts for mounting points...





It is definitely top heavy but manageable.

[Careless]

I think I'm just going to have to cut some 1/16th metal strips and shove them into the tube gaps and tighten it all up again with no weight on it. to minimize movement from within the rotisserie tubes.

 

will report back when i figure it out!

[EuroDat]

Filling the gaps should help a lot. That free movement is what causes most of your problems. The shear strength of 4x M10 bolts should handle the +/- 300lbs on the rear.

The more flex in the rotisserie the more the shear force on the bolts will change to a pulling force and then it depends on how strong your threads are.

[Careless]

2 hours ago, EuroDat said:

Filling the gaps should help a lot. That free movement is what causes most of your problems. The shear strength of 4x M10 bolts should handle the +/- 300lbs on the rear.

The more flex in the rotisserie the more the shear force on the bolts will change to a pulling force and then it depends on how strong your threads are.

indeed. I was not worried about the bolts themselves- I was just describing which mounts I was referring to. After lifting a 400lb engine with two M8 bolts, I'm sure that if suspended by a chain, 2 x M10 bolts would be enough to suspend the entire chassis if it were to sit still, let alone 4 + the ones at the front. Not that I'll be suspending 240Z's from chains or only using two bolts total, but I'm sure there are enough.

My main concern is about how the mounts are held onto the car. I will have to look at them again tonight. The M10 bolts that I am using have long enough thread to be tied in from behind the bumper bracket as well, which is what I will do once it's level. I will put another nut there a long with the metal shims.

Since the rear valance panel has to be replaced, I might look into having the body guy call me over when it's removed so I can replace the nuts on the back of these mounts if the threads are poop.

 

Thanks for all the insight. Gonna see her again tonight and stiffen up her rear.