Strange Penthouse Scissor Bolt?

[boywonder]

Originally Posted by MKRyan

Did you and Boywonder get your penthouse put back together?

Yup...used lots of muscle and a hose clamp to keep the bars together.........

[bet on black]

so the SMB tops scissor lift pivot on a pin that is just run through some holes drilled in the tube without a sleeve? interesting.

[rallypanam]

Originally Posted by bet on black

so the SMB tops scissor lift pivot on a pin that is just run through some holes drilled in the tube without a sleeve? interesting.

Yup. Which is why so many tops have bent arms...

[86Scotty]

Originally Posted by rallypanam

Yup. Which is why so many tops have bent arms...

Well, I agree and disagree. Those poles are pretty thick. Mine had a mild bend in them and it didn't appear to have anything to do with the center pivot hole. I guess it could've. Mine just had a general arc all the way through them, top to bottom. Anyway, I did sleeve them when I redid the bolts and think it's necessary, but lots of SMBs with no weight on top have lasted for a long time this way.

[BroncoHauler]

Originally Posted by 86Scotty

Well, I agree and disagree. Those poles are pretty thick. Mine had a mild bend in them and it didn't appear to have anything to do with the center pivot hole. I guess it could've. Mine just had a general arc all the way through them, top to bottom. Anyway, I did sleeve them when I redid the bolts and think it's necessary, but lots of SMBs with no weight on top have lasted for a long time this way.

I agree. Also, there are two implementations of sleeving. One is to sleeve the lengths of the tubes themselves (or even replace the tube with sturdier tubing material), but I think the pivot point hole should have a free floating sleeve running through both tubes pivot points with a bolt then keeping it all together.

Bent tubes will typically come from fatigue, an overloaded top while raising the top, or from trying to raise the top while a latch is still engaged.

Elongated pivot point holes will come from age (though I think the sleeve I mentioned above would help a lot), but the pivot point holes will elongate much faster when a standard bolt, rather than a shoulder bolt, is used. Exposed threads on pivoting tubing will eat up the tubing eventually.


Herb

[boywonder]

Originally Posted by bet on black

so the SMB tops scissor lift pivot on a pin that is just run through some holes drilled in the tube without a sleeve? interesting.

Either a clevis pin (as in this thread) or more commonly a 1/4-20 bolt and nut. The bolt and nut method has the tubes bearing on the bolt threads...bad in a few ways....the plastic spacer used by SMB is also a bit underwhelming.

This is a great application for using shoulder screws, and this fix has been documented here by a number of members, either 1/4" shoulder or 5/16" shoulder, as well as sleeving the tubes.

[daveb]

I was told my frame arms have chrome moly tubing inserts but what I don't know is if the tubing is one piece with a corresponding pivot hole or if its two sections above and below the bolt???

The power tops were built with the inserts from what I was told. That was in 2005. I'd think (hope) the insert is a single insert. If not, the shoulder bolt is by far a better choice. I had a similar issue with my Aluminess swing gates. I was concerned that an un-sleeved pivot hole would raise havoc with the aluminum hinges. After that Aluminess made a bolt retro fit kit and switched to shoulder bolts. I figured they would have changed the top bolts to a shoulder type as well...guess not.

[bet on black]

Originally Posted by rallypanam

Yup. Which is why so many tops have bent arms...

i would think the lack of sleeving would cause the pivot pin/bolt to get sheared or bent.

Originally Posted by BroncoHauler

I agree. Also, there are two implementations of sleeving. One is to sleeve the lengths of the tubes themselves (or even replace the tube with sturdier tubing material), but I think the pivot point hole should have a free floating sleeve running through both tubes pivot points with a bolt then keeping it all together.
Herb

i think each tube should be sleeved separately. i would want the bearing surface to be the the sleeve and the bolt shoulder. eliminate the movement of the tubing walls against anything as there is far more pressure there due to the small surface area the force is applied upon. i would want a nylon washer or similar between the sleeves to reduce friction during movement.

[boywonder]

Originally Posted by daveb

I was told my frame arms have chrome moly tubing inserts but what I don't know is if the tubing is one piece with a corresponding pivot hole or if its two sections above and below the bolt???

If the sleeved tubing inside the crossbars is interrupted at the pivot bolt holes it won't do much good.....it has to be one piece to provide any meaningful benefit (since the maximum bending moment is right at the pivot bolt)

Originally Posted by bet on black

i would think the lack of sleeving would cause the pivot pin/bolt to get sheared or bent.


i think each tube should be sleeved separately. i would want the bearing surface to be the the sleeve and the bolt shoulder. eliminate the movement of the tubing walls against anything as there is far more pressure there due to the small surface area the force is applied upon. i would want a nylon washer or similar between the sleeves to reduce friction during movement.

Sleeves welded in the tubing would be wonderful, but SMB designs are far below that mark......

Bent screws/pins/bolts are usually caused by space/slop between the bars; when the bars are right next to each other and the joint is snug, the fastener is loaded in shear, not bending. If the nylon spacer breaks, falls off, then lots of bending.

The other big issue with using a regular bolt is that one bearing surface is on the bolt shank (ok...not great) and the other is bearing on the threads (much worse)....the threads wear at the hole and the fastener only has the root diameter (the solid part below the threads) to react the shear loading.